# document

id: 5547524fa553b470d74b718f02c93a68
created_at: 2023-03-16 14:00:38
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"This Cross-Chapter Box presents the AR6 WGI assessment of observed global warming and describes improvements and updates since \r\nAR5 and subsequent Special Reports. The revised estimates result from: the availability of new and revised observational datasets; the \r\noccurrence of recent record warm years; and the evaluation of the two primary metrics used to estimate global warming in past IPCC \r\nreports: 'Global mean surface temperature' (GMST) and 'Global surface air temperature' (GSAT). Implications for threshold crossing \r\ntimes, remaining carbon budgets and impacts assessments across AR6 WGs are discussed. "


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"Since AR5, all major datasets used for assessing observed temperature change based upon GMST have been updated and improved \r\n(Section 2.3.1.1.3). A number of new products have also become available, including new datasets (e.g., Berkeley Earth, Rohde and \r\nHausfather, 2020) and new interpolations based on existing datasets (e.g., Cowtan and Way, 2014 and Kadow et al., 2020). These \r\nvarious estimates are not fully independent. "


id: 244b0d9fcc408f18d0fc06e85775fd25
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"Overall, dataset innovations and the availability of new datasets have led to an assessment of increased GMST change relative to the \r\ndirectly equivalent estimates reported in AR5 (Cross-Chapter Box 2.3, Table 1 and Figure 1)."


id: 4418535e02d6dfaa7db79b56ac995605
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"Observed changes in global mean temperature since the pre-industrial era\r\nAR5 used 1850-1900 as an approximate pre-industrial baseline for global temperature change, whilst using an earlier pre-industrial \r\nbaseline of 1750 for radiative forcings. Cross-Chapter Box 1.2 assesses that there was an observed GMST change from the period \r\naround 1750 to 1850-1900 of around 0.1degC (likely range -0.1 to +0.3degC, medium confidence). This additional global temperature \r\nchange before 1850-1900 is not included when making AR6 assessments on global warming to date, global temperature threshold \r\ncrossing times, or remaining carbon budgets to ensure consistency with previous ARs."


id: b241132200ea51ab390e158efd5c4d05
created_at: 2023-03-16 14:00:38
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"Physical understanding\r\nA well-understood physical constraint on the vertical gradient between the air and sea surface temperature is that it is approximately \r\nproportional to the turbulent sensible heat flux in the atmospheric surface layer (Chor et al., 2020). Similarly, the latent heat flux scales \r\nwith the vertical humidity gradient and, in the global mean and in most oceanic regions, the latent heat flux is substantially larger than \r\nthe sensible heat flux (Sections 7.2.1 and 9.2.1.3). If GSAT were to warm faster than GMST, the sensible surface heat flux would respond \r\nso as to reduce this difference. However, it is the sum of the sensible, latent, and radiative heat fluxes that controls GMST, so the sensible"


id: a3a9dd7c749dec6a2a66e9f7de0ce15a
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"Overall, with medium evidence and low agreement, available observational products suggest that NMAT is warming less than SST \r\nby up to 15%. Given that these ocean observations cover roughly two thirds of the globe, this implies that GMST is warming up to at \r\nmost 10% faster than GSAT. Substantial uncertainty remains and the effect is highly sensitive to the choice of both time period and \r\nchoice of NMAT and SST observational products to compare. Observed NMAT warming faster than observed SST cannot be precluded."


id: ca3df30b3c1dff736b919fcc9016912a
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"Marine boundary layer behaviour and parameterizations in all CMIP models are based upon Monin-Obukhov similarity theory \r\n(e.g.,  Businger et  al., 1971), which informs assumptions around gradients in the near-surface boundary layer dependent upon \r\ntemperature, wind speed and humidity. This leaves open the possibility of a common model bias, while Druzhinin et al. (2019) also \r\npoint to departures of temperature profiles from theoretical predictions under certain conditions. There remain inadequacies in \r\nunderstanding and modelling of key processes (Edwards et al., 2020), and biases in the representation of the absolute SST-MAT \r\ndifference have been identified in climate models and reanalyses (Gainusa-Bogdan et al., 2015; Zhou et al., 2020)."


id: 21211db73e85d52761255dbf8fb904fe
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"Simmons et al. (2017) found that in JRA-55 and ERA-Interim (following an adjustment to account for an apparent discontinuity), GSAT \r\nincreased 2-4% faster than GMST over the period 1979-2016. In atmospheric reanalyses, SST is given as a lower boundary condition \r\nfrom an observed globally interpolated product (such as HadISST; Rayner et al., 2003) whereas the air temperature is reliant upon \r\nmodel parameterizations and assimilated observations that do not include MAT observations (Simmons et al., 2017), thereby limiting \r\ntheir capability to constrain differences in GMST and GSAT trends. Furthermore, it is unclear what the lack of dynamic coupling at the \r\nocean-atmosphere interface might imply for the representativeness of reanalysis-based estimates. "


id: 31b30c8704b42f4e7ce8d3aef6e5920b
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"Cross Chapter Box 2.3, Table 1 | Summary of key observationally based global warming estimates (in degC) to various reference periods in the \r\npresent report and selected prior reports (AR5 WGI and SR1.5) and their principal applications (see Section 1.4.1 for further information on \r\nreference periods). Further details on data sources and processing are available in the chapter data table (Table 2.SM.1)."


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"a\r\n As the uncertainty in the relationship between GMST and GSAT changes is independent of the uncertainty in the assessed change in GMST, these uncertainties are \r\ncombined in quadrature."


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"b\r\n The SR1.5 derived a GSAT estimate by taking the CMIP5 ensemble mean GSAT change of 0.99degC, sub-sampling to HadCRUTv4.6, noting the offset in trends \r\n(0.84degC HadCRUT4 observed GMST vs. 0.86degC modelled GMST) and adjusting by this to arrive at an estimate of 0.97degC change in GSAT. The likely uncertainty range \r\nof +-0.12degC was not further adjusted."


id: 386eb9291e7eab3e3a649a73dc7e3f3
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"c\r\n Note that the AR5 approach for the change from 1850-1900 to both 1986-2005 and 2003-2012 was based upon one dataset (HadCRUT4) and its parametric \r\nuncertainty estimates are known to underestimate the true uncertainty."


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"GMST and GSAT are physically distinct. There is high confidence that long-term changes in GMST and GSAT differ by at most 10% in \r\neither direction. However, conflicting lines of evidence from models and direct observations combined with limitations in theoretical \r\nunderstanding lead to low confidence in the sign of any difference in long-term trends. The very likely range of estimated historical \r\nGMST warming is combined with the assessed +- 10% uncertainty in the relationship between GMST and GSAT changes to infer \r\na GSAT equivalent, accounting for any possible real-world physical difference. Improvements in understanding may yield a robust \r\nbasis to apply a scaling-factor to account for the difference in future assessments."


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"climate response to cumulative emissions of CO2 (TCRE) translates into remaining carbon budgets about 70 [40-140] GtCO2 larger \r\ncompared to SR1.5 on a like-for-like basis. Meanwhile, on the same like-for-like basis, updates to historical observational products \r\nwould reduce remaining carbon budgets reported in AR5 SYR based on WGIII scenario projections by about 180 [120 to 370] GtCO2. \r\nBox 5.2 provides a further overview of updates to estimates of the remaining carbon budget since AR5. "


id: d425f480f576ed47158b23c84d06fe7c
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"There is therefore high confidence that assessment of the magnitude and timing of impacts-related climate quantities at 1.5degC is \r\nnot substantially affected by the revised estimate of historical global warming. The assessment of the implications of limiting global \r\nwarming to 1.5degC compared to 2degC will also remain broadly unchanged by the updated estimate of historical warming, as this depends \r\non the relative impacts rather than the absolute impacts at any specific definition of global temperature anomaly (high confidence). "


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"comprising more than 35,000 station records. These advances, both \r\nof which have substantially improved spatial coverage, have reduced \r\nuncertainties in assessments of both land and marine data. "


id: b118aa1583a8caff67065df70b3eac4f
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"The AR5 concluded that it was certain that GMST had increased \r\nsince the late 19th century. Total warming in GMST was assessed \r\nas 0.85 [0.65 to 1.06] degC over 1880-2012, while the change from \r\n1850-1900 to 2003-2012 was assessed at 0.78 [0.72 to 0.85] degC, \r\nand from 1850-1900 to 1986-2005 at 0.61 [0.55 to 0.67] degC. The \r\nSR1.5 reported warming of GMST from 1850-1900 to 2006-2015 \r\nof 0.87degC, with an 1880-2012 trend of 0.86degC and an 1880-2015 \r\ntrend of 0.92degC. The SRCCL concluded that since the pre-industrial \r\nperiod, surface air temperature over land areas has risen nearly twice \r\nas much as the global mean surface temperature (high confidence). "


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"Since AR5, there have been substantial improvements in the \r\navailability of instrumental archive data both over the ocean and \r\non land. A new version of the International Comprehensive Ocean\u0002Atmosphere Dataset (ICOADS Release 3.0, Freeman et  al., 2017) \r\ncomprises over 450 million in situ marine reports and incorporates \r\nnewly digitized data, increasing coverage in data sparse regions and \r\ntimes (e.g., polar oceans and World War I). The International Surface \r\nTemperature Initiative released a much improved collection of \r\nfundamental land surface air temperature records (Rennie et al., 2014) "


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"independently-derived analyses and the assessed uncertainties \r\n(Kennedy, 2014; Kent et al., 2017) show unambiguously that global \r\nmean SST increased since the start of the 20th century, a conclusion \r\nthat is insensitive to the method used to treat gaps in data coverage \r\n(Kennedy, 2014). "


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"dataset (Xu et al., 2018) has higher network density in some regions \r\n(particularly Asia) than previously existing datasets. Global trends \r\nderived from CLSAT are generally consistent with those derived from \r\nother land datasets through 2014 (Xu et al., 2018)."


id: f23b564b91b8d9219948d1ff862c64a4
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"The AR5 identified diurnal temperature range (DTR) as a substantial \r\nknowledge gap. The most recent analysis of Thorne et al. (2016a, b) \r\ncompared a broad range of gridded estimates of change in DTR, \r\nincluding a new estimate derived from the ISTI databank release \r\nusing the pairwise homogenization algorithm used to create \r\nGHCNMv4, and estimates derived from Vose et al. (2005), HadEX2 \r\n(Donat et al., 2013a), HadGHCND (Donat et al., 2013b), GHCNDEX \r\n(Donat et al., 2013b), Berkeley Earth (Rohde et al., 2013), and CRU TS \r\n(Harris et al., 2014). The analysis highlighted substantial ambiguity \r\nin pre-1950 estimates arising from sparse data availability. After \r\n1950 estimates agreed that DTR had decreased globally with most \r\nof that decrease occurring over the period 1960-1980. A subsequent \r\nDTR analysis using CLSAT further confirmed this behaviour (X. Sun \r\net al., 2018). "


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"No recent literature has emerged to alter the AR5 finding that it is \r\nunlikely that any uncorrected effects from urbanization (Box 10.3), or \r\nfrom changes in land use or land cover (Section 2.2.7), have raised \r\nglobal Land Surface Air Temperature (LSAT) trends by more than \r\n10%, although larger signals have been identified in some specific \r\nregions, especially rapidly urbanizing areas such as eastern China \r\n(Y. Li et al., 2013; Liao et al., 2017; Z. Shi et al., 2019). There is also no \r\nclear indication that site-specific data homogeneity issues have had \r\nany significant impact on global trends since the early 20th century; \r\nthere is more uncertainty in the 19th century, mainly arising from \r\na lack of standardization of instrument shelters, which has been \r\nlargely accounted for in data from central Europe (Jones et al., 2012), \r\nbut less so elsewhere. "


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"The GHCNMv4 dataset (Menne et al., 2018) includes many more land \r\nstations than GHCNMv3, arising from the databank efforts of Rennie \r\net al. (2014), and calculates a 100-member parametric uncertainty \r\nensemble drawing upon the benchmarking analysis of Williams et al. \r\n(2012), as well as accounting for sampling effects. A new version of \r\nthe CRUTEM dataset (CRUTEMv5, Osborn et al., 2021) has increased \r\ndata completeness and additional quality control measures. A new \r\nglobal land dataset, the China Land Surface Air Temperature (CLSAT) "


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"the polar regions. GSAT trends from ERA5 reanalysis (Hersbach \r\net  al., 2020) are also broadly consistent with GMST trends from \r\nconventional surface datasets. However, the MERRA-2 reanalysis \r\n(Gelaro et  al., 2017) GSAT spuriously cooled sharply relative to \r\nERA-Interim and JRA-55 in about 2007 (Funk et al., 2019). Since the \r\nearly 2000s, analyses of surface temperature, from which near-surface \r\ntemperature may be derived, have also been available from various \r\nsatellites (Famiglietti et  al., 2018; Prakash et  al., 2018; Susskind \r\net  al., 2019), which have the potential to improve assessments of \r\ntemperature changes over data-sparse regions. "


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"variations and the verification of the methods, it is extremely likely\r\nthat interpolation results in a less-biased estimate of the actual \r\nglobal temperature change than ignoring regions with limited or no \r\ndata."


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"In total there are five conventional datasets which meet spatial \r\ncoverage requirements and draw from the most recent generation \r\nof SST analyses, four of which have sufficient data in the 1850-1900 \r\nperiod to allow an assessment of changes from that baseline \r\n(Table 2.3). A fifth dataset is added to the assessment for changes \r\nover land areas. Datasets share SST and LSAT data products and \r\nin several cases differ solely in the post-processing interpolation \r\napplied meaning that there are far fewer methodological degrees \r\nof freedom than implied by a straight count of the number of \r\navailable estimates."


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"Most land areas in the extratropical Northern Hemisphere (NH) have \r\nwarmed faster than the GMST average over both the 1900-2020 \r\nand 1980-2020 periods (Figure 2.11b), although at more regional \r\nscales, particularly in data sparse regions, considerable uncertainty \r\nis introduced by sometimes large differences in trends between \r\ndifferent LSAT datasets (Rao et  al., 2018). Temperatures averaged \r\nover land areas globally have warmed by 1.59 [1.34 to 1.83] degC \r\nfrom 1850-1900 to 2011-2020, substantially higher than the SST \r\nwarming of 0.88 [0.68 to 1.01] degC. The four conventional surface \r\ntemperature products which meet all criteria to be included in the \r\nfinal assessment (Table 2.4) agree that each of the last four decades \r\nhas consecutively been the warmest globally since the beginning of \r\ntheir respective records (Figure 2.11c and Table 2.4). Each of the six \r\nyears 2015 to 2020 has very likely been at least 0.9degC warmer than \r\nthe 1850-1900 average."


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"Estimates of GMST have also benefitted from improved estimation \r\nof parametric uncertainties. New versions of three long-standing \r\nproducts from NASA GISTEMP v4 (Lenssen et  al., 2019), NOAA \r\nGlobalTempv5 (B. Huang et  al., 2019b) and HadCRUT5 (Morice \r\net  al.,  2021) are all now available as ensemble estimates. These \r\nensembles each account for a variety of systematic and random \r\nuncertainty effects in slightly different ways, giving broadly similar \r\nresults, which are incorporated into the present assessment, with the \r\ntotal uncertainty generally declining up until the mid-20th century as \r\ndata coverage improves."


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"To conclude, from 1850-1900 to 1995-2014, GMST increased by \r\n0.85 [0.69 to 0.95] degC, to the first two decades of the 21st century \r\n(2001-2020) by 0.99 [0.84 to 1.10] degC, and to the most recent \r\ndecade (2011-2020) by 1.09 [0.95 to 1.20] degC. Each of the last four \r\ndecades has in turn been warmer than any decade that preceded it \r\nsince 1850. Temperatures have increased faster over land than over \r\nthe oceans since 1850-1900, with warming to 2011-2020 of 1.59 \r\n[1.34 to 1.83] degC versus 0.88 [0.68 to 1.01] degC, respectively."


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"Another significant development has been the incorporation of \r\nreanalysis products (Section 1.5.2) into operational monitoring \r\nof GSAT. It was reported in AR5 that various reanalyses were broadly \r\nconsistent with conventional surface datasets in the representation \r\nof trends since the mid-20th century. Since that time, Simmons et al. \r\n(2017) found that the ERA-Interim (Dee et  al., 2011) and JRA-55 \r\n(Kobayashi et al., 2015) reanalyses continued to be consistent, over \r\nthe last 20 years, with those surface datasets which fully represented "


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"The AR5 reported that it was virtually certain that tropospheric \r\ntemperatures have risen, and stratospheric temperatures fallen, since \r\nthe mid-20th century, but that assessments of the rate of change \r\nand its vertical structure had only medium confidence in the NH \r\nextratropics and low confidence elsewhere. In particular there was \r\nlow confidence in the vertical structure of temperature trends in the \r\nupper tropical troposphere."


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"Temperatures averaged through the full lower stratosphere (roughly \r\n10-25 km) have decreased over 1980-2019 in all data products, \r\nwith the bulk of the decrease prior to 2000. The decrease holds \r\neven if the influence of the El Chichon (1982) and Pinatubo (1991) \r\nvolcanic eruptions on the trend, found by Steiner et al. (2020a) to \r\nhave increased the 1979-2018 cooling trend by 0.06degC per decade, \r\nis removed. Most datasets show no significant or only marginally \r\nsignificant trends over 2000-2019, and the results of Philipona et al. \r\n(2018) show weak increases over 2000-2015 in the very lowermost \r\nstratosphere sampled by radiosondes."


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"The STAR dataset shows cooling in the middle and upper stratosphere \r\nwith a trend of -0.56degC +- 0.16degC per decade for the mid-stratosphere \r\nand -0.62degC +- 0.29degC per decade for the upper stratosphere over \r\n1980-2019, although both cooling rates have slowed substantially \r\nsince the mid-1990s. The overall post-1980 trend is reduced in \r\nmagnitude by about 0.10degC per decade at both levels if the influences \r\nof the El Chichon and Pinatubo eruptions, and the solar cycle, are "


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"removed (Zou and Qian, 2016). The results obtained by McLandress \r\net al. (2015) for 1980-2012, Randel et al. (2016) for 1979-2015, and \r\nMaycock et al. (2018) for 1979-2016 are broadly consistent with this."


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"in  tropopause height has experienced a similar recent slowdown \r\nto that of the cooling of the lower stratosphere, as short-period \r\ntrends are typically inconclusive due to significant natural variability \r\n(Scherllin-Pirscher et al., 2021). RO data (Gao et al., 2015) indicate \r\nlittle change in tropopause height over the short period from 2006 \r\nto 2014, but a warming below the tropopause is observed over 2002 \r\nto 2019 (Figure 2.12). "


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"A rise in the tropopause height of 40 to 120 m per decade between \r\n1981 and 2015 was determined from both radiosonde and reanalysis \r\ndatasets (Xian and Homeyer, 2019). Local studies (e.g., Tang et al., 2017; \r\nX. Chen et al., 2019) found stronger trends in some regions near the \r\nsubtropical jet linked to tropical expansion (Section 2.3.1.4.1). Whilst \r\nSeidel and Randel (2006) found that the tropopause height was more \r\nclosely coupled with temperatures in the  stratosphere than those \r\nin the troposphere, it is not yet clear whether the rate of increase "


id: 373c108702c788310ad51135ce60e086
created_at: 2023-03-16 14:00:38
updated_at: 2023-03-16 14:00:38
content_type: text
index: climate_gpt_only_giec
vector_id: 6079
content:
"In summary, the troposphere has warmed since the mid-20th century. \r\nThere is medium confidence that temperatures in the tropical upper \r\ntroposphere have warmed faster than those at the surface since 2001, \r\nbut low confidence in changes prior to 2001. It is virtually certain"


id: 46b3e17555366279f4370e0aa359c776
created_at: 2023-03-16 14:00:38
updated_at: 2023-03-16 14:00:38
content_type: text
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vector_id: 8509
content:
"that the lower stratosphere has cooled since the mid-20th century. \r\nHowever, most datasets show that lower stratospheric temperatures \r\nhave stabilized since the mid-1990s with no significant change over \r\nthe last 20 years. It is likely that middle and upper stratospheric \r\ntemperatures have decreased since 1980, but there is low confidence\r\nin the magnitude. It is virtually certain that the tropopause height has \r\nrisen over 1980-2019 but there is low confidence in the magnitude \r\nof this rise, or whether the rate of change has reduced commensurate \r\nwith stabilized lower stratospheric temperatures."


id: ed12ebf8adc53f9d95a2a3c6d4095779
created_at: 2023-03-16 14:00:38
updated_at: 2023-03-16 14:00:38
content_type: text
index: climate_gpt_only_giec
vector_id: 34777
content:
"The AR5 assessed large-scale indicators of terrestrial paleo \r\nhydroclimate, including as part of its assessment of paleo floods and \r\ndroughts, but did not assess proxy evidence for paleo hydroclimate \r\nindicators over continental and larger scales. The paleoclimate \r\nevidence assessed in AR5 was broadly consistent with global \r\nhydroclimate scaling with temperature: warmer periods were wetter \r\n(e.g., the Pliocene; increased precipitation) with colder periods being \r\ndrier (e.g., the LGM; decreased precipitation). "


id: b70c2e24597fcc25a7c57fe5d50d496f
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 26326
content:
"Table 2.5 | Observed change (degC) in free atmospheric temperatures in various \r\ndatasets, for the lower tropospheric and lower stratospheric layers. Numbers \r\nin square brackets indicate 5-95% confidence ranges. Trend values are calculated \r\nwith ordinary least squares following (Santer et al., 2008) and are expressed as a total \r\nchange over the stated period. Further details on data sources and processing are \r\navailable in the chapter data table (Table 2.SM.1)."


id: 20b7721a2c90081da941a274f02123eb
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 2588
content:
"New analyses suggest that during the Holocene, the NH mid\u0002latitudes became increasingly wet, in phase with the strength of \r\nthe latitudinal temperature and insolation gradients (Shuman and \r\nMarsicek, 2016; Routson et al., 2019). Nevertheless, there was also \r\nconsiderable spatial heterogeneity and variability on centennial to \r\nmillennial timescales (Newby et  al., 2014; Shuman and Marsicek, \r\n2016; H. Zhang et  al., 2018; Liefert and Shuman, 2020). The NH \r\ntropics and many regions of the SH deep tropics experienced \r\nwetting up until the early to mid-Holocene but drying thereafter "


id: 852bd3c7eec76c789b0a51060bc8ef4b
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
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vector_id: 18477
content:
"This section focuses on large-scale changes in a subset of components \r\nof the hydrological cycle (Cross-Chapter Box 2.2). Chapter 8 undertakes \r\na holistic assessment of changes in the hydrological cycle integrating \r\nobservations, modelling and theoretical understanding, while Chapter 11 \r\nassesses hydrological cycle extremes such as droughts and floods. "


id: 4a74de4ec2d029e6ac2c4ba9bb0d963d
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
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vector_id: 9119
content:
"(Shanahan et al., 2015; Nash et al., 2016; Munoz et al., 2017; Quade \r\net al., 2018). Evidence for the SH is limited, with a wetting trend \r\nduring the Holocene in low latitudes of South America (Kanner et al., \r\n2013; Mollier-Vogel et  al., 2013) and parts of the African tropics \r\n(Schefuss et  al., 2011; Chevalier and Chase, 2015) but a drying \r\ntendency over southern Australia and New Zealand (van den Bos \r\net al., 2018; Barr et al., 2019) and South America (Quade and Kaplan, \r\n2017; Moreno et al., 2018)."


id: 9aa6367f32116f6034d802036b1b0f9
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 21860
content:
"and ocean has remained well above the 1973-2019 average and \r\nreached record or near-record values (Figure 2.13b), with the strong \r\n2015-2016 El  Nino event boosting surface moisture levels (Byrne \r\nand O'Gorman, 2018). The abatement from around 2000 to 2012 \r\nreported in AR5 has not persisted. This is consistent with increases \r\nin total column water vapour (Section 2.3.1.3.3) and a resumption of \r\nrapid warming in surface temperatures (Section 2.3.1.1.3). The global \r\naveraged relative humidity however has remained depressed since \r\n2000 (Figure 2.13d; Simmons et al., 2010; Willett et al., 2014, 2020; \r\nDunn et al., 2017; Vicente-Serrano et al., 2018). "


id: 20cab9760de2cd582b2ab0e0e8f6c704
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 2597
content:
"To summarize, since AR5 there has been considerable progress in \r\ndetecting the variations of the global hydrological cycle prior to the \r\ninstrumental period. There are indications from multiple sources of \r\na wetting trend during the Holocene, particularly for the NH and parts \r\nof the SH tropics (medium confidence). Hydroclimate during the CE \r\nis dominated by regional variability, generally precluding definitive \r\nstatements on changes at continental and larger scales, with a general \r\nreduction of mega-drought occurrences over the last about 500 years \r\n(medium confidence). Availability of proxy data for assessing Holocene \r\nhydroclimate variability is biased towards the NH, with medium \r\nevidence but low agreement for the assessment of SH changes. "


id: 149442f6046645b59de477e27009929b
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 746
content:
"In summary, observations since the 1970s show a very likely increase \r\nin near surface specific humidity over both land and oceans. A very \r\nlikely decrease in relative humidity has occurred over much of the \r\nglobal land area since 2000, particularly over mid-latitude regions of \r\nthe NH, with increases at northern high latitudes. "


id: e9247b2249845747d2ba750beabc2e67
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 34194
content:
"The AR5 concluded that total column water vapour (TCWV) very likely\r\nincreased since the 1970s, at a rate that was overall consistent with \r\nthe Clausius-Clapeyron relationship (about 7% per degC) given the \r\nobserved increase in atmospheric temperature."


id: 7094cebafc55bff2ebff638a14e0e56e
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 15330
content:
"The AR5 reported very likely widespread increases in near-surface air \r\nspecific humidity since the 1970s, abating from around 2000 to 2012 \r\n(medium confidence). This abatement resulted in a recent decline in \r\nrelative humidity over the land."


id: 62da9859f920cce377c44d81cf3bab57
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 13121
content:
"Records prior to the instigation of quasi-global coverage by radiosondes \r\nrequire the use of statistical relationships to infer TCWV from historical \r\nSST observations or the evaluation of centennial-scale reanalysis \r\nproducts (Smith and Arkin, 2015). These approaches reveal two \r\nperiods of positive trends, one from 1910 to 1940 and the other from \r\n1975 onwards (Zhang et al., 2013; Mieruch et al., 2014; Shi et al., \r\n2018), concurrent with periods of positive SST trends (Figure 2.11). \r\nPotential sources of errors in the SST-based estimation of TCWV \r\ninclude both uncertainties in historical SST and uncertainties in the \r\nparameters that define the relationship between the variables (Smith \r\nand Arkin, 2015). Trends based on 20CRv2c, ERA-20C and ERA-20CM \r\nindicate an increase in TCWV over much of the global ocean since \r\nthe beginning of the 20th century, particularly over the tropics (Bordi \r\net al., 2015; Smith and Arkin, 2015; Poli et al., 2016). TCWV trends "


id: bf8c76c95a69a66bf7175d12ddf924bd
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 27694
content:
"Near surface humidity has been monitored using in-situ data \r\n(e.g., NOCSv2.0; Berry and Kent, 2011), satellite-derived estimations \r\n(e.g.,  HOAPS3, Liman et  al., 2018; J-OFURO3, Tomita et  al., 2019), \r\nglobal gridded products such as HadISDH (Willett et al., 2014, 2020), \r\nand reanalyses (e.g.,  ERA5, JRA-55 and 20CRv3). In-situ based \r\nhumidity products suffer from uncertainties over poorly sampled \r\nregions particularly in the SH (Berry and Kent, 2011; Kent et  al., \r\n2014; Willett et al., 2014). There is general consensus in the inter\u0002annual variability and sign of trends implying high confidence in \r\nincreasing specific humidity since the 1970s and decreasing relative \r\nhumidity since 2000, particularly over land (Simmons et  al., 2010; \r\nWillett et al., 2014, 2020). Since 2012, specific humidity over land "


id: cfb855f3945a8ca76daf6070716671ec
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 30215
content:
"estimated since the middle of the 20th century from radiosonde \r\nobservations show significant increases over North America and \r\nlarge portions of Eurasia, while decreases are restricted to Australia, \r\neastern Asia and the Mediterranean region (Y. Zhang et al., 2018). \r\nOverall, there is a significant increase in TCWV over global land areas \r\nsince 1979 (Chen and Liu, 2016)."


id: 37d9274931d66eb5c26b4f366d8a36c0
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 6158
content:
"account for the observed TCWV-temperature scaling. Substantial \r\npotential inhomogeneities affect trend estimates based on satellite, \r\nreanalysis and merged products in particular over Central Africa, the \r\nSahara and central South America (Schroder et al., 2016, 2019; J. Wang \r\net al., 2016). Moreover, data gaps in observations from ground-based \r\nGNSS receivers and radiosondes lead to low confidence in TCWV \r\nestimation in these regions. "


id: d5e7888faa2d1661af8c0138004e693
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 31169
content:
"In summary, positive trends in global total column water vapour \r\nare very likely since 1979 when globally representative direct \r\nobservations began, although uncertainties associated with changes \r\nin the observing system imply medium confidence in estimation of the \r\ntrend magnitudes. Low confidence in longer-term trends arises from \r\nuncertainties in the SST-TCWV relationship and current centennial \r\nscale reanalyses, particularly during the first half of the 20th century."


id: 2461cdd12f48152c22697609c4518c82
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 3170
content:
"The AR5 concluded that there was low confidence in precipitation \r\nchange averaged over global land areas prior to 1950, and medium \r\nconfidence thereafter with no significant global trends. There was \r\na likely overall increase in precipitation in the well-sampled NH \r\nmid-latitudes, with high confidence after 1951."


id: 49f07998e1c733fb5c0d429e088a9bb3
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 9038
content:
"In summary, globally averaged land precipitation has likely increased \r\nsince the middle of the 20th century (medium confidence), with low \r\nconfidence in trends prior to 1950. A faster increase in global land \r\nprecipitation was observed since the 1980s (medium confidence), \r\nwith large interannual variability and regional heterogeneity. \r\nOver the global ocean there is low confidence in the estimates of \r\nprecipitation trends, linked to uncertainties in satellite retrievals, \r\nmerging procedures and limited in situ observations."


id: afcd41c828378746dcd8243b0eb2ab8e
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 25177
content:
"Table 2.6 | Globally averaged trend estimates over land and 90% confidence \r\nintervals for annual precipitation for each time series in Figure 2.15c over \r\nthree periods all ending in 2019. Trends are calculated using OLS regression with \r\nsignificance assessed after Santer et al. (2008). Further details on data sources and \r\nprocessing are available in the chapter data table (Table 2.SM.1)."


id: bfacb1e3e304c8ee9e19a7bdf7773e08
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 27715
content:
"Estimating global-scale trends in P-E using direct observations \r\nalone is challenging due to limited evaporation measurements and \r\ninhomogeneities in satellite-derived precipitation and evaporation \r\ndatasets (Hegerl et al., 2015; Lopez et al., 2017). Hence, the assessment \r\nof global P-E trends is generally performed using reanalyses, although \r\nchanges in the observing system imply considerable uncertainty \r\n(Skliris et al., 2014). Since the second half of the 20th century, several \r\nreanalyses and observational datasets have shown increases in P-E \r\nover global land, although 75% of land areas exhibit no significant "


id: 20f94a62c761456f4c4c883efda651de
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 2619
content:
"The AR5 concluded that the pattern of precipitation minus evaporation \r\n(P-E) over the ocean had been enhanced since the 1950s (medium \r\nconfidence). Saline surface waters had become saltier, while the \r\nrelatively fresh surface waters had become fresher. The inferred \r\nchanges in P-E were consistent with the observed increased TCWV, \r\nalthough uncertainties in the available products prevented identifying \r\nrobust trends."


id: a5f8126a7b82d5e6a80b55eba3276d77
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 23666
content:
"changes and both internal variability and observational uncertainty \r\nare substantial (Greve et al., 2014; Robertson et al., 2016). The recently \r\nreleased ERA5 (Hersbach et  al., 2020) showed improvements in the \r\nrepresentation of tropical precipitation, although it overestimates \r\nglobal precipitation trends in comparison to ERA-Interim and GPCP \r\n(Nogueira, 2020), and suffers from temporal changes in the annual \r\nbalance between precipitation and evaporation (Hersbach et al., 2020). \r\nThe spatial pattern of P-E trends over 1980-2019 (Figure 2.16a) are \r\nlargely consistent with the trends in the GPCP v2.3 precipitation dataset \r\n(Figure 2.15f and Section 2.3.1.3.4) and agrees in sign with the trends \r\nfrom other reanalyses such as JRA-55 and MERRA-2 (L. Yu et al., 2020). "


id: 9ba7c9953689e0f90e0c9c6ccee1023c
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 22045
content:
"A variety of reanalysis products exhibit diverse temporal evolutions \r\nof P-E (Figure 2.16b-d). Globally MERRA-2, ERA20C and ERA20CM \r\nexhibit little change whereas JRA-55, ERA5 and 20CRv3 all \r\nimply long-term changes (Figure 2.16d). A potential limitation in \r\nestimating P-E from some reanalysis products is readily apparent \r\nwhen considering the temporal evolution of global P-E from CFSR \r\nand MERRA (Figure 2.16d) which both exhibit strong discontinuities \r\nover the global ocean in the late 1990s. Over global land as a whole, "


id: 49b0393c33d2f9654140680266e8b3e5
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 8989
content:
"Figure 2.16 | Changes in precipitation minus evaporation. (a) Trends in precipitation minus evaporation (P-E) between 1980 and 2019. Trends are calculated using OLS \r\nregression with significance assessed following AR(1) adjustment after Santer et al. (2008) ('x' marks denote non-significant trends). Time series of (b) global, (c) land-only and \r\n(d) ocean-only average annual P-E (mm day-1). Further details on data sources and processing are available in the chapter data table (Table 2.SM.1)."


id: 26fede781a7ec36e728f1d837420438b
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 3526
content:
"2.2). Chapter 8 assesses large-scale as well as regional aspects of \r\ncirculation components and their impact on the hydrological cycle, \r\nwhile Chapter 11 assesses the association of circulation changes and \r\nvariability with extreme events."


id: 5e8a537390df0254a21fc1403cea07cb
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 12409
content:
"In conclusion, observational uncertainty yields low confidence  in \r\nglobally averaged trends in P-E over the 20th century, with a spatial \r\npattern dominated by precipitation changes over land and by \r\nevaporation increases over the ocean. Different reanalyses disagree \r\non the sign of long-term changes in the global mean P-E."


id: 75003a7ad50049cb6a02403c7b35ac47
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 16002
content:
"The AR5 reported low confidence in trends in the strength of the \r\nHadley circulation (HC) and the Walker circulation (WC) due \r\nto uncertainties in available reanalysis datasets and the large \r\ninterannual-to-decadal variability of associated circulation patterns. \r\nHowever, AR5 indicated a likely widening of the tropical belt since the \r\n1970s, albeit with large uncertainty in the magnitude of this change. \r\nThere was high confidence that the post-1990s strengthening of \r\nthe Pacific WC reversed its weakening observed from the mid-19th \r\ncentury to the 1990s."


id: 8320e6e207fbb0a11e1e1ab73c27e027
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 18157
content:
"The AR5 concluded that there was low confidence in a positive trend \r\nin global river discharge during the 20th century. It noted that many \r\nof the largest rivers with long term streamflow records have been \r\nimpacted by non-climatic human influences such as dam construction \r\nor land-use change."


id: 51ab06a3cf154568cc99fdfdccbaf1d4
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 10309
content:
"River discharge is monitored widely, although gaps remain at \r\na subcontinental scale over central Asia and Africa (Wei et al., 2020). \r\nSubstantial recent efforts have been made to generate new global \r\nstreamflow datasets, consolidating observations from many stream \r\ngauges to create streamflow indices (Do et al., 2018; Gudmundsson \r\net al., 2018) and gridded products using neural networks (Barbarossa \r\net al., 2018) or combinations between observations and reanalyses \r\n(Suzuki et al., 2018; Ghiggi et al., 2019). "


id: 702782473d06a13cf246ef199dd0f638
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 15262
content:
"From centennial-scale reanalyses, Liu et  al. (2012) and D'Agostino \r\nand Lionello (2017) found divergent results on HC extent over the \r\nlast 150 years, although with unanimity upon an intensification of \r\nthe SH HC. A substantial discrepancy between HC characteristics \r\nin centennial-scale reanalyses and in ERA-Interim (D'Agostino and \r\nLionello, 2017) since 1979 yields significant questions regarding \r\ntheir ability to capture changes in HC behaviour. Taken together \r\nwith the existence of apparent non-climatic artefacts in the datasets \r\n(Nguyen et al., 2015), this implies low confidence in changes in the \r\nextent and intensity of HC derived from centennial-scale reanalyses. \r\nHowever, using multiple observational datasets and centennial-scale \r\nreanalyses, Bronnimann et  al. (2015) identified a  southward shift \r\nin the NH HC edge from 1945 to 1980 of about 0.25deg latitude per \r\ndecade, consistent with observed changes in global land monsoon \r\nprecipitation (Section 2.3.1.4.2)."


id: aa75e7b4ffcb935933cdc6ee5f2523ee
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 24353
content:
"In summary, the sign of global streamflow trends remains uncertain, \r\nwith slightly more globally gauged rivers experiencing significantly \r\ndecreasing flows than significantly increasing flows since the 1950s \r\n(low confidence)."


id: 5e8343bbfbe6b4ea4ea0c7f543040ec4
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 12406
content:
"Trends in the HC intensity since 1979 differ between reanalyses, \r\nalthough there is a tendency toward HC intensification (Figure 2.17b; \r\nNguyen et al., 2013; Chen et al., 2014; D'Agostino and Lionello, 2017; \r\nR. Huang et al., 2019), which is more marked in the NH than the SH \r\n(Studholme and Gulev, 2018). However, the ability of reanalyses to \r\nrepresent the HC strength has been questioned due to inaccurate \r\nrepresentation of latent heating distribution, which is directly related \r\nto tropical convection and influences the HC dynamics (Chemke and \r\nPolvani, 2019; Mathew and Kumar, 2019)."


id: f9ca4507ade8a6a6ea84ed5064366c36
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 36808
content:
"Paleo evidence during the LGM indicates a weaker WC over the Indian \r\nOcean (DiNezio et  al., 2018; Windler et  al., 2019) with a  stronger \r\nPacific WC (DiNezio and Tierney, 2013). During the Holocene, \r\na  transition from a strong WC located more westward during the \r\nEarly-to-Mid Holocene towards a weak and eastward shifted WC \r\nduring the late Holocene was inferred from proxy records from the \r\nPacific Warm Pool and South East Asia (Barr et al., 2019; Dang et al., \r\n2020; Griffiths et al., 2020), in concurrence with changes in ENSO \r\nactivity (Section 2.4.2). Reconstructions for the CE showed weakened \r\nWC during 1000-1250 and since 1850, with an intensified circulation \r\nduring 1500-1850 CE (Xu et al., 2016; Deng et al., 2017). "


id: 75c827554ab31ae5c20630c988b142a2
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 16126
content:
"Considering instrumental records, there is considerable interdecadal \r\nvariability in the strength of the WC, resulting in time-period dependent \r\nmagnitude and even sign of trends (Carilli et al., 2015; Bordbar et al., \r\n2017; Hou et al., 2018), with some studies reporting weakening over \r\nthe 20th century (e.g.,  Power and Kociuba, 2011; Liu et  al., 2019), \r\nwhile others reported strengthening (Z. Li et  al., 2020), particularly "


id: 506c7b988543c374bb00bea71ae404a7
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 10100
content:
"on  millennial time scales. The intensity of the monsoon systems \r\nis generally out of phase between hemispheres, being associated \r\nwith the precession cycle (about 21-23 kyr) (An et al., 2015; P.X. \r\nWang et al., 2017; Seth et al., 2019), with intensified NH monsoon \r\nsystems during precession minima (Toucanne et al., 2015; Wagner \r\net  al., 2019). The eccentricity forcing (about 100 kyr cycle) shows \r\nstronger GM during interglacial periods (P.X. Wang et  al., 2014, \r\n2017; An et al., 2015; Mohtadi et al., 2016). Changes in obliquity \r\n(about 41 kyr cycle) modify the strength of monsoon systems, with \r\nincreased summer monsoon rainfall when obliquity is maximal (Y. \r\nLiu et al., 2015b; Mohtadi et al., 2016). Millennial scale variability in \r\nGM during the LDT was also linked to the occurrences of Heinrich \r\nstadials, resulting in weakened NH monsoons and intensified SH \r\nmonsoons (An et al., 2015; P.X. Wang et al., 2017; Margari et al., \r\n2020). "


id: f8bedd975d95892eaf3a1670541d595e
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 36648
content:
"In summary, there has been a likely widening of the Hadley circulation \r\nsince the 1980s, mostly due to its extension in the NH, although \r\nthere is only medium confidence in the extent of the changes. This \r\nhas been accompanied by a strengthening of the Hadley circulation, \r\nparticularly in the NH (medium confidence). There is low confidence\r\nin the estimation of long-term trends in the strength of the Walker \r\ncirculation, which are time period dependent and subject to dataset \r\nuncertainties. Trends since 1980 are better characterized and consistent \r\nwith a very likely strengthening that resembles a La Nina-like Walker \r\ncirculation and a westward shift of the Walker circulation, although \r\nwith medium confidence in the magnitude of the changes, arising from \r\nthe differences between satellite observations and reanalysis products."


id: f9bee920dc426fe0fe0dfa9e9991e433
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 36805
content:
"The AR5 reported a weakening of the global monsoon (GM) circulation \r\nas well as a decrease of global land monsoon rainfall over the second \r\nhalf of the 20th century. Nevertheless, there was low confidence in the \r\nobserved circulation trends due to uncertainties in reanalysis products \r\nand in the definition of the monsoon area. From a paleo perspective, \r\nAR5 only assessed regional monsoon changes."


id: 7d1b6b5b792033480f27df30a866386f
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 17272
content:
"In summary, observed trends during the last century indicate that the \r\nGM precipitation decline reported in AR5 has reversed since the 1980s, \r\nwith a likely increase mainly due to a significant positive trend in the NH \r\nsummer monsoon precipitation (medium confidence). However, GM "


id: 350243c6e90380e2d2ecf2b352556009
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
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vector_id: 5750
content:
"precipitation has exhibited large multi-decadal variability over the last \r\ncentury, creating low confidence in the existence of centennial-length \r\ntrends in the instrumental record. Proxy reconstructions show a likely\r\nNH monsoons weakening since the mid-Holocene, with opposite \r\nbehaviour for the SH monsoons. "


id: e4c23f6ac7cbde78cc2c0048413c9330
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 33469
content:
"Cattiaux  et  al., 2016; Vavrus, 2018). Hypothesized links to Arctic \r\nwarming are assessed in Cross-Chapter Box 10.1. "


id: 49af2bb7c9bca8757ea50b7861feebe7
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 8987
content:
"The AR5 reported a likely poleward shift of storm tracks and jet \r\nstreams since the 1970s from different datasets, variables and \r\napproaches. These trends were consistent with the HC widening and \r\nthe poleward shifting of the circulation features since the 1970s. \r\nThere was low confidence in any large-scale change in blocking. "


id: ddd5215afb2724bc349e2ffd0f32c03c
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
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vector_id: 32396
content:
"During 950-1400 CE, hydroclimate indicators suggest a northward \r\nshift of Pacific storm tracks over North America (McCabe-Glynn et al., \r\n2013; Steinman et al., 2014) which was comparable in magnitude \r\nto that over 1979-2015 (J. Wang et al., 2017a). Storm tracks over \r\nthe North Atlantic-European sector shifted northward as indicated \r\nby multi-proxy indicators over the North Atlantic (Wirth  et  al., \r\n2013; Orme et al., 2017) and Mediterranean (Roberts et al., 2012). \r\nReconstructed westerly winds in the SH suggest a poleward shift \r\n(Lamy et al., 2010; Schimpf et al., 2011; Goodwin et al., 2014; Koffman \r\net al., 2014; Moreno et al., 2018), with latitudinal change comparable \r\nto that during recent decades (Swart and Fyfe, 2012; Manney and \r\nHegglin, 2018). "


id: 8b7ce2e92dfb817753810411e988c319
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
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vector_id: 19465
content:
"Multiple reanalyses show that since 1979 the subtropical jet \r\nwind speeds have generally increased in winter and decreased \r\nin summer in both hemispheres, but the trends are regionally \r\ndependent (Pena-Ortiz et al., 2013; Manney and Hegglin, 2018; S.H. \r\nLee et  al., 2019). Over NH mid-latitudes, the summer zonal wind \r\nspeeds have weakened in the mid-troposphere (Francis and Vavrus, \r\n2012; Coumou et  al., 2014, 2015; Haimberger and Mayer, 2017). \r\nMeanwhile there are indications of enhanced jetstream meandering \r\nin boreal autumn at the hemispheric scale (Francis and Vavrus, 2015; \r\nDi Capua and Coumou, 2016), whereas the regional arrangement of \r\nmeandering depends on the background atmospheric state (Cohen \r\net al., 2020). These meandering trends, however, are sensitive to the \r\nmetrics used (Screen and Simmonds, 2013; Hassanzadeh et al., 2014; "


id: 31e699ddd0f97b95a173ca1d926cce2c
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 5266
content:
"Robust trends in blocking have only been found in certain regions \r\nand specific seasons during recent decades. Increases in blocking \r\nfrequency have occurred over low-latitude regions in the North \r\nAtlantic in boreal winter (Davini et al., 2012), the South Atlantic in \r\naustral summer (Dennison et al., 2016) and the southern Indian Ocean \r\nin austral spring (Schemm, 2018). Over the subpolar North Atlantic \r\nsustained periods of positive Greenland blocking were identified \r\nduring 1870-1900 and from the late 1990s to 2015 (Hanna et al., \r\n2015). Further analysis of association of Greenland blocking with the \r\nNAM is provided in Section 2.4.1.1. Meanwhile, a reduced blocking \r\nfrequency has been found over winter in Siberia (Davini et al., 2012) "


id: 21fa7b21b5577699f8d63b19a4bea6e8
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
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vector_id: 2793
content:
"and the south-western Pacific in austral spring (Schemm, 2018). \r\nOver eastern European Russia and western Siberia (40degE-100degE) a \r\ntendency towards longer blocking events was reported by Luo et al. \r\n(2016) for 2000-2013 and by Tyrlis et  al. (2020) for 1979-2017. \r\nInter-annual variance in the number of blocking events over the SH \r\n(Oliveira et  al., 2014) and North Atlantic (Kim and Ha, 2015) has \r\nenhanced. Blocking events and their trends are sensitive to choice \r\nof datasets, calculation periods and methods (Cheung et al., 2013; \r\nBarnes et al., 2014; Pepler et al., 2018; Rohrer et al., 2018; Woollings \r\net  al., 2018b; Kononova and Lupo, 2020). As a result, hemispheric \r\nand global trends in blocking frequency have overall low confidence."


id: 76450053bd2fc39ab8a9a7f9904a6eaf
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 16199
content:
"shifting of extratropical jets in the NH during the mid-Holocene and \r\nover 950-1400 CE to latitudes that likely were similar to those since \r\n1979. There is low confidence in observed global-scale changes in the \r\noccurrence of blocking events."


id: fe39298d488fb8f54aba5d25daf7b774
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 37527
content:
"The AR5 concluded that surface winds over land had generally \r\nweakened. The confidence for both land and ocean surface wind \r\ntrends was low owing to uncertainties in datasets and measures \r\nused. Sea level pressure (SLP) was assessed to have likely decreased \r\nfrom 1979-2012 over the tropical Atlantic and increased over large \r\nregions of the Pacific and South Atlantic, but trends were sensitive to \r\nthe period analysed. "


id: 759e28c259688ef0f770a04d4d99d108
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 16097
content:
"In summary, the total number of extratropical cyclones has likely\r\nincreased since the 1980s in the NH (low confidence), but with \r\nfewer deep cyclones particularly in summer. The number of strong \r\nextratropical cyclones has likely increased in the SH (medium \r\nconfidence). The extratropical jets and cyclone tracks have likely been \r\nshifting poleward in both hemispheres since the 1980s with marked \r\nseasonality in trends (medium confidence). There is low confidence in "


id: a51412f9ba966852da68a3f14c1b9a8e
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 23537
content:
"Terrestrial in situ wind datasets have been updated and the quality\u0002control procedures have been improved, with particular attention to \r\nhomogeneity and to better retaining true extreme values (Dunn et al., \r\n2012, 2014, 2016). Global mean land wind speed (excluding Australia) "


id: 9032359dc2ee3e9ca8f68dcb7e949814
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 20220
content:
"from HadISD for 1979-2018 shows a reduction (stilling) of 0.063 m s-1\r\nper decade (Azorin-Molina et al., 2019). Trends are broadly insensitive \r\nto the subsets of stations used. Although the meteorological \r\nstations are unevenly distributed worldwide and sparse in South \r\nAmerica and Africa, the majority exhibit stilling particularly in the \r\nNH (Figure 2.19). Regionally, strong decreasing trends are reported \r\nin central Asia and North America (-0.106 and -0.084 m s-1 per \r\ndecade respectively) during 1979-2018 (McVicar et al., 2012; Vautard \r\net al., 2012; J. Wu et al., 2018; Azorin-Molina et al., 2019). This stilling \r\ntendency has reversed after 2010 and the global mean surface winds \r\nhave strengthened (Zeng et al., 2019b; Azorin-Molina et al., 2020), \r\nalthough the robustness of this reversal is unclear given the short \r\nperiod and interannual variability (Kousari et al., 2013; Kim and Paik, \r\n2015; Azorin-Molina et al., 2019)."


id: 5c621f96a16dd6bccf8fe4186baba1bf
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 12048
content:
"Over the ocean, datasets demonstrate considerable disagreement in \r\nsurface wind speed trends and spatial features (Kent et  al., 2013). \r\nGlobal ocean surface winds from NOCv2.0 demonstrate upward \r\ntrends of about 0.11 m s-1 per decade (1979-2015) with somewhat \r\nsmaller trends from WASwind for 1979-2011 (Azorin-Molina et al., \r\n2017, 2019). The trends are consistent until 1998, but diverge \r\nthereafter. Both ERA5 and JRA-55 reanalyses show consistently "


id: 6e75ed443c6190f24f4e2faa089de2c8
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 15004
content:
"The modern era reanalyses exhibit SLP increases over the SH \r\nsubtropics with stronger increases in austral winter over 1979-2018. \r\nOver the NH, SLP increased over the mid-latitude Pacific in boreal \r\nwinter and decreased over the eastern subtropical and mid-latitude \r\nNorth Atlantic in boreal summer. Discrepancies in the low-frequency \r\nvariations during the first half of the 20th century exist in the "


id: e3e968412bd204bd7ef77e24192211dc
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 33335
content:
"centennial-scale reanalysis products (Befort et  al., 2016). Overall, \r\nmodern reanalysis datasets support the AR5 conclusion that \r\nthere is no clear signal for trends in the strength and position of \r\nthe  permanent and quasi-permanent pressure centres of action \r\nsince the 1950s. Instead, they highlight multi-decadal variations. \r\nLarge-scale SLP is strongly associated with the changes in modes of \r\nvariability (Section 2.4 and Annex IV)."


id: e86344e01774efa8fbf8adae19c36dd2
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 34063
content:
"In summary, since the 1970s a worldwide weakening of surface wind \r\nhas likely occurred over land, particularly marked in the NH, with low \r\nconfidence in a recent partial recovery since around 2010. Differences \r\nbetween available wind speed estimates lead to low confidence in \r\ntrends over the global ocean as a whole but with most estimates \r\nshowing strengthening globally over 1980-2000 and over the last \r\nfour decades in the Southern Ocean, western North Atlantic and the \r\ntropical eastern Pacific. "


id: 5b6993bbb1379bc0950595596211fa69
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 11883
content:
"The AR5 assessed changes in the polar vortices and reported a likely\r\ndecrease in the lower-stratospheric geopotential heights over Antarctica \r\nin spring and summer at least since 1979. "


id: 32d6f4ffa024dbd4a053d226dead4aed
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 5414
content:
"In summary, it is likely that the northern lower stratospheric polar \r\nvortex has weakened since the 1980s in midwinter, and its location \r\nhas shifted more frequently toward the Eurasian continent. The short \r\nrecord and substantial decadal variability yields low confidence in \r\nany trends in the occurrence of SSW events in the NH winter and such \r\nevents in the SH are rare."


id: bb71580545fdfef311cf54d202fc3966
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 27049
content:
"Multiple definitions for the polar vortex strength and sudden \r\nstratospheric warming (SSW) events have been proposed and \r\ncompared (Butler et al., 2015; Palmeiro et al., 2015; Waugh et al., 2017; \r\nButler and Gerber, 2018), and new techniques identifying daily vortex \r\npatterns and SSWs have been developed (D.M. Mitchell et al., 2013; \r\nKretschmer et al., 2018). Errors in reanalysis stratospheric winds were \r\nassessed and discrepancies in stratospheric atmospheric circulation \r\nand temperatures between reanalyses, satellites and radiosondes have \r\nbeen reported (D.M. Mitchell et al., 2013; Duruisseau et al., 2017). "


id: 919408aa337bebeb9290699d8f43bbb5
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 20444
content:
"This section focuses on large-scale changes in a subset of components \r\nof the cryosphere (Cross-Chapter Box 2.2). Chapter 9 undertakes \r\na holistic assessment of past and possible future changes and \r\nunderstanding of key processes in the cryosphere, including those at \r\nregional scales, integrating observations, modelling and theoretical \r\nunderstanding, while, here in chapter 2, the focus is on past large\u0002scale, observation-based cryospheric changes. "


id: daaffbb004a6d57fafd3a0def003b60a
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 31935
content:
"The AR5 reported that the annual mean Arctic sea-ice extent (SIE) \r\nvery likely decreased by 3.5-4.1% per decade between 1979 and \r\n2012 with the summer sea-ice minimum (perennial sea ice) very \r\nlikely decreasing by 9.4-13.6% per decade. This was confirmed by \r\nSROCC reporting the strongest reductions in September (12.8 +- 2.3% \r\nper decade; 1979-2018) and stating that these changes were likely\r\nunprecedented in at least 1 kyr (medium confidence). The spatial \r\nextent had decreased in all seasons, with the largest decrease for \r\nSeptember (high confidence). The AR5 reported also that the average \r\nwinter sea ice thickness within the Arctic Basin had likely decreased \r\nby between 1.3 m and 2.3 m from 1980 to 2008 (high confidence), \r\nconsistent with the decline in multi-year and perennial ice extent. "


id: b3b2ea34053a8e12ab9a5eb0808fd9f6
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 25787
content:
"The SROCC stated further that it was virtually certain that Arctic sea \r\nice had thinned, concurrent with a shift to younger ice. Lower sea ice \r\nvolume in 2010-2012 compared to 2003-2008 was documented in \r\nAR5 (medium confidence). There was high confidence that, where the \r\nsea ice thickness had decreased, the sea-ice drift speed had increased. "


id: 2ba3cf34c7ec9b53c3a30a80456373fe
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 4300
content:
"Proxy records are used in combination with modelling to assess Arctic \r\npaleo sea ice conditions to the extent possible. For the Pliocene, \r\nlimited proxy evidence of a reduced sea ice cover compared to \r\n'modern' winter conditions (Knies et al., 2014; Clotten et al., 2018) \r\nand model simulations of a largely ice-free Arctic Ocean during \r\nsummer (Howell et al., 2016; Feng et al., 2019; F. Li et al., 2020) imply \r\nmedium confidence that the Arctic Ocean was seasonally ice covered. \r\nOver the LIG, sparse proxy reconstructions (Stein et al., 2017; Kremer \r\net al., 2018) and proxy evidence from marine sediments (Kageyama \r\net al., 2021b) provide medium confidence of perennial sea ice cover. "


id: 8f4c0e98bad0d33039a28510006deea3
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 20093
content:
"Over the past 13 kyr proxy records suggest extensive sea-ice \r\ncoverage during the Younger Dryas (at the end of the LDT), followed \r\nby a decrease in sea ice coverage during the Early Holocene, and \r\nincreasing sea-ice coverage from the MH to the mid-15th century \r\n(De Vernal et al., 2013; Belt et al., 2015; Cabedo-Sanz et al., 2016; \r\nArmand et al., 2017; Belt, 2018). There is limited evidence that the \r\nCanadian Arctic had less multiyear sea ice during the Early Holocene \r\nthan today (Spolaor et al., 2016). For more regional details on paleo \r\narctic sea ice see Section 9.3.1.1. "


id: cc1dfcc58f6f16abeab0c63c49d6e63e
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 29654
content:
"Pan-Arctic SIE conditions (annual means and late summer) during the \r\nlast decade were unprecedented since at least 1850 (Figure 2.20a; \r\nWalsh et al., 2017, 2019; Brennan et al., 2020), while, as reported \r\nin SROCC, there remains medium confidence that the September \r\n(late  summer) Arctic sea ice loss during the last decade was \r\nunprecedented during the past 1 kyr. Sea-ice charts since 1850 \r\n(Walsh et al., 2017, 2019) suggest that there was no significant trend \r\nbefore the 1990s, but the uncertainty of these estimates is large and \r\ncould mask a trend, a possibility illustrated by Brennan et al. (2020), \r\nwho found a loss of Arctic sea ice between 1910 and 1940 in an \r\nestimate based on a data assimilation approach."


id: 3b1f4fe13beb4ad424d344868bd84ff
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 6661
content:
"Over the past two decades, first-year sea ice has become more \r\ndominant and the oldest multiyear ice (older than 4 years) which \r\nin March 1985 made up 33% of the Arctic sea-ice cover, has nearly \r\ndisappeared, making up 1.2% in March 2019 (Perovich et  al., \r\n2020). The loss of older ice is indicative of a thinning overall of ice \r\ncover (Tschudi et  al., 2016), but also the remaining older ice has \r\nbecome thinner (E. Hansen et al., 2013). Since in situ ice thickness \r\nmeasurements are sparse, information about ice thickness is mainly \r\nbased on airborne and satellite surveys. Records from a combination "


id: 81915ba2f0500738e4751aafdb86a83
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 17918
content:
"The SROCC noted the lack of continuous records of snow on sea \r\nice. Nevertheless in recent decades, more snow on sea ice has been \r\nobserved in the Atlantic sector in the Arctic than in the western Arctic \r\nOcean (Webster et al., 2018). Previously, Warren et al. (1999) showed \r\nthat over 1954-1991 there were weak trends towards declining snow \r\ndepth on sea ice in the Pacific sector. Recent observations indicate \r\na substantial thinning of the spring snowpack in the western Arctic \r\n(Cavalieri et al., 2012; Brucker and Markus, 2013; Kurtz et al., 2013; \r\nLaxon et al., 2013; Webster et al., 2018). In contrast, thick snow over \r\nArctic sea ice in the Atlantic sector north of Svalbard (snow thickness \r\naround 0.4 m or more) has been observed in the 1970s and since the \r\n1990s (Rosel et al., 2018), but data are too sparse to detect trends. "


id: c0e24d0427cdab7bf4231dfbfddac1aa
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 27918
content:
"In summary, over 1979-2019 Arctic SIA has decreased for all months, \r\nwith the strongest decrease in summer (very high confidence). \r\nDecadal means for SIA decreased from the first to the last decade \r\nin that period from 6.23 to 3.76 million km2 for September, and from \r\n14.52 to 13.42 million km2 for March. Arctic sea ice has become \r\nyounger, thinner and faster moving (very high confidence). Snow \r\nthickness on sea ice has decreased in the western Arctic Ocean \r\n(medium confidence). Since the Younger Dryas at the end of the LDT, \r\nproxy indicators show that Arctic sea ice has fluctuated on multiple \r\ntime scales with a decrease in sea ice coverage during the Early \r\nHolocene and an increase from the MH to the mid-15th century. \r\nCurrent pan-Arctic sea ice coverage levels (annual mean and late \r\nsummer) are unprecedentedly low since 1850 (high confidence), and \r\nwith medium confidence for late summer for at least the past 1 kyr. "


id: 5dc38997bf8d6ce6dd70be57829cb55d
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 12279
content:
"The AR5 reported a small but significant increase in the total annual \r\nmean Antarctic SIE that was very likely in the range of 1.2-1.8% per \r\ndecade between 1979 and 2012 (0.13-0.20 million km2 per decade) \r\n(very high confidence), while SROCC reported that total Antarctic sea \r\nice coverage exhibited no significant trend over the period of satellite \r\nobservations (1979-2018) (high confidence). The SROCC noted that \r\na significant positive trend in mean annual sea ice cover between \r\n1979 and 2015 had not persisted, due to three consecutive years of \r\nbelow-average sea ice cover (2016-2018). The SROCC stated also \r\nthat historical Antarctic sea ice data from different sources indicated a \r\ndecrease in overall Antarctic sea ice cover since the early 1960s, but was \r\ntoo small to be separated from natural variability (high confidence)."


id: c725defa300876f6222d358b71b9b046
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 28918
content:
"There is only limited evidence from predominantly regional paleo \r\nproxies for the evolution of Southern Ocean sea ice before the \r\ninstrumental record and estimates are not available for all proxy \r\ntarget periods (Section 9.3.2). Proxies from marine sediments for \r\nintervals preceding and following the MPWP indicate open water \r\nconditions with less sea ice than modern conditions (Taylor-Silva and \r\nRiesselman, 2018; Ishino and Suto, 2020). During the LGM, proxies \r\nindicate that austral winter sea ice coverage reached the polar ocean \r\nfront (e.g., Nair et al., 2019). More recently, sea ice coverage appears \r\nto have fluctuated substantially throughout the Holocene (e.g., for the \r\nwestern Amundsen Sea, Lamping et al., 2020). At the beginning of the \r\nCE, regional summer sea ice coverage in the north-western Ross Sea \r\nwas lower than today (Tesi et al., 2020). Crosta et al. (2021) suggest, \r\nbased on different proxies, four different phases with 7-10 months "


id: 9d125f829375c3425e0acddf22c71e5c
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 22252
content:
"periods of sea ice occurrence per year in the Antarctic region off Adelie \r\nLand during the CE, where each phase was several hundred years long. "


id: 29bc0b925189e780a10cc71c5ba172db
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 3998
content:
"In summary, Antarctic sea ice has experienced both increases and \r\ndecreases in SIA over 1979-2019, and substantively lower levels \r\nsince 2016, with only minor differences between decadal means \r\nof SIA for the first (for February 2.04 million km2, for September \r\n15.39 million km2) and last decades (for February 2.17 million km2, \r\nfor September 15.75 million km2) of satellite observations (high \r\nconfidence). There remains low confidence in all aspects of Antarctic \r\nsea ice prior to the satellite era owing to a paucity of records that are \r\nhighly regional in nature and often seemingly contradictory."


id: c247a14c3f746845bddaa83347a9e796
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 28149
content:
"The AR5 concluded that snow cover extent (SCE) had decreased in the \r\nNH, especially in spring (very high confidence). For 1967-2012, the \r\nlargest change was in June and March-April SCE very likely declined. \r\nNo trends were identified for the SH due to limited records and large \r\nvariability. The SROCC concluded with high confidence that Arctic \r\nJune SCE declined between 1967 and 2018 and in nearly all mountain \r\nregions, snow cover declined in recent decades."


id: 5b1e6bf1fe6657086660bbef644b9889
created_at: 2023-03-16 14:00:39
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vector_id: 11845
content:
"mass, although there were considerable inter-annual and regional \r\nvariations. Between 2006 and 2015 the global glacier mass change \r\nassessed by SROCC was -278 +- 113 Gt yr-1. "


id: f97c9875bf1e314fe95f77b75931208b
created_at: 2023-03-16 14:00:39
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vector_id: 36764
content:
"There has been a commensurate decrease in the snow-cover duration \r\nand persistence, particularly in higher latitudes due to earlier \r\nspring melt and, in some cases, later autumn onset of snow cover \r\n(Chen et al., 2015; Derksen et al., 2015; Hori et al., 2017; Hammond \r\net al., 2018). Arctic snow-cover duration has decreased by 2-4 days \r\nper decade since the 1970s (Brown et al., 2017). Significant decreases \r\nin snow-cover duration have been documented over western Eurasia \r\nsince 1978 (Hori et al., 2017). "


id: b44d47d9194a6001bd6806328ea20d3b
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 25878
content:
"For the NH, maximum snow depth has generally decreased since \r\nthe 1960s, with more robust trends for North America and greater \r\nuncertainty for Eurasia (Kunkel et al., 2016). Several satellite-based \r\npassive microwave and other products indicate general declines in \r\npre-melt snow water equivalent since 1981 although there is regional \r\nand inter-dataset variability (Brown et al., 2017; Jeong et al., 2017; \r\nMarty et  al., 2017; Mortimer et  al., 2020; Mudryk et  al., 2020; \r\nPulliainen et al., 2020, Section 9.5.3). "


id: 56e9541074b26971f59b9263de496b2f
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 11148
content:
"In summary, substantial reductions in spring snow cover extent have \r\noccurred in the NH since 1978 (very high confidence) with limited \r\nevidence that this decline extends back to the early 20th century. \r\nSince 1981 there has been a general decline in NH spring snow water \r\nequivalent (high confidence)."


id: be47b48c1a054cdecde393ac1843ed46
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 27487
content:
"The AR5 concluded with high confidence that, during the Holocene, \r\nglaciers were at times smaller than at the end of the 20th century. \r\nThe AR5 stated further with very high confidence that most glaciers \r\nhad been shrinking since the mid-1800s, and the mass loss from \r\nall glaciers worldwide very likely increased from 1970 to 2009. The \r\nSROCC reported a globally coherent picture of continued glacier \r\nrecession in recent decades (very high confidence) based on in situ \r\nand satellite observations of changes in glacier area, length and "


id: 39f1abaa11a1553905198429f81d9b9c
created_at: 2023-03-16 14:00:39
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vector_id: 6491
content:
"Figure 2.23 | Mountain glacier advance and annual mass change. (a) Number of a finite selection of surveyed glaciers that advanced during the past 2000 years. \r\n(b) Annual and decadal global glacier mass change (Gt yr-1) from 1961 until 2018. In addition, mass change mean estimates are shown. Ranges show the 90% confidence \r\ninterval. Further details on data sources and processing are available in the chapter data table (Table 2.SM.1)."


id: 95c7e3562a0f6773f25361b1a361b3bc
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 21064
content:
"In summary, there is very high confidence that, with few \r\nexceptions, glaciers worldwide have retreated since the second \r\nhalf of the 19th century, and continue to retreat. The current global \r\ncharacter of glacier mass loss is highly unusual (almost all glaciers \r\nsimultaneously receding) in the context of at least the last 2 kyr \r\n(medium confidence). Glacier mass loss rates have increased since \r\nthe 1970s (high confidence). Although many surveyed glaciers are \r\ncurrently more extensive than during the MH (high confidence), \r\nthey generally are in disequilibrium with respect to current climate \r\nconditions and hence are committed to further ice loss. "


id: 6d362de2ee2ab5f9fddee3b2eb7c023a
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 14803
content:
"Recent studies of marine and lake sediments, glacier ice, and \r\ngeomorphic features show that the GrIS retreated rapidly during the \r\nearly Holocene but halted periodically, with a complex ice-margin \r\nchronology (Carlson et al., 2014; Larsen et al., 2014, 2015; Young and \r\nBriner, 2015; Briner et al., 2016; Young et al., 2020). It is probable that \r\nits total volume during 8-3 ka was smaller than today (Larsen et al., \r\n2015; Young and Briner, 2015; Briner et al., 2016), but uncertainties \r\nexist regarding precisely when the minimum MH extent and volume \r\nwas reached, due to uncertainties in reconstructions. The GrIS then \r\nre-advanced reaching its maximum extent in most places during \r\n1450-1850 CE, although the timing and extent of this maximum \r\ndiffered by sector (Larsen et al., 2015; Briner et al., 2016)."


id: 858fcd8d31947825e33babd269d33570
created_at: 2023-03-16 14:00:39
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vector_id: 18548
content:
"During glacial periods, ice sheets were more extensive and the state \r\nof knowledge on their paleo-reconstruction can be found in recent \r\npublications (e.g.,  Stokes et  al., 2015; Batchelor et  al., 2019). This \r\nsection focuses only on the large-scale aspects of those ice sheets, \r\nGreenland and Antarctic, that still exist today. "


id: 8cde4841334e73cbace1a77a87bbbc03
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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content:
"Greenland-wide estimates of mass change based on direct observations \r\nwere limited prior to 1992 at the time of AR5 (Kjeldsen et al., 2015). \r\nCombined records based on airborne observations, model-based \r\nestimates and geodetic approaches indicate an average mass loss of \r\n75 +- 29.4 Gt yr-1 for 1900-1983 (Kjeldsen et al., 2015). Integration \r\nof proxies and modelling indicates that the last time the rate of mass \r\nloss of the GrIS was plausibly similar to 20th century rates was during \r\nthe early Holocene (Buizert et al., 2018; Briner et al., 2020)."


id: 4e42880439b003cbad4174b837d8e21f
created_at: 2023-03-16 14:00:39
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vector_id: 9738
content:
"The AR5 concluded the volume of the Greenland Ice Sheet (GrIS) was \r\nreduced compared to present during periods of the past few million \r\nyears that were globally warmer than present (high confidence). \r\nIt reported that the GrIS had lost ice during the prior two decades \r\n(very high confidence), that the ice loss had occurred in several sectors, \r\nand that high rates of mass loss had both expanded to higher elevations \r\n(high confidence) and very likely accelerated since 1992. The SROCC \r\nconcluded that it was extremely likely that ice loss increased through \r\nthe early 21st century. The SROCC also found that summer melting \r\nrate had increased since the 1990s to a rate unprecedented over the \r\nlast 350 years (very high confidence), being two to five times greater \r\nthan the pre-industrial rates (medium confidence)."


id: 5206462a7a98490fc21dfd9b0c5d4747
created_at: 2023-03-16 14:00:39
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vector_id: 10358
content:
"Since AR5, a combination of remote sensing, in situ observations and \r\nmodelling has provided new insights regarding surface processes and \r\ntheir contribution to recent GrIS mass changes (AMAP, 2017; van den \r\nBroeke et al., 2017; Bamber et al., 2018; Mouginot et al., 2019; IMBIE \r\nConsortium, 2020; Khan et al., 2020). Estimates of total ice loss during \r\nthe post-1850 period (Kjeldsen et al., 2015) and recent observations \r\nshow that the rate of loss has increased since the beginning of the \r\n21st century (IMBIE Consortium, 2020; Sasgen et al., 2020; Velicogna \r\net al., 2020) (Section 9.4.1.1 and Figures 2.24 and 9.17)."


id: 78a67bc6cb70a9939d25bcb1cab2fc6b
created_at: 2023-03-16 14:00:39
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"Details of the history of the GrIS fluctuations during warm \r\ninterglacials continue to be elucidated. Oscillations over the past \r\n7.5 Myr, including the Pliocene and through the glacial - interglacial \r\ncycles of the Pleistocene are not well-constrained, but most studies \r\nindicate that Greenland was at least partially glaciated over this "


id: fe81752e121c3450d79599e66e4d4e34
created_at: 2023-03-16 14:00:39
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content:
"The GrIS lost 4890 [4140 to 5640] Gt (SLE 13.5 [11.4 to 15.6] mm) \r\nof ice between 1992 and 2020 (Section 9.4.1 and Figure 2.24; IMBIE \r\nConsortium, 2020). The ice sheet was close to mass balance in the 1990s, "


id: 799ec9af4a67c033ff15f0d3ac7ff3cc
created_at: 2023-03-16 14:00:39
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vector_id: 16702
content:
"de Boer et al., 2015; DeConto and Pollard, 2016; Levy et al., 2016). \r\nResults from sediment studies suggest a smaller AIS during the \r\nMPWP compared with current levels, with main differences in the \r\nWAIS (Section 9.6.2; SROCC, IPCC, 2019; Bertram et  al., 2018; \r\nShakun et  al., 2018). Marine sediments indicate that during the \r\nPleistocene repeated ungrounding and loss of large marine-based \r\nparts of the AIS occurred during interglacial periods, with at least \r\nseven transitions between floating and grounded ice in the Ross \r\nSea during the last 780 kyr (McKay et al., 2012) and at least three \r\nreductions in ice volume in the Wilkes Basin during the last 500 kyr \r\n(Wilson et al., 2018). Proxies, modelling and process understanding \r\n(Rohling et  al.,  2019; Clark et  al., 2020) indicate that the AIS was \r\nsmaller during the LIG than present. "


id: 79521e944cc6e38610870e362cd3b022
created_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 16655
content:
"but increases in mass loss have occurred since (Bamber et al., 2018; \r\nWCRP Global Sea Level Budget Group, 2018; Mouginot et al., 2019; \r\nIMBIE Consortium, 2020). The rate of ice-sheet (including peripheral \r\nglaciers) mass loss rose from 120 [70  to  170]  Gt  yr-1 (SLE  0.33 \r\n[0.18  to  0.47] mm yr-1) in 1901-1990 to 330 [290 to 370] Gt  yr-1\r\n(SLE  0.91 [0.79 to 1.02] mm yr-1) for 2006-2018 (Section  9.4.1, \r\nTable 9.5)."


id: e11504e66e03c497c6c30959b73eff03
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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content:
"In summary, the GrIS was smaller than present during the MPWP \r\n(medium confidence), LIG (high confidence) and the MH (high \r\nconfidence). GrIS mass loss began following a peak volume attained \r\nduring the 1450-1850 period and the rate of loss has increased \r\nsubstantially since the turn of the 21st century (high confidence)."


id: f7acb51a4491d3b76861e6d2774c2c7c
created_at: 2023-03-16 14:00:39
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content:
"The AR5 reported that there was high confidence that the Antarctic \r\nIce Sheet (AIS) was losing mass. The average ice mass loss from \r\nAntarctica was 97 [58 to 135] Gt yr-1 (GMSL equivalent of 0.27 \r\n[0.16 to 0.37] mm yr-1) over 1993-2010, and 147 [74 to 221] Gt yr-1\r\n(0.41 [0.20 to 0.61] mm yr-1) over 2005-2010. These assessments \r\nincluded the Antarctic peripheral glaciers. The AR5 reported with high \r\nconfidence that the volume of the West Antarctic Ice Sheet (WAIS) \r\nwas reduced during warm periods of the past few million years. The \r\nSROCC concluded that over 2006-2015, the AIS lost mass at an \r\naverage rate of 155 +- 19 Gt yr-1 (very high confidence). The SROCC \r\nalso stated that it is virtually certain that the Antarctic Peninsula \r\nand WAIS combined have cumulatively lost mass since widespread \r\nmeasurements began in 1992, and that the rate of loss has increased \r\nsince around 2006."


id: f36fae955a3729b8cd23c19806300ed2
created_at: 2023-03-16 14:00:39
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content:
"Process understanding and, to some extent, paleoclimate records \r\nshow that changes in parts of the AIS can occur over multi-century \r\ntime scales (<2kyr; Sections 9.4.2.3 and 9.6.2; e.g.,  Dowdeswell \r\net al., 2020). Based on physical understanding, paleo evidence and \r\nnumerical simulations, it is very likely that the AIS has been smaller \r\nthan today during at least some past warm climates (such as MCO \r\nand LIG), in particular the WAIS (Figure 9.18; Golledge et al., 2014; "


id: 258032f3035e21b03b9e448f4b21fb7b
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 3324
content:
"balance is not significantly different from zero (Bamber et al., 2018; \r\nIMBIE Consortium, 2018; Mohajerani et al., 2018; Rignot et al., 2019)."


id: 65f2d2614b12ae93152493315de794c6
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 13629
content:
"In summary, the AIS has lost mass between 1992 and 2020 (very high \r\nconfidence), and there is medium confidence that this mass loss has \r\nincreased. During the MPWP and LIG, the ice sheet was smaller than \r\npresent (medium confidence). There is low confidence as to whether \r\nthe total mass of the ice sheet was larger or smaller around 6 ka \r\ncompared to now."


id: 8d818973096a830fb1261fa258ab128e
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 19790
content:
"The AR5 concluded that in most regions and at most monitoring \r\nsites permafrost temperatures since the 1980s had increased (high \r\nconfidence). Negligible change was observed at a few sites, mainly \r\nwhere permafrost temperatures were close to 0degC, with slight cooling \r\nat a limited number of sites. The AR5 also noted positive trends in \r\nactive layer thickness (ALT; the seasonally thawed layer above the \r\npermafrost) since the 1990s for many high latitude sites (medium \r\nconfidence). The SROCC concluded permafrost temperatures have \r\nincreased to record high levels since the 1980s (very high confidence) \r\nwith a recent increase by 0.29degC +- 0.12degC from 2007 to 2016 \r\naveraged across polar and high mountain regions globally."


id: 994eac45e4644c1d4bcd5b2722c05f52
created_at: 2023-03-16 14:00:39
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content:
"is minimal) were the highest ever directly observed at most sites \r\n(Romanovsky et al., 2020), with temperatures in colder permafrost \r\nof northern North America being more than 1degC higher than they \r\nwere in 1978. Increases in temperature of colder Arctic permafrost \r\nare larger (average 0.4degC-0.6degC per decade) than for warmer \r\n(temperature >-2degC) permafrost (average 0.17degC per decade) of \r\nsub-Arctic regions (Figures 2.25, 9.22). "


id: 590ac873abc1f22c3d313bdae13c3f7
created_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 11502
content:
"Increases in permafrost temperature over the last 10-30 years of \r\nup to 0.3degC per decade have been documented at depths of about \r\n20 m in high elevation regions in the NH (European Alps, the Tibetan \r\nPlateau and some other high elevation areas in Asia; G. Liu et al., \r\n2017; Cao et al., 2018; Biskaborn et al., 2019; Noetzli et al., 2020; \r\nZhao et al., 2020). In Antarctica, where records are limited and short \r\n(most <10 years) trends are less evident (Noetzli et al., 2019)."


id: ad08333867241de7604e9167d126bf9a
created_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 24769
content:
"Records of permafrost temperature measured in several boreholes \r\nlocated throughout the northern polar regions indicate general \r\nwarming of permafrost over the last 3-4 decades (Figure 2.25), \r\nwith marked regional variations (Romanovsky et al., 2017a, b, 2020; \r\nBiskaborn et al., 2019). Recent (2018-2019) permafrost temperatures \r\nin the upper 20-30 m layer (at depths where seasonal variation "


id: 7328b13b08017f96d689467fe1c0a8e1
created_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 15733
content:
"Observations of ground subsidence and other landscape change \r\n(e.g.,  thermokarst, slope instability) since the middle of the \r\n20th  century in the Arctic associated with ground ice melting \r\nhave been documented in several studies and provide additional \r\nindications of thawing permafrost (Sejourne et  al., 2015; Liljedahl \r\net al., 2016; Borge et al., 2017; Kokelj et al., 2017; Nitze et al., 2017; \r\nStreletskiy et al., 2017; Derksen et al., 2019; Farquharson et al., 2019; \r\nLewkowicz and Way, 2019; O'Neill et al., 2019; see Section 9.5.2.1). \r\nIn mountain areas, destabilization and acceleration of rock glacier \r\ncomplexes that may be associated with warming permafrost have \r\nalso been observed (Eriksen et al., 2018; Marcer et al., 2019)."


id: a89df69c4666191c0709eafa740858d4
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 24059
content:
"In summary, increases in permafrost temperatures in the upper 30 m \r\nhave been observed since the start of observational programs over \r\nthe past three to four decades throughout the permafrost regions \r\n(high confidence). Limited evidence suggests that permafrost was \r\nless extensive during the MPWP (low confidence). Permafrost that \r\nformed after 3ka still persists in areas of the NH, but there are \r\nindications of thaw after the mid-1800s (medium confidence)."


id: b31492b1b143a10575d2ac0c4200e263
created_at: 2023-03-16 14:00:39
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vector_id: 25691
content:
"This section focuses on large-scale changes in a subset of physical \r\ncomponents of the ocean (Cross-Chapter Box 2.2). Chapter 7 assesses \r\nthe role of the ocean in Earth system heating and evaluates the Earth's \r\nenergy budget. Chapter 9 undertakes a holistic assessment of changes \r\nin the ocean integrating observations, modelling and theoretical \r\nunderstanding. Chapter 11 assesses extremes such as marine heat \r\nwaves and storm surges. SSTs are assessed in Section 2.3.1.1 as they \r\nconstitute a critical component of GMST estimation. "


id: be701c78238aef0931ec458d63678c88
created_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 27511
content:
"AR5 assessed that since 1971, global ocean warming was virtually \r\ncertain for the upper 700 m and likely for the 700-2000 m layer. \r\nThe SROCC reported linear warming trends for the 0-700 m and \r\n700-2000 m layers of the ocean, respectively, of 4.35 +- 0.8 and 2.25 \r\n+- 0.64 ZJ yr-1 over 1970-2017; 6.28 +- 0.48 and 3.86 +- 2.09 ZJ yr-1\r\nover 1993-2017; and 5.31 +- 0.48 and 4.02 +- 0.97 ZJ yr-1 over 2005-\r\n2017. Both AR5 and SROCC assessed that the ocean below 2000 \r\nm had likely warmed since 1992. The SROCC reported global mean \r\nthermosteric sea level (ThSL) rise, associated with thermal expansion \r\nof the ocean, with a trend of 0.89 +- 0.05 mm yr-1 for 1970-2015; \r\n1.36 +- 0.40 mm yr-1 for 1993-2015; and 1.40 +- 0.40 mm yr-1 for \r\n2006-2015, and also reported that the rate of ocean warming over \r\n1993-2017 had likely more than doubled since 1969-1992."


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vector_id: 22048
content:
"New ocean heat content (OHC) reconstructions derived from paleo \r\nproxies (Bereiter et  al., 2018; Baggenstos et  al., 2019; Shackleton \r\net al., 2019; Gebbie, 2021) indicate that the global ocean warmed by \r\n2.57degC +- 0.24degC, at an average rate of about 0.3degC ka-1 (equivalent \r\nto an OHC change rate of 1.3 ZJ yr -1) from the LGM (about 20 ka) to \r\nthe early Holocene (about 10 ka; Section 9.2.2.1 and Figure 9.9). Over \r\nthe LDT, ocean warming occurred in two stages, offset by some heat \r\nloss during the Antarctic Cold Reversal (14.58-12.75 ka). Only during "


id: ff6e4491d1b995be912ae638d8e4f356
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 37739
content:
"Collectively, the new and updated analyses strengthen AR5 and \r\nSROCC findings of a sustained increase in global OHC (Figure 2.26 \r\nand Table 2.7) and associated ThSL rise. Larger warming rates are \r\nobserved in the upper 700 m compared to deeper layers, with \r\nmore areas exhibiting significant warming than significant cooling \r\n(Johnson and Lyman, 2020). There is an improved consistency among "


id: c27cb1e5190c35bbab19da2e4fb0ba18
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
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vector_id: 28191
content:
"available estimates of OHC rates in the upper 2000 m since 2006. \r\nCheng et al. (2020), von Schuckmann et al. (2020) and Johnson et al. \r\n(2020) have further confirmed that the central estimates of rates of \r\nOHC change in the upper 2000 m depths have increased after 1993 \r\nand particularly since 2010 (Section 3.5.1.3 and Figures 2.26 and \r\n3.26), although uncertainties are large (Table 2.7). Ocean reanalyses \r\nsupport findings of continued upper ocean warming (Balmaseda \r\net al., 2013; von Schuckmann et al., 2018; Meyssignac et al., 2019), \r\nalbeit with higher spread than solely observational estimates, \r\nparticularly in the poorly sampled deep ocean below 2000 m (Storto \r\net al., 2017; Palmer et al., 2018). "


id: 2f8739295094cdc95b8082b0dfbcb58b
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 4896
content:
"In summary, current multi-decadal to centennial rates of OHC \r\ngain are greater than at any point since the last deglaciation \r\n(medium confidence). At multi-centennial timescales, changes in OHC \r\nbased upon proxy indicators demonstrate a tight link with surface \r\ntemperature changes during the last deglaciation (high confidence), \r\nas well as during the Holocene and CE (low confidence). It is likely the \r\nglobal ocean has warmed since 1871, consistent with the observed \r\nincrease in sea surface temperature. It is virtually certain that OHC \r\nincreased between 1971 and 2018 in the upper 700 m and very \r\nlikely in the 700-2000 m layer, with high confidence since 2006. It is \r\nlikely the OHC below 2000 m has increased since 1992. Confidence in \r\nthe assessment of multi-decadal OHC increase is further strengthened \r\nby consistent closure of both global sea level and energy budgets \r\n(Section 7.2.2.2, Box 7.2, Cross-Chapter Box 9.1)."


id: c4bba97d04af03eb6f6ae538d198b661
created_at: 2023-03-16 14:00:39
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vector_id: 28525
content:
"had very likely become fresher since the 1950s, both at the near\u0002surface, and in the ocean interior along ventilation pathways. From \r\n1950 to 2008, the mean surface contrast between high- and low\u0002salinity regions increased by 0.13 [0.08 to 0.17] (PSS-78, UNESCO/\r\nICES/SCOR/IAPSO, 1981). Across basins, the Atlantic Ocean had "


id: 441e07c0909f4ec715a0a35a26203f13
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
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vector_id: 8134
content:
"average, with freshening in subpolar regions and salinification in the \r\nsubtropical gyres (Durack and Wijffels, 2010; Good et al., 2013; Skliris \r\net  al., 2014; Durack, 2015; Aretxabaleta et  al., 2017; Cheng et  al., \r\n2020). Regional changes in salinity are assessed in Section 9.2.2.2."


id: 87503082523675b2e4e32f1884cedf98
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 18830
content:
"In summary, it is virtually certain that since 1950 near-surface high \r\nsalinity regions have become more saline, while low salinity regions \r\nhave become fresher, and it is very likely that this extends to the ocean \r\ninterior along ventilation pathways. Across basins, it is very likely that \r\nthe Atlantic has become saltier and the Pacific and Southern oceans \r\nhave freshened. The differences between high-salinity and low\u0002salinity regions are linked to an intensification of the hydrological \r\ncycle (medium confidence). "


id: d068359e281cd29cc7cbc0bf4503e3cb
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 30315
content:
"Since AR5, new and extended multi-decadal analyses have \r\nstrengthened the observational support for increased contrast \r\nbetween high and low near-surface salinity regions and inter-basin \r\ncontrast since the mid-20th century (Section 9.2.2.2; Durack and \r\nWijffels, 2010; Good et  al., 2013; Skliris et  al., 2014; Aretxabaleta \r\net  al., 2017; Cheng et  al., 2020). These analyses employ different \r\nstatistical algorithms for interpolation, and only Cheng et al. (2020) \r\nuse CMIP5 model simulations to constrain observation-based signals \r\nin data-sparse regions."


id: 3ba0f381eb678640a05043ff8cecd12a
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 6735
content:
"Changes in the global patterns of near-surface salinity contrast \r\nare transferred to the ocean interior via ventilation pathways \r\n(Figure 2.27b). Large scale similarities in subsurface salinity changes \r\nacross observational estimates point to decreasing (increasing) \r\nsalinity in regions where salinity is lower (higher) than the global "


id: 53e302d5593618110773b509ea4d4a0e
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 10664
content:
"Few sites globally have well-preserved MIS 11 sea-level indicators \r\n(Dutton et al., 2015). As reported in AR5, Raymo and Mitrovica (2012) \r\nused glacial isostatic adjustment models to correct the elevation of \r\nMIS 11 sea-level proxies from Bermuda and Bahamas to estimate \r\na peak MIS 11 GMSL between 6 and 13 m above present-day. This \r\nagrees with the elevation of 13 +- 2 m for the MIS 11 subtidal-intertidal \r\ntransition in South Africa (Roberts et  al., 2012). A  revised glacial \r\nisostatic adjustment at this location resulted in a peak GMSL estimate \r\nof 8-11.5 m (Chen et al., 2014). In light of these data, and the review \r\nby Dutton et al. (2015), the AR5 estimate of 6-13 m for MIS 11 remains \r\nthe best available (medium confidence)."


id: 6ae638ce920b4947785faf75c270b22c
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 14436
content:
"The Earth was largely ice free during the EECO (Cramer et al., 2011; \r\nMiller et al., 2020, Section 9.6.2), and complete loss of current land \r\nice reservoirs would raise GMSL by 65.6 +- 1.8 m (Morlighem et al., \r\n2017, 2020; Farinotti et al., 2019). Given that GMSL change must be \r\ndue to some combination of transient land ice growth and changes \r\nin terrestrial water storage, additional global mean thermosteric \r\nsea-level increase of 7 +- 2 m (Fischer et al., 2018) implies a peak \r\nEECO GMSL of 70-76 m (low confidence). Changes in ocean basin \r\nsize driven by plate tectonics contributed a comparable amount to \r\nglobal mean geocentric sea level in the Eocene, but are definitionally \r\nexcluded from GMSL assessment (Wright et al., 2020)."


id: 94f82668e44f40bb8929f4718f823c1d
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 20944
content:
"New geological proxies and glacial isostatic adjustment (GIA) \r\nmodelling studies confirm that, at the LGM, GMSL was 125-134 m \r\nbelow present (Lambeck et al., 2014; Yokoyama et al., 2018). During \r\nthe LDT, GMSL rose from approximately -120 m to -50 m, implying an \r\naverage rate of about 10 mm yr-1 (Lambeck et al., 2014). The fastest \r\nrise occurred during Meltwater Pulse 1A, at about 14.6-14.3  ka \r\n(Deschamps et al., 2012; Sanborn et al., 2017), when GMSL rose by \r\nbetween 8 m and 15 m (medium confidence) (J. Liu et al., 2016) at an \r\naverage rate of 24-44 mm yr-1. "


id: 4dd780bc1e7cc81afdd31fe91a1b3fba
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 9674
content:
"For the MPWP, several studies of coastal features have provided \r\nadditional quantitative sea-level estimates of: 5.6-19.2 m from \r\nSpain (Dumitru et al., 2019), approximately 14 m from South Africa \r\n(Hearty et  al., 2020), 15 m from the United States (Moucha and \r\nRuetenik, 2017), and 25 m from New Zealand (Grant et al., 2019). \r\nThus, consistent with SROCC, GMSL during the MPWP was higher \r\nthan present by 5-25 m (medium confidence)."


id: 93049e93190af6105863d9642e666ae4
created_at: 2023-03-16 14:00:39
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vector_id: 20648
content:
"Reconstructions of GMSL from marine oxygen isotopes in foraminifera \r\nshells show variations of more than 100 m over intervals of 10-100 kyr \r\nduring glacial-interglacial cycles of the Quaternary (Shackleton, 1987; \r\nMcManus et  al., 1999; Waelbroeck et  al., 2002; Miller et  al., 2020). \r\nCorrection for past temperatures and a calibration for ice-volume \r\nchanges implies uncertainty estimates of +- 10-13 m (1 SD) (Grant \r\net al., 2014; Shakun et al., 2015; Spratt and Lisiecki, 2016). A recent \r\nmarine oxygen-isotope-based GMSL reconstruction (Spratt and Lisiecki, \r\n2016) agrees with previous reconstructions, while focusing on the past \r\n800 kyr (Figure 2.28). It shows that GMSL during the Holocene was \r\namong the highest over this entire interval, and was surpassed only \r\nduring the LIG (Marine Isotope Stage (MIS 5e)) and MIS 11 (medium \r\nconfidence); however, relatively brief (about 2 kyr) highstands during \r\nother interglacial periods might be obscured by dating limitations."


id: 2b3b20184263e98dc7f7aede51a4dd4a
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 4237
content:
"Recent GIA modelling studies tuned to both near- and far-field relative \r\nsea level (RSL) data yield MH GMSL estimates of -3.8 to -1.0  m \r\n(Lambeck et al., 2014; Peltier et al., 2015; Bradley et al., 2016; Roy \r\nand Peltier, 2017). Estimates from relatively stable locations where \r\nthe effects of GIA are small and relatively insensitive to parameters \r\ndefining Earth rheology, and where RSL is expected to approximate \r\nGMSL to within about 1 m (e.g., Milne and Mitrovica, 2008), suggest \r\nthat RSL was between about -6 to +1.5 m at around 6 ka at multiple \r\nlocations (Camoin et al., 1997; Braithwaite et al., 2000; Frank et al., \r\n2006; Montaggioni and Faure, 2008; Vacchi et al., 2016; Khan et al., \r\n2017; Hibbert et al., 2018). The assessment of GMSL change at 6 kyr \r\nis challenging considering the proportionately large GIA effect (Kopp \r\net al., 2016), insufficient resolution of marine geochemical proxies "


id: 3efb7df97217d11a5a460d8fa742abd2
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 7294
content:
"(d18O, Mg/Ca) and uncertainties in the contribution of the Antarctic \r\nIce Sheet during the MH (Section 2.3.2.4). The possibility that GMSL \r\nwas at least somewhat higher than present cannot be excluded."


id: 31cd17b61e03d54dc9337659ab799e20
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 5248
content:
"salt-marsh records with decimetre scale vertical resolution and sub\u0002centennial temporal resolution (Kopp et al., 2016; Kemp et al., 2018). \r\nOver the last about 1.5 kyr, the most prominent century-scale GMSL \r\ntrends include average maximum rates of lowering and rising of \r\n-0.7 +- 0.5 mm yr-1 (2 SD) over 1020-1120 CE, and 0.3 +- 0.5 (2 SD) \r\nover 1460-1560, respectively. Between 1000 and 1750 CE, GMSL is "


id: 9024b08117063217ff81b4d28fa5650f
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 20210
content:
"Figure 2.28 | Changes in global mean sea level. (a) Reconstruction of sea-level from ice core oxygen isotope analysis for the last 800 kyr. For target paleo periods (CCB2.1) \r\nand MIS11 the estimates based upon a broader range of sources are given as box whiskers. Note the much broader axis range (200 m) than for later panels (tenths of metres). \r\n(b) Reconstructions for the last 2500 years based upon a range of proxy sources with direct instrumental records superposed since the late 19th century. (c) Tide-gauge and, more \r\nlatterly, altimeter-based estimates since 1850. The consensus estimate used in various calculations in Chapters 7 and 9 is shown in black. (d) The most recent period of record from \r\ntide-gauge and altimeter-based records. Further details on data sources and processing are available in the chapter data table (Table 2.SM.1)."


id: 6c28f50e3276e0d486d8e8a3dd5bbf63
created_at: 2023-03-16 14:00:39
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vector_id: 14646
content:
"emerging evidence in sustained observations, both in situ (2004-2017) \r\nand revealed from SST-based reconstructions, that the AMOC had \r\nweakened during the instrumental era relative to 1850-1900 (medium \r\nconfidence), although there were insufficient data to quantify the \r\nmagnitude of the weakening. SROCC also concluded with low \r\nconfidence an increase of the Southern Ocean upper cell overturning \r\ncirculation. SROCC also reported with medium confidence that the \r\nproduction of Antarctic Bottom Water had decreased since the 1950s \r\nconsistent with a decreased lower cell overturning circulation, and \r\npotentially modulating the strength of the AMOC."


id: eb84d642726682a191aa792d80927429
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 34552
content:
"estimated to have been within the range of about -0.11 to +0.09 m \r\nrelative to 1900 (Kemp et al., 2018). This was followed by a sustained \r\nincrease of GMSL that began between 1820 and 1860 and has \r\ncontinued to the present day. New analyses demonstrate that it is very \r\nlikely that GMSL rise over the 20th century was faster than over any \r\npreceding century in at least 3 kyr (Kopp et al., 2016; Kemp et al., 2018) \r\n(Figure 2.28). "


id: ca3a2467970ef571a93fd34e4fda2812
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 29373
content:
"Numerous proxy records collectively imply that AMOC is currently at \r\nits weakest point in the past 1.6 ka (Rahmstorf et al., 2015; Caesar \r\net al., 2018, 2021; Thibodeau et al., 2018; Thornalley et al., 2018). \r\nCaesar et al. (2021) analyse a compilation of various available indirect \r\nAMOC proxies from marine sediments, in situ-based reconstructions \r\nand terrestrial proxies, which show a decline beginning in the late \r\n19th century and over the 20th century superimposed by large \r\ndecadal variability in the second half of the 20th century. Indirect \r\nreconstructions of AMOC components based on coastal sea level \r\nrecords in the western North Atlantic (Ezer, 2013; McCarthy et al., \r\n2015; Piecuch, 2020) show an AMOC decline since the late 1950s, \r\nwith only a short period of recovery during the 1990s."


id: b1af60e1471e83d12b9a55edb92e8b7d
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 25451
content:
"In summary, GMSL is rising, and the rate of GMSL rise since the \r\n20th century is faster than over any preceding century in at least the \r\nlast three millennia (high confidence). Since 1901, GMSL has risen by \r\n0.20 [0.15 to 0.25] m at an accelerating rate. Further back in time, there \r\nis medium confidence that GMSL was within -3.5 to +0.5 m (very likely \r\nrange) of present during the MH, 5-10 m higher (likely range) during \r\nthe LIG, and 5-25 m higher (very likely range) during the MPWP."


id: 4750da91b2edabb1924c4777e03077eb
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 8606
content:
"The AR5 concluded that there was no evidence of a trend in the \r\nAMOC during the period of instrumental observations. However, AR5 \r\nalso stressed insufficient evidence to support a finding of change \r\nin the heat transport of the AMOC. SROCC assessed that there was "


id: 755cb6519a41017f3ae0c60c26daeffe
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 16046
content:
"However, other studies highlight that proxy records do not show such \r\nclear signals (Moffa-Sanchez et  al., 2019), and the use of SST- and \r\ncoastal sea level-based proxies of AMOC places uncertainties on these \r\nresults (Little et al., 2019; Jackson and Wood, 2020; Menary et al., 2020). "


id: 25e615f839ae9ad08f9d3eb633bbb1b2
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 3386
content:
"(high confidence) cannot be distinguished between decadal-scale \r\nvariability or a long-term trend (high confidence)."


id: 9e423abe4701b69ade2c850f68d40582
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 22423
content:
"For instance, SSTs are additionally influenced by atmospheric and \r\nnon-AMOC related ocean variability (Josey et al., 2018; Keil et al., 2020; \r\nMenary et al., 2020), while sea level responds to a variety of factors \r\n(e.g., atmospheric pressure and local winds) independent of the AMOC \r\n(Woodworth et al., 2014; Piecuch and Ponte, 2015; Piecuch et al., 2016). \r\nFinally, large decadal variability is present in many reconstructions and \r\nobscures estimation of the long-term trend over the 20th century (Ezer, \r\n2013; McCarthy et al., 2015; Yashayaev and Loder, 2016; Thornalley \r\net al., 2018; Caesar et al., 2021). It is also noted that the proxy reported \r\nAMOC decline, beginning in the late 19th century, is not supported by \r\nmodel-based evidence (Sections 3.5.4.1 and 9.2.3.1)."


id: 265146b3b2f9e6dae92b9ad0070f3490
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 3443
content:
"Both AR5 and SROCC reported that western boundary currents \r\n(WBCs) have undergone an intensification, warming and poleward \r\nexpansion, except for the Gulf Stream and the Kuroshio, but did \r\nnot provide confidence statements. The AR5 reported with medium\r\nto high confidence intensification of the North Pacific subpolar \r\ngyre, the South Pacific subtropical gyre, and the subtropical cells, \r\nalong with an expansion of the North Pacific subtropical gyre \r\nsince the 1990s. It  was pointed out that these changes are likely\r\npredominantly due to interannual-to-decadal variability, and in the \r\ncase of the subtropical cells represent a reversal of earlier multi\u0002decadal changes. SROCC concluded that it was unlikely that there \r\nhas been a statistically significant net southward movement of the \r\nmean Antarctic Circumpolar Current (ACC) position over the past \r\n20 years, in contrast to AR5, where this change had been assessed \r\nwith medium confidence. "


id: 1267d247ff1dd4fa3a3f47e7790ebddc
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 397
content:
"Repeated full depth in situ measurements report that deep \r\nconvection - a major driver for AMOC - has recently returned to the \r\nLabrador Sea, particularly in 2015 (Yashayaev and Loder, 2016; Rhein \r\net al., 2017), and to the Irminger Sea (de Jong and de Steur, 2016; \r\nGladyshev et al., 2016; de Jong et al., 2018) following an extended \r\nperiod with weak convection since 2000. An associated strengthening \r\nof the outflow from the Labrador Sea has not been observed (Zantopp \r\net al., 2017; Lozier et al., 2019), while strengthening of the AMOC is \r\ntentative (Desbruyeres et al., 2019; Moat et al., 2020). A long-term \r\nincrease of the upper overturning cell in the Southern Ocean since \r\nthe 1990s can be assessed with low confidence, and there is medium \r\nconfidence of a decrease in Antarctic bottom water (AABW) volume \r\nand circulation, which has potential implications for the strength of \r\nthe AMOC (Section 9.2.3.2)."


id: 5348d563e0f6dd6befe5b566f9a2f16
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 10572
content:
"A latitudinal shift of subtropical/subpolar gyres on the order of \r\n0.1 +- 0.04deg per decade is derived by an indirect method using remote \r\nsensing data during 1993-2018 (Yang et al., 2020). Direct observations \r\nshow a systematic poleward migration of WBCs (Wu  et  al., 2012; \r\nYang et al., 2016, 2020; Bisagni et al., 2017). However, they do not \r\nsupport an intensification of WBCs, with a weakening, broadening, \r\nor little change reported for the Kuroshio (Y.-L. Wang et  al., 2016; "


id: d7631259a8aa388e0c79f1aeb7923a7d
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 31406
content:
"In summary, proxy-based reconstructions suggest that the AMOC \r\nwas relatively stable during the past 8 kyr (medium confidence), \r\nwith a weakening beginning since the late 19th century (medium \r\nconfidence), but due to a lack of direct observations, confidence in \r\nan overall decline of AMOC during the 20th century is low. From the \r\nmid-2000s to mid-2010s, the directly observed weakening in AMOC "


id: 346d5e2fcb1a52db6e397ca0a4bacd9
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 5665
content:
"Wang and Wu, 2018; Collins et  al., 2019), Gulf Stream (McCarthy \r\net  al., 2018; Collins et  al., 2019; Dong et  al., 2019; Andres et  al., \r\n2020), Agulhas (Beal and Elipot, 2016; Elipot and Beal, 2018) and \r\nEast Australian (Sloyan and O'Kane, 2015) currents. The Gulf Stream \r\nhas recently reversed a long-term poleward migration (Bisagni \r\net al., 2017). Multidecadal variability of the strength and position of \r\nWBCs (Hsin, 2015; Bisagni et al., 2017; McCarthy et al., 2018) and \r\nshort records from direct observations obscure the detection of any \r\nlong-term trends (Yang et al., 2020)."


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vector_id: 11595
content:
"The AR5 assessed with high confidence that the pH of the ocean \r\nsurface had decreased since preindustrial times, primarily as a \r\nresult of ocean uptake of CO2. SROCC concluded that the global \r\nocean absorbed 20-30% of total CO2 emissions since the 1980s, \r\nwith virtually certain ocean surface pH decline. The SROCC assessed \r\na rate of surface pH decline of 0.017-0.027 pH units per decade \r\nacross a range of time series of pH observations longer than 15 \r\nyears. The decline in surface open ocean pH was assessed by SROCC \r\nas having very likely already emerged from background natural \r\nvariability for more than 95% of the global surface open ocean."


id: 491f1fba077f54146b27f1140d7868a
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
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vector_id: 8894
content:
"The Pacific to Arctic exchange at the Bering Strait plays a minor role in \r\nthe total Arctic exchange with the global ocean, which has increased \r\nfrom 0.8 Sv to 1.0 Sv over 1990-2015 (Woodgate, 2018). For Atlantic\u0002Arctic exchange, major branches of Atlantic Water inflow from the \r\nNorth Atlantic into the Arctic across the Greenland-Scotland Ridge \r\nhave remained stable since the mid-1990s (Berx et al., 2013; Hansen \r\net  al., 2015; Jochumsen et  al., 2017; Osterhus et  al., 2019), with \r\nonly the smaller pathway of Atlantic Water north of Iceland showing \r\na strengthening trend during 1993-2018 (Casanova-Masjoan et al., \r\n2020), but with associated heat transport strengthening through \r\nthe 1990s (Rossby et al., 2020; Tsubouchi et al., 2021). The Arctic \r\noutflow remained broadly stable from the mid-1990s to the mid \r\n2010s (Osterhus et al., 2019). "


id: ba89ca91efe32355d65b4f764b094701
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
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vector_id: 26881
content:
"The heat and mass transport of the Indonesian throughflow  (ITF) \r\nshows substantial variability at seasonal to decadal time scales \r\n(Zhuang et al., 2013; Q.-Y. Liu et al., 2015; Susanto and Song, 2015; \r\nFeng et al., 2017, 2018; M. Li et al., 2018; Sprintall et al., 2019; Xie \r\net al., 2019). Q.-Y. Liu et al. (2015) reported an increasing trend in \r\nthe ITF geostrophic transport of 1 Sv per decade over 1984-2013, \r\nconsistent with direct estimates (Sprintall et al., 2014), and results \r\nfrom reanalyses (M. Li et al., 2018), and this appears to be linked to \r\nmulti-decadal scale variability rather than a long-term trend (Kosaka \r\nand Xie, 2013; England et al., 2014; Lee et al., 2015). "


id: 4fcda453f15af8ba7124464e45643407
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
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vector_id: 9997
content:
"Southern Ocean circulation changes are assessed in SROCC (Meredith \r\net al., 2019), and are confirmed and synthesized in Section 9.2.3.2 \r\nwhich shows that there is no indication of ACC transport change, \r\nand that it is unlikely that the mean meridional position of the ACC \r\nhas moved southward in recent decades."


id: a1dbd29d997c431edb4e495decac2284
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 23028
content:
"In summary, over the past 3-4 decades, the WBC strength is highly \r\nvariable (high confidence), and WBCs and subtropical gyres have \r\nshifted poleward since 1993 (medium confidence). Net Arctic Ocean \r\nvolume exchanges with the other ocean basins remained stable over \r\nthe mid-1990s to the mid-2010s (high confidence). There is high \r\nconfidence that the ITF shows strong multi-decadal scale variability \r\nsince the 1980s."


id: 4a74c8a12c5117b7cb8796a5cd861175
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 9118
content:
"For subsurface pH changes, estimates arise from direct ship \r\nmeasurements from repeated hydrography programs (Carter et  al., \r\n2019), indirect estimates of pH through calcite and aragonite saturation \r\nhorizons (Osborne et al., 2020; Ross et al., 2020), and the very recent \r\nbiogeochemical Argo floats equipped with pH sensors (Claustre \r\net  al.,  2020). Global subsurface pH has decreased over the past 20 \r\nto 30 years, with signals observed to at least 1000 m depths (Lauvset \r\net al., 2020). Global findings are supplemented by regional findings \r\nfrom the Pacific Ocean (Carter et al., 2019; Ross et al., 2020); the South \r\nAtlantic (Salt et  al., 2015) and Southern Ocean (Jones et  al., 2017); \r\nthe North Atlantic Ocean and along the AMOC (Woosley et al., 2016; \r\nPerez et al., 2018), the Arctic Ocean (Qi et al., 2017) and marginal seas \r\n(C.-T.A. Chen et al., 2017). Further details are given in Section 5.3.3.1."


id: cdb3cea3fb7481c5e15a84098f24b30f
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 29890
content:
"To conclude, it is virtually certain that surface open ocean pH has \r\ndeclined globally over the last 40 years by 0.003-0.026 pH per \r\ndecade, and a decline in the ocean interior has been observed in \r\nall ocean basins over the past 2-3 decades (high confidence). \r\nA  long-term increase in surface open ocean pH occurred over the \r\npast 50 Myr (high confidence), and surface open ocean pH as low \r\nas recent times is uncommon in the last 2 Myr (medium confidence). \r\nThere is very high confidence that open ocean surface pH is now the \r\nlowest it has been for at least 26 kyr and current rates of pH change \r\nare unprecedented since at least that time. "


id: eb78795c8665116ae5f191aaa231d72
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 34546
content:
"SROCC concluded that there has very likely been a net loss of \r\noxygen over all ocean depths since the 1960s linked to global ocean \r\ndeoxygenation at a range of 0.3-2.0%, and that the oxygen levels in the \r\nglobal upper 1000 m of the ocean had decreased by 0.5-3.3% during \r\n1970-2010 (medium confidence), alongside an expansion of oxygen \r\nminimum zones (OMZ) by 3-8%. For the surface ocean (0-100 m) \r\nand the thermocline at 100-600 m, the very likely range of oxygen \r\ndecline was assessed to be 0.2-2.1% and 0.7-3.5%, respectively. \r\nMultidecadal rates of deoxygenation showed variability throughout \r\nthe water column and across ocean basins (high confidence)."


id: 53912fd00f0b4d873d8008d0f8dd4e07
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 10617
content:
"Findings since SROCC provide further support that the volume of \r\nseverely oxygen-depleted water has expanded in some locations \r\nof the global ocean (Section 5.3.3.2). For example, vertical expansion \r\nof low oxygen zones is reported in the North Pacific at a rate of \r\n3.1 +- 0.5 m yr-1 (Ross et al., 2020), and suboxic waters have increased \r\nby 20% at a rate of about 19 m per decade from 1982-2010 in the \r\nArabian Sea (Al-Said et al., 2018; Lachkar et al., 2019), and expanded \r\noff the coast of Mexico (Sanchez-Velasco et al., 2019)."


id: 347d8eb70efd7be35f99edfb33f5112f
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 5669
content:
"In summary, episodes of widespread and long-lasting (100 ka scales) \r\nopen-ocean deoxygenation were related to warm climate intervals of \r\nthe Permian-Cretaceous, with conditions becoming generally better \r\noxygenated as the climate cooled over the course of the Cenozoic (high \r\nconfidence). The largest expansions of oxygen depleted waters over \r\nthe past 25 ka were strongly linked to rapid warming rates (medium \r\nconfidence). Open-ocean deoxygenation has occurred in most regions \r\nof the open ocean during the mid-20th to early 21st centuries (high \r\nconfidence), and shows decadal variability (medium confidence). \r\nEvidence further confirms SROCC that OMZs are expanding at many \r\nlocations (high confidence)."


id: f9d13cd3e8f9085fe33a1058863334c0
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 36813
content:
"This section is limited to a few biological indicators to demonstrate the \r\nclose links between the biosphere and physical forcing. In selecting \r\nthe indicators, we focussed on (i) those that are observable at large \r\n(global) spatial scales and over long (two decades or more) temporal \r\nscales, using standardized and consistent procedures; and (ii) those \r\nthat are illustrative of the influence of the physical system on the \r\nbiological realm. Chapters 2 and 3 of AR6 WGII undertake a more \r\nholistic assessment of biospheric impacts."


id: 6ba2f081a5d08c78438c41bdb6783041
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 14560
content:
"New findings for ocean oxygen content since SROCC are limited \r\nto regional scale assessments. The magnitude of change is difficult \r\nto compare across regions to arrive at a global assessment due to \r\ndifferences in depth range, time period, baseline climatology, \r\nmethodology, and particularly the use of different units. To facilitate \r\ncomparisons, data are presented as change per decade, and \r\nconversions of the SROCC global mean percentage of oxygen decline \r\nestimates are provided as a loss of 3.2 mmol kg-1 in the upper 1000 m \r\nof the global ocean (1.93%), 2.0 mmol kg-1 (0.8 mmol kg-1 per decade) \r\nin the upper 1000 m of the global ocean (1.93%), and 2.0  mmol \r\nkg-1 (0.5 mmol kg-1 per decade) in the entire water column (1.15%) \r\nbetween 1970 and 2010 (Bindoff et al., 2019). Oxygen change also \r\nshows decadal variability (Ito et al., 2016; Stramma et al., 2020) that \r\ncan influence estimates of trends. "


id: e9b6918f49da8cacf764b33352413646
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 34268
content:
"The AR5 noted that because CO2 uptake by photosynthesis occurs \r\nonly during the growing season, the greater land mass in the NH \r\nimparts a characteristic 'sawtooth' seasonal cycle in atmospheric \r\nCO2. The SRCCL similarly stated that due to strong seasonal patterns \r\nof growth, NH terrestrial ecosystems are largely responsible for \r\nthe seasonal variations in global atmospheric CO2 concentrations. \r\nNeither AR5 nor SRCCL made a confidence statement about observed \r\nchanges in the amplitude of the seasonal cycle of CO2. "


id: bbcf154a99b35b98db344a1b97feece8
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
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vector_id: 27104
content:
"In situ observations of CO2 generally depict a rising amplitude of the \r\nseasonal cycle over the past half century, especially north of about \r\n45degN (Figure 2.30). For example, an amplitude increase of 6 +- 2.6% \r\nper decade has been observed at the Barrow surface observatory in \r\nAlaska over 1961-2011 (Graven et  al., 2013), with slightly slower \r\nincreases thereafter. Aircraft data north of 45degN exhibit an amplitude \r\nincrease of 57 +- 7% at 500 mb versus an increase of 26 +- 18% for \r\n35degN-45degN between field campaigns in 1958-1961 and 2009-2011 \r\n(Graven et  al., 2013). Increases in amplitude for the period \r\n1980-2012 are apparent at eight surface observatories north of 50degN \r\n(Piao et al., 2018), related primarily to a larger drawdown in June \r\nand July. Trends in seasonal cycle amplitude at lower latitudes are \r\nsmaller (if present at all); for instance, the increase at the Mauna Loa "


id: 8f386484ce59c3e79a3b0253f01b0833
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 20072
content:
"observatory in Hawaii since the early 1960s is only about half as \r\nlarge as at Barrow (Graven et al., 2013), and only one other low\u0002latitude observatory has a significant increase from 1980-2012 (Piao \r\net al., 2018). There is a weak signal of an increase in amplitude at the \r\nSinhagad observatory in western India in recent years (Chakraborty \r\net al., 2020). Generally speaking, larger increases in the Arctic and \r\nboreal regions are indicative of changes in vegetation and carbon \r\ncycle dynamics in northern ecosystems (Forkel et al., 2016), though \r\nincreased carbon uptake can also result from other factors such as \r\nwarmer- and wetter-than-normal conditions. "


id: 2a422ef16e2ade35f95b57436b5b6a49
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 4074
content:
"Recent satellite-based, global-scale estimates of seasonal variations \r\nin atmospheric CO2 for the period 2003-2018 show that the seasonal \r\nvariations in the SH are out of phase with those in the NH (Reuter \r\net  al., 2020), which is consistent with the phenological shifts in \r\nprimary productivity between hemispheres. The net effect of the \r\nphase shift between the two hemispheres is to dampen the amplitude \r\nof the global average seasonal cycle. These integrated results also \r\nshow that the amplitude of the oscillations has been increasing in \r\nthe SH, from about 2009, but comparison with data from Baring head \r\nsuggests that periods of high seasonal oscillation had occurred at \r\nthat location in the SH prior to 1995."


id: 1127fa9fe8dd69a2447c94b5ada1427a
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 177
content:
"In summary, there is very high confidence that the amplitude of the \r\nseasonal cycle of atmospheric CO2 has increased at mid-to-high NH \r\nlatitudes since the early 1960s. The observed increase is generally \r\nconsistent with greater greening during the growing season and an \r\nincrease in the length of the growing season over the high northern \r\nlatitudes. Similarly, globally-integrated results from the SH also show \r\nan increase in seasonal amplitude of atmospheric CO2 signal, from \r\naround 2009 to 2018 (low confidence)."


id: 3785651644f7aea12192563cca659822
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 6116
content:
"SROCC pointed out that long-term global observations of many \r\nkey ocean variables, including phytoplankton, have not reached the \r\ndensity and accuracy necessary for detecting change. But SROCC \r\nnoted the good comparability between short time-scale single-sensor \r\nocean-colour products and a longer time-scale, climate-quality \r\ntime series of multi-sensor, inter-sensor-bias-corrected, and error\u0002characterized, global data on chlorophyll-a concentration in the \r\nsurface layers of the ocean. With respect to oligotrophic gyres, \r\nAR5 WGII concluded that the oligotrophic subtropical gyres of the \r\nAtlantic and Pacific Oceans are expanding and that they indicate \r\ndeclining phytoplankton stocks in these waters (limited evidence, \r\nlow agreement). With respect to distributions of marine organisms, \r\nAR5 WGII reported range shifts of benthic, pelagic, and demersal \r\nspecies and communities (high confidence), though the shifts were \r\nnot uniform. "


id: 2cac401e9206588078a67408067744a4
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 4456
content:
"Phytoplankton are responsible for marine primary production \r\nthrough photosynthesis; they are a major player in the ocean carbon \r\ncycle. They have a high metabolic rate and respond fast to changes in \r\nenvironmental conditions (light, temperature, nutrients, mixing), and \r\nas such, serve as a key indicator for change in marine ecosystems. "


id: d688e7f8494164b7132fd65a9088bff6
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 31265
content:
"data in many regions is strongly tied to indices of climate variability \r\n(Section 2.4 and Annex IV) and changes in total concentration are \r\ntypically associated with changes in phytoplankton community \r\nstructure (e.g., Brewin et al., 2012; Racault et al., 2017b). Variability \r\nin community structure related to El Nino has, in turn, been linked to \r\nvariability in fisheries, for example in the catch of anchovy (Engraulis \r\nringens) in the Humboldt current ecosystem (Jackson et al., 2011)."


id: 3748c3a09cb468181aaf3184d54d0cfb
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 6085
content:
"Concentration of chlorophyll-a, the major photosynthetic pigment \r\nin all phytoplankton, is often used as a measure of phytoplankton \r\nbiomass. As primary producers, they are also food for organisms at \r\nhigher trophic levels. The multi-sensor time series of chlorophyll-a \r\nconcentration has now been updated (Sathyendranath et  al., \r\n2019) to cover 1998-2018. Figure 2.31 shows that global trends in \r\nchlorophyll-a for the last two decades are insignificant over large \r\nareas of the global ocean (von Schuckmann et al., 2019), but some \r\nregions exhibit significant trends, with positive trends in parts of the \r\nArctic and the Antarctic waters (>3% yr-1), and both negative and \r\npositive trends (within +- 3% yr-1) in parts of the tropics, subtropics \r\nand temperate waters. The interannual variability in chlorophyll-a "


id: 86f5aeed5ff4a4c469e751f8ae69c72a
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 18768
content:
"In summary, there is high confidence that the latitudinal and depth \r\nlimits of the distribution of various organisms in the marine biome \r\nare changing. There is medium confidence that there are differences \r\nin the responses of individual species relative to each other, such that \r\nthe species compositions of ecosystems are changing. There is medium \r\nconfidence that chlorophyll concentration in the surface shows weak \r\nnegative and positive trends in parts of low and mid latitudes, and \r\nweak positive trends in some high-latitude areas. There is medium \r\nconfidence that the large-scale distribution of the oligotrophic \r\ngyre provinces is subject to significant inter-annual variations, but "


id: d42f4a56cadbed742595a3e5dc1cd4a5
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 30904
content:
"low confidence in the long-term trends in the areal extent of these \r\nprovinces because of insufficient length of direct observations."


id: fc19abc86178bc2559d28c483517eb38
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 37164
content:
"when subjected to the same environmental changes (Edwards \r\nand Richardson, 2004). Furthermore, different factors could be \r\nresponsible for triggering phenological responses in different stages \r\nin the life cycle of a single organism (Koeller et al., 2009). The shift \r\nin the distribution of many benthic invertebrates on the North-west \r\nAtlantic shelf, including some commercially important shellfish, \r\ncould be explained by phenology and larval transport, and the \r\nshift and contraction of species range have been associated with \r\nhigher mortality (Fuchs et  al., 2020). Changes in phytoplankton \r\nphenological indicators globally (Racault et al., 2012; Sapiano et al., \r\n2012) have been linked to indicators of climate variability, such as \r\nthe multivariate ENSO Index (Racault et al., 2017a), with responses \r\nvarying across ecological provinces of the ocean (Longhurst, 2007). "


id: cfd03341d6dc6476c4448105a2d4a991
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 30226
content:
"SROCC expressed low confidence in satellite-based estimates of \r\ntrends in marine primary production, citing insufficient length of the \r\ntime series and lack of corroborating in situ measurements and \r\nindependent validation time series. The report also cites significant \r\nmismatches in absolute values and decadal trends in primary \r\nproduction when different satellite-based products are compared."


id: e7139c44a29f85f2808667c983e8ee9e
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 33852
content:
"In conclusion, there is low confidence because of the small number of \r\nrecent studies and the insufficient length of the time series analysed \r\nthat marine primary production is 47 (+- 7.8) PgC yr-1. A small decrease \r\nin productivity is evident globally for the period 1998-2015, but \r\nregional changes are larger and of opposing signs (low confidence). "


id: 98eb17da1ff0f6b99bfd2a16e0925e19
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 21575
content:
"In summary, new in situ data as well as satellite observations \r\nstrengthen AR5 and SROCC findings that various phenological metrics \r\nfor many species of marine organisms have changed in the last half \r\ncentury (high confidence), though many regions and many species \r\nof marine organisms remain under-sampled or even unsampled. The \r\nchanges vary with location and with species (high confidence). There \r\nis a strong dependence of survival in higher trophic-level organisms \r\n(fish, exploited invertebrates, birds) on the availability of food at \r\nvarious stages in their life cycle, which in turn depends on phenologies \r\nof both (high confidence). There is a gap in our understanding of how \r\nthe varied responses of marine organisms to climate change, from \r\na phenological perspective, might threaten the stability and integrity \r\nof entire ecosystems. "


id: 37bb1f8ee37c670cf2ee68d18879aec1
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 6142
content:
"Phenology is the study of the timing of important events in the \r\nannual life cycle of organisms (plants or animals; see also Annex VII: \r\nGlossary). The AR5 WGII noted that the timing of various seasonal \r\nbiological events in the ocean had advanced by more than four days \r\nper decade over the previous 50-year period and concluded that there \r\nwas high confidence in observed changes in the phenological metrics \r\nof marine organisms. The AR5 WGII further reported that, of those \r\nobservations that showed a response, 81% of changes in phenology, \r\ndistribution and abundance were consistent with anticipated \r\nresponses to climate warming according to theoretical expectations, \r\ncorroborated by updates in SROCC. The consequent current and future \r\nimpacts on interactions between species, including competition and \r\npredator-prey dynamics, were noted with high confidence."


id: 29794882e6fe03c16cc23b393fb9eaab
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 3959
content:
"There are additional indications that phenological metrics related to \r\ndifferent species are changing, but not always in a similar manner. \r\nFor example, many seabirds are breeding earlier, while others are \r\nbreeding later (Sydeman et  al., 2015). Planktonic organisms in \r\nthe North Atlantic are also responding differently to each other "


id: 12479a640297609c1ef08a4dc63fa8d7
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 380
content:
"The AR5 WGII briefly discussed large-scale changes in the length of the \r\ngrowing season but made no confidence statement about observed \r\ntrends. However, AR5 did conclude with high confidence that warming \r\ncontributed to an overall spring advancement in the NH."


id: 47ef8d9c89278421813f14ea8522fd4f
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 8690
content:
"increased by at least 1.0 days per decade since 1960 (Xia et  al., \r\n2018) and by several days per decade in South Korea since 1970 \r\n(Jung et al., 2015). In general, changes in phenological indicators are \r\nconsistent with the increase in growing season length documented by \r\ninstrumental data (Parmesan and Hanley, 2015). Several long-term, \r\nsite-specific records illustrate the unusualness of recent phenological \r\nchanges relative to interannual variability; for example, peak bloom \r\ndates for cherry blossoms in Kyoto, Japan have occurred progressively \r\nearlier in the growing season in recent decades, as have grape harvest \r\ndates in Beaune, France (Figure 2.32)."


id: 74fd8e13db0a919c37c36a48cf40e843
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vector_id: 16000
content:
"Recent in situ analyses document increases in the length of the thermal \r\ngrowing season (i.e., the period of the year when temperatures are \r\nwarm enough to support growth) over much of the extratropical land \r\nsurface since at least the mid-20th century. Over the NH as a whole, \r\nan increase of about 2.0 days per decade is evident for 1951-2018 \r\n(Dunn et  al., 2020), with slightly larger increases north of 45degN \r\n(Barichivich et al., 2013). Over North America, a rise of about 1.3 days \r\nper decade is apparent in the United States for 1900-2014 (Kukal \r\nand Irmak, 2018), with larger increases after 1980 (McCabe et  al., \r\n2015); likewise, all ecozones in Canada experienced increases from \r\n1950-2010 (Pedlar et  al., 2015). Growing season length in China "


id: fc50ac4955787e4d0a9cca4416679284
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 37200
content:
"The general consistency between in situ and satellite estimates \r\nover the NH is noteworthy given that many factors independently \r\ncontribute to uncertainty in observed changes. For example, there \r\nis no universally accepted definition of growing season length \r\nacross in situ analyses; some define the growing season as the \r\nperiod based on a temperature threshold (e.g.,  5degC) whereas \r\nothers use the frost-free period. Spatial and temporal coverage \r\ncan also affect conclusions based upon in situ studies (Donat et al., \r\n2013b). For satellite analyses, uncertainties can be related to the \r\nsatellite datasets themselves (e.g., satellite drift, sensor differences, \r\ncalibration uncertainties, atmospheric effects); and to the methods \r\nfor determining phenological metrics (e.g., start, end, and length of \r\nseason; S. Wang et al., 2016). "


id: acd3b1d240c10448cbf6b7cb57b16998
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 24740
content:
"In summary, based on multiple independent analyses of in situ, \r\nsatellite, and phenological data, there is high confidence that \r\nthe length of the growing season has increased over much of the \r\nextratropical NH since at least the mid-20th century."


id: bda8418e217ba107429e006584f3bfe0
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 27404
content:
"The AR5 WGII concluded that many terrestrial species have shifted \r\ntheir geographic ranges in recent decades (high confidence). Similarly, \r\nSRCCL assessed that many land species have experienced range size \r\nand location changes as well as altered abundances over recent \r\ndecades (high confidence). SROCC noted that species composition \r\nand abundance have markedly changed in high mountain ecosystems \r\nin recent decades (very high confidence)."


id: 5ca9ecf79dd274d2bab380e896663210
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
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vector_id: 12099
content:
"Paleoclimate reconstructions document large-scale biome shifts from \r\nthe deep past through the Holocene (e.g., Hoogakker et al., 2016). \r\nThe northernmost location of the treeline is a representative indicator \r\nin this regard (Figure 2.34). During the MPWP, boreal forest extended \r\nto the Arctic coast, with the northernmost treeline being about 4deg \r\nto 10deg latitude further north than at present; temperate forests and \r\ngrasslands were also shifted poleward (with reduced tundra extent), \r\nwhile savannahs and woodlands were more expansive in Africa \r\nand Australia at the expense of deserts (Cross-Chapter Box  2.4, \r\nFigure  1b; Salzmann et  al., 2008, 2013; Sniderman et  al., 2016; \r\nAndrae et al., 2018). During the LGM, tundra and steppe expanded \r\nwhereas forests were globally reduced in extent (Prentice et al., 2000; "


id: 17a634c438f69aada9466345c15763ff
created_at: 2023-03-16 14:00:39
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vector_id: 1218
content:
"There are exceptions to the general pattern of poleward/upslope \r\nmigration. For some species, various biotic and abiotic factors (such \r\nas precipitation and land use) supersede the physiological effects of \r\ntemperature (Vanderwal et  al., 2013; Gibson-Reinemer and Rahel, \r\n2015; Ordonez et al., 2016; Scheffers et al., 2016; Lenoir et al., 2020). \r\nFor other species, poleward migration is slower than expectations \r\nfrom the observed temperature increases. Trees are one such example \r\nbecause of their long lifespan and gradual maturity (Renwick and \r\nRocca, 2015); in fact, poleward advance is only evident at about \r\nhalf of the sites in a large global dataset of treeline dynamics for "


id: 23ea35cb659c406bd2da21bcc5df3d22
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 3091
content:
"1900-present (Harsch et  al., 2009). Furthermore, the northernmost \r\nextent of treeline at present (roughly 73degN) is actually somewhat \r\nsouth of its location in the MH (MacDonald et al., 2008) despite an \r\nexpanding growing season in the extratropical NH since the mid-20th \r\ncentury (Section 2.3.4.3.1)."


id: 608819119645068d807abc19f14132d0
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 12761
content:
"In summary, there is very high confidence that many terrestrial species \r\nhave shifted their geographic ranges poleward and/or upslope over \r\nthe past century, with increased rates of species turnover. There is \r\nhigh confidence that the geographical distribution of climate zones \r\nhas shifted in many parts of the world. "


id: 1f2543c2d2ba25f1eecfeb0af1b67a37
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 2338
content:
"The AR5 WGII briefly discussed changes in global vegetation \r\ngreenness derived from satellite proxies for photosynthetic activity. \r\nObserved trends varied in their strength and consistency, and AR5 \r\nthus made no confidence statement on observed changes. The SRCCL \r\nsubsequently concluded that greening had increased globally over \r\nthe past 2-3 decades (high confidence)."


id: de4fcde14f8946973738d9811e4d27c8
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 32467
content:
"Figure 2.33 | Satellite-based trends in fraction of absorbed photosynthetically \r\nactive radiation (per decade) for 1998-2019. Trends are calculated using OLS \r\nregression with significance assessed following AR(1) adjustment after Santer et al. \r\n(2008); 'x' marks denote non-significant trend). Unvegetated areas such as barren \r\ndeserts (grey) and ice sheets (white) have no trend in FAPAR. Further details on data \r\nsources and processing are available in the chapter data table (Table 2.SM.1)."


id: 4ee9d8188727bd33b552b45e281da3f0
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 9854
content:
"phenological metrics from satellite data as well as a variety of statistical \r\ntechniques for analysing historical changes (S. Wang et al., 2016)."


id: c7d586429406600f7b676ad351e3d0b6
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 29016
content:
"coming up to the present day. This synthesis serves as an assessment \r\nof the evidence for change across the climate system as represented \r\nby the instrumental record and its unusualness in the longer-term \r\ncontext. Building upon previous sections assessing the observational \r\nevidence for each key indicator individually, this section integrates \r\nthe evidence across multiple indicators to arrive at a holistic and \r\nrobust final assessment."


id: d22ce86591b0275f3e3198ee3c3a0d75
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 30592
content:
"In summary, there is high confidence that vegetation greenness \r\n(i.e., green leaf area and/or mass) has increased globally since the \r\nearly 1980s. However, there is low confidence in the magnitude of \r\nthis increase owing to the large range in available estimates."


id: 86ae0ccfc6f9818c7cfa9e2994e11397
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
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vector_id: 18728
content:
"Climate has varied across a broad range of timescales (Figure 2.34). \r\nDuring the Cenozoic Era temperatures generally decreased over tens \r\nof millions of years, leading to the development of ice sheets. During \r\nthe last two million years, climate has fluctuated between glacials \r\nand interglacials. Within the current Holocene interglacial and, with \r\nincreasing detail in the CE, it is possible to reconstruct a history both "


id: 6167bdfe9053e6888f1974a67334ed7d
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 12895
content:
"Section 2.3 has assessed the observational evidence for changes in key \r\nindicators across the atmosphere, cryosphere, ocean and biosphere \r\nstarting, where applicable, from paleoclimate proxy  records and "


id: bcd0ff028dd5040aa9217d754ee3f78f
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 27278
content:
"Figure 2.34 | Selected large-scale climate indicators during paleoclimate and recent reference periods of the Cenozoic Era. Values are based upon \r\nassessments carried out in this chapter, with confidence levels ranging from low to very high. Refer to Cross-Chapter Box 2.1 for description of paleoclimate reference periods \r\nand Section 1.4.1 for recent reference periods. Values are reported as either the very likely range (x to y), or best estimates from beginning to end of the reference period with \r\nno stated uncertainty (x - y), or lowest and highest values with no stated uncertainty (x ~ y). Temperature is global mean surface temperature. Glacier extent is relative and \r\ncolour scale is inverted so that more extensive glacier extent is intuitively blue."


id: bfdc9f30683d0da05522060e021a7c0f
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 27743
content:
"it has been on a centennially-averaged basis in the CE and more likely \r\nthan not since the peak of the LIG. Many more integrative components \r\nof the climate system (e.g., glaciers, GMSL) are experiencing conditions \r\nunseen in millennia, whereas the most slowly responding components \r\n(e.g.,  ice-sheet extent, permafrost, tree line) are at levels unseen in \r\ncenturies (high confidence). The rate at which several assessed climate \r\nindicators (e.g., GMSL, OHC, GSAT) have changed over recent decades \r\nis highly unusual in the context of preceding slower changes during the \r\ncurrent post-glacial period (high confidence)."


id: 194d160cf487e8f24b737922d664a7c8
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 1464
content:
"of more indicators of the climate system and, with increasing fidelity, \r\nthe rates of change. Solely for the last 150 years or so are instrumental \r\nobservations of globally distributed climate indicators available. \r\nHowever, only since the late 20th century have observational \r\nsystems attained essentially global monitoring capabilities. The \r\ndirect observations point unequivocally to rapid change across many \r\nindicators of the climate system since the mid-19th century. These are \r\nall consistent in indicating a world that has warmed rapidly. "


id: 2cd6726a012ca62a67ca3818ee0bf198
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 4489
content:
"Assessing the long-term context of recent changes is key to \r\nunderstanding their potential importance and implications. The climate \r\nsystem consists of many observable aspects that vary over a very \r\nbroad range of timescales. Some biogeochemical indicators of change \r\nsuch as atmospheric CO2 concentrations and ocean pH have shifted \r\nrapidly and CO2 concentrationsare currently at levels unseen in at least \r\n800 kyr (the period of continuous polar ice-core records) and very likely\r\nfor millions of years. The GMST in the past decade is likely warmer than "


id: 5f6ce93c8d95570d65ce322de5cd9562
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 12584
content:
"In summary, directly observed changes in the atmosphere, ocean, \r\ncryosphere and biosphere represent unequivocal evidence of \r\na warming world. Key climate indicators are now at levels not \r\nexperienced for centuries to millennia. Since the late 19th century \r\nmany indicators of the global climate system have changed at a rate \r\nunprecedented over at least the last two thousand years."


id: 31d315d97a88238b51ab69f6467718b
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 5250
content:
"Cross-Chapter Box 2.4 | The Climate of the Pliocene (Around 3 Million Years Ago), When CO2\r\nConcentrations Were Last Similar to Those of the Present Day"


id: 3e315a7c8ff395592eada8193c8788d1
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 7154
content:
"Contributing Authors: Alan M. Haywood (United Kingdom), Darrell S. Kaufman (United States of America), Nicholas R. Golledge \r\n(New Zealand/United Kingdom), Dabang Jiang (China), Daniel J. Lunt (United Kingdom), Erin L. McClymont (United Kingdom), \r\nUlrich Salzmann (United Kingdom/Germany, United Kingdom), Jessica Tierney (United States of America)"


id: 707e604806a928e5a167eed6f6101089
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 15315
content:
"Throughout this Report, information about past climate states is presented in the context of specific climate variables, processes or \r\nregions. This Cross-Chapter Box focuses on a single paleoclimate reference period as an example of how proxy data, models and \r\nprocess understanding come together to form a more complete representation of a warm climate state that occurred during the \r\nrelatively recent geologic past."


id: 5af59a67cac802bab121d7c5f1bac42d
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 11825
content:
"During the MPWP (3.3-3.0 Ma) the atmospheric CO2 concentration was similar to present, and the slow-response, large-scale \r\nindicators reflect a world that was warmer than present. With very high confidence, relative to present, global surface temperature, \r\nsea level, and precipitation rate were higher, NH latitudinal temperature gradient was lower, and major terrestrial biomes expanded \r\npoleward. With medium confidence from proxy-based evidence alone (Section 2.3.2), combined with numerical modelling, analysis \r\nof the sea-level budget, and process understanding (Section 9.6.2), there is high confidence that cryospheric indicators were \r\ndiminished. There is medium confidence that the Pacific longitudinal temperature gradient was weaker and monsoon systems \r\nwere stronger."


id: 7c131d24ab7bd91e2e9deab0ed9f1374
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 17123
content:
"Modes of climate variability that are important for large-scale climate \r\non interannual and longer timescales (Cross-Chapter Box 2.2) are \r\nassessed herein and defined and summarized in Annex IV. Though \r\nthe modes of variability discussed here are assessed and classified on \r\nthe basis of physical variables, it is important to recognize that the \r\ndistribution and function of various components of the terrestrial and \r\nmarine biospheres are modified in response to them. "


id: 66d141ce8ed924b5c51c23a15b898ecb
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 13771
content:
"The AR5 reported that the shift towards a positive NAO, a mode \r\nof variability in the North Atlantic that is closely related to the \r\nhemispheric-scale NAM, from the 1950s to the 1990s was largely \r\nreversed by more recent changes (high confidence). Moreover, \r\nperiods of persistent negative or positive NAO states observed during \r\nthe latter part of the 20th century were not unusual, based on NAO \r\nreconstructions spanning the last half millennium (high confidence)."


id: 52a67bd380ab815b142d2cd259066f73
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 10464
content:
"In summary, positive trends for the NAM/NAO winter indices \r\nwere observed between the 1960s and the early 1990s, but these \r\nindices have become less positive or even negative thereafter (high \r\nconfidence). The NAO variability in the instrumental record was very \r\nlikely not unusual in the millennial and multi-centennial context."


id: 8e7577af411e3226c5de20c74cdb5164
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 19936
content:
"The AR5 concluded that it was likely that the SAM had become more \r\npositive since the 1950s and that this increase was unusual in the \r\ncontext of the prior 400 years (medium confidence). Both AR5 and \r\nSROCC reported statistically significant trends in the SAM during the \r\ninstrumental period for the austral summer and autumn. "


id: d7d859940e7b664a26e568195855fdc0
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 31485
content:
"Prolonged periods of negative SAM values were identified during the \r\nperiod 1400-1700 CE in several reconstructions (Figure 2.35, Villalba \r\net al., 2012; Abram et al., 2014; Datwyler et al., 2018), with a minimum \r\nidentified during the 15th century (Hernandez et al., 2020), although "


id: 606b57b86c1766da84b7210d5e6ddb6
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 12742
content:
"least the past millennium, although medium confidence arises due to \r\nthe differences between proxy records before 1800 CE."


id: c303a93a3ffce8da427017170374469f
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 28263
content:
"some disagreements exist between proxy records before 1800 CE \r\n(Hessl et  al., 2017). Abram et  al. (2014) concluded that the mean \r\nSAM index during recent decades is at its highest levels for at least \r\nthe last 1 kyr. Similarly, the summer SAM reconstruction by Datwyler \r\net al. (2018) indicates a strengthening over the last 60 years that is \r\noutside the very likely range of the last millennium natural variability. \r\nThe largest 30- and 50-year trends in the annual SAM index occurred \r\nat the end of the 20th century (after 1969 and 1950 respectively), \r\nindicating that the recent increase in the SAM is unprecedented in \r\nthe context of at least the past three centuries (Yang and Xiao, 2018). "


id: 15cffe0360123e4b280bb5a3fe09e855
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 953
content:
"The AR5 reported with medium confidence that ENSO-like variability \r\nexisted, at least sporadically, during the warm background state of the \r\nPliocene. It was also found (high confidence) that ENSO has remained \r\nhighly variable during the last 7 kyr with no discernible orbital \r\nmodulation. The AR5 concluded that large variability on interannual \r\nto decadal timescales, and differences between datasets, precluded \r\nrobust conclusions on any changes in ENSO during the instrumental \r\nperiod. The SROCC reported epochs of strong ENSO variability \r\nthroughout the Holocene, with no indications of a systematic trend in \r\nENSO amplitude, but with some indication that the ENSO amplitude \r\nover 1979-2009 was greater than at any point in the period from \r\n1590-1880 CE. It was also reported that the frequency and intensity \r\nof El Nino events in the period from 1951-2000 was high relative to \r\n1901-1950. "


id: ac6f9f4869c28b27b05965b2eeddec
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 24667
content:
"In summary, historical station-based reconstructions of the SAM \r\nshow that there has been a robust positive trend in the SAM index, \r\nparticularly since 1950 and for the austral summer (high confidence). \r\nThe recent positive trend in the SAM is likely unprecedented in at "


id: f6adde9c1f4c4edc9c2d671028e6946
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 36325
content:
"Numerous studies (J. Li et al., 2013; S. McGregor et al., 2013; Rustic et al., \r\n2015; Hope et al., 2017; Y. Liu et al., 2017) find substantial variability \r\nin ENSO activity on multi-decadal to centennial timescales over the \r\nlast 500 to 1 kyr (Figure 2.36). Different proxies show a wide spread \r\nin the specific timing and magnitude of events in the pre-instrumental \r\nperiod (e.g., Datwyler et al., 2019). Most investigators find that ENSO "


id: 5bf12c87b38630cf181568a8d72bbdf3
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 11977
content:
"activity in recent decades was higher than the most recent centuries \r\nprior to the instrumental period. Grothe et al. (2019) also found that \r\nENSO variance of the last 50 years was 25% higher than the average \r\nof the last millennium, and was substantially higher  than the \r\naverage of the mid- to late-Holocene. S. McGregor et al., (2010, 2013) \r\nlooked for common variance changes in pre-existing ENSO proxies, \r\nfinding stronger ENSO variance for the 30-year period 1979-2009 \r\ncompared to any 30-year period within the timespan 1590-1880 CE. \r\nThis finding also holds when adding more recently developed ENSO \r\nproxies (Figure 2.36). Koutavas and Joanides (2012), Ledru et  al. \r\n(2013) and Thompson et al. (2017) identify various periods within the \r\nrange 1000 BCE to 1300 CE when ENSO activity was greater than \r\nin the following centuries, and more closely comparable to the mid\u000220th century onwards behaviour."


id: 98681edd098d1a53c3116147be8e64b0
created_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 21488
content:
"Since AR5, updates to datasets used widely in prior ENSO assessments \r\nresulted in substantial and important revisions to observed tropical \r\nPacific SST data (Section 2.3.1.1). In particular, ERSSTv4, and then "


id: 70adc07d91ddce7594d968576845bcfe
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 15348
content:
"There is a distinction (Annex IV.2.3.1) between El Nino events \r\ncentred in the eastern Pacific ('Eastern Pacific' (EP) or 'classical' \r\nevents) and those centred in the Central Pacific ('Central Pacific' (CP) \r\nor 'Modoki' events), which have different typical teleconnections \r\n(e.g., Ashok et al., 2007; Ratnam et al., 2014; Capotondi et al., 2015; "


id: 1b88994f3b964f1bc572e1b80db9f76a
created_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 1794
content:
"teleconnections associated with these, being beyond the range of \r\nvariability on decadal to millennial timescales. A high proportion of \r\nEl Nino events in the last 20-30 years have been based in the central, \r\nrather than eastern Pacific, but there is low confidence that this \r\nrepresents a long-term change. "


id: 41385bb46a17a0f812efc357db48a747
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content:
"Timmermann et  al., 2018). A number of studies, using a range of \r\nindicators, have found an increase in recent decades of the fraction \r\nof  CP El Nino events, particularly after 2000 (Yu and Kim, 2013; \r\nLubbecke and McPhaden, 2014; Pascolini-Campbell et  al., 2015; \r\nJiang and Zhu, 2018). Johnson (2013) found that the frequency of \r\nCP El Nino events had increased (although not significantly) over the \r\n1950-2011 period, being accompanied by a significant increase in \r\nthe frequency of La Nina events with a warm (as opposed to cool) \r\nwestern Pacific warm pool. A coral-based reconstruction starting \r\nin 1600 CE (Freund et  al., 2019) found that the ratio of CP to EP \r\nevents in the last 30 years was substantially higher than at any other \r\ntime over the last 400 years. Variations in the proportion of CP and \r\nEP events have also been found in earlier periods, with Carre et al. \r\n(2014) finding a period of high CP activity around 7 ka."


id: 8cbe60eafca09ef8998b182fbbdee88c
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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content:
"The AR5 did not provide an assessment of the Indian Ocean Dipole \r\n(IOD) records based on paleo reconstructions. For the instrumental \r\nera, AR5 reported that there were no trends in the IOD behaviour. \r\nHowever, the strength of the Indian Ocean Basin-wide (IOB) mode, \r\nquantified by the basin-scale averaged SST index, increased in all \r\nassessed periods except 1979-2012, but the AR5 neither quantified \r\ntrends nor provided a confidence statement. "


id: 52ba3cc81c381faf393634ecf3f211ca
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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content:
"From the coral d18O record from the Seychelles over 1854-1994, \r\nDu  et  al. (2014) showed a 3-7 year dominant period associated \r\nwith the IOB in response to ENSO forcing. They identified multi\u0002decadal variability in the IOB, with more active IOB phases during \r\n1870-1890, 1930-1955, and 1975-1992, while decadal variability in \r\nthe IOB dominated during 1940-1975 (Du et al., 2014). Evidence for \r\nchanges in IOB characteristics during earlier periods (e.g., MH, LGM) \r\nis limited. "


id: 4d63b7064713d19a29a42ee24ea93b3f
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 9609
content:
"In summary, there is medium confidence that both ENSO amplitude \r\nand the frequency of high-magnitude events since 1950 are higher \r\nthan over the period from 1850 and possibly as far back as 1400, \r\nbut low confidence that they are outside the range of variability over \r\nperiods prior to 1400, or higher than the average of the Holocene \r\nas a whole. Overall, there is no indication of a recent sustained shift \r\nin ENSO or associated features such as the Walker Circulation, or in "


id: 3e6dbb14bfff7aafbdd01dcbdeecf96d
created_at: 2023-03-16 14:00:39
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vector_id: 7199
content:
"the seasonal evolution and the type of ENSO (Section 2.4.2) may \r\ninfluence the character of the IOD (Guo et al., 2015; Zhang et al., \r\n2015; Fan et al., 2016), the occurrence of some IOD events may be \r\nindependent of ENSO (Sun et al., 2015). "


id: 71550aaf89c122251304dc8f34f2e23c
created_at: 2023-03-16 14:00:39
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content:
"The role of decadal to multi-decadal variability has recently emerged \r\nas an important aspect of the IOD with many indications of the effects \r\nof Pacific Ocean processes on IOD variability through atmospheric \r\nand oceanic mechanisms (Dong et  al., 2016; Krishnamurthy and \r\nKrishnamurthy, 2016; Zhou et  al., 2017; Jin et  al., 2018). Positive \r\nevents in the 1960s and 1990s were linked to a relatively shallow \r\neastern Indian Ocean thermocline, and a primarily negative IOD \r\nstate in the 1970s and 1980s was related to a deeper thermocline \r\n(Ummenhofer et al., 2016). Positive IOD events may have increased \r\nin frequency during the second half of the 20th century (Abram et al., \r\n2020a, b). Earlier observations of apparent changes in the frequency \r\nand/or magnitude of the IOD events are considered unreliable, \r\nparticularly prior to the 1960s (Hernandez et  al., 2020). Although "


id: 584636610c150888604ab384de8f765d
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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content:
"To summarize, there is low confidence in any multi-decadal IOD \r\nvariability trend in the instrumental period due to data uncertainties \r\nespecially before the 1960s. In addition to data uncertainties, \r\nunderstanding of the IOB variability during the instrumental period is \r\nalso limited by large-scale warming of the Indian Ocean. Neither the \r\nIOD nor the IOB have exhibited behaviour outside the range implied \r\nby proxy records (low confidence)."


id: 6f7fddd7e8a3b8ff315e06e043a755cd
created_at: 2023-03-16 14:00:39
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content:
"Figure 2.37 | Indices of interannual climate variability from 1950-2019 based upon several sea surface temperature data products. Shown are the following \r\nindices from top to bottom: IOB mode, IOD, Nino3.4, AMM and AZM. All indices are based on area-averaged annual data (see Annex IV). Further details on data sources and \r\nprocessing are available in the chapter data table (Table 2.SM.1)."


id: 4093d0d49118a0765e07bb0d4fb3bebf
created_at: 2023-03-16 14:00:39
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"with a  predominantly positive phase until the end of the 1990s, \r\nbeing mainly negative afterwards. There was no significant change \r\nassessed in the PDO during the instrumental period as a whole, and \r\nno confidence level was assigned. Changes in the pre-instrumental \r\nera PDO were not assessed in AR5. "


id: fbd13a8d3c2d769ee6f2f7c49ba39c40
created_at: 2023-03-16 14:00:39
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vector_id: 37116
content:
"The AR5 reported no changes in the Atlantic Meridional Mode \r\n(AMM) during the 20th century or shorter periods thereof. For the \r\nAtlantic Zonal Mode (AZM), also referred as the Atlantic Nino, \r\nthe AR5 reported increases during the 1950-2012 period but neither \r\nassessed trends nor provided a confidence statement. The AR5 did \r\nnot assess paleo evidence for the AZM and AMM."


id: 116a1bb7337c51fd1a3fd20709d0fb70
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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content:
"Paleo-reconstructions of these two modes remain rather limited. \r\nNonetheless, the interhemispheric cross-equatorial SST gradients linked \r\nto changes in ITCZ locations characteristic of the AMM has been found \r\nduring the LGM, Heinrich Stadial 1, and the MH, with the largest shift \r\noccurring during HS1 (McGee et al., 2014). Similarly, the dipole-like SST \r\npattern in the South Atlantic subtropics, which is related to the AZM \r\n(Venegas et al., 1996; Morioka et al., 2011; Nnamchi et al., 2016, 2017; \r\nLubbecke et al., 2018; Rouault et al., 2018; Foltz et al., 2019), has been \r\nreconstructed using SST proxies from marine sediment cores during \r\nthe past 12 kyr (Wainer et al., 2014). The reconstructed index captures \r\ntwo significant cold events that occurred during the 12.9-11.6 ka and \r\n8.6-8.0 ka periods in the South Atlantic (Wainer et al., 2014). "


id: 2adadb24dade506f9a3400283576c385
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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content:
"The PDO and IPO indices are significantly correlated during the \r\ninstrumental period, showing regime shifts in the 1920s, 1940s, 1970s \r\nand around 1999. Positive PDV phases were observed from the 1920s \r\nto the mid-1940s and from the late 1970s to the late 1990s, while \r\nnegative phases occurred from mid-1940s until the late 1970s, and \r\nsince 1999 (Figure 2.38; Han et al., 2014; Chen and Wallace, 2015; \r\nM. Newman et al., 2016). The associated spatial patterns are quite \r\nsimilar, but the PDO pattern exhibits stronger SST anomalies in the \r\nextra-tropical North Pacific than the IPO (Chen and Wallace, 2015). \r\nThe strength and structure of the SST patterns also differ among the \r\nperiods (M. Newman et al., 2016)."


id: 82524c610b17df70260387f998e8cc78
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 18028
content:
"In summary, confidence is low in any sustained changes to the AZM \r\nand AMM variability in instrumental observations. There is very low \r\nconfidence in changes of the paleo AZM and AMM due to extremely \r\nlimited availability of paleo reconstructions."


id: d8d28e2fc6990b3847b72d3613ea0489
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 31623
content:
"Instrumental observations are sparse prior to 1950, and thus \r\nthe fidelity of any PDV index derived for the second part of the \r\n19th  century and early decades of the 20th century is relatively \r\nlow (Figure 2.38; Deng et  al., 2013; Wen et  al., 2014). This results \r\nin low agreement in the classification of the PDO/IPO phase among \r\nseveral indices, even during recent years with the availability of high\u0002quality data. Nevertheless, the teleconnection patterns are robust \r\nregardless of the index used to characterize the PDO (McAfee, 2017). \r\nAnalysis of time series of PDO and IPO highlights the (multi-) decadal \r\nnature  of this mode of variability with no significant trends, but \r\nhighlights a recent switch from a positive to a negative phase since \r\n1999/2000 across all indicators (England et al., 2014; Henley, 2017). "


id: ea9926603bbec6ca292c47efad906b92
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content:
"Pacific Decadal Variability (PDV) refers to the ocean-atmosphere \r\nclimate variability over the Pacific Ocean at decadal-to-interdecadal \r\ntime scales and is usually described by the Pacific Decadal Oscillation \r\n(PDO) or the Inter-decadal Pacific Oscillation (IPO) indices. The AR5 \r\nand SROCC reported a large shift of the PDO in the late 1970s, "


id: 545c8ae2ddf1f5ae622ce3318a2e4c9a
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content:
"Instrumental observations show that AMV is characterized by \r\nbasin-wide warm and cool periods with an average variation in \r\nSST of about 0.4degC, but with larger variations in the North Atlantic \r\nsubpolar gyre. Despite small differences in indices used to define the \r\nAMV (Annex IV), they all show warm periods occurring approximately \r\nbetween 1880-1900, 1940-1960, and from the mid-1990s to \r\npresent, with cool periods in between (Figure 2.38) but no overall \r\nsustained change during the instrumental period (Booth et al., 2012; \r\nGulev et al., 2013; Bellomo et al., 2018)."


id: 3b0ce944b2c52c5cd9e1310a5d354c52
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content:
"The oceanic changes are seen in salinity and temperature variations \r\nover the upper 3000 m of the North Atlantic (Polyakov et al., 2005; \r\nKeenlyside et al., 2015), and in sea level variations in the western \r\nNorth Atlantic along the Gulf Stream passage (McCarthy et  al., \r\n2015). The pattern and strength of the AMV differs among the \r\nperiods (e.g.,  Svendsen et  al., 2014b; Reynolds et  al., 2018) and \r\nthere are indications that there may have been a shift since 2005 \r\ntoward a negative phase of the AMV (Robson et al., 2016)."


id: 5027995ea733eb8fe9ff21111144c792
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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content:
"In summary, no sustained change in AMV indices has been \r\nobserved over the instrumental period (high confidence). However, \r\ninstrumental records may not be long enough to distinguish any \r\noscillatory behaviour from trends in the AMV. There is low confidence\r\nin the paleo AMV reconstructions due to a paucity of high-resolution \r\nrecords. "


id: 299513264c69f32aacb6e229db27e07
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 3979
content:
"In summary, the PDV in the instrumental record is dominated by \r\n(multi-)decadal-scale shifts between positive and negative phases \r\nover the last 150 years with no overall trend (high confidence). There \r\nis low confidence in paleo-PDV reconstructions due to discrepancies \r\namong the various available time series in terms of phasing and \r\ntiming. However, there is high confidence in the occurrence of a shift \r\nfrom predominantly negative to positive PDO conditions from the \r\nmiddle to the late Holocene. "


id: 84f23b7bea488feaed877f1de7086186
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
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vector_id: 18441
content:
"The assessment in this chapter is based upon an ever-expanding \r\nvolume of available proxy and observational records and a growing \r\nbody of literature. Since AR5, improvements have been made in all \r\naspects of data collection, data curation, data provision and data \r\nanalysis permitting improved scientific insights. The chapter has \r\nalso benefitted from the availability of new products from a range \r\nof emerging, mainly space-based, observing capabilities and new \r\ngenerations of reanalysis products. However, a number of key \r\nchallenges still remain which, if addressed, would serve to strengthen \r\nfuture reports."


id: 842bafddf73a6c75973746df420c7ac5
created_at: 2023-03-16 14:00:39
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content:
"The AR5 reported no robust changes in Atlantic Multi-decadal Variability \r\n(AMV) reconstructions based on paleo records due to low consistency \r\nbetween different AMV reconstructions prior to 1900. AR5 concluded \r\nthat there have been no significant trends in the AMV index during the \r\ninstrumental period and there was difficulty in interpreting the AMV \r\nsignal because of the long-term underlying SST warming trend. "


id: 6da6b7d64fdb40da78d96d15fe8759b2
created_at: 2023-03-16 14:00:39
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content:
"The AR5 conclusions about large uncertainties in AMV paleo \r\nreconstructions (Hernandez et  al., 2020) have been reinforced by \r\nrecent studies of tree rings (J. Wang et  al., 2017b), Greenland ice \r\n(Chylek et  al., 2012), and corals (Kilbourne et  al., 2014; Svendsen \r\net al., 2014b; J. Wang et al., 2017b). The AMV exhibited a generally \r\npositive state over the first millennium of the CE (Mann et al., 2009; \r\nSingh et  al., 2018). Paleo reconstructions over the last millennium \r\nconsistently show a negative AMV phase during 1400-1850 CE and \r\na positive phase during 900-1200 CE (Mann et al., 2009; J. Wang \r\net  al., 2017b; Singh et  al., 2018), consistent with warmer surface \r\ntemperatures from tropical Atlantic records (Kilbourne et al., 2014). "


id: ae313cb4eea9b8c8c0e583c4d2e2544e
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content:
"forcers, especially for components of the climate system where \r\nthe dominant response is on multi-decadal and longer time \r\nscales. Targeted rescue of early marine data records, especially \r\nfrom waters of the tropical oceans and the Southern Ocean, could \r\nhelp constrain modes of variability and important teleconnection \r\nchanges in, for example, the hydrological cycle and patterns of \r\nglobal temperature change. {2.2, 2.3, 2.4}"


id: d8ea00f00d9b1d2cff467908b9af4b92
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updated_at: 2023-03-16 14:00:39
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vector_id: 31636
content:
"The authors of Chapter 2 would like to extend their gratitude to \r\nSara Veasey, Deborah Riddle, Deborah Misch (all NOAA NCEI, USA) \r\nand Robert Fawcett (BoM, Australia) for providing substantial \r\nsupport in the production and finalization of all figures. We wish \r\nto acknowledge Raphael Neukom (University of Bern, Switzerland) \r\nand Michael Bosilovich (NASA/GFSC, USA) for their assistance in the \r\nprovision of data."


id: 750ca09d21b9145b8b4a5d3f7278da9
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updated_at: 2023-03-16 14:00:39
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vector_id: 16009
content:
"Earth's climate has always changed naturally, but both the global extent and rate of recent warming are unusual. \r\nThe recent warming has reversed a slow, long-term cooling trend, and research indicates that global surface \r\ntemperature is higher now than it has been for millennia."


id: 95e7df0f1ffb1f5732d741754127acb3
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vector_id: 21088
content:
"While climate can be characterized by many variables, temperature is a key indicator of the overall climate state, and \r\nglobal surface temperature is fundamental to characterizing and understanding global climate change, including \r\nEarth's energy budget. A rich variety of geological evidence shows that temperature has changed throughout \r\nEarth's history. A variety of natural archives from around the planet, such as ocean and lake sediments, glacier \r\nice and tree rings, shows that there were times in the past when the planet was cooler, and times when it was \r\nwarmer. While our confidence in quantifying large-scale temperature changes generally decreases the farther \r\nback in time we look, scientists can still identify at least four major differences between the recent warming and \r\nthose of the past."


id: 6ae70411d97091da64ab55e3efe52e27
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vector_id: 14437
content:
"It's warming almost everywhere. During decades and centuries of the past 2000 years, some regions warmed \r\nmore than the global average while, at the same time, other regions cooled. For example, between the 10th \r\nand 13th centuries, the North Atlantic region warmed more than many other regions. In contrast, the pattern of \r\nrecent surface warming is globally more uniform than for other decadal to centennial climate fluctuations over \r\nat least the past two millennia."


id: dc323c3a3ffb39c1f458aa90883808a6
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index: climate_gpt_only_giec
vector_id: 32154
content:
"Recent warming reversed a long-term global cooling trend. Following the last major glacial period, global \r\nsurface temperature peaked by around 6500 years ago, then slowly cooled. The long-term cooling trend was \r\npunctuated by warmer decades and centuries. These fluctuations were minor compared with the persistent and \r\nprominent warming that began in the mid-19th century when the millennial-scale cooling trend was reversed. "


id: f42f833819dd1fb62e3032384bd519ec
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index: climate_gpt_only_giec
vector_id: 35927
content:
"It's been a long time since it's been this warm. Averaged over the globe, surface temperatures of the past decade \r\nwere probably warmer than when the long cooling trend began around 6500 years ago. If so, we need to look \r\nback to at least the previous interglacial period, around 125,000 years ago, to find evidence for multi-centennial \r\nglobal surface temperatures that were warmer than now. "


id: 5f17ce229b4a04e6b74f4d50692231ef
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 12510
content:
"Previous temperature fluctuations were caused by large-scale natural processes, while the current warming is \r\nlargely due to human causes (see, for example, FAQ 1.3, FAQ 3.1). But understanding how and why temperatures \r\nhave changed in the past is critical for understanding the current warming and how human and natural \r\ninfluences will interact to determine what happens in the future. Studying past climate changes also makes it \r\nclear that, unlike previous climate changes, the effects of recent warming are occurring on top of stresses that \r\nmake humans and nature vulnerable to changes in ways that they have never before experienced (for example, \r\nsee FAQ 11.2, FAQ12.3). "


id: c88a22a1a02eda4aec34e6b99ec17d72
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updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 29114
content:
"Climate has always changed, but warming like that of recent \r\ndecades has not been seen for millennia or longer."


id: 21edacaac7aa8fe3cc9fe3bfed0885f
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 2782
content:
"The evidence for climate change rests on more than just increasing surface temperatures. A broad range of \r\nindicators collectively leads to the inescapable conclusion that we are witnessing rapid changes to many aspects \r\nof our global climate. We are seeing changes in the atmosphere, ocean, cryosphere, and biosphere. Our scientific \r\nunderstanding depicts a coherent picture of a warming world."


id: 975debd573abec028ce63edf39fc29d4
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 21339
content:
"We have long observed our changing climate. From the earliest scientists taking meteorological observations \r\nin the 16th and 17th centuries to the present, we have seen a revolution in our ability to observe and diagnose \r\nour changing climate. Today we can observe diverse aspects of our climate system from space, from aircraft \r\nand weather balloons, using a range of ground-based observing technologies, and using instruments that can \r\nmeasure to great depths in the ocean. "


id: 84fd73e351c57b6fadd7c8f094c67529
created_at: 2023-03-16 14:00:39
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content:
"Observed changes in key indicators point to warming over land areas. Global surface temperature over land has \r\nincreased since the late 19th century, and changes are apparent in a variety of societally relevant temperature \r\nextremes. Since the mid-1950s the troposphere (i.e., the lowest few km of the atmosphere) has warmed, and \r\nprecipitation over land has increased. Near-surface specific humidity (i.e., water vapour) over land has increased \r\nsince at least the 1970s. Aspects of atmospheric circulation have also evolved since the mid-20th century, including \r\na poleward shift of mid-latitude storm tracks."


id: f0924d2112eb01c3e3f9a6a09efd9c
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content:
"Changes in the global ocean point to warming as well. Global average sea surface temperature has increased \r\nsince the late 19th century. The heat content of the global ocean has increased since the 19th century, with more \r\nthan 90% of the excess energy accumulated in the climate system being stored in the ocean. This ocean warming \r\nhas caused ocean waters to expand, which has contributed to the increase in global sea level in the past century. \r\nThe relative acidity of the ocean has also increased since the early 20th century, caused by the uptake of carbon \r\ndioxide from the atmosphere, and oxygen loss is evident in the upper ocean since the 1970s."


id: 78b5e8ccbc3908e6d216c79e09999eae
created_at: 2023-03-16 14:00:39
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vector_id: 16555
content:
"Significant changes are also evident over the cryosphere - the portion of the Earth where water is seasonally or \r\ncontinuously frozen as snow or ice. There have been decreases in Arctic sea ice area and thickness and changes \r\nin Antarctic sea ice extent since the mid-1970s. Spring snow cover in the Northern Hemisphere has decreased \r\nsince the late-1970s, along with an observed warming and thawing of permafrost (perennially frozen ground). \r\nThe Greenland and Antarctic ice sheets are shrinking, as are the vast majority of glaciers worldwide, contributing \r\nstrongly to the observed sea level rise. "


id: a7784275ea374c00157596aef1223982
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 23855
content:
"Many aspects of the biosphere are also changing. Over the last century, long-term ecological surveys show that \r\nmany land species have generally moved poleward and to higher elevations. There have been increases in green \r\nleaf area and/or mass (i.e., global greenness) since the early 1980s, and the length of the growing season has \r\nincreased over much of the extratropical Northern Hemisphere since at least the mid-20th century. There is also \r\nstrong evidence that various phenological metrics (such as the timing of fish migrations) for many marine species \r\nhave changed in the last half century."


id: 5119b95761a160650913f13a02724d63
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 10211
content:
"Change is apparent across many components of the climate system. It has been observed using a very broad range \r\nof techniques and analysed independently by numerous groups around the world. The changes are consistent in \r\npointing to a climate system that has undergone rapid warming since the industrial revolution."


id: 7f43ab85da1d730e331aa007726146f3
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 17575
content:
"Krishna M.Achuta Rao (India), Rondrotiana Barimalala (South Africa/Madagascar), Marcelo Barreiro \r\nParrillo (Uruguay), Nicolas Bellouin (United Kingdom/France), Christophe  Cassou (France), \r\nPaul J. Durack (United States of America/Australia), Yu Kosaka (Japan), Shayne McGregor (Australia), \r\nSeung-Ki Min (Republic of Korea), Olaf Morgenstern (New Zealand/Germany), Ying Sun (China)"


id: eb4797ee22f25f59a1bd1293ab14aa5a
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 34512
content:
"Tomas Halenka (Czech Republic), Jose A. Marengo Orsini (Brazil/Peru), Daniel Mitchell \r\n(United Kingdom)"


id: 9e3ac7f31dd73947c46370838b886d30
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 22417
content:
"Eyring, V., N.P. Gillett, K.M. Achuta Rao, R. Barimalala, M. Barreiro Parrillo, N. Bellouin, C. Cassou, P.J. Durack, \r\nY. Kosaka, S.  McGregor, S. Min, O. Morgenstern, and Y. Sun, 2021: Human Influence on the Climate System. In \r\nClimate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment \r\nReport of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. \r\nConnors, C. Pean, S. Berger, N. Caud, Y. Chen, L.  Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. \r\nMatthews, T.K. Maycock, T. Waterfield, O. Yelekci, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, \r\nCambridge, United Kingdom and New York, NY, USA, pp. 423-552, doi:10.1017/9781009157896.005."


id: 570948e456ff143d3173a3fe4998c08
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 11173
content:
"It is unequivocal that human influence has warmed the \r\natmosphere, ocean and land since pre-industrial times. Combining \r\nthe evidence from across the climate system increases the level of \r\nconfidence in the attribution of observed climate change to human \r\ninfluence and reduces the uncertainties associated with assessments \r\nbased on single variables. Large-scale indicators of climate change in \r\nthe atmosphere, ocean, cryosphere and at the land surface show clear \r\nresponses to human influence consistent with those expected based \r\non model simulations and physical understanding. {3.8.1}"


id: a26b7f580bf862c1874121b6c0540078
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 23117
content:
"The slower rate of GMST increase observed over 1998-2012 \r\ncompared to 1951-2012 was a temporary event followed \r\nby a strong GMST increase (very high confidence). Improved \r\nobservational datasets since AR5 show a larger GMST trend over \r\n1998-2012 than earlier estimates. All the observed estimates of \r\nthe 1998-2012 GMST trend lie within the 10th-90th percentile \r\nrange of CMIP6 simulated trends (high confidence). Internal \r\nvariability, particularly Pacific Decadal Variability, and variations in \r\nsolar and volcanic forcings partly offset the anthropogenic surface \r\nwarming trend over the 1998-2012 period (high confidence). Global \r\nocean heat content continued to increase throughout this period, \r\nindicating continuous warming of the entire climate system (very "


id: d25a95dfc8a98c8e2984343b52a89453
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 30621
content:
"high confidence). Since 2012, GMST has warmed strongly, with the \r\npast five years (2016-2020) being the warmest five-year period \r\nin the instrumental record since at least 1850 (high confidence). \r\n{Cross-Chapter Box 3.1, 3.3.1; 3.5.1}"


id: 68bfeb1198eb8f6b49fd9394a30ef697
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 14072
content:
"It is very likely that anthropogenic forcing, mainly due to \r\ngreenhouse gas increases, was the main driver of Arctic sea \r\nice loss since the late 1970s. There is new evidence that increases \r\nin anthropogenic aerosols have offset part of the greenhouse \r\ngas-induced Arctic sea ice loss since the 1950s (medium confidence). \r\nIn the Arctic, despite large differences in the mean sea ice state, loss \r\nof sea ice extent and thickness during recent decades is reproduced \r\nin all CMIP5 and CMIP6 models (high confidence). By contrast, global \r\nclimate models do not generally capture the small observed increase \r\nin Antarctic sea ice extent during the satellite era, and there is low \r\nconfidence in attributing the causes of this change. {3.4.1}"


id: b1fa1d5977cba9781a0069f3ba59411a
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 25498
content:
"It is likely that human influence has contributed to3 moistening \r\nin the upper troposphere since 1979. Also, there is medium \r\nconfidence that human influence contributed to a global increase \r\nin annual surface specific humidity, and medium confidence that it \r\ncontributed to a decrease in surface relative humidity over mid-latitude \r\nNorthern Hemisphere continents during summertime. {3.3.2}"


id: 3dc8ac4b12806f4c494cb75ddf8013f3
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 7074
content:
"It is very likely that human influence contributed to the \r\nobserved reductions in Northern Hemisphere spring snow cover \r\nsince 1950. The seasonal cycle in Northern Hemisphere snow cover is \r\nbetter reproduced by CMIP6 than by CMIP5 models (high confidence). \r\nHuman influence was very likely the main driver of the recent global, \r\nnear-universal retreat of glaciers. It is very likely that human influence \r\nhas contributed to the observed surface melting of the Greenland \r\nIce Sheet over the past two decades, and there is medium confidence\r\nin an anthropogenic contribution to recent overall mass loss from the \r\nGreenland Ice Sheet. However, there is only limited evidence, with \r\nmedium agreement, of human influence on Antarctic Ice Sheet mass \r\nbalance through changes in ice discharge. {3.4.2, 3.4.3}"


id: 83f772b246266fec1ca6f1678760d647
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 18300
content:
"Human-induced greenhouse gas forcing is the main driver of \r\nthe observed changes in hot and cold extremes on the global \r\nscale (virtually certain) and on most continents (very likely).\r\nIt is likely that human influence, in particular due to greenhouse \r\ngas forcing, is the main driver of the observed intensification of \r\nheavy precipitation in global land regions during recent decades. \r\nThere is high confidence in the ability of models to capture the \r\nlarge-scale spatial distribution of precipitation extremes over land. \r\nThe magnitude and frequency of extreme precipitation simulated \r\nby CMIP6 models are similar to those simulated by CMIP5 models \r\n(high confidence). {Cross-Chapter Box 3.2}"


id: 179e600258bf26796f09bbd1f86445f8
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 1209
content:
"It is extremely likely that human influence was the main driver \r\nof the ocean heat content increase observed since the 1970s, \r\nwhich extends into the deeper ocean (very high confidence).\r\nSince AR5, there is improved consistency between recent observed \r\nestimates and model simulations of changes in upper (<700 m) ocean \r\nheat content, when accounting for both natural and anthropogenic \r\nforcings. Updated observations and model simulations show \r\nthat warming extends throughout the entire water column (high \r\nconfidence), with CMIP6 models simulating 58% of industrial-era \r\nheat uptake (1850-2014) in the upper layer (0-700 m), 21% in \r\nthe intermediate layer (700-2000 m) and 22% in the deep layer \r\n(>2000 m). The structure and magnitude of multi-model mean ocean \r\ntemperature biases have not changed substantially between CMIP5 \r\nand CMIP6 (medium confidence). {3.5.1}"


id: da02a20046504b9eafd877558717bc6c
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 31828
content:
"It is likely that human influence has contributed to the poleward \r\nexpansion of the zonal mean Hadley cell in the Southern\r\nHemisphere since the 1980s. There is medium confidence that \r\nthe observed poleward expansion of the zonal mean Hadley cell in \r\nthe Northern Hemisphere is within the range of internal variability. \r\nThe causes of the observed strengthening of the Pacific Walker \r\ncirculation since the 1980s are not well understood, and the observed \r\nstrengthening trend is outside the range of trends simulated in the \r\ncoupled models (medium confidence). While CMIP6 models capture \r\nthe general characteristics of the tropospheric large-scale circulation \r\n(high confidence), systematic biases exist in the mean frequency of \r\natmospheric blocking events, especially in the Euro-Atlantic sector, \r\nsome of which reduce with increasing model resolution (medium \r\nconfidence). {3.3.3}"


id: c78a4f3ef1dcbb28e2d70d05d5ea8d17
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 28979
content:
"It is extremely likely that human influence has contributed \r\nto observed near-surface and subsurface ocean salinity \r\nchanges since the mid-20th century. The associated pattern of \r\nchange corresponds to fresh regions becoming fresher and salty \r\nregions becoming saltier (high confidence). Changes to the coincident \r\natmospheric water cycle and ocean-atmosphere fluxes (evaporation \r\nand precipitation) are the primary drivers of the observed basin-scale \r\nsalinity changes (high confidence). The observed depth-integrated \r\nbasin-scale salinity changes have been attributed to human influence, \r\nwith CMIP5 and CMIP6 models able to reproduce these patterns "


id: 64ede94eeb49c8295cc4030f4aa05bf5
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 13449
content:
"influence. There is high confidence that Earth system models simulate \r\na realistic time evolution of the global mean ocean carbon sink. {3.6.2}"


id: e79647b8a694e6bc45d7e3976212cefb
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 33935
content:
"only in simulations that include greenhouse gas increases (medium \r\nconfidence). The basin-scale changes are consistent across models and \r\nintensify through the historical period (high confidence). The structure \r\nof the biases in the multi-model mean has not changed substantially \r\nbetween CMIP5 and CMIP6 (medium confidence). {3.5.2}"


id: 54b178f0578eded9a42e6e1ee36f846c
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 10781
content:
"It is very likely that human influence has contributed to the \r\nobserved trend towards the positive phase of the Southern \r\nAnnular Mode (SAM) since the 1970s and to the associated \r\nstrengthening and southward shift of the Southern \r\nHemispheric extratropical jet in austral summer. The influence of \r\nozone forcing on the SAM trend has been small since the early 2000s \r\ncompared to earlier decades, contributing to a weaker SAM trend \r\nobserved over 2000-2019 (medium confidence). Climate models \r\nreproduce the summertime SAM trend well, with CMIP6 models \r\noutperforming CMIP5 models (medium confidence). By  contrast, \r\nthe cause of the Northern Annular Mode (NAM) trend towards its \r\npositive phase since the 1960s and associated northward shifts of \r\nthe Northern Hemispheric extratropical jet and storm track in boreal \r\nwinter is not well understood. Models reproduce the observed \r\nspatial features and variance of the SAM and NAM very well (high \r\nconfidence). {3.3.3, 3.7.1, 3.7.2}"


id: 3e5d7237f7be0e08e47e64d1d49fd1a4
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 7181
content:
"Combining the attributable contributions from glaciers, \r\nice-sheet surface mass balance and thermal expansion, it is \r\nvery likely that human influence was the main driver of the \r\nobserved global mean sea level rise since at least 1971. Since \r\nAR5, studies have shown that simulations that exclude anthropogenic \r\ngreenhouse gases are unable to capture the sea level rise due to \r\nthermal expansion (thermosteric) during the historical period \r\nand that model simulations that include all forcings (anthropogenic \r\nand natural) most closely match observed estimates. It is very likely\r\nthat human influence was the main driver of the observed global \r\nmean thermosteric sea level increase since 1970. {3.5.3, 3.5.1, 3.4.3}"


id: ae56b00e42e7d7891ff762d2262abefe
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 24956
content:
"While observations show that the Atlantic Meridional \r\nOverturning Circulation (AMOC) has weakened from the mid\u00022000s to the mid-2010s (high confidence) and the Southern \r\nOcean upper overturning cell has strengthened since the \r\n1990s (low confidence), observational records are too short \r\nto determine the relative contributions of internal variability, \r\nnatural forcing, and anthropogenic forcing to these changes \r\n(high confidence). No changes in Antarctic Circumpolar Current \r\ntransport or meridional position have been observed. The mean zonal \r\nand overturning circulations of the Southern Ocean and the mean \r\noverturning circulation of the North Atlantic (the Atlantic Meridional \r\nOverturning Circulation, AMOC) are broadly reproduced by CMIP5 \r\nand CMIP6 models. However, biases are apparent in the modelled \r\ncirculation strengths (high confidence) and their variability (medium \r\nconfidence). {3.5.4}"


id: b89a505a0c9754764db2e1296e4ea7a7
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 26573
content:
"Human influence has not affected the principal tropical modes \r\nof interannual climate variability or their associated regional \r\nteleconnections beyond the range of internal variability (high \r\nconfidence). Further assessment since AR5 confirms that climate and \r\nEarth system models are able to reproduce most aspects of the spatial \r\nstructure and variance of the El Nino-Southern Oscillation and Indian \r\nOcean Basin and Dipole modes (medium confidence). However, despite \r\na slight improvement in CMIP6, some underlying processes are still \r\npoorly represented. In the Tropical Atlantic basin, which contains the \r\nAtlantic Zonal and Meridional modes, major biases in modelled mean \r\nstate and variability remain. {3.7.3 to 3.7.5}"


id: bf24b6632f172c79a5fc2203a1e3076a
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 27627
content:
"There is medium confidence that anthropogenic and volcanic \r\naerosols contributed to observed changes in the Atlantic \r\nMulti-decadal Variability (AMV) index and associated regional \r\nteleconnections since the 1960s, but there is low confidence\r\nin the magnitude of this influence. There is high confidence that \r\ninternal variability is the main driver of Pacific Decadal Variability \r\n(PDV) observed since pre-industrial times, despite some modelling \r\nevidence for potential human influence. Uncertainties remain in \r\nquantification of the human influence on AMV and PDV due to \r\nbrevity of the observational records, limited model performance in \r\nreproducing related sea surface temperature (SST) anomalies despite \r\nimprovements from CMIP5 to CMIP6 (medium confidence), and \r\nlimited process understanding of their key drivers. {3.7.6, 3.7.7}"


id: f72abbaa452a1f49c3fe025f12a6525c
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 36403
content:
"The main driver of the observed increase in the amplitude of \r\nthe seasonal cycle of atmospheric CO2 is enhanced fertilization \r\nof plant growth by the increasing concentration of atmospheric \r\nCO2 (medium confidence). However, there is only low confidence\r\nthat this CO2 fertilization has also been the main driver of observed \r\ngreening because land management is the dominating factor in \r\nsome regions. Earth system models simulate globally averaged \r\nland carbon sinks within the range of observation-based estimates \r\n(high confidence), but global-scale agreement masks large regional \r\ndisagreements. {3.6.1}"


id: 2f53f2b7c023836d35f7bf5c83bdedf2
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 4866
content:
"It is virtually certain that the uptake of anthropogenic CO2\r\nwas the main driver of the observed acidification of the global \r\nsurface open ocean. The observed increase in CO2 concentration \r\nin the subtropical and equatorial North Atlantic since 2000 is likely\r\nassociated in part with an increase in ocean temperature, a response \r\nthat is consistent with the expected weakening of the ocean carbon \r\nsink with warming. Consistent with AR5 there is medium confidence\r\nthat deoxygenation in the upper ocean is due in part to human "


id: a272a1c292348affb288f24764ea6cf9
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 23123
content:
"the IPCC Special Report on the Ocean and Cryosphere in a Changing \r\nClimate (SROCC; IPCC, 2019b), and assessments of attribution of \r\nchanges in the terrestrial carbon cycle in the IPCC Special Report on \r\nClimate Change and Land (SRCCL, IPCC, 2019a)."


id: 13bcb53adadb29229113d2ab34c8366e
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 607
content:
"This chapter assesses the extent to which the climate system has \r\nbeen affected by human influence and to what extent climate models \r\nare able to simulate observed mean climate, changes and variability. \r\nThis assessment is the basis for understanding what impacts of \r\nanthropogenic climate change may already be occurring and informs \r\nour confidence in climate projections. Moreover, an understanding \r\nof the amount of human-induced global warming to date is key to \r\nassessing our status with respect to the Paris Agreement goals of \r\nholding the increase in global average temperature to well below \r\n2degC above pre-industrial levels and pursuing efforts to limit the \r\ntemperature increase to 1.5degC (UNFCCC, 2016)."


id: 6630df63ba46f7292d9eab94f24a76d9
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 13667
content:
"process-based evaluation of climate and Earth system models against \r\nobservations that have rapidly advanced since the publication of AR5 \r\n(Eyring et al., 2019) as well as newly developed CMIP evaluation \r\ntools that allow a more rapid and comprehensive evaluation of the \r\nmodels with observations (Eyring et al., 2016a, b)."


id: b4985b3610b3dc71520223d9a18cda31
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 25948
content:
"(Eyring et al., 2016a; Gillett et al., 2016). In addition to the assessment \r\nof model performance and human influence on the climate system \r\nduring the instrumental era up to the present-day, this chapter also \r\nincludes evidence from paleo-observations and simulations over past \r\nmillennia (Kageyama et al., 2018)."


id: 6de6b0215ecf4bcbf3f7c10eb2717c7b
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 14903
content:
"An introduction to recent developments in detection and attribution \r\nmethods in the context of this Report is provided in the Cross\u0002Working Group Box on Attribution in Chapter 1. Here we discuss new \r\nmethods and improvements applicable to the attribution of changes in \r\nlarge-scale indicators of climate change which are used in this chapter."


id: d5fd17e89033b013c9b62b7aa76c2ea0
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 31182
content:
"In order to improve the signal-to-noise ratio, observations and \r\nmodel-simulated responses are usually normalized by an estimate \r\nof internal variability derived from climate model simulations. This "


id: 4f210f24be2feaff1fd06fa1b895024a
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 9891
content:
"New methods for model evaluation that are used in this chapter \r\nare described in Section 1.5.4. These include new techniques for "


id: 76535dde27e50575356381c8e6928c1a
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 16206
content:
"Climate change signals can vary with time and discriminant analysis \r\nhas been used to obtain more accurate estimates of time-varying \r\nsignals, and has been applied to different variables such as seasonal \r\ntemperatures (Jia and DelSole, 2012) and the South Asian monsoon \r\n(Srivastava and DelSole, 2014). The same approach was applied \r\nto separate aerosol forcing responses from other forcings (X. Yan \r\net al., 2016) and results using climate model output indicated \r\nthat detectability of the aerosol response is maximized by using \r\na  combination of temperature and precipitation data. Paeth et al. \r\n(2017) introduced a detection and attribution method applicable for \r\nmultiple variables based on a discriminant analysis and a Bayesian \r\nclassification method. Finally, a systematic approach has been \r\nproposed to translating quantitative analysis into a description of \r\nconfidence in the detection and attribution of a climate response \r\nto anthropogenic drivers (Stone and Hansen, 2016)."


id: 9a87f7b7186d29f29009a82aa16d2521
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 21842
content:
"Overall, these new fingerprinting and other probabilistic methods for \r\ndetection and attribution as well as efforts to better incorporate the \r\nassociated uncertainties have addressed a number of shortcomings in \r\npreviously applied detection and attribution techniques. They further \r\nstrengthen the confidence in attribution of observed large-scale \r\nchanges to a combination of external forcings as assessed in the \r\nfollowing sections."


id: 8c0bf5c735efa3a4e3a491a9cd3035d4
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 19545
content:
"Surface temperature change is the aspect of climate in which the \r\nclimate research community has had most confidence over past IPCC \r\nassessment reports. This confidence comes from the availability of longer \r\nobservational records compared to other indicators, a large response to \r\nanthropogenic forcing compared to variability in the global mean, and \r\na strong theoretical understanding of the key thermodynamics driving \r\nits changes (Collins et al., 2010; Shepherd, 2014). The AR5 assessed \r\nthat it was extremely likely that human activities had caused more than "


id: 22756543026d915f2d4c6804623fee4c
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 2870
content:
"Considering the difficulty in accounting for climate modelling \r\nuncertainties in the regression-based approaches, Ribes et al. (2017) \r\nintroduced a new statistical inference framework based on an "


id: 1e15550c02739071aa1491b7402cd0b1
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 2169
content:
"half of the observed increase in global mean surface temperature from \r\n1951 to 2010, and virtually certain that internal variability alone could \r\nnot account for the observed global warming since 1951 (Bindoff et al., \r\n2013). The AR5 also assessed with very high confidence that climate \r\nmodels reproduce the general features of the global-scale annual \r\nmean surface temperature increase over 1850-2011 and with high \r\nconfidence that models reproduce global and Northern Hemisphere \r\ntemperature variability on a wide range of time scales (Flato et al., \r\n2013). This section assesses the performance of the new generation \r\nCMIP6 models (see Table AII.5) in simulating the patterns, trends, and \r\nvariability of surface temperature, and the evidence from detection \r\nand attribution studies of human influence on large-scale changes in \r\nsurface temperature."


id: 1291d208a7c6a11f514b3a047bed7cbb
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 418
content:
"To be fit for detecting and attributing human influence on globally\u0002averaged surface temperatures, climate models need to represent, based \r\non physical principles, both the response of surface temperature  to \r\nexternal forcings and the internal variability in surface temperature \r\nover various time scales. This section assesses the performance of \r\nthose aspects in the latest generation CMIP6 climate models. See \r\nSection 3.8 for evaluation at continental scales, Chapter 10 for model \r\nevaluation in the context of regional climate information, and the Atlas \r\nfor region-by-region assessments of model performance."


id: 6bcc6e52a355c4874caaa374a1f6127b
created_at: 2023-03-16 14:00:39
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content:
"When interpreting model simulations of historical temperature change, \r\nit is important to keep in mind that some models are tuned towards \r\nrepresenting the observed trend in global mean surface temperature \r\nover the historical period (Hourdin et al., 2017). In Figure  3.4 the \r\nCMIP6 models that are documented to have been tuned to reproduce \r\nobserved warming, typically by tuning aerosol forcing or factors \r\nthat influence the model's ECS, are marked with an asterisk. Such \r\ntuning of a model can strongly impact its temperature projections \r\n(Mauritsen and Roeckner, 2020). However, Bock et al. (2020) reported "


id: f33eb03955990b1d143f0141c7ad51b2
created_at: 2023-03-16 14:00:39
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vector_id: 35781
content:
"based attribution studies are based (Bock et al., 2020). Therefore, we \r\nassess with high confidence that the tuning of a small number of \r\nCMIP6 models to observed warming has not substantially influenced \r\nattribution results assessed in this chapter."


id: 4e05ce9cc077f62cd8fda4300d1ffcd9
created_at: 2023-03-16 14:00:39
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"that there is no statistically significant difference in multi-model \r\nmean GSAT between the models that had been tuned based on \r\nobserved warming compared to those which had not. Moreover, \r\nonly two of thirteen models used for the Detection and Attribution \r\nModel Intercomparison Project (DAMIP) simulations on which CMIP6 \r\nattribution studies are based were tuned towards historical warming \r\n(Bock et al., 2020; Gillett et al., 2021). Further, tuning is done on \r\nglobally averaged quantities, so does not substantially change the \r\nspatio-temporal pattern of response on which many regression\u0002"


id: 3a446a26c4f3d4c9850cb3e7d6667620
created_at: 2023-03-16 14:00:39
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content:
"The reliance of detection and attribution studies on climate models \r\n(see  Section 3.2) requires that those models simulate realistic \r\nstatistics of internal variability on multi-decadal time scales. An \r\nincorrect estimate of variability in models would affect confidence "


id: dfbada721a4a0de69c38eff323d762d6
created_at: 2023-03-16 14:00:39
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"Friedman et al. (2020) found biases in interhemispheric SST contrast \r\nin some models that may be consistent with underestimated cooling \r\nafter early-20th century eruptions or underestimated Pacific Decadal \r\nVariability, but could also be due to an imperfect separation between \r\ninternal variability and forced signal in the observations. Figure 3.2c, \r\nupdated from PAGES 2k Consortium (2019), compares modelled \r\ntemperatures to reconstructions over the last millennium. It indicates \r\nthat models reproduce the observed variability well, at least for the \r\ntime scales between 20 and 50 years that paleo reconstructions \r\ntypically resolve and that the figure represents. In summary, decadal "


id: 955e5640cf32f570cb0681dd479362d0
created_at: 2023-03-16 14:00:39
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content:
"is also higher than that from proxy reconstructions. CMIP6 models \r\nmay not share the underestimation by CMIP5 models of variability \r\nin decadal to multi-decadal modes of variability, such as Pacific \r\nDecadal Variability (Section 3.7.6; England et al., 2014; Thompson \r\net al., 2014; Schurer et al., 2015) and Atlantic Multi-decadal \r\nVariability (AMV), which may be partly forced, (see Section 3.7.7) \r\nbut this assessment is limited by the small number of available \r\nstudies. For the Southern Hemisphere, Hegerl et al. (2018) found an \r\ninstance of internal variability in the early 20th century larger than \r\nthat modelled, but indicated that could be an observational issue. "


id: 624eeaffb324470b95b81d56de446a29
created_at: 2023-03-16 14:00:39
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vector_id: 13018
content:
"GMST variability simulated in CMIP6 models spans the range of \r\nresidual decadal variability in large-scale reconstructions (medium \r\nevidence, low agreement)."


id: 309d9b393485240c9cbccb4b62761036
created_at: 2023-03-16 14:00:39
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vector_id: 5069
content:
"In summary, there is high confidence that CMIP6 models reproduce \r\nobserved large-scale mean surface temperature patterns and internal \r\nvariability as well as their CMIP5 predecessors, but with little evidence \r\nfor reduced biases. CMIP6 models also reproduce historical GSAT \r\nchanges similarly to their CMIP5 counterparts (medium confidence). \r\nHowever, in spite of model imperfections, there is very high confidence\r\nthat biases in surface temperature trends and variability simulated \r\nby the CMIP5 and CMIP6 ensembles are small enough to support \r\ndetection and attribution of human-induced warming."


id: 57a6eee9585101f281de92bb555b4a72
created_at: 2023-03-16 14:00:39
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content:
"In addition, new literature suggests that anthropogenic forcing \r\nitself may locally increase or decrease variability in surface \r\ntemperatures (Screen et al., 2014; Qian and Zhang, 2015; Brown \r\net al., 2017; Park et al., 2018; Santer et al., 2018; Weller et al., \r\n2020). These studies imply limitations in the use of pre-industrial \r\ncontrol simulations to quantify the role of unforced variability over \r\nthe historical period. Some recent attribution studies (Gillett et al., \r\n2021; Ribes et al., 2021) have estimated variability from ensembles \r\nof forced simulations instead, which would be expected to resolve \r\nany such changes in variability."


id: 1f2ca30619b7a888fb8154e86faa7301
created_at: 2023-03-16 14:00:39
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content:
"Figure  3.5 shows the standard deviation of zonal-mean surface \r\ntemperature in CMIP6 pre-industrial control simulations and observed \r\ntemperature datasets. Results are consistent with those based \r\non CMIP5 models, which showed the largest model spread where \r\nvariability is also large, in the tropics and mid- to high latitudes (Flato \r\net al., 2013). Modelled variability is within a factor two of observed \r\nvariability over most of the globe. The apparent overestimation of \r\nhigh latitude variability in models compared to observations may \r\nbe due to interpolation and infilling over data sparse high latitude \r\nregions in the observational products shown here (Jones, 2016)."


id: 36470bf69a334319a517c4cf3b2eeb95
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"here treated together in deriving assessed warming ranges. Studies \r\nalso increasingly validate their multi-model approaches using imperfect \r\nmodel tests (Schurer et al., 2018; Gillett et al., 2021; Ribes et al., 2021). \r\nAlternative techniques, based purely on statistical or econometric \r\napproaches, without the need for climate modelling, have also been \r\napplied (Estrada et al., 2013; Stern and Kaufmann, 2014; Dergiades \r\net al., 2016) and match the results of physically-based methods. The \r\nlarger range of attribution techniques and improvements to those \r\ntechniques increase confidence in the results compared to AR5."


id: a4627a6db24dcf477930ba25f88f8bfd
created_at: 2023-03-16 14:00:39
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content:
"In contrast, studies published since AR5 indicate that closely \r\nconstraining the separate contributions of greenhouse gas changes \r\nand aerosol changes to observed temperature changes remains \r\nchallenging. Nonetheless, attribution of warming to greenhouse gas \r\nforcing has been found as early as the end of the 19th century (Schurer \r\net al., 2014; Owens et al., 2017; PAGES 2k Consortium, 2019). Hegerl \r\net al. (2019) found that volcanism cooled global temperatures by \r\nabout 0.1degC between 1870 and 1910, then a lack of volcanic activity \r\nwarmed temperatures by about 0.1degC between 1910 and 1950, "


id: c9caf92eb1d6d7064b7796a515787611
created_at: 2023-03-16 14:00:39
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vector_id: 29307
content:
"attributable to greenhouse gases and aerosols separately based on \r\nindividual models are not all consistent, and detection of the aerosol \r\ninfluence fails more often than that of greenhouse gases. Hence, \r\nresults of recent studies emphasize the need to use multi-model \r\nmeans to better constrain estimates of GSAT changes attributable to \r\ngreenhouse gas and aerosol forcing (Schurer et al., 2018; Gillett et al., \r\n2021; Ribes et al., 2021)."


id: 1176eccc670b22e81f7d7ca7ae2b2cc2
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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content:
"Figure 3.8 compares attributable changes in globally complete GSAT \r\nfor the period 2010-2019 relative to 1850-1900 from three detection \r\nand attribution studies, two of which use CMIP6 multi-model means \r\n(Gillett et al., 2021; Ribes et al., 2021), and an estimate based on \r\nassessed effective radiative forcing and transient and equilibrium \r\nclimate sensitivity (see Section 7.3.5.3). The reference period \r\n1850-1900 is used to assess attributable temperature changes \r\nbecause this is when the earliest gridded surface temperature \r\nrecords start, this is when the CMIP6 historical simulations start, "


id: 4ffa5d425dd8ba0ee2bd1a1f652c77b8
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content:
"detected an anthropogenically forced response of inter-hemispheric \r\ncontrast in surface temperature change, which has a complex time \r\nevolution but shows the Northern Hemisphere cooling relative \r\nto the Southern Hemisphere until around 1975 but then warming \r\nafter that. Bonfils et al. (2020) attribute the Northern Hemisphere \r\nreversal to a combination of reduced aerosol forcing and greenhouse \r\ngas induced warming of Northern Hemisphere land masses. \r\nFriedman et al. (2020) found that CMIP5 models simulate the "


id: e69a70688dc4e8ce64fa1f1be1f7a49e
created_at: 2023-03-16 14:00:39
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vector_id: 33762
content:
"of a different approach. This agreement enhances confidence in the \r\nmagnitude and causes of attributable surface temperature warming."


id: 65639388b454e2fe21b9bff6960e57e6
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 13527
content:
"The AR5 found high confidence for a major role for anthropogenic \r\nforcing in driving warming over each of the inhabited continents, \r\nexcept for Africa where they found only medium confidence\r\nbecause of limited data availability (Bindoff et al., 2013). At the \r\nhemispheric scale, Friedman et al. (2020) and Bonfils et al. (2020) "


id: b5a7656fd28e33becb429a397fdf21df
created_at: 2023-03-16 14:00:39
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content:
"aerosol forcing, and inter-model differences in the historical global \r\nmean temperature evolution and in diagnosed cooling attributable to \r\naerosols (Figure 3.8). Moreover, like previous generations of coupled \r\nmodel simulations, historical and single forcing CMIP6 simulations \r\nfollow a common experimental design (Eyring et al., 2016a; Gillett \r\net al., 2016) and are thus all driven by the same common set of \r\nforcings, even though these forcings are uncertain. Hence, forcing \r\nuncertainty is not directly accounted for in most of the attribution and \r\nmodel evaluation studies assessed here, although this limitation can \r\nto some extent be addressed by comparing with previous generation \r\nmulti-model ensembles or individual model studies using different \r\nsets of forcings."


id: d6de1a184d252c6651ce3f482d2c7391
created_at: 2023-03-16 14:00:39
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vector_id: 31313
content:
"Table  3.1 | Estimates of warming in GSAT attributable to human influence for different periods in degC, all relative to the 1850-1900 base period.\r\nUncertainty ranges are 5-95% ranges for individual studies and likely ranges for the assessment. The results shown in the table use the methods described in the three studies \r\nindicated, but applied to additional periods and the warming trend. Ribes et al. (2021) results were updated using a corrected natural forcing time series, and Haustein et al. \r\n(2017) results were updated to use HadCRUT5."


id: 5e4341495a709ce5b15ca048f599ea92
created_at: 2023-03-16 14:00:39
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vector_id: 12356
content:
"to a half of this difference was due to an overestimate of the SST trend \r\nduring this period (Flato et al., 2013). Since AR5, additional studies \r\nbased on CMIP5 and CMIP6 models show that this warming bias in \r\ntropospheric temperatures remains. Recent studies have investigated \r\nthe role of observational uncertainty, the model response to external \r\nforcings, the influence of the time period considered, and the role \r\nof biases in SST trends in contributing to this bias."


id: e954e995bf6f1d1190bd7ba7bf88a53e
created_at: 2023-03-16 14:00:39
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content:
"Chapter 2 assessed that the troposphere has warmed since at least \r\nthe 1950s, that it is virtually certain that the stratosphere has cooled, \r\nand that there is medium confidence that the upper troposphere \r\nin the tropics has warmed faster than the near-surface since at \r\nleast 2001 (Section 2.3.1.2). The AR5 assessed that anthropogenic \r\nforcings, dominated by greenhouse gases, likely contributed to the \r\nwarming of the troposphere since 1961 and that anthropogenic \r\nforcings, dominated by the depletion of the ozone layer due to \r\nozone-depleting substances, very likely contributed to the cooling \r\nof the lower stratosphere since 1979. Since AR5, understanding \r\nof observational uncertainties in the radiosonde and satellite data \r\nhas improved with more available data and longer coverage, and \r\ndifferences between models and observations in the tropical \r\natmosphere have been investigated further."


id: 70664fc89168e517a248d03c1ae4fc9f
created_at: 2023-03-16 14:00:39
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content:
"Mitchell et al. (2013) and Mitchell et al. (2020) found a smaller \r\ndiscrepancy in tropical tropospheric temperature trends in models \r\nforced with observed SSTs (see also Figure  3.10a), and CMIP5 \r\nmodels and observations were found to be consistent below 150 hPa \r\nwhen viewed in terms of the ratio of temperature trends aloft to \r\nthose at the surface (Mitchell et al., 2013). Flannaghan et al. (2014) \r\nand Tuel (2019) showed that most of the tropospheric temperature \r\ntrend difference between CMIP5 models and the satellite-based \r\nobservations over the 1970-2018 period is due to respective \r\ndifferences in SST warming trends in regions of deep convection, \r\nand Po-Chedley et al. (2021) showed that CMIP6 models with a more "


id: 1dd427d46529b6906c270d9eb79d86
created_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 2129
content:
"The AR5 assessed with low confidence that most, though not \r\nall, CMIP3 (Meehl et al., 2007) and CMIP5 (Taylor et al., 2012) \r\nmodels overestimated the observed warming trend in the tropical \r\ntroposphere during the satellite period 1979-2012, and that a third "


id: d51840638d3d5a2d185b684ee5cae8aa
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content:
"realistic SST simulation in the central and eastern Pacific show \r\na better performance than other models. Though systematic biases \r\nstill remain, this indicates that the bias in tropospheric temperature \r\nwarming in models is in part linked to surface temperature warming \r\nbiases, especially in the lower troposphere."


id: ae51c9814f9d23177c178e903947ecf2
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"(1979-1997) and underestimate it over the ozone stabilization era \r\n(1998-2014; Figure 3.10b,c). They speculate that those disagreements \r\nare due to poor representations of stratospheric ozone forcing."


id: 62bf1e839089c64333b395f4ead1c1a7
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 13103
content:
"models driven by anthropogenic forcing show consistent amplitude \r\nincreases at mid-latitudes in both hemispheres, amplitude decreases \r\nat high latitudes in the Southern Hemisphere, and small changes in \r\nthe tropics."


id: 14a61931827a0b1964f6d7163dd68c2b
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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index: climate_gpt_only_giec
vector_id: 754
content:
"In summary, these studies confirm the dominant role of human activities \r\nin tropospheric temperature trends. We therefore assess that it is very \r\nlikely that anthropogenic forcing, dominated by greenhouse gases, \r\nwas the main driver of the warming of the troposphere since 1979."


id: 513ce4a4fb6ca86ba73f7f7deee67482
created_at: 2023-03-16 14:00:39
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vector_id: 10234
content:
"The AR5 concluded that the CMIP5 models simulated a generally \r\nrealistic evolution of lower-stratospheric temperatures (Bindoff et al., \r\n2013; Flato et al., 2013), which was better than that of the CMIP3 \r\nmodels, in part because they generally include time-varying ozone \r\nconcentrations, unlike many of the CMIP3 models. Nonetheless, it was \r\nnoted that there was a tendency for the simulations to underestimate \r\nstratospheric cooling compared to observations. Bindoff et al. \r\n(2013) concluded that it was very likely that anthropogenic forcing, \r\ndominated by stratospheric ozone depletion by chemical reactions \r\ninvolving trace species known as ozone-depleting substances (ODS), \r\nhad contributed to the cooling of the lower stratosphere since 1979. \r\nIncreased greenhouse gases cause near-surface warming but cooling \r\nof stratospheric temperatures."


id: 6d51693c862f1e12c58e987d6876b94
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content:
"Contributors: Christophe Cassou (France), Yu Kosaka (Japan), John C. Fyfe (Canada), Nathan P. Gillett (Canada), Ed Hawkins \r\n(United Kingdom), Blair Trewin (Australia)"


id: 7774dc20cfe2a757ed733c5a0a706be0
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"(Flato et al., 2013). This apparent slowdown of surface global warming compared to the 62-year rate was assessed with medium \r\nconfidence to have been caused in roughly equal measure by a cooling contribution from internal variability and a reduced trend in \r\nexternal forcing (particularly associated with solar and volcanic forcing) in AR5 based on expert judgement (Flato et al., 2013). In AR5 \r\nit was assessed that almost all CMIP5 simulations did not reproduce the observed slower warming, and that there was medium \r\nconfidence that the trend difference from the CMIP5 ensemble mean was to a substantial degree caused by internal variability \r\nwith possible contributions from forcing error and model response uncertainty. This Cross-Chapter Box assesses new findings from \r\nobservational products and statistical and physical models on trends over the 1998-2012 period considered in AR5."


id: 7106ddec21c48bf1ea1e27f3da1bf13
created_at: 2023-03-16 14:00:39
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content:
"With these updates, all the observed trends assessed here lie within the 10th-90th percentile range of the simulated trends in the \r\nCMIP5 and CMIP6 simulations (Cross-Chapter Box 3.1, Figure 1a). This result is insensitive to whether model GSAT (based on surface \r\nair temperature) or GMST (based on a blend of surface air temperature over land and sea ice and SST over open ocean) is used, and to \r\nwhether or not masking with the observational data coverage is applied. Therefore, the observed 1998-2012 trend is consistent with \r\nboth the CMIP5 or CMIP6 multi-model ensemble of trends over the same period (high confidence)."


id: 7de99db0054c73644fef712da91a2d19
created_at: 2023-03-16 14:00:39
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content:
"All the observation-based GMST and GSAT trends are lower than the multi-model mean GMST and GSAT trends of both CMIP5 and \r\nCMIP6 for 1998-2012 (Cross-Chapter Box 3.1, Figure 1a). This suggests a possible cooling contribution from internal variability during \r\nthis period. This is supported by initialized decadal hindcasts, which account for the phase of the multi-decadal modes of variability \r\n(Sections 3.7.6 and 3.7.7), and which reproduce observed global mean SST and GSAT trends better than uninitialized historical \r\nsimulations (Guemas et al., 2013; Meehl et al., 2014)."


id: 16930a2e22c974e072e3cc8d751a65d6
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content:
"Such internally-driven variation of decadal GSAT trends is not unique to the 1998-2012 period (Section 1.4.2.1; Lovejoy, 2014; Roberts \r\net al., 2015; Dai and Bloecker, 2019). Due to the nature of internal variability, surface temperature changes over the 1998-2012 period "


id: fd5fa1108d6ba7a933d4e77ab6e706e9
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content:
"are regionally- and seasonally-varying (Cross-Chapter Box 3.1, Figure 1c; Trenberth et al., 2014; Zang et al., 2019). Further, there was no \r\nslowdown in the increasing occurrence of hot extremes over land (Kamae et al., 2014; Seneviratne et al., 2014; Imada et al., 2017). Thus, \r\nthe internally-driven slowdown of GSAT increase does not correspond to slowdown of warming everywhere on the Earth's surface."


id: e0461b28ca84674ab501809e5c5e12ac
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vector_id: 32778
content:
"With updated observation-based GMST datasets and forcing, improved analysis methods, new modelling evidence and deeper \r\nunderstanding of mechanisms, there is very high confidence that the slower GMST and GSAT increase inferred from observations in \r\nthe 1998-2012 period was a temporary event induced by internal and naturally-forced variability that partly offset the anthropogenic \r\nwarming trend over this period. Nonetheless, the heating of the climate system continued during this period, as reflected in the \r\ncontinued warming of the global ocean (very high confidence) and in the continued rise of hot extremes over land (medium confidence). \r\nConsidering all the sources of uncertainties, it is impossible to robustly identify a single cause of the early 2000s slowdown (Hedemann \r\net al., 2017; Power et al., 2017); rather, it should be interpreted as due to a combination of several factors (Huber and Knutti, 2014; \r\nSchmidt et al., 2014; Medhaug et al., 2017)."


id: b72a143a294367f31e603a6bc8fefd05
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
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vector_id: 26351
content:
"A major El Nino event in 2014-2016 led to three consecutive years of record annual GMST with unusually strong heat release from \r\nthe North-western Pacific Ocean (Yin et al., 2018), which marked the end of the slower warming period (Hu and Fedorov, 2017; J. Su \r\net al., 2017; Cha et al., 2018). The past five-year period (2016-2020) is the hottest five-year period in the instrumental record up to \r\n2020 (high confidence). This rapid warming was accompanied by a PDV shift toward its positive phase (J. Su et al., 2017; Cha et al., \r\n2018). A higher rate of warming following the 1998-2012 period is consistent with the predictions in AR5 Box 9.2 (Flato et al., 2013) \r\nand with a statistical prediction system (Sevellec and Drijfhout, 2018). Initialized decadal predictions show higher GMST trends in the \r\nearly 2020s compared to uninitialized simulations (Thoma et al., 2015; Meehl et al., 2016a)."


id: a9f84f3912c880b28dcbfe1709051f76
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 24277
content:
"While some recent studies find that internal decadal GSAT variability may become weaker under GSAT warming, associated in part \r\nwith reduced amplitude PDV (Section 4.5.3.5; Brown et al., 2017), the weakening is small under a realistic range of warming. A \r\nlarge volcanic eruption would temporarily cool GSAT (Cross-Chapter Box 4.1). Thus, there is very high confidence that reduced and \r\nincreased GMST and GSAT trends at decadal time scales will continue to occur in the 21st century (Meehl et al., 2013; Roberts et al., \r\n2015; Medhaug and Drange, 2016). However, such internal or volcanically forced decadal variations in GSAT trend have little effect on \r\ncentennial warming (England et al., 2015; Cross-Chapter Box 4.1)."


id: 57cb52729f6bdfd5f530a5abb76cb253
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 11311
content:
"A fact hindering detection and attribution studies in precipitation \r\nand other hydrological variables is the large internal variability of \r\nthese fields relative to the anthropogenic signal. This low signal-to\u0002noise ratio hinders the emergence of the anthropogenic signal from \r\nnatural variability. Moreover, the sign of the change depends on \r\nlocation and time of the year. Paleoclimate records provide valuable \r\ncontext for observed trends in the 20th and 21st century and assist \r\nwith the attribution of these trends to human influence (see also \r\nSection 2.3.1.3.1). By nature, hydrological proxy data represent \r\nregional conditions, but taken together can represent large-scale \r\npatterns. As an example of how paleorecords have helped assessing \r\nthe origin of changes, we consider some, mainly subtropical, regions \r\nwhich have experienced systematic drying in recent decades (see also \r\nSection 8.3.1.3). Paleoclimate simulations of monsoons are assessed \r\nin Section 3.3.3.2."


id: bc58e90c8c9da97fb9af55c97072f767
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 27214
content:
"Records of tree ring width have provided evidence that recent \r\nprolonged dry spells in the Levant and Chile are unprecedented in the \r\nlast millennium (high confidence) (Cook et al., 2016a; Garreaud et al., \r\n2017). East Africa has also been drying in recent decades (Rowell et al., \r\n2015; Hoell et al., 2017), a trend that is unusual in the context of the "


id: 5a87d2d8a3d623a993667afc86f7bc67
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 11757
content:
"Paleoclimate records also allow for model evaluation under \r\nconditions different from present-day. The AR5 concluded that \r\nmodels can successfully reproduce to first-order patterns of past \r\nprecipitation changes during the Last Glacial Maximum (LGM) and \r\nmid-Holocene, though simulated precipitation changes during the "


id: b3415ae38781d9fcfcb4525bc6e1c2d7
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 25716
content:
"is not incompatible with reconstructions. Over the Sahara/Sahel and \r\nWest Africa regions, where reconstructions suggest positive anomalies \r\nduring the mid-Holocene, both CMIP5 and CMIP6 models also \r\nsimulate a rainfall increase, but it is much weaker (see also Section \r\n3.3.3.2). Overall, however, large discrepancies remain between \r\nsimulations and reconstructions."


id: a4dd9e47a3d91cd8b6f1525b1c60d854
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 23508
content:
"Liu et al. (2018) evaluated the soil moisture changes that occurred \r\nduring the LGM and concluded that the multi-model median from \r\nCMIP5 is consistent with available paleo-records in some regions, \r\nbut not in others. CMIP5 models accurately reproduce an increase \r\nin moisture in the western United States, related to an intensified \r\nwinter storm track and decreased evaporative demand (Oster et al., \r\n2015; Ibarra et al., 2018; Lora, 2018). On the other hand, CMIP5 \r\nmodels show a wide variety of responses in the tropical Indo-Pacific \r\nregion, with only a few matching the pattern of change inferred from \r\nthe paleoclimate record (DiNezio and Tierney, 2013; DiNezio et al., \r\n2018). The variable response across models is related to the effect \r\nof the exposure of the tropical shelves during glacial times, which "


id: 39af76a8696a29f9420f60da964cfa27
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 6452
content:
"Figure 3.12 | Total column water vapour trends (% per decade) for the period 1988-2019 averaged over the near-global oceans (50degS-50degN). The figure \r\nshows satellite data (RSS) and ERA5.1 reanalysis, as well as CMIP5 (blue) and CMIP6 (red) historical simulations. All available ensemble members were used (see Section 3.2). \r\nFits to the model trend probability distributions were performed with kernel density estimation. Figure is updated from Santer et al. (2007). Further details on data sources and \r\nprocessing are available in the chapter data table (Table 3.SM.1)."


id: b53f22ca5f6a018d38ae5103c16d966f
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 26057
content:
"variously intensifies or weakens convection in the rising branch of \r\nthe Walker cell, depending on model parameterization (DiNezio \r\net al., 2011). For the Last Interglacial, CMIP6 models reproduce \r\nthe proxy-based increased precipitation relative to pre-industrial in the \r\nNorth African, South Asian and North American regions, but not in \r\nAustralia (Scussolini et al., 2019)."


id: 123e80fe2641c79cec0673fb2a0db3a8
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 374
content:
"In summary, there is medium confidence that CMIP5 and CMIP6 \r\nmodels can reproduce broad aspects of precipitation changes during \r\npaleo reference periods, but large discrepancies remain. Further \r\nassessment of model performance and comparison between CMIP5 \r\nand CMIP6 during past climates can be found in Section 3.8.2.1."


id: 2891c1b94d8099fec5c13b88c8e612c8
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 3804
content:
"The AR5 concluded that an anthropogenic contribution to increases \r\nin specific humidity is found with medium confidence at and near the \r\nsurface. A levelling off of atmospheric water vapour over land in \r\nthe last two decades that needed better understanding, and remaining \r\nobservational uncertainties, precluded a more confident assessment \r\n(Bindoff et al., 2013). Sections 4.5.1.3 and 8.3.1.4 show that there \r\nhave been significant advances in the understanding of the processes \r\ncontrolling land surface humidity. In particular, there has been a focus \r\non the role of oceanic moisture transport and land-atmosphere \r\nfeedbacks in explaining the observed trends in relative humidity."


id: a9de85c5472e8e2947f4106c95bf4da0
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 24259
content:
"In summary, we assess that it is likely that human influence has \r\ncontributed to moistening in the upper troposphere since 1979. \r\nAlso, there is medium confidence that human influence contributed \r\nto a global increase in annual surface specific humidity, and medium \r\nconfidence that it contributed to a decrease in surface relative humidity \r\nover mid-latitude Northern Hemisphere continents during summertime."


id: 66b98461e3927e9df6ce9579ae43f42c
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 13752
content:
"The detection and attribution of tropospheric water vapour changes \r\ncan be traced back to Santer et al. (2007), who used estimates of \r\natmospheric water vapour from the satellite-based Special Sensor \r\nMicrowave Imager (SSM/I) and from CMIP3 historical climate \r\nsimulations. They provided evidence of human-induced moistening "


id: ab2346842b7b816d3c787f0e24dc5a54
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 24445
content:
"AR5 concluded that there was medium confidence that human \r\ninfluence had contributed to large-scale precipitation changes over \r\nland since 1950, including an increase in the Northern Hemisphere \r\nmid- to high latitudes. Moreover, AR5 concluded that observational \r\nuncertainties and challenges in precipitation modelling precluded \r\na more confident assessment (Bindoff et al., 2013). Overall, it found \r\nthat large-scale features of mean precipitation in CMIP5 models were \r\nin modest agreement with observations, but there were systematic \r\nerrors in the tropics (Flato et al., 2013)."


id: b948a34e9582ab2bbd4a6b31d695fec2
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 26686
content:
"The CMIP5 models have also been shown to adequately simulate \r\nthe mean and interannual variability of the global monsoon \r\n(Section 3.3.3.2), but maintain the double ITCZ bias in the equatorial \r\nPacific (Lee and Wang, 2014; Tian, 2015; Ni and Hsu, 2018). Despite \r\nthe ITCZ bias, CMIP5 models have been used to detect in reanalysis \r\na southward shift in the ITCZ prior to 1975, followed by a northward \r\nshift in the ITCZ after 1975, in response to forced changes in \r\ninter-hemispheric temperature contrast (Sections 3.3.1.1 and 8.3.2.1, \r\nand Figure 8.11; Bonfils et al., 2020; Friedman et al., 2020). CMIP5 \r\nmodels perform better than CMIP3 models, in particular regarding the \r\nglobal monsoon domain and intensity (Lee and Wang, 2014)."


id: 5c225eb44e99d7491893566bb72a0410
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 12008
content:
"Recent studies comparing observations and CMIP5 simulations have \r\nshown that tropical volcanic eruptions induce a significant reduction \r\nin global precipitation, particularly over the wet tropics, including the \r\nglobal monsoon regions (Iles and Hegerl, 2014; Paik and Min, 2017; \r\nPaik et al., 2020a). Reconstructions and modelling studies also suggest \r\na distinct remote influence of volcanic forcing such that large volcanoes \r\nerupting in one hemisphere can enhance monsoon precipitation in the \r\nother hemisphere (F. Liu et al., 2016; Zuo et al., 2019). The climatic effect \r\nof volcanic eruptions is further assessed in Cross-Chapter Box 4.1."


id: 58bf907edd3957173417a4984f7b3725
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 11457
content:
"In observations at time scales less than a day intermittent rainfall \r\nfluctuations dominate variability, but CMIP5 models systematically \r\nunderestimate them (Covey et al., 2018). Moreover, as noted in \r\nprevious generation models, CMIP5 models produce rainfall too early \r\nin the day (Covey et al., 2016). Also, models overpredict precipitation \r\nfrequency but have weaker intensity, although comparison with \r\nobserved datasets is complex as there are large differences in intensity \r\namong them (Herold et al., 2016; Pendergrass and Deser, 2017; \r\nTrenberth et al., 2017). Regarding trends in precipitation intensity, \r\nmodels have also been shown to reproduce the compensation "


id: 1cae40703f6a89090b490e25395bad84
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 1962
content:
"An intensification of the wet-dry zonal mean patterns, consisting of \r\nthe wet tropical and mid-latitude bands becoming wetter, and the dry \r\nsubtopics becoming drier is expected in response to greenhouse gas \r\nand ozone changes (Section 8.2.2.2). However, detecting these changes "


id: 47eca0ff3844cd3ca4ecd77b90b0db17
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 8685
content:
"is complicated by model errors in locating the main features of rainfall \r\npatterns. To deal with this issue, Marvel and Bonfils (2013) identified \r\nin each CMIP5 historical simulation the latitudinal peaks and troughs \r\nof the rainfall latitudinal patterns, measured the amplification and shift \r\nof these patterns in a pattern-based fingerprinting study, and found \r\nthat the simultaneous amplification and shift in zonal precipitation \r\npatterns are detectable in Global Precipitation Climatology Project \r\n(GPCP) observations over the 1979-2012 period. Similarly, Bonfils \r\net al. (2020) found that the intensification of wet-dry zonal patterns \r\nidentified in CMIP5 historical simulations is detectable in reanalyses \r\nover the 1950-2014 period (see also Figure 8.11)."


id: 765ba0a51292e3afc3012a07d6034440
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 16211
content:
"wet-gets-wetter, dry-gets-drier paradigm over tropical land areas as \r\nwell. Other studies suggest that this paradigm does not necessarily hold \r\nover dry regions where moisture is limited (see also Section 8.2.2.1; \r\nGreve et al., 2014; Kumar et al., 2015). Polson and Hegerl (2017) \r\nexplained this discrepancy by taking into account the seasonal and \r\ninterannual movement of the regions (Allan, 2014). A follow-up study \r\nusing CMIP6 models also found that the observed strengthening \r\ncontrast of precipitation over wet and dry regions was detectable, \r\nalthough the increase was significantly larger in observations than in \r\nthe multi-model mean. The change was attributed to a combination \r\nof anthropogenic and natural forcings, with anthropogenic forcings \r\ndetectable in multi-signal analyses (Figure 3.14; Schurer et al., 2020)."


id: a6cfd068d93cb11a449123d2f39e26af
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 23762
content:
"Based on long-term island precipitation records, Polson et al. (2016) \r\nidentified significant increases in precipitation in the tropics and \r\ndecreases in the subtropics, which are consistent with those simulated \r\nby the CMIP5 models. Moreover, results from Polson and Hegerl (2017) \r\ngive support to an intensification of the water cycle according to the "


id: aa5b23b5c74e2f36e4441f6562d02cd
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 24339
content:
"Global land precipitation has likely increased since the middle of the \r\n20th century (medium confidence), while there is low confidence\r\nin trends in land data prior to 1950 and over the ocean during the \r\nsatellite era due to disagreement between datasets (Section 2.3.1.3.4). "


id: 64eead38d41c9b1bc96aaef64d17491a
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 13452
content:
"Figure  3.15a shows the time evolution of the global mean land \r\nprecipitation since 1950, as well as the trend during the period. Adler \r\net al. (2017) found no significant trend in the global mean precipitation \r\nduring the satellite era, consistent with model simulations (Wu \r\net al., 2013) and physical understanding of the energy budget (Section \r\n8.2.1). This has been suggested to be due to the negative effect of \r\nanthropogenic sulphate aerosol that opposed the positive influence of \r\nrising global mean temperatures due to greenhouse gases (Salzmann, \r\n2016; Richardson et al., 2018). The precipitation change expected from \r\nocean warming is also partly offset by the fast atmospheric adjustment \r\nto increasing greenhouse gases (Section 8.2.1). Over the ocean, the \r\nnegligible trend may be due to the cancelling effects of CO2 and \r\naerosols (Richardson et al., 2018)."


id: 79fc02a2950d7d0d35f2c152ddcaa8a3
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 16766
content:
"observed and simulated trends found that detectable anthropogenic \r\nincreasing trends have occurred prominently over many mid- to \r\nhigh-latitude regions of the Northern Hemisphere and subtropics \r\nof the Southern Hemisphere. The observed trends in many cases are \r\nsignificantly stronger than modelled in the CMIP5 historical runs for \r\nthe 1901-2010 period (though not for 1951-2010), which may be \r\ndue to disagreement between observed datasets (Section 2.3.1.3.4), \r\nand/or suggest possible deficiencies in models."


id: 70c33122ccaa0656964f3a039566c32a
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 15367
content:
"The observed precipitation increase in the Northern Hemisphere high \r\nlatitudes over the period 1966-2005 was attributed to anthropogenic \r\nforcing by a study using CMIP5 models (Wan et al., 2015) supporting \r\nthe AR5 assessment. Initial results from CMIP6 also support the role \r\nof anthropogenic forcing in the precipitation increase observed in \r\nNorthern Hemisphere high latitudes (see Figure 3.15c): the observed \r\npositive trend detected for the band 60degN-90degN can only be "


id: d790a4f1c37fafcef0a42aee236fad32
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 31438
content:
"reproduced when anthropogenic forcing is included, although models \r\ntend to simulate overall a larger positive trend. A similar positive trend, \r\nbut less significant, is also detected between 30degN-60degN, while in the \r\nsouthern mid-latitudes no trend is simulated (see Figure 3.15d, f)."


id: c697ffdb18b4b52a89b386e337d71154
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 28812
content:
"the timing of peak streamflow, and the qualitative evaluation of \r\nstudies reporting on observed and simulated trends, AR5 concluded \r\nthat there is medium confidence that anthropogenic influence on \r\nclimate has affected streamflow in some middle and high latitude \r\nregions (Bindoff et al., 2013). The AR5 also noted that observational \r\nuncertainties are large and that often only a limited number of \r\nmodels were considered."


id: 4ad856696a6ee42b855a5d96b5963f0e
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 9192
content:
"Over the ocean, observations show coherent large-scale patterns of \r\nfresh ocean regions becoming fresher and salty ocean regions saltier \r\nacross the globe, which has been related through modelling studies \r\nto changes in precipitation minus evaporation and is consistent with \r\nthe wet-gets-wetter, dry-gets-drier paradigm (see Sections 3.5.2.2 \r\nand 8.2.2.1; Durack et al., 2012, 2013; Skliris et al., 2014; Durack, \r\n2015; Hegerl et al., 2015; Levang and Schmitt, 2015; Zika et al., 2015; \r\nGrist et al., 2016; Cheng et al., 2020)."


id: 832b4add6c12cf0e2961b2bd3e720e3d
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 18163
content:
"Recently, Gudmundsson et al. (2021) performed a global detection \r\nand attribution study on streamflow and found that some regions are \r\ndrying and others are wetting. Moreover, the simulated streamflow \r\ntrends are consistent with observations only if externally forced \r\nclimate change is considered, and the simulated effects of water and \r\nland management cannot reproduce the observed trends. The effects \r\nof volcanic eruptions in driving reduced streamflow have also been \r\ndetected in the wet tropics (Iles and Hegerl, 2015; Zuo et al., 2019)."


id: 5290277a450617bec71e296b7908c0b4
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 10449
content:
"In summary, there is medium confidence that anthropogenic climate \r\nchange has altered local and regional streamflow in various parts \r\nof the world and that the associated global-scale trend pattern is \r\ninconsistent with internal variability. Moreover, human interventions \r\nand water withdrawals, while affecting streamflow, cannot explain \r\nthe observed spatio-temporal trends (medium confidence)."


id: fb21858ce9af1c73a5cebab75dcbc8ec
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 37020
content:
"Streamflow is to-date the only variable of the terrestrial water \r\ncycle with enough in-situ observations to allow for detection and \r\nattribution analysis at continental to global scales. Based on evidence \r\nfrom a few formal detection and attribution studies, particularly on "


id: e6f8316e5db0cbd9310fe7049fd2a09e
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 33823
content:
"Cross-Chapter Box 3.2 | Human Influence on Large-scale Changes in Temperature \r\nand Precipitation Extremes"


id: 6b214ca163223e9a82c9f9b858e7451c
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 14477
content:
"Contributors: Nathan P. Gillett (Canada), Seung-Ki Min (Republic of Korea), Krishnan Raghavan (India), Ying Sun (China), \r\nXuebin Zhang (Canada)"


id: 32179da5d90967aa9c7b346a1ef72d1e
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 5291
content:
"Understanding how temperature and precipitation extremes have changed at large scales and the causes of these changes is an \r\nimportant part of our overall assessment of human influence on the climate system. Chapter 11 assesses changes in extremes and \r\ntheir causes, while this Cross-Chapter Box summarizes relevant assessments and supporting evidence in Chapters 8 and 11 and relates \r\nchanges in extremes to mean changes on global and continental scales."


id: 88730d81ad9edcd3d738942c1a7716b5
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 18996
content:
"One important aspect of various indicators of temperature extremes is their connection to mean temperature at local, regional and \r\nglobal scales. For example, the highest daily temperature in a summer is often highly correlated with the summer mean temperature. \r\nModel projections show that changes in temperature extremes are often closely related to shifts in mean temperature (Seneviratne \r\net al., 2016; Kharin et al., 2018). It is thus no surprise that changes in temperature extremes are consistent with warming mean \r\ntemperature, with warming leading to more hot extremes and fewer cold extremes. Given the attribution of mean warming to \r\nhuman influence (Section 3.3.1), and the connection between changes in mean and extreme temperatures, it is to be expected that \r\nanthropogenic forcing has also influenced temperature extremes."


id: 541e5d7be78893bd4567ed82416be104
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 10700
content:
"Chapter 11 assesses that it is virtually certain that human-induced greenhouse gas forcing is the main contributor to the observed \r\nincrease in the likelihood and severity of hot extremes and the observed decrease in the likelihood and severity of cold extremes on \r\nglobal scales, and very likely that this applies on most continents."


id: e6da2899181371cadd4bdb37f57325a1
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 33804
content:
"panel of Cross-Chapter Box 3.2, Figure 1 demonstrates the consistency between changes in global average annual maximum daily \r\nprecipitation in the observations and model simulations under combined anthropogenic and natural forcing, and inconsistency with \r\nsimulations under natural forcing alone. While there is more evidence in the literature to quantify the net anthropogenic influence on \r\nextreme precipitation than the influence of individual forcing components, a dominant contribution of greenhouse gas forcing to the \r\nlong-term intensification of extreme precipitation on global and continental scales has recently been quantified separately from the \r\ninfluence of anthropogenic aerosol and natural forcings (Dong et al., 2020; Paik et al., 2020b)."


id: b10c0f614e547a6ac090f1b20e64508c
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 25362
content:
"Chapter 11 assesses that it is likely that human influence, in particular due to greenhouse gas forcing, is the main driver of the \r\nobserved intensification of heavy precipitation in global land regions during recent decades (Section 11.4.4)."


id: 144c822e8799995113de733505618ca2
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 706
content:
"range in the Northern Hemisphere (Quan et al., 2018; Grise et al., \r\n2019), whereas the trend in the annual-mean Southern Hemisphere \r\nedge is outside the 5th-95th percentile range of internal variability \r\nin CMIP6 in three out of the four reanalyses (Figure 3.16b). For the \r\nSouthern Hemisphere summer when the simulated human influence \r\nis strongest, the 1981-2000 trend in three out of the four reanalyses \r\nfalls outside the 5th-95th percentile range of internal variability \r\n(Figure 3.16c; L. Tao et al., 2016; Grise et al., 2018, 2019)."


id: 2ce78595a524c3bc70a0797a0a573183
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 4503
content:
"The tropical tropospheric circulation features meridional and zonal \r\noverturning circulations, called Hadley and Walker circulations. In the \r\nzonal mean, the downwelling branch of the Hadley circulation cell \r\nis located in the subtropics and is often used as an indicator of the \r\nmeridional extent of the tropics. In the equatorial zonal-vertical \r\nsection, the major rising branch of the Walker circulation is located \r\nover the Maritime continent with secondary ascending regions over \r\nnorthern South America and Africa. The zonal component of the \r\nsurface trade winds over most of the equatorial Pacific and Atlantic \r\nis associated with the Walker circulation. This section assesses the \r\nzonal-mean Hadley cell extent and the Pacific Walker circulation \r\nstrength. Regional and water cycle aspects of these circulations are \r\nassessed in more detail in Section 8.3.2."


id: a3b15a9ba0045f28bae4a41cb52b59f
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 23317
content:
"In CMIP5 simulations, greenhouse gas increases and, in austral summer, \r\nstratospheric ozone depletion, contribute to the Southern Hemisphere \r\nexpansion (Gerber and Son, 2014; Nguyen et al., 2015; L. Tao et al., \r\n2016; Y.H. Kim et al., 2017), but the ozone influence is not significant \r\nin available CMIP6 simulations (Figure 3.16b-c). Since the 2000s, the \r\nstabilization or slight recovery of stratospheric ozone (Section 2.2.5.2) \r\nis consistent with the smaller observed trends (Banerjee et al., 2020). \r\nWhile many CMIP5 models under-represent the magnitude of the PDV, \r\nimplying potential overconfidence on the detection of human influence \r\non the Hadley cell expansion, this is less the case for the CMIP6 models \r\n(Section 3.7.6). However, the mechanism underlying the Hadley cell \r\nexpansion remains unclear (Staten et al., 2018, 2020), precluding \r\na process-based validation of the simulated human influence."


id: d8c3ec1e387aeac4935f9b38baa70ce2
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 31616
content:
"AR5 found medium confidence that the depletion of stratospheric \r\nozone had contributed to Hadley cell widening in the Southern \r\nHemisphere in austral summer (Bindoff et al., 2013). It also noted \r\nthat in contrast to a simulated weakening in response to greenhouse \r\ngas forcing, the Walker circulation had actually strengthened since \r\nthe early 1990s, precluding any detection of human influence."


id: 4a44cefcbdf302aa617b4cd008c2614b
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 9091
content:
"Grise et al. (2019) found that a metric based on surface zonal winds, \r\nwhich are well constrained by surface observations, best compares \r\nreanalyses with CMIP5 models. With this method and new reanalysis \r\nproducts, the CMIP5 historical simulations exhibit comparable mean \r\nstates and variability of the subtropical edge latitude of the Hadley \r\ncells to those observed (Grise et al., 2019)."


id: 6bfedd61ebaa01ed24aff2386f72a328
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 14615
content:
"Chapter 2 assesses that there has very likely been a widening of the \r\nHadley circulation since the 1980s (Section 2.3.1.4.1). The CMIP5 \r\n(Davis and Birner, 2017; Grise et al., 2018) and CMIP6 (Grise and \r\nDavis, 2020) historical simulation ensembles span the observed \r\ntrends of the zonal-mean Hadley cell edges since the 1980s \r\n(Figure 3.16a-c). Studies based on CMIP5 models find a contribution \r\nfrom human influence to the observed widening trend, especially in \r\nthe Southern Hemisphere (Gerber and Son, 2014; Staten et al., 2018, \r\n2020; Grise et al., 2019; Jebri et al., 2020), which is confirmed based \r\non CMIP6 (Figure 3.16b,c; Grise and Davis, 2020)."


id: a37975d3ad834e3d7f2bcd463269be8c
created_at: 2023-03-16 14:00:39
updated_at: 2023-03-16 14:00:39
content_type: text
index: climate_gpt_only_giec
vector_id: 23282
content:
"In the annual mean, internal variability, including Pacific Decadal \r\nVariability (PDV; Annex IV.2.6), contributed to the observed \r\nzonal-mean Hadley cell expansion since 1980 comparably with \r\nhuman influence (Allen et al., 2014; Allen and Kovilakam, 2017; \r\nMantsis et al., 2017; Amaya et al., 2018; Grise et al., 2018). Indeed, \r\nthe ensemble-mean expansion in historical simulations is significantly \r\nweaker than in most of the reanalyses shown in Figure  3.16a-c, \r\nwhile the Atmospheric Model Intercomparison Project (AMIP) \r\nsimulations forced by observed SSTs (Figure 3.16a-c) show stronger \r\ntrends than historical coupled simulations on average (Nguyen et al., \r\n2015; Davis and Birner, 2017; Grise et al., 2018). The human-induced \r\nchange has not yet clearly emerged out of the internal variability "


id: 73d247318a9ee914b4d3e2595aba61c2
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 15837
content:
"those simulations are forced by one reconstruction of SST, which \r\nitself is subject to uncertainty before the 1970s (Deser et al., 2010; \r\nTokinaga et al., 2012)."


id: 95a65dd6dba9c13f02ffa69383740e81
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 21043
content:
"Trends since the 1980s in in-situ and satellite observations and \r\nreanalyses  exhibit strengthening of the Pacific Walker circulation \r\nand SST gradient (Section 2.3.1.4.1 and Figure 3.16f; L'Heureux et al., \r\n2013; Boisseson et al., 2014; England et al., 2014; Kociuba and \r\nPower, 2015; Ma and Zhou, 2016). AMIP simulations reproduce this \r\nstrengthening (Figure 3.16d; Boisseson et al., 2014; Ma and Zhou, 2016), \r\nindicating a dominant role of SST changes. However, all reanalysis \r\ntrends lie outside the 5-95% range of simulated CMIP6 historical \r\nWalker circulation trends over this period (Figure 3.16f), consistent with \r\nCMIP5 results (England et al., 2014; Kociuba and Power, 2015). This \r\nmay be in part caused by the underestimation of the PDV magnitude \r\nespecially in CMIP5 models (Section 3.7.6; Kociuba and Power, 2015; \r\nChung et al., 2019), but also suggests a potential error in simulating the "


id: 90433aebd0c01375826c30b0d536e45d
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 20232
content:
"Observational SST products indicate that the equatorial zonal SST \r\ngradient from the western to the eastern equatorial Pacific has \r\nstrengthened since 1870 (Section 7.4.4.2.1). While CMIP5 historical \r\nsimulations on average simulate a weakening, large ensemble \r\nsimulations span the observed strengthening since the 1950s \r\n(Watanabe et al., 2021) suggesting an important contribution from \r\ninternal variability. Coats and Karnauskas (2017) also find that the \r\nanthropogenic influence on the SST gradient is yet to emerge out of \r\ninternal variability even on centennial time scales."


id: 978bd4da89a81b18ff74d90c6ada234b
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 21372
content:
"et al., 2000), momentum and energy budgets (Biasutti et al., 2018; \r\nGeen et al., 2020). Assessments of regional monsoon changes are \r\nmade in Sections 8.3.2.4, 10.4.2.1 and 10.6.3."


id: 4a1e68f84b457967468b050174e1c9fd
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 9064
content:
"forced changes of the Walker circulation. Specifically, anthropogenic \r\nand volcanic aerosol changes over this period may have driven \r\na strengthening (DiNezio et al., 2013; Takahashi and Watanabe, 2016; \r\nHua et al., 2018). This aerosol influence may be indirect via Atlantic \r\nMulti-decadal Variability (AMV; Annex IV.2.7) through inter-basin \r\nteleconnections (McGregor et al., 2014; Chikamoto et al., 2016; \r\nKucharski et al., 2016; X. Li et al., 2016a; Ruprich-Robert et al., 2017), \r\nwhich may be underestimated in models due to SST biases in the \r\nequatorial Atlantic (Section 3.5.1.2.2; McGregor et al., 2018). Note \r\nalso the large uncertainty in aerosol influence on the Walker circulation \r\n(Kuntz and Schrag, 2016; Hua et al., 2018; Oudar et al., 2018), which is \r\nalso seen in CMIP6 (Figure 3.16f)."


id: 83f3751c450a60aff17343857c39a389
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 18293
content:
"AR5 assessed that CMIP5 models simulated monsoons better than \r\nCMIP3 models but that biases remained in domains and intensity \r\n(high confidence) (Flato et al., 2013). There were no detection and \r\nattribution assessment statements on the decreasing trend of global \r\nmonsoon precipitation over land from the 1950s to the 1980s or \r\nthe increasing trend of global monsoon precipitation afterwards. \r\nIn the paleoclimate context, it was determined with high confidence\r\nthat orbital forcing produces strong interhemispheric rainfall variability \r\nevident in multiple types of proxies (Masson-Delmotte et al., 2013)."


id: a60204cea7c0d7f58d67df3d4ca72e5b
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 23671
content:
"Paleoclimate data from the Pliocene epoch suggest that there \r\nwas a reduction in the zonal SST gradient in the tropical Pacific \r\nunder a similar CO2 concentration as today (Section 7.4.4.2.2 and \r\nCross-Chapter Box 2.4). Tierney et al. (2019) found that this weaker \r\ngradient compared to pre-industrial, which suggests a weaker Walker \r\ncirculation, is captured by climate models under Pliocene CO2 levels, \r\nin agreement with the CMIP6 response to greenhouse gas forcing \r\n(Figure 3.16d), though the magnitude of this effect varies strongly \r\nbetween models (Corvec and Fletcher, 2017)."


id: 9e9f2b6919a600380a2569b3a3a74f3f
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 22496
content:
"During the mid-Holocene, global monsoons were stronger especially \r\nin the Northern Hemisphere with an expansion of the West African \r\nmonsoon domain in response to orbital forcing (Biasutti et al., 2018; \r\nSection 2.3.1.4.2). Simulations of the mid-Holocene with CMIP5 \r\nand CMIP6 models qualitatively capture the stronger Northern \r\nHemisphere monsoon (Jiang et al., 2015; Brierley et al., 2020), mainly \r\ndriven by atmospheric circulation changes (D'Agostino et al., 2019). \r\nHowever, the models underestimate the monsoon expansion found \r\nin proxy reconstructions (Perez-Sanz et al., 2014; Harrison et al., \r\n2015; Tierney et al., 2017), which may be linked to mean biases in \r\nthe monsoon domain (Brierley et al., 2020) and may be improved \r\nby imposing vegetation and dust changes (Pausata et al., 2016). The \r\nmodels simulate the weaker Southern Hemisphere monsoon during "


id: 28e6fe05d8f342bffb7ad912ff7ae714
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 3869
content:
"Monsoons are seasonal transitions of regimes in atmospheric \r\ncirculation and precipitation with the annual cycle of solar insolation, \r\nin association with redistribution of moist static energy (Wang and \r\nDing, 2008; P.X. Wang et al., 2014; Biasutti et al., 2018). The global \r\nmonsoon can be defined to encompasses all monsoon systems based \r\non precipitation contrast in the solstice seasons (Wang and Ding, \r\n2008; Figure 3.17). All regional monsoons are intimately connected \r\nto the global tropical atmospheric overturning by mass (Trenberth "


id: 8c16e61943c181dfe3ae1bb6bd848464
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 19549
content:
"the mid-Holocene (D'Agostino et al., 2020), consistent with proxy \r\nevidence (Section 2.3.1.4.2). These studies indicate that models \r\ncan qualitatively reproduce past global monsoon changes seen in \r\nproxies, though issues remain in quantitatively reproducing proxy \r\nobservations. Studies of last millennium simulations show that \r\nsimulated global monsoon precipitation increases with global mean \r\ntemperature, while changes in monsoon circulation and hemispheric \r\nmonsoon precipitation depend on forcing sources (Liu et al., 2012; \r\nChai et al., 2018). Compared to greenhouse gas and solar variations, \r\nvolcanic forcing is more effective in changing the global monsoon \r\nprecipitation over the last millennium (Chai et al., 2018)."


id: a22887fb415f4991d77e2c0a3c6a542f
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 23077
content:
"the timings of onset and withdrawal of the Southern Hemisphere \r\nmonsoon. Notable inter-model differences were identified in \r\nCMIP5, with the multi-model ensemble mean outperforming \r\nindividual models (Lee and Wang, 2014). Common biases were \r\nidentified across CMIP5 models in moist static energy and upper\u0002tropospheric temperature associated with the South Asian summer \r\nmonsoon, which may arise from overly smoothed model topography \r\n(Boos and Hurley, 2012). However, in atmospheric models with \r\nincreasing resolution approaching 20 km, improvements in monsoon \r\nprecipitation are not universal across regions and models, and overall \r\nimprovements are unclear (Johnson et al., 2016; Ogata et al., 2017; \r\nL. Zhang et al., 2018b)."


id: d64bb41d845be5bd3adbe45ea637c318
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 31226
content:
"Reproducing monsoons in terms of domain, precipitation amount, \r\nand timings of onset and retreat over the historical period also \r\nremains difficult. While CMIP5 historical simulations broadly capture \r\nglobal monsoon domains and intensity based on summer and winter \r\nprecipitation differences, they underestimate the extent and intensity \r\nof East Asian and North American monsoons while overestimating \r\nthem over the tropical western North Pacific (Lee and Wang, 2014; \r\nM. Yan et al., 2016). B. Wang et al. (2020) reported that CMIP6 \r\nmodels simulate the global monsoon domain and precipitation better \r\n(Figure 3.17a,b), albeit with biases in annual mean precipitation and "


id: 3aa4d02fc3bea1aef190bb001bc37a73
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 6597
content:
"In instrumental records, global summer monsoon precipitation \r\nintensity (measured by summer precipitation averaged over the \r\nmonsoon domain) decreased from the 1950s to 1980s, followed \r\nby an increase (Section 2.3.1.4.2 and Figure 3.17c), arising mainly \r\nfrom variations in Northern Hemispheric land monsoons. A CMIP5 \r\nmulti-model study by Y. Zhang et al. (2018) found that observed \r\n1951-2004 trends of the global and Northern Hemisphere summer \r\nland monsoon precipitation intensity are well captured by historical \r\nsimulations, and CMIP6 models show similar results for global land "


id: 5e45a117b5bb7036f16ea815f12f323c
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 12359
content:
"there is high confidence that orbital forcing contributed to higher \r\nNorthern Hemisphere monsoon precipitation in the mid-Pliocene and \r\nmid-Holocene than pre-industrial. While CMIP5 models can capture \r\nthe domain and precipitation intensity of the global monsoon, biases \r\nremain in their regional representations, and they are unsuccessful \r\nin quantitatively reproducing changes in paleo reconstructions (high \r\nconfidence). CMIP6 models reproduce the domain and precipitation \r\nintensity of the global monsoon observed over the instrumental \r\nperiod better than CMIP5 models (medium confidence). However, \r\nCMIP5 and CMIP6 models fail to fully capture the variations of the \r\nNorthern Hemisphere summer monsoon circulation (Figure 3.17d), but \r\nthere is low confidence in this assessment due to a lack of evidence in \r\nthe literature."


id: 7ec53628c7ceb1b4daa080251b6f6a38
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 17509
content:
"Extratropical jets are wind maxima in the upper troposphere which \r\nare often associated with storms, blocking, and weather extremes. \r\nBlocking refers to long-lived, stationary high-pressure systems that \r\nare often associated with a poleward displacement of the jet, causing \r\ncold spells in winter and heatwaves in summer (e.g., Sousa et al., \r\n2018). Sections 2.3.1.4.3, 8.3.2.7, and 11.7.2 discuss these features \r\nin more detail."


id: e7a20c8973e4175fbeb0bd5ee723af5f
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 33944
content:
"AR5 concluded that models were able to capture the general \r\ncharacteristics of extratropical cyclones and storm tracks, although \r\nit also noted that most models underestimated cyclone intensity, \r\nthat biases in cyclone frequency were linked to biases in sea surface \r\ntemperatures, and that resolution can play a significant role in the \r\nquality of the simulation of storms (Flato et al., 2013). Similarly, AR5 \r\nfound with high confidence that simulation of blocking was improved \r\nwith increases in resolution. The AR5 did not specifically assess changes \r\nin Southern Hemisphere storm track characteristics or blocking."


id: a17f72fdd2d03c6cd7e02b9b94f14de
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 22967
content:
"underestimated, has not improved from CMIP5 to CMIP6 (Schiemann \r\net al., 2020). Section 10.3.3.3 discusses the implications of the biases \r\ndiscussed here for regional climate."


id: 6de9b75fed8f33f68b7a09d8431e7ce
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 14904
content:
"summer do Patterson et al. (2019) find a systematic, multi-model \r\nunderestimation of the blocking frequency in and around the Tasman \r\nSea. The blocking frequency is anticorrelated with the amplitude \r\nof the SAM. Ozone depletion, through stratosphere-troposphere \r\ncoupling, may have caused an increase in the blocking frequency in \r\nthe South Atlantic sector (Dennison et al., 2016); this finding requires \r\nconfirmation using a multi-model approach."


id: 98122eb699208be9fe1caabb8f1c8877
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 21432
content:
"For the North Pacific storm track CMIP6 simulations exhibit large \r\nremaining underestimations of cyclone frequencies during summer \r\n(June to August), which for the low-resolution models have essentially \r\nremained unchanged versus CMIP5, and there is only a small resolution \r\ndependence of this bias (Priestley et al., 2020). During winter (December \r\nto February), both CMIP5 and CMIP6 models tend to place the North \r\nPacific storm track too far equatorward (M. Yang et al., 2018; Priestley \r\net al., 2020), leading to an overestimation of cyclones between 30degN \r\nand 40degN in the Pacific and an underestimation to the north of \r\nthis. Both low- and high-resolution models show this pattern, but \r\nlow-resolution models generally simulate fewer cyclones throughout \r\nthe North Pacific (Priestley et al., 2020)."


id: 7057c6494c8793a0f7a3d030f6d9e653
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 15291
content:
"In addition to inadequate resolution, blocking and storm track biases \r\nin both hemispheres also result from mean state biases, in particular, \r\nbiases related to the parameterization of orographic effects and to \r\nthe misrepresentation of the Gulf Stream SST front (Anstey et al., \r\n2013; Berckmans et al., 2013; Davini and D'Andrea, 2016; O'Reilly \r\net al., 2016a; Pithan et al., 2016; Schiemann et al., 2017). Nonetheless \r\noverall SST biases have been suggested to have only a weak relevance \r\nto blocking (Davini and D'Andrea, 2016)."


id: c0515ecb0f164df77c260cffb5ab01d7
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 27817
content:
"Section 2.3.1.4.3 assesses that the total number of extratropical \r\ncyclones has likely increased since the 1980s in the Northern \r\nHemisphere (low confidence), but with fewer deep cyclones \r\nparticularly in summer. This observed reduction in cyclone activity \r\nby about 4% per decade in the Northern Hemisphere in summer \r\n(Chang et al., 2016; Section 2.3.1.4.3) may be associated with \r\nhuman-induced warming. CMIP5 historical simulations generally \r\nreproduce a reduction but underestimate its magnitude (Chang \r\net al., 2016). Furthermore, feedback mechanisms associated with \r\nclouds may be responsible for substantial inter-model spread (Chang \r\net al., 2016; Voigt and Shaw, 2016). In boreal winter, recent studies \r\nhave suggested a potential influence of the rapid Arctic warming on \r\nobserved intensification of Northern Hemisphere storm track activity \r\nin the past few decades, while other studies question this possibility \r\n(Cross-Chapter Box 10.1)."


id: 491e0ef09199139bdb4fb2c75dadf001
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 8892
content:
"In winter, the North Atlantic storm track remains displaced to the \r\nsouth and east in many models (Harvey et al., 2020), leading to \r\nunderestimation of cyclone frequencies near the North American coast \r\nand overestimation in the eastern North Atlantic. Higher-resolution \r\nCMIP6 models perform slightly better in this regard than low\u0002resolution models. In summer (June to August), cyclone frequencies \r\nthroughout the extratropical North Atlantic, which were substantially \r\nunderestimated in CMIP5, have improved in CMIP6 high-resolution \r\nmodels. In low-resolution CMIP6 models, the problem is essentially \r\nunchanged (Priestley et al., 2020); this is associated with generally \r\nunderestimated variability of sea level pressure in CMIP models \r\n(Harvey et al., 2020)."


id: 8206f4123a3902a87d2be2125230a130
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 17976
content:
"There is only one contiguous blocking region in the Southern \r\nHemisphere, with the blocking frequency maximizing in the South \r\nPacific and minimizing in the southern Indian Ocean regions (Parsons \r\net al., 2016; Patterson et al., 2019). CMIP5 simulations agree relatively \r\nwell with ERA-Interim in this region regarding the distribution of \r\nblocking events (Parsons et al., 2016). Individual models exhibit \r\nconsiderable biases in the blocking frequency; however only in austral "


id: b1fd9e0a39e380600e8a770a1b406c0b
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 25503
content:
"In summary, there is low confidence that an observed decrease in \r\nthe frequency of Northern Hemisphere summertime extratropical \r\ncyclones is linked to anthropogenic influence. In the Southern \r\nHemisphere, there is high confidence that human influence, in the \r\nform of ozone depletion, has contributed to the observed poleward \r\nshift of the jet in austral summer, while confidence is low for "


id: d5ff029cd871b3291bdf514a82576f3e
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 31185
content:
"Figure 3.18 | Instantaneous Northern-Hemisphere blocking frequency (% of days) in the extended northern winter season (December-January-February-\r\nMarch - DJFM) for the years 1979-2000. Results are shown for the ERA5 reanalysis (black), CMIP5 (blue) and CMIP6 (red) models. Coloured lines show multi-model means and \r\nshaded ranges show corresponding 5-95% ranges constructed with one realization from each model. Figure is adapted from Davini and D'Andrea (2020), their Figure 12 and \r\nfollowing the D'Andrea et al. (1998) definition of blocking. Further details on data sources and processing are available in the chapter data table (Table 3.SM.1)."


id: 7d63eb00ede4544b6fcfea542f23a525
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 17299
content:
"human influence on historical blocking activity. The low confidence\r\nstatements are due to the limited number of studies available. The \r\nshift of the Southern Hemisphere jet is correlated with modulations \r\nof the SAM (Section 3.7.2). There is medium confidence in model \r\nperformance regarding the simulation of the extratropical jets, storm \r\ntrack and blocking activity, with increased resolution sometimes \r\ncorresponding to better performance, but important shortcomings \r\nremain, particularly for the Euro-Atlantic sector of the Northern \r\nHemisphere. Nonetheless, synthesizing across Sections 3.3.3.1-\r\n3.3.3.3, there is high confidence that CMIP6 models capture the \r\ngeneral characteristics of the tropospheric large-scale circulation."


id: 18c356d20c2860d31d665934d14bfa9e
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 1396
content:
"In summary, an anthropogenic influence on the frequency or other \r\naspects of SSWs has not yet been robustly detected. There is low \r\nconfidence in the ability of models to simulate any such trends over \r\nthe historical period because of large natural interannual variability \r\nand also due to substantial common biases in the simulated mean \r\nstate affecting the simulated frequency of SSWs."


id: 3c96b42502bc2691ff31075cf56d3b44
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 6902
content:
"Sudden stratospheric warmings (SSWs) are stratospheric weather \r\nevents associated with anomalously high temperatures at high \r\nlatitudes persisting from days to weeks. Section 2.3.1.4.5 discusses \r\nthe definition and observational aspects of SSWs. SSWs are often \r\nassociated with anomalous weather conditions, for example, winter \r\ncold spells, in the lower atmosphere (e.g., Butler et al., 2015; Baldwin \r\net al., 2021)."


id: 5e59878934fa7d39bfa0093a50c7f46
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 12378
content:
"Some studies find an increase in the frequency of SSWs under \r\nincreasing greenhouse gases (e.g., Schimanke et al., 2013; Young \r\net al., 2013; J. Kim et al., 2017). However, this behaviour is not \r\nrobust across ensembles of chemistry-climate models (Mitchell et al., \r\n2012; Ayarzaguena et al., 2018; Rao and Garfinkel, 2021). There is \r\nan absence of studies specifically focusing on simulated trends in \r\nSSWs during recent decades, and the short record and substantial \r\ndecadal variability yields low confidence in any observed trends in \r\nthe occurrence of SSW events in the Northern Hemisphere winter \r\n(Section 2.3.1.4.5). Such an absence of a trend and large variability \r\nwould also be consistent with a recent reconstruction of SSWs \r\nextending back to 1850, based on sea level pressure observations \r\n(Domeisen, 2019), although this time series has limitations as it is not \r\nbased on direct observations of SSWs."


id: 798c0aa9b6bf32ce4ca765ddcc509ab9
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 16696
content:
"and Eisenman, 2017). Sea ice thermodynamic considerations \r\nindicate that the magnitude of sea ice variability and loss depends \r\non ice thickness (Bitz, 2008; Massonnet et al., 2018) and  hence \r\nthe climatology simulated by different models may influence their \r\nsimulated sea ice trends (medium confidence), as indicated by the \r\nregression lines in Figure 3.20."


id: f7cf8b9449e99655aa10071e6fa595f
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 36509
content:
"the period 1953-2012. They further showed that about a quarter of the \r\ngreenhouse gas induced decrease in SIE has been offset by an increase \r\ndue to other anthropogenic forcing (mainly aerosols). Similarly, Gagne \r\net al. (2017b) suggested that the observed increase in Arctic sea \r\nice concentration over the 1950-1975 period was primarily due to \r\nthe cooling contribution of anthropogenic aerosol forcing based on \r\nsingle model simulations. Gagne et al. (2017a) identified a detectable \r\nincrease in Arctic SIE in response to volcanic eruptions using CMIP5 \r\nmodels and four observational datasets. Polvani et al. (2020) suggested \r\nthat ozone depleting substances played a substantial role in the Arctic \r\nsea ice loss over the 1955-2005 period."


id: 6ae5e79b3c7d4d08733d68e3a1da7fc6
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 14435
content:
"An important consideration in comparing Arctic sea ice loss in \r\nmodels and observations is the role of internal variability (medium \r\nconfidence). Using ensemble simulations from a single model, \r\nKay et al. (2011) suggested that internal variability could account \r\nfor about half of the observed September ice loss. More recently, \r\nlarge ensemble simulations have been performed with many more \r\nensemble members (Kay et al., 2015). These enable a more robust \r\ncharacterization of internal variability in the presence of forced \r\nanthropogenic change. Using such large ensembles, some studies \r\ndiscussed the influence of internal variability on Arctic sea ice trends \r\n(Swart et al., 2015). Song et al. (2016) also compared the trends in the "


id: edf5919e219a4017f2a35db98776b63
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 34913
content:
"Differences in sea ice loss among the models (Figure  3.20) have \r\nbeen attributed to a number of factors (see also Section 9.3.1.1). \r\nThese factors include the late 20th century simulated sea ice state \r\n(Massonnet et al., 2012), the magnitude of changing ocean heat \r\ntransport (Mahlstein and Knutti, 2011), and the rate of global warming \r\n(e.g., Gregory et al., 2002; Mahlstein and Knutti, 2012; Rosenblum "


id: 51c7625351129685f81e226926bbeac6
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 10326
content:
"Figure 3.20 | Mean (x-axis) and trend (y-axis) of Arctic sea ice area (SIA) in September (left) and Antarctic SIA in February (right) for 1979-2017 from \r\nCMIP5 (upper) and CMIP6 (lower) models. All individual models (ensemble means) and the multi-model mean values are compared with the observations (OSISAF, NASA \r\nTeam, and Bootstrap; see Figure 9.13). Solid line indicates a linear regression slope with corresponding correlation coefficient (r) and p-value provided. Note the different scales \r\nused on the y-axis for Arctic and Antarctic SIA. Results remain essentially the same when using sea ice extent (SIE; not shown). Further details on data sources and processing \r\nare available in the chapter data table (Table 3.SM.1)."


id: 605c295a175e96bd751d723e2713ac83
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 12735
content:
"Some recent studies evaluated the human contribution to recent \r\nrecord minimum SIE events in the Arctic. Analysing CMIP5 simulations, \r\nZhang and Knutson (2013) found that the observed 2012 record low \r\nin September Arctic SIE is inconsistent with internal climate variability \r\nalone. Based on several large ensembles, Kirchmeier-Young et al. \r\n(2017) concluded that the observed 2012 SIE minimum cannot be \r\nreproduced in a simulation excluding human influence. Fuckar et al. \r\n(2016) showed that climate change contributed to the record low \r\nMarch Arctic SIE in 2015, which was accompanied by the record \r\nminimum SIE in the Sea of Okhotsk (Paik et al., 2017)."


id: d7b8d42ff6a027d716d2e2b4a8536cef
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 31464
content:
"Based on the new attribution studies since AR5, we conclude that it \r\nis very likely that anthropogenic forcing mainly due to greenhouse \r\ngas increases was the main driver of Arctic sea ice loss since \r\n1979. Increases in anthropogenic aerosols have offset part of the \r\ngreenhouse gas induced Arctic sea ice loss since the 1950s (medium \r\nconfidence). Despite large differences in the mean sea ice state in \r\nthe Arctic, Arctic sea ice loss is captured by all CMIP5 and CMIP6 \r\nmodels. Nonetheless, large inter-model differences in the Arctic sea \r\nice decline remain, limiting our ability to quantify forced changes and \r\ninternal variability contributions."


id: c561562fadfc4ec98f0f8577d5e23f2c
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 28636
content:
"AR5 concluded that 'there is low confidence in the attribution of the \r\nobserved increase in Antarctic SIE since 1979' (Bindoff et al., 2013) due \r\nto the limited understanding of the external forcing contribution as well \r\nas the role of internal variability. Based on a difference between the \r\nfirst and last decades, Antarctic sea ice cover exhibited a small increase \r\nin summer and winter over the 1979-2017 period (Section 2.3.2.1.2, \r\nand Figures 3.20 and 3.21). However, these changes are not statistically \r\nsignificant and starting in late 2016, anomalously low sea ice area \r\nhas been observed (Section 2.3.2.1.2). The mean hemispheric sea ice \r\nchanges result from much larger, but partially compensating, regional \r\nchanges with increases in the western Ross Sea and Weddell Sea "


id: 72158f9a8bfebf71b5606b791925f489
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 15577
content:
"GSAT and SCE also exists in CMIP6 (Mudryk et al., 2020). Like CMIP5, \r\nthe CMIP6 models capture the negative trend in spring snow cover \r\nthat has occurred in recent decades (Figure  3.22). However, the \r\nmedian CMIP6 model now produces slightly stronger post-1981 \r\ndeclines in the March to April mean SCE than the CMIP5 median \r\n(Mudryk et al., 2020). Until about 1980, the models produce a \r\ngenerally stable March to April SCE, but after that a substantial \r\ndecline, reaching a loss of about 2 x 106 km2 in 2012-2017 relative \r\nto the 1971-2000 average. Compared to earlier studies which found \r\nthat models underestimate observed trends for the 1979-2005 \r\nperiod (Brutel-Vuilmet et al., 2013), both CMIP5 and CMIP6 models "


id: e1bdc97765b44a484ce5db2fa4867f1
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 33011
content:
"In conclusion, the observed small increase in Antarctic sea ice extent \r\nduring the satellite era is not generally captured by global climate \r\nmodels, and there is low confidence in attributing the causes of \r\nthe change."


id: 1c9e349bb85c24005e422e8e9c7c2247
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 1950
content:
"Seasonal snow cover is a defining climate feature of the northern \r\ncontinents. It is therefore of considerable interest that climate \r\nmodels correctly simulate this feature. It is discussed in more detail in \r\nSection 9.5.3, and observational aspects of snow cover are assessed \r\nin Section 2.3.2.2."


id: 94799a424e3afcaa8c17839d68f0cb9d
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 20873
content:
"CMIP6 models improve on CMIP5 models in producing slightly \r\nincreased SCE versus CMIP5, correcting the low bias in CMIP5 \r\n(Mudryk et al., 2020). The linear relationship noted above between "


id: 99e14fb6f5788776c9a01ec23f3ef35a
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 21738
content:
"show improved agreement with the observations over the period to \r\n2017 (Figure 3.22). One remaining concern is a failure of most CMIP6 \r\nmodels to correctly represent the relationship between snow cover \r\nextent and snow mass, reflecting too slow seasonal increases and \r\ndecreases of SCE in the models (Mudryk et al., 2020)."


id: 4743e829a421986357ae25da529b06bd
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 8596
content:
"Several CMIP5 and CMIP6 based studies have consistently \r\nattributed the observed Northern Hemisphere spring SCE changes \r\n(Section 2.3.2.2) to anthropogenic influences (Rupp et al., 2013; Najafi \r\net al., 2016; Paik and Min, 2020), with the observed changes being \r\nfound to be inconsistent with natural variability alone. Similarly, spring \r\nsnow thickness (Snow Water Equivalent) changes on the scale of the \r\nNorthern Hemisphere have been attributed to greenhouse gas forcing \r\n(Jeong et al., 2017). Using individual forcing simulations from multiple \r\nCMIP6 models, Paik and Min (2020) detected greenhouse gas influence \r\nin the observed decrease of early spring SCE between 1925 and 2019, \r\nwhich was found to be separable from the responses to other forcings."


id: 897bc419d02a8bc2d14c6300518e5aab
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 19168
content:
"Glaciers are defined as perennial surface land ice masses \r\nindependent of the Antarctic and Greenland Ice Sheets (Sections 9.5 \r\nand 2.3.2.3). The AR5 assessed that anthropogenic influence had \r\nlikely contributed to the retreat of glaciers observed since the 1960s \r\n(Bindoff et al., 2013), based on a high level of scientific understanding \r\nand robust estimates of observed mass loss, internal variability, and \r\nglacier response to climatic drivers. The SROCC (Hock et al., 2019b) \r\nconcluded that atmospheric warming was very likely the primary \r\ndriver of glacier recession."


id: 3da9cc5ae0b53248935cea11677bc52
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 7055
content:
"Simulations of glacier mass changes under climate change rely on \r\nglacier models driven by climate model output, often in collaborative \r\nresearch efforts such as GlacierMIP (Hock et al., 2019a; Marzeion \r\net al., 2020). The GlacierMIP project is a systematic coordinated \r\nmodelling effort designed to further understanding of glacier loss \r\nusing global models. While the low resolution and remaining biases \r\nof climate model-derived boundary forcing data is a limitation, the \r\nrelease of the Randolph Glacier Inventory (Pfeffer et al., 2014; RGI \r\nConsortium, 2017) has supported more sophisticated, systematic and \r\ncomprehensive modelling of glaciers worldwide (Hock et al., 2019a)."


id: 79c96c275692a49e89e31ab6608c5786
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 16731
content:
"naturally-forced simulations exhibited a substantial negative mass \r\nbalance, which Roe et al. (2021) argued is unrealistic. Moreover, \r\nMarzeion et al. (2014) estimated that anthropogenic influence \r\ncontributed 69 +- 24% of glacier mass loss for the period 1991 to \r\n2010, consistent with a progressively increasing fraction of mass loss \r\nattributable to anthropogenic influence found by Roe et al. (2021)."


id: 91a5de53e077556f1920d185384820c1
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 20458
content:
"In summary, considering together the SROCC assessment that \r\natmospheric warming was very likely the primary driver of glacier \r\nrecession, the results of Roe et al. (2017, 2021) and our assessment of \r\nthe dominant role of anthropogenic influence in driving atmospheric \r\nwarming (Section 3.3.1), we conclude that human influence is very \r\nlikely the main driver of the near-universal retreat of glaciers globally \r\nsince the 1990s."


id: 4125f7d8827152a82331299d370db047
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 7638
content:
"The AR5 assessed that it is likely that anthropogenic forcing \r\ncontributed to the surface melting of the Greenland Ice Sheet since \r\n1993 (Bindoff et al., 2013). The SROCC did not directly assess the \r\nattribution of Greenland Ice Sheet change to anthropogenic forcing, \r\nbut it did assess with medium confidence that summer melting of the \r\nGreenland Ice Sheet has increased to a level unprecedented over at \r\nleast the last 350 years, which is two-to-fivefold the pre-industrial \r\nlevel (see also Trusel et al., 2018)."


id: 2f83032f66d16c373271f49dd44c9216
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 4894
content:
"Section 2.3.2.4.1 assesses that Greenland Ice Sheet mass loss began \r\nin the latter half of the 19th century and that the rate of loss has \r\nincreased substantially since the turn of the 21st century (high \r\nconfidence), and also notes that integration of proxy evidence and \r\nmodelling indicates that the last time the rate of mass loss was similar \r\nto the 20th century rate was during the early Holocene. Models of \r\nGreenland Ice Sheet evolution are evaluated in detail in Section \r\n9.4.1.2, which assesses that there is overall medium confidence in \r\nthese models. Model evaluation of surface mass balance changes \r\nover the Greenland Ice Sheet, including regional aspects, is also \r\nassessed in Atlas.11.2.3."


id: a9e022c34b42b9d680303e835864b38f
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 24260
content:
"Drawing together the evidence from the continued and strengthened \r\nobserved mass loss, the agreement between anthropogenically \r\nforced climate simulations and observations, and historical and paleo \r\nevidence for the unusualness of the observed rate of surface melting \r\nand mass loss, we assess that it is very likely that human influence has \r\ncontributed to the observed surface melting of the Greenland Ice Sheet \r\nover the past two decades, and that there is medium confidence in an \r\nanthropogenic contribution to recent overall mass loss from Greenland."


id: 29f6c039461f38711933ef6a784a22e6
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 4032
content:
"coverage. Observed changes to ocean temperature (Section 2.3.3.1), \r\nsalinity (Section 2.3.3.2), sea level (Section 2.3.3.3) and ocean \r\ncirculation (Section 2.3.3.4) are reported in Chapter 2.  A more \r\nprocess-based assessment of ocean changes, alongside the \r\nassessment of variability and changes in ocean properties with \r\nspatial scales smaller than ocean basins, is presented in Chapter 9."


id: 1a10ca1eb4a89b774d38e1c327542a28
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 1567
content:
"Model evaluation of surface mass balance over the Antarctic Ice \r\nSheet, including regional aspects, is also assessed in Atlas.11.1.3."


id: ca442439a8a382b05f14006d3ca0b36b
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 29386
content:
"Ocean temperature and ocean heat content are key physical variables \r\nconsidered for climate model evaluation and are primary indicators \r\nof a changing ocean climate. This section assesses the performance \r\nof climate models in representing the mean state ocean temperature \r\nand heat content (Section 3.5.1.1), with a particular focus on the \r\ntropical oceans given the importance of air-sea coupling in these \r\nareas (Section 3.5.1.2). This is followed by an assessment of detection \r\nand attribution studies of changes in ocean temperature and heat \r\ncontent (Section 3.5.1.3). Changes in global surface temperature are \r\nassessed in Section 3.3.1.1."


id: 292b07043ccae1c29b5f729f324e230d
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 3910
content:
"Overall, there is medium agreement but limited evidence of \r\nanthropogenic influence on Antarctic mass balance through changes \r\nin ice discharge."


id: 1c1eb5c23fc0a15aa12af225d9988ff
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 1882
content:
"The global ocean plays an important role in the climate system, as it \r\nis responsible for transporting and storing large amounts of heat \r\n(Sections 3.5.1 and 9.2.2.1), freshwater (Sections 3.5.2 and 9.2.2.2) \r\nand carbon (Sections 3.6.2 and 5.2.1.3) that are exchanged with the \r\natmosphere. Therefore, accurate ocean simulation in climate models \r\nis essential for the realistic representation of the climatic response \r\nto anthropogenic warming, including rates of warming, sea level \r\nrise and carbon uptake, and the representation of coupled modes of \r\nclimate variability."


id: 30529cc088d41d3ca582eaf6427bb8b0
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
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vector_id: 5031
content:
"Ocean model development has advanced considerably since AR5 \r\n(Section 1.5.3.1). Ongoing model developments since AR5 have \r\nfocused on improving the realism of the simulated ocean in coupled \r\nmodels, with horizontal resolutions increasing to 10-100 km (from \r\nabout 200 km in CMIP5), and increased vertical resolutions in \r\nmany modelling systems of 0-1 m for near-surface levels (from the \r\nhighest resolution of 10 m in CMIP5). These developments are aimed \r\nat improving the representation of the diurnal cycle and coupling \r\nto the atmosphere (e.g., Bernie et al., 2005, 2007, 2008). General \r\nimprovements to simulated ocean fidelity in response to increasing \r\nresolution are expected (Hewitt et al., 2017), and the effects of model \r\nresolution on the fidelity of ocean models are discussed in more \r\ndetail in Sections 9.2.2 and 9.2.4."


id: fdb39c614fcf4f6e8f770021d10c81b2
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
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index: climate_gpt_only_giec
vector_id: 37433
content:
"Overall, the simulated and observed trends in SST patterns are \r\ngenerally consistent for the historical period (Olonscheck et al., \r\n2020). The CMIP6 models generally represent the observed pattern of \r\ntrends better than the CMIP5 models, and observed trends fall within \r\nthe range of simulated trends over a larger area for CMIP6 models \r\nthan for CMIP5 models (Olonscheck et al., 2020)."


id: a22b0cff2d1cae9379c4f278d7474a23
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 23081
content:
"The CMIP5 multi-model mean zonally averaged subsurface ocean \r\ntemperature showed warm biases between 200 m and 2000 m \r\n(mid-depth) over most latitudes, with exceptions in the Southern \r\nOcean (>60degS, 100-2000 m) and upper (0-400 m) Arctic Ocean. Cold \r\nbiases were simulated near the surface (0-200 m) at most latitudes \r\n(Flato et al., 2013). CMIP6 biases are broadly consistent with those \r\nreported in CMIP5 for the near-surface (<200 m) and mid-depth \r\n(200-2000 m) ocean (Voldoire et al., 2019b; Beadling et al., 2020; \r\nY. Zhu et al., 2020). The warm bias begins between 100 and 400 m \r\ndepth in all three basins, however, it is most prominent in the Atlantic "


id: 3d75583d934a9dcc22308eaa1f35fdd
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 7026
content:
"Figure 3.24 | Biases in zonal mean and equatorial sea surface temperature \r\n(SST) in CMIP5 and CMIP6 models. CMIP6 (red), CMIP5 (blue) and HighResMIP \r\n(green) multi-model mean (a) zonally averaged SST bias; (b) equatorial SST bias; \r\nand (c) equatorial SST compared to observed mean SST (black line) for 1979-1999. \r\nThe inter-model 5th and 95th percentiles are depicted by the respective shaded \r\nrange. Model climatologies are derived from the 1979-1999 mean of the historical \r\nsimulations, using one simulation per model. The Hadley Centre Sea Ice and Sea Surface \r\nTemperature version 1 (HadISST) (Rayner et al., 2003) observational climatology for \r\n1979-1999 is used as the reference for the error calculation in (a) and (b); and for \r\nobservations in (c). Further details on data sources and processing are available in the \r\nchapter data table (Table 3.SM.1)."


id: a3b135f4397a7502730d212bf0488adc
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 23316
content:
"Ocean, with a maximum magnitude in the equatorial latitudes, as \r\nin CMIP5 (Figure  3.25). In the Pacific, the large warm biases are \r\nmostly seen in the subtropical regions (30degN-60degN and 30degS-60degS). \r\nThe cool near surface tropical bias is most prominent in the Pacific \r\nOcean and also present in the Atlantic, with a smaller magnitude \r\n(Figure 3.25). Relative to CMIP5, the most prominent difference is an \r\nincrease to the mid-depth (300-2000 m) warm bias in CMIP6 and a \r\nchange in sign of the bias from cold to warm for the Southern Ocean \r\nmid-depth (>60degS) from CMIP5 to CMIP6 (Figure 3.25). Compared \r\nto CMIP3 and CMIP5, there is improved agreement between most \r\nCMIP6 models and observations in their representation of the \r\nzonal mean temperature of the upper 100 m of the Southern Ocean \r\n(Beadling et al., 2020)."


id: e9066f163e45c4d5c3c804e8e2d2fdf4
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 34181
content:
"Focusing on the deep ocean (>2000 m), the CMIP6 ensemble mean \r\nshows a prominent and consistent warm bias (Figure 3.25), in all basins \r\nexcept the equatorial and northern Pacific, which contrasts to a cold \r\nbias seen in CMIP5 (Flato et al., 2013). We note that while an updated \r\nobservational temperature dataset is used in this assessment (WOA09 \r\nwas used in AR5, while WOA18, 1981-2010 is used in AR6), the deep\u0002ocean warm bias remains and is approaching double the magnitude \r\n(about 0.5degC) of the equivalent CMIP5 multi-model mean bias, a feature \r\nwhich is particularly prominent in the Atlantic and southern Indian "


id: a21e98f40e54cd07b0c7aea0a613d948
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
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index: climate_gpt_only_giec
vector_id: 23069
content:
"eddy transport, and reducing temperature drifts in the deeper ocean \r\n(Griffies et al., 2015; von Storch et al., 2016). For some models, the mean \r\nabsolute error in ocean temperature below 500 m is smaller in the high \r\nresolution version compared to the low resolution version, particularly \r\nin eddy-active regions such as the North Atlantic (Rackow et al., 2019). \r\nIncreasing the horizontal resolution of individual climate models often \r\nleads to an overall decrease in the surface temperature biases over \r\nregions where they persisted through earlier CMIP generations, such \r\nas the central and western equatorial Pacific, as well as the North \r\nand tropical Atlantic (Figure 3.3e; Roberts et al., 2019; Hewitt et al., \r\n2020). Despite this, as a group the four HighResMIP models included \r\nin Figures 3.3e and 3.24 do not on average show smaller SST biases \r\nthan the CMIP6 multi-model mean, demonstrating the importance of \r\nfactors other than resolution in contributing to SST biases."


id: b60c1b25e62d9dcb148686180945f2b7
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 26172
content:
"Oceans. Increased horizontal resolution as well as the choice of the \r\nvertical coordinate are reported to partly improve these biases in some \r\nmodels (Adcroft et al., 2019; Rackow et al., 2019; Hewitt et al., 2020)."


id: dc74d92ff5c2daa077eabf3733e3bdbc
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 32186
content:
"Since AR5, there has been growing evidence that the representation \r\nof mean surface and deeper ocean temperatures in coupled climate \r\nmodels can be improved by increasing the horizontal resolution both \r\nin the ocean and the atmosphere (e.g., Small et al., 2014; Hewitt et al., \r\n2016; Iovino et al., 2016; Roberts et al., 2019). At an ocean resolution \r\nof around 1deg, which is typical of CMIP6 models, some processes are \r\nparameterized rather than explicitly resolved, leading to a compromise \r\nin their dynamical representation. An increase in the model resolution \r\nallows for processes to be explicitly resolved, and can for example, \r\nenhance the simulation of eddies, thus improving simulated vertical "


id: 5a8aa4ca6ee911bf9f66aefa6fe43a2c
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 11759
content:
"In summary, there is little improvement in the multi-model mean \r\nsea surface and zonal mean ocean temperatures from CMIP5 to \r\nCMIP6 (medium confidence). Nevertheless, the CMIP6 models show \r\na somewhat more realistic pattern of SST trends (low confidence)."


id: 86485998f388290532137aefadfe6649
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 18670
content:
"a large spread in the thermocline depth, particularly in the equatorial \r\npart of the basin (Saji et al., 2006; Fathrio et al., 2017b), which has \r\nbeen linked to the parameterization of the vertical mixing and the wind \r\nstructure, leading to a misrepresentation of the ventilation process in \r\nsome models (Schott et al., 2009; Richter, 2015; Shikha and Valsala, \r\n2018). A common problem with the CMIP5 models is therefore a warm \r\nbias in the subsurface, mainly at depths around the thermocline, which \r\nis also apparent in the CMIP6 models (Figure 3.25g)."


id: 530a95b5a65b5ea40be1ee4a7670d356
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 10523
content:
"In the CMIP6 multi-model mean, the western tropical Indian Ocean \r\nshows a slightly larger warm bias compared to CMIP5 (Figure 3.24 b,c), \r\nwhich in part could be related to excessive supply of warm water \r\nfrom the Red Sea (Grose et al., 2020; Semmler et al., 2020). The \r\nHighResMIP models show decreases in SST bias across the Indian \r\nOcean with increasing resolution (Figure  3.3e; Bock et al., 2020), \r\nthough as a group the SST biases in the HighResMIP models are no \r\nsmaller than those of the full CMIP6 ensemble."


id: 494aa41affa4c910d09684983c053b41
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 8916
content:
"In summary, the structure and magnitude of multi-model mean ocean \r\ntemperature biases have not changed substantially between CMIP5 \r\nand CMIP6 (medium confidence). Although biases remain in the latest \r\ngeneration models, the broad consistency between the observed and \r\nsimulated basin-scale ocean properties suggests that CMIP5 and CMIP6 \r\nmodels are appropriate tools for investigating ocean temperature \r\nand ocean heat content responses to forcing. This also provides \r\nhigh confidence in the utility of CMIP-class models for detection and \r\nattribution studies, for both ocean heat content (Section 3.5.1.3) and \r\nthermosteric sea level applications (Section 3.5.3.2)."


id: cb50fa7828599bcc85e2bb0be555fc31
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 29539
content:
"The ocean plays an important role as the Earth's primary energy store. \r\nThe AR5 and SROCC assessed that the ocean accounted for more than \r\n90% of the Earth's energy change since the 1970s (Rhein et al., 2013; \r\nBindoff et al., 2019). These assessments are consistent with recent \r\nstudies assessed in Section 7.2 and Cross-Chapter Box  9.1, which \r\nfind that 91% of the observed change in Earth's total energy from \r\n1971 to 2018 was stored in the ocean (von Schuckmann et al., 2020). \r\nThe AR5 concluded that anthropogenic forcing has very likely made \r\na substantial contribution to ocean warming above 700 m, whereas \r\nbelow 700  m, limited measurements restricted the assessment of \r\nocean heat content changes in AR5 and prevented a robust comparison \r\nbetween observations and models (Bindoff et al., 2013)."


id: ecd1460ac524d081026e24ff5f9a8522
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
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index: climate_gpt_only_giec
vector_id: 34737
content:
"With the recent increase in ocean sampling by Argo to 2000 m \r\n(Roemmich et al., 2015; Riser et al., 2016; von Schuckmann et al., \r\n2016) and the resulting improvements in estimates of ocean heat \r\ncontent (Abraham et al., 2013; Balmaseda et al., 2013; Durack et al., \r\n2014b; Cheng et al., 2017; von Schuckmann et al., 2020), a more \r\nquantitative assessment of the global ocean heat content changes \r\nthat extends into the intermediate ocean (700-2000 m) over the \r\nmore recent period (from 2005 to the present; Durack et al., 2018) \r\ncan be performed. Observed ocean heat content changes are \r\ndiscussed in Section 2.3.3.1, where it is reported that it is virtually \r\ncertain that the global upper ocean (0-700 m) and very likely that "


id: f22b8503283e3a5d9dd80191ac153fa6
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 35633
content:
"The tropical Indian Ocean mean state is reasonably well simulated both \r\nin CMIP5 and CMIP6 (Figure 3.24b,c). However, CMIP5 models show "


id: a3addc6544b1c8474e4a09f783f9ccc0
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 23313
content:
"et al., 2019; Tokarska et al., 2019). Temporary (<10 years) surface \r\nand subsurface cooling during and after large volcanic eruptions \r\nis also captured in the upper-ocean, and global mean ocean heat \r\ncontent (Balmaseda et al., 2013). The ocean heat content increase is \r\nalso reflected in the corresponding ocean thermal expansion which is \r\na leading contributor to global mean sea level rise (Sections 3.5.3.2 \r\nand 9.2.4, and Box 9.1)."


id: 8601a8a35dabbabcd88681df189c4948
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 18619
content:
"For the period 1971-2014, the rate of ocean heat uptake for the \r\nglobal ocean in the CMIP6 models is about 6.43 [2.08-8.66] \r\nZJ yr-1, with the upper, intermediate and deeper layers respectively \r\naccounting for 68%, 16% and 16% of the full depth global heat \r\nuptake (Figure  3.26). Overall, the simulated ocean heat content \r\nchanges are consistent with the updated and improved observational \r\nanalyses, within the very likely uncertainty range defined for each \r\n(see also Section 2.3.3.1, Table 2.7; Domingues et al., 2008; Purkey \r\nand Johnson, 2010; Levitus et al., 2012; Good et al., 2013; Cheng \r\net al., 2017; Ishii et al., 2017; Zanna et al., 2019) as well as with the \r\nocean components of total Earth heating assessed in Section 7.2.2.2, \r\nTable  7.1. Nevertheless, large uncertainties remain, particularly in \r\nthe deeper layers due to the poor temporal and spatial sampling \r\ncoverage, particularly in the Atlantic, Southern and Indian Oceans "


id: eb74aab8ac34711dca7da0de52af3895
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
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index: climate_gpt_only_giec
vector_id: 34541
content:
"The multi-model means of both CMIP5 and CMIP6 historical \r\nsimulations forced with time varying natural and anthropogenic \r\nforcing shows robust increases in ocean heat content in the upper \r\n(0-700 m) and intermediate (700-2000 m) ocean (high confidence) \r\n(Figure 3.26; Cheng et al., 2016, 2019; Gleckler et al., 2016; Bilbao "


id: 603187348c5783e954989c3a0d780907
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
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index: climate_gpt_only_giec
vector_id: 12707
content:
"(Garry et al., 2019). The very likely ranges of the simulated trends \r\nfor the full ocean depth and below 2000 m fall within the very \r\nlikely range of observed uptake during the last two decades. In the \r\nintermediate layer, the multi-model ensemble mean mostly stays \r\nabove the observed 5th-95th percentile range before the year \r\n2000, and below that range after 2000. For the upper ocean, some \r\nindividual model realizations show a reduced ocean heat content \r\nincrease during the 1970s and 1980s, which is then compensated \r\nby a greater warming than the observations from the early 1990s. \r\nThese discrepancies have been linked with a temporary increase in \r\nthe Southern Ocean deep water formation rate, as well as with the \r\nmodels' strong aerosol cooling effects and high equilibrium climate \r\nsensitivity (see also Section 7.5.6 and Box 7.2; Andrews et al., 2019, \r\n2020; Golaz et al., 2019; Dunne et al., 2020; Winton et al., 2020)."


id: ef7a0267cd1c7508cd81d2734309da63
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 35167
content:
"deeper ocean (very high confidence). Updated observations, like \r\nmodel simulations, show that warming extends throughout the \r\nentire water column (high confidence)."


id: 7f4b075429bbd99fa1e98970a518bf8f
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 17580
content:
"Nevertheless, simulations show that the rate of ocean heat uptake \r\nhas doubled in the past few decades, when contrasted to the rate \r\nover the complete 20th century (Figure 3.26), with over a third of \r\nthe accumulated heat stored below 700 m (Cheng et al., 2016, 2019; \r\nGleckler et al., 2016; Durack et al., 2018). The Southern Ocean shows \r\nthe strongest ocean heat uptake that penetrates to deeper layers \r\n(Section 9.2.3.2), whereas ocean heat content increases in the Pacific \r\nand Indian Oceans largely occur in the upper layers (Bilbao et al., \r\n2019)."


id: 5edd2a8f30c9fba919396dad80e7424b
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 12467
content:
"Unlike SSTs, simulated sea surface salinity (SSS) does not provide \r\na direct feedback to the atmosphere. However, some recent work \r\nhas identified indirect radiative feedbacks through sea-salt aerosol \r\ninteractions (Ayash et al., 2008; Amiri-Farahani et al., 2019; Z. Wang \r\net al., 2019) that can act to strengthen tropical cyclones, and increase \r\nprecipitation (Balaguru et al., 2012, 2016; Grodsky et al., 2012; Reul \r\net al., 2014; Jiang et al., 2019). The absence of a direct feedback is one \r\nof the primary reasons why salinity simulation is difficult to constrain \r\nin ocean modelling systems, and why deviations from the observed \r\nnear-surface salinity mean state between models and observations \r\nare often apparent (Durack et al., 2012; Shi et al., 2017)."


id: 1d3929789bb3029d9ff27cb42d9a2fad
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
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index: climate_gpt_only_giec
vector_id: 2038
content:
"When compared to the routine assessment of simulated SST, \r\nsimulated SSS has not received the same research attention at \r\nglobal- to basin-scales. For CMIP3, there was reasonable agreement \r\nbetween the basin-scale patterns of salinity, with a comparatively \r\nfresher Pacific when contrasted to the salty Atlantic, and basin \r\nsalinity maxima features aligning well with the corresponding \r\natmospheric evaporation minus precipitation field (Durack et al., \r\n2012). Similar features are also reproduced in CMIP5 along with \r\nrealistic variability in the upper layers, but less variability than \r\nobservations at 300 m and deeper, especially in the poorly sampled "


id: 99783d89451c7698afbb9b0f51a2e779
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 21668
content:
"In summary, there is strong evidence for an improved understanding \r\nof the observed global ocean heat content increase. It is extremely \r\nlikely that human influence was the main driver of the ocean heat \r\ncontent increase observed since the 1970s, which extends into the "


id: 384ca0c0f8b5eab3fcbc7dc8d5649aa
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 6234
content:
"Antarctic region (Pierce et al., 2012). In a regional study, only \r\nconsidering the Indian Ocean, CMIP5 SSS was assessed and it \r\nwas shown that model biases were primarily linked to biases in \r\nthe precipitation field, with ocean circulation biases playing a \r\nsecondary role (Fathrio et al., 2017a). The sea surface salinity bias \r\nin CMIP6 models is shown in Figure 3.23b."


id: 63b955b4b8ba9eb3b14fef554608935b
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 13257
content:
"AR5 concluded that it was very likely that anthropogenic forcings \r\nhad made a discernible contribution to surface and subsurface ocean \r\nsalinity changes since the 1960s (Bindoff et al., 2013; Rhein et al., \r\n2013). It highlighted that the spatial patterns of salinity trends, and \r\nthe mean fields of salinity and evaporation minus precipitation are all \r\nsimilar, with an enhancement to Atlantic Ocean salinity and freshening \r\nin the Pacific and Southern Oceans. Since AR5 all subsequent work \r\non assessing observed and modelled salinity changes has confirmed \r\nthese results."


id: 24113283b46dd44ded051f2b4b28b7fa
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 3118
content:
"For the first time in AR5, alongside global zonal mean temperature, \r\nglobal zonal mean salinity bias with depth was assessed for \r\nthe CMIP5 models. This showed a strong upper ocean (<300 m) \r\nnegative salinity (fresh) bias of order 0.3 PSS-78, with a tendency \r\ntoward a positive salinity (salty) bias (<0.25 PSS-78) in the Northern \r\nHemisphere intermediate layers (200-3000 m) (Flato et al., 2013). \r\nThese biases are also present in CMIP6, albeit with slightly smaller \r\nmagnitudes (Figure  3.25). Here we expand the global zonal mean \r\nbias assessment to consider the three independent ocean basins \r\nindividually, which allows for an assessment as to which basin \r\nbiases are dominating the global zonal mean. The basin with the \r\nmost pronounced biases is the Atlantic, with a strong upper ocean \r\n(<300 m) fresh bias, of order 0.3 PSS-78 just like the global zonal \r\nmean, and a marked subsurface salinity bias that exceeds 0.5 PSS-78 \r\nin equatorial waters between 400-1000 m."


id: 109412f50447e6d7c75bce778d44b2a3
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 87
content:
"Considerable changes to observed broad- or basin-scale ocean \r\nnear-surface salinity fields have been reported (see Section 2.3.3.2), \r\nand these have been linked to changes in the evaporation minus \r\nprecipitation patterns at the ocean surface through model simulations, \r\ntypically expressing a pattern of change where climatological mean \r\nfresh regions become fresher and corresponding salty regions \r\nbecoming saltier (Durack et al., 2012, 2013; Zika et al., 2015; Lago \r\net al., 2016; Skliris et al., 2016, 2018; Cheng et al., 2020), also broadly \r\npresent in the CMIP6 multi-model mean (Figure 3.27). At basin-scales, "


id: 2788ec51b20e03c20bda8f6cf95e7ba1
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 3624
content:
"The Pacific Ocean shares the strongest similarity to the global bias, \r\nwith a similar upper ocean (<300 m) fresh bias. Lower magnitude \r\npositive salinity biases (about 0.3 PSS-78) are also present in both \r\nhemispheres between 200 and 3000 m, and deeper in the Southern \r\nHemisphere (Figure 3.25). The Indian Ocean shows similar features \r\nto the Southern Hemisphere Pacific, with a marked upper ocean \r\n(<500 m) fresh bias of order 0.3 PSS-78, and a strong near-surface \r\npositive bias of order 0.4 PSS-78 associated with the Arabian Sea \r\n(Figure 3.25)."


id: dc0337b2ef7d5665f80f40af4924b101
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 32129
content:
"For the Southern Ocean in CMIP5, considerable fresh biases \r\nexist through the water column, and are most pronounced in the \r\nventilated layers representing the subtropical mode and intermediate \r\nwater masses (Sallee et al., 2013). A fresh bias in upper and \r\nintermediate layers of comparable magnitude is also seen in CMIP6 \r\n(Figure 3.25). The structure of the biases in the CMIP6 multi-model \r\nmean (which averages across many simulations with differing \r\nsubsurface geographies and differing Southern Ocean salinity \r\nbiases (Beadling et al., 2020)) is similar to that evident in the CMIP5 \r\nmulti-model mean, but with slightly smaller magnitudes. The Arctic \r\nOcean also on average exhibits a surface-enhanced fresh bias in the \r\nupper ocean (Figure 3.25), which is much larger than its Southern \r\nHemisphere counterpart."


id: 450140b05e4673d9fbcf6bc31c31951a
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vector_id: 8284
content:
"In summary, the structure of the salinity biases in the multi-model \r\nmean has not changed substantially between CMIP5 and CMIP6 \r\n(medium confidence), though there is limited evidence that the \r\nmagnitude of subsurface biases has been reduced. Biases are \r\nsufficiently small to provide confidence in the utility of CMIP-class \r\nmodels for detection and attribution of ocean salinity."


id: 4b2db27731f2b5a52f771c3c428b70f8
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
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vector_id: 9249
content:
"Figure 3.27 | Maps of multi-decadal salinity trends for the near-surface \r\nocean. Units are Practical Salinity Scale 1978 [PSS-78] per decade. (Top) The best \r\nestimate (Section 2.3.3.2) observed trend (1950-2019, Durack and Wijffels, 2010). \r\n(Bottom) Simulated trend from the CMIP6 historical experiment multi-model mean \r\n(1950-2014). Black contours show the climatological mean salinity in increments of \r\n0.5 PSS-78 (thick lines 1 PSS-78). Further details on data sources and processing are \r\navailable in the chapter data table (Table 3.SM.1)."


id: dde96f56d4c8b8e0ccac4f39d1ca9608
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
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vector_id: 32409
content:
"the depth-integrated effect of mean salinity changes as captured in \r\nhalosteric sea level for the top 0 to 2000 m has also been assessed \r\nbased on observational products, and these results mirror near-surface \r\npatterns in the CMIP5 and CMIP6 models, with most areas that are \r\nbecoming fresher at the surface exhibiting increases in halosteric sea \r\nlevel, and areas becoming saltier exhibiting decreases (Durack et al., \r\n2014a; Figure  3.28). Further investigations using observations and \r\nmodels together have tied the long-term patterns of surface and \r\nsubsurface salinity changes to coincident changes to the evaporation "


id: 5220c9ab85f986af93e7eb048ec7b8d0
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 10374
content:
"minus precipitation field over the ocean (Durack et al., 2012, 2013; \r\nDurack, 2015; Levang and Schmitt, 2015; Zika et al., 2015, 2018; Grist \r\net al., 2016; Lago et al., 2016; Cheng et al., 2020), however the rate of \r\nthese changes through time continues to be an active area of active \r\nresearch (Skliris et al., 2014; Zika et al., 2015, 2018; Cheng et al., \r\n2020; Sallee et al., 2021)."


id: 9bebe4e915e259504f7fa1c159d45ed0
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 22087
content:
"Climate change detection and attribution studies have considered \r\nsalinity, with the first of these assessed in AR5 (Bindoff et al., 2013). Since "


id: e177668e659d33d59986cceddce78a08
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 32965
content:
"change have focused on thermosteric sea level changes (i.e., thermal \r\nexpansion due to warming) and ocean dynamic sea level change, \r\nboth of which are simulated in the CMIP5-generation of models. \r\nThe improved agreement between modelled thermal expansion and \r\nobserved estimates during the historical period led the SROCC to \r\nassess a high confidence level in the simulated thermal expansion \r\nusing climate models and high confidence in their ability to project \r\nfuture thermal expansion."


id: d736951826f7d000988d651ab4d2d8c1
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 31375
content:
"that time, the positive detection conclusions (Stott et al., 2008; Pierce \r\net al., 2012; Terray et al., 2012) have been supported by a number of \r\nmore recent and independent assessments which have reproduced the \r\nmulti-decadal basin-scale patterns of change in observations and models \r\n(Figures 3.27 and 3.28; Durack et al., 2014a; Durack, 2015; Levang and \r\nSchmitt, 2015; Skliris et al., 2016). Observed depth-integrated basin \r\nresponses, contrasting the Pacific and Atlantic basins (freshening Pacific \r\nand enhanced salinity Atlantic) were also shown to be replicated in most \r\nhistorical (natural and anthropogenically forced) simulations, with \r\nthis basin contrast absent in CMIP5 and CMIP6 natural-only simulations \r\nthat exclude anthropogenic forcing (Durack et al., 2014a; Figure 3.28)."


id: f168cc3e57dc0eb21269d15eb6999128
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 35488
content:
"Since CMIP5 models do not include all necessary components of sea \r\nlevel change, this gap has been bridged by using offline models (for \r\nglacier melt and ice-sheet surface mass balance) driven by reanalyses \r\nand model output. Some studies have used offline mass inputs to \r\naccount for dynamic ice-sheet and terrestrial contributions. Slangen \r\net al. (2017) and Meyssignac et al. (2017) suggested including \r\ncorrections to several contributions to sea level changes including to \r\nthe Greenland surface mass balance and glacier contributions, based \r\non differences between CMIP5-driven model results and reanalysis\u0002driven results. This helps close the gap between models and \r\nobservations for the 20th century globally, as well as providing better \r\nagreement with tide gauge observations in terms of interannual and \r\nmulti-decadal variability at the regional scale."


id: 863882c880aeb2c4e974f687d41cc1b3
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 18658
content:
"While observational sparsity considerably limits quantification of \r\nregional changes, a recent study by Friedman et al. (2017) assessed \r\nsalinity changes in the Atlantic Ocean from 1896 to 2013 and \r\nconfirmed the pattern of mid-to-low latitude enhanced salinity \r\nand  high latitude North Atlantic freshening over this period exists \r\neven after accounting for the effects of the NAO and AMO."


id: 5eb4676c9d5be3e0f639e6932b818231
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 12438
content:
"In CMIP6, ice sheets (see Sections 3.4.3.2 and 9.4) are included for \r\nthe first time in ISMIP6 (Nowicki et al., 2016). There is also scope \r\nfor  new insights into terrestrial water contributions from land \r\nsurface (and sub-surface) modelling in the Land Surface, Snow and \r\nSoil moisture Model Intercomparison Project (LS3MIP; van den Hurk \r\net al., 2016). In parallel, the GlacierMIP project (Hock et al., 2019a; \r\nMarzeion et al., 2020; see Sections 3.4.3.1 and 9.5) is also underway, \r\nand has provided more quantitative guidance and a comprehensive \r\nassessment of the uncertainties and best estimates of the current and \r\nfuture contributions of glaciers to the sea level budget."


id: b591972674327c173db24671b09af4a5
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 26098
content:
"The SROCC concluded with high confidence that the dominant \r\ncause of GMSL rise since 1970 is anthropogenic forcing. Prior to \r\nthat, AR5 had concluded that it is very likely that there has been \r\na  substantial contribution from anthropogenic forcings to GMSL \r\nrise since the 1970s. Since AR5, several studies have identified \r\na human contribution to observed sea level change resulting from \r\na warming climate as manifest in thermosteric sea level change and \r\nthe contribution from melting glaciers and ice sheets."


id: 2019c4a01c9dfe418fae74783b09b9d8
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 2496
content:
"In keeping with the scope of this chapter, this section addresses \r\nglobal and basin-scale sea level changes, whereas regional and local \r\nsea level changes are assessed in Section 9.6. In AR5, the observed \r\nsea level budget was closed by considering all contributing factors \r\nincluding ocean warming, mass contributions from terrestrial \r\nstorage, glaciers, and the Antarctic and Greenland ice sheets \r\n(Church et al., 2013b). The SROCC found that the observed global \r\nmean sea level (GMSL) rise is consistent within uncertainties with \r\nthe sum of the estimated observed contributions for 1993-2015 \r\nand 2006-2015."


id: 359d16ed896092ff504acb3739cc1731
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 5841
content:
"For the global mean thermosteric sea level change, Slangen et al. \r\n(2014) showed the importance of anthropogenic forcings (combined \r\ngreenhouse gas and aerosol forcings) for explaining the magnitude \r\nof the observed changes between 1957 and 2005, considering the \r\nfull depth of the ocean and natural forcings in order to capture the \r\nvariability (see also Figure 3.29). Over the 1950-2005 period, Marcos \r\nand Amores (2014) found that human influence explains 87% of \r\nthe 0-700 m global thermosteric sea level rise. Both thermosteric \r\nand regional dynamic patterns of sea level change in individual \r\nforcing experiments from CMIP5 were considered by Slangen et al. \r\n(2015) who showed that responses to anthropogenic forcings are \r\nsignificantly different from both internal variability and inter-model "


id: ae8052eb4ae04d3cfbcffe7e3134130b
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 24985
content:
"The current generation of climate models do not fully resolve many \r\nof the components required to close the observed sea level budget, \r\nsuch as glaciers, ice sheets and land water storage (see Section 9.6 \r\nand Box 9.1). Consequently, most CMIP-based analyses of sea level "


id: c374b290482f78f42e3bb56484114c09
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
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index: climate_gpt_only_giec
vector_id: 28322
content:
"a 95% probability that by 1970 GMSL was higher than that which \r\nwould have occurred in the absence of increasing GMST (Kopp et al., \r\n2016). Richter et al. (2020) compared modelled sea level change \r\nwith the satellite altimeter observations from 1993 to 2015; a period \r\nshort enough that internal variability can dominate the spatial \r\npattern of change. They found that when GMSL is not removed, \r\nmodel simulated zonally averaged sea level trends are consistent \r\nwith altimeter observations globally as well as in each ocean basin \r\nand much larger than might be expected from internal variability. \r\nUsing spatial correlation, Fasullo and Nerem (2018) showed that the \r\nsatellite altimeter trend pattern is already detectable."


id: e0e7aabb0e74f3a717654132ed99b53c
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 32883
content:
"differences and that although greenhouse gas and anthropogenic \r\naerosol forcings produce opposite GMSL responses, there are \r\ndifferences in the response on regional scales. Based on these \r\nstudies, we conclude that it is very likely that anthropogenic forcing \r\nwas the main driver of the observed global mean thermosteric sea \r\nlevel change since 1970."


id: ffc09dfcf2fe5ce361decaf8c4ceba38
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 37782
content:
"We note that current detection and attribution studies do not \r\nyet include all processes that are important for sea-level change \r\n(see Section 9.6). However, based on the body of literature available, \r\nwe conclude that the main driver of the observed GMSL rise since \r\nat least 1971 is very likely anthropogenic forcing. The assessed \r\nperiod starts in 1971 for consistency with observations assessed in \r\nCross-Chapter Box 9.1."


id: 555eb7ff2d9f33ca2a5cde3e35bebd80
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 10901
content:
"Circulation of the ocean, whether it be wind or density driven, plays \r\na prominent role in the heat and freshwater transport of the Earth \r\nsystem (Buckley and Marshall, 2016). Thus, its accurate representation \r\nis crucial for the realistic representation of water mass properties, and \r\nreplication of observed changes driven by atmosphere-land-ocean \r\ncoupling. Here, we assess the ability of CMIP models to reproduce \r\nthe observed large-scale ocean circulation, along with assessment \r\nof the detection and attribution of any anthropogenically-driven \r\nchanges. We also note that the process-based understanding of these \r\ncirculation changes and circulation changes occurring at smaller \r\nscales is assessed in Section 9.2.3."


id: 795a952c049477e85bcfe300b9c4d1e4
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 16664
content:
"The Atlantic Meridional Overturning Circulation (AMOC) represents \r\na large-scale flow of warm salty water northward at the surface \r\nand a return flow of colder water southward at depth. As such, \r\nits mean state plays an important role in transporting heat in the \r\nclimate system, while its variability can act to redistribute heat (see \r\nSections 2.3.3.4.1 and 9.2.3.1 for more details). Paleo-climatic and \r\nmodel evidence suggest that changes in AMOC strength have played \r\na prominent role in past transitions between warm and cool climatic \r\nphases (e.g., Dansgaard et al., 1993; Ritz et al., 2013)."


id: 8dd3fa9470bef58477d2eba136da0150
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 19842
content:
"The AR5 concluded that while climate models suggested that an \r\nAMOC slowdown would occur in response to anthropogenic forcing, \r\nthe short direct observational AMOC record precluded it from being \r\nused to support this model finding. Chapter  2 reports with high \r\nconfidence, a weakening of the AMOC was observed in the mid-2000s \r\nto the mid-2010s, while again also noting that the observational \r\nrecord was too short to determine whether this is a significant \r\ntrend or a manifestation of decadal and multi-decadal variability \r\n(Section  2.3.3.4.1). Indirect evidence of AMOC weakening since at \r\nleast the 1950s is also presented, but confidence in this longer-term \r\ndecrease was low (Section 2.3.3.4.1)."


id: 47832a0172107c515f8b5846e1a08768
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
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vector_id: 8637
content:
"simulations (Robson et al., 2012; Danabasoglu et al., 2016), which \r\nshow AMOC changes that are broadly consistent with the CMIP6 \r\nresponse, appear to disagree with observational estimates of AMOC \r\nover the historical period (Ezer et al., 2013; Caesar et al., 2018). It is \r\nnoted, however, that the relatively short length of the forced ocean \r\nsimulations and ocean reanalysis precludes a comparable assessment \r\nof 20th century trends. Furthermore, despite the similar AMOC \r\nevolution seen in forced ocean model simulations and the CMIP6 \r\nmodels, it is unclear whether the same underlying mechanisms are \r\nresponsible for the changes."


id: 5ac1dcf255dae9d8fca71d62b15b8bda
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
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vector_id: 11791
content:
"As  such, the simulated net forced response in AMOC is a balance \r\nbetween the different forcing factors (Section 9.2.3.1; Delworth and \r\nDixon, 2006; Menary et al., 2020). The differing AMOC response of \r\nCMIP5 and CMIP6 models during the historical period has been \r\nassociated with stronger aerosol effective radiative forcing in the \r\nCMIP6 models (Menary et al., 2020), such that the aerosol-induced \r\nAMOC increase during the 1940-1985 period overcomes the \r\ngreenhouse gas induced decline (Figure  3.30e). However, models \r\nsimulate a range of anthropogenic aerosol effective radiative forcing \r\nand a range of historical AMOC trends in CMIP6 (Menary et al., 2020) \r\nand there remains considerable uncertainty over the realism of the \r\nCMIP6 AMOC response during the 20th century (Figure 3.30d-f) due \r\nto disagreement among the differing lines of evidence. For example, \r\nocean reanalysis (Jackson et al., 2019) and forced ocean model "


id: e9e6b2fffd4efb85a5d4ddc2290cf4eb
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 34299
content:
"overturning (Sallee et al., 2013). As the lower overturning cell is \r\nclosely related to Antarctic Bottom Water formation and deep \r\nconvection, both fields also display substantial errors in CMIP5 \r\nmodels (Heuze et al., 2013, 2015). CMIP6 climate models show \r\nclear improvements compared to CMIP5 in their representation of \r\nAntarctic Bottom Water, which suggests an improved representation \r\nof the lower overturning cell (Heuze, 2021)."


id: 8d4665213310ae495db5e06ddb409d53
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 19751
content:
"to have occurred with high confidence in Section 2.3.3.4.1, as \r\nthe changes are outside of the range of modelled AMOC trends \r\n(regardless of whether they are forced or internally generated) in \r\nmost models. Thus, we have low confidence that anthropogenic \r\nforcing has influenced the observed changes in AMOC strength \r\nin the post-2004 period. In addition, there remains considerable \r\nuncertainty over the realism of the CMIP6 AMOC response during \r\nthe 20th century due to disagreement among the differing lines \r\nof observational and modelled evidence (i.e., historical AMOC \r\nestimates, ocean reanalysis, forced ocean simulations and \r\nhistorical CMIP6 simulations). Thus, we have low confidence that \r\nanthropogenic forcing has had a significant influence on changes \r\nin AMOC strength during the 1860-2014 period."


id: c098855840e81ebc6f5b0b4e4f77fbfd
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 27863
content:
"The Southern Ocean circulation provides the principal connections \r\nbetween the world's major ocean basins through the circulation of \r\nthe Antarctic Circumpolar Current (ACC), while also largely controlling \r\nthe connection between the deep and upper layers of the global \r\nocean circulation, through its upper and lower overturning cells."


id: 50e7faf275f6b7fb35be1359ea18c464
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 10177
content:
"The assessment of observations presented in Sections 2.3.3.4.2 \r\nand 9.2.3.2 reports that there is no evidence of an ACC transport \r\nchange, and it is unlikely that the mean meridional position of the \r\nACC has moved southward in recent decades (Sections 2.3.3.4.2 \r\nand 9.2.3.2). This is despite observations of surface wind displaying \r\nan intensification and southward shift (Section 2.4.1.2). There \r\nis low confidence in an observed intensification of upper ocean \r\noverturning in the Southern Ocean and there is medium confidence\r\nfor a slowdown of the Antarctic Bottom Water circulation and \r\ncommensurate Antarctic Bottom Water volume decrease since the \r\n1990s (Section 9.2.3.2). Section 9.2.3.2 presents new evidence, since \r\nSROCC, which assessed with medium confidence that the lower \r\ncell can episodically increase as a response to climatic anomalies, \r\ntemporally counteracting the forced tendency for reduced bottom \r\nwater formation."


id: 6ba3fd34d7daf0d9ea8c90a33000e76d
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 14561
content:
"In summary, while there have been improvements across successive \r\nCMIP phases (from CMIP3 to CMIP6) in the representation of \r\nthe Southern Ocean circulation, such that the mean zonal and \r\noverturning circulations of the Southern Ocean are now broadly \r\nreproduced, substantial observational uncertainty and climate \r\nmodel challenges preclude attribution of Southern Ocean circulation \r\nchanges (high confidence)."


id: f5fb1db95eef2bc343b79a277a4d8433
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 36212
content:
"and land management options (Erb et al., 2018; Harper et al., 2018) \r\n(see Sections 5.2.1.4.1 and 5.4, Figure 5.24 and Table 5.4 for details)."


id: 80fa626027f9dc05452cc615363af4a2
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 17813
content:
"Leaf area index increases attributed to CO2 fertilization are due \r\nto a direct raised physiological response. However, for drylands, \r\nCO2-induced stomatal closure may act to conserve soil moisture and \r\nthereby indirectly drive higher photosynthesis through higher water \r\nuse efficiency (Lu et al., 2016). In models with nitrogen deposition, \r\nthere is evidence that this simulated effect also influences leaf area \r\nindex trends, however, because of a lack of literature based on \r\nlarge-scale land simulations including both nutrient limitation and \r\ncrop intensification, it is not yet possible to make an attribution \r\nstatement about their individual roles in leaf area index changes."


id: 7ac7de72a9d45b48d717ee9d86552714
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 16898
content:
"In summary, Earth system models simulate globally averaged land \r\ncarbon sinks within the range of observation-based estimates \r\n(high confidence), but global-scale agreement masks large \r\nregional disagreements. Based on new studies that attribute \r\nchanges in atmospheric CO2 seasonal cycle to CO2 fertilization, \r\nalbeit counteracted by other factors, combined with the medium \r\nconfidence that models represent the processes driving changes in "


id: e8719cc830766c1a9b6dd13e8059e912
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 34077
content:
"carbon fluxes and surface chlorophyll concentrations show moderate \r\nimprovements between CMIP5 and CMIP6. Similar improvements are \r\nseen in the representation of subsurface oxygen concentrations in \r\nmost ocean basins, while the representation of surface macronutrient \r\nconcentrations in CMIP6 is shown to have improved with respect \r\nto silicic acid but declined slightly with respect to nitrate. Model \r\nrepresentation of the micronutrient iron has not improved substantially \r\nsince CMIP5, but many more models are capable of representing iron. \r\nIn addition, a comparison of the carbon concentration and carbon \r\nclimate feedbacks shows no significant change between CMIP5 and \r\nCMIP6 (Arora et al., 2020)."


id: 63cbc31c931d9dd6bcfdb566eb229a79
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 13271
content:
"Since AR5, research has also focused on the detection and attribution \r\nof regional patterns in ocean biogeochemical change relating to \r\ninterior deoxygenation, air-sea CO2 flux, and ocean carbon uptake and \r\nassociated acidification. Characterization of flux variability requires \r\nunderstanding of the suite of physical and biological processes \r\nincluding transport, heat fluxes, interior ventilation, biological \r\nproduction and gas exchange which can have very different controls \r\non seasonal versus interannual time scales in both the North Pacific \r\n(Ayers and Lozier, 2012) and North Atlantic (Breeden and McKinley, \r\n2016). In the Southern Ocean, models have difficulty reproducing \r\nthe observed seasonal cycle and interannual variability, making \r\nattribution particularly challenging (Lovenduski et al., 2016; Mongwe \r\net al., 2016, 2018)."


id: 9271b4b765be09fefc0e2792386b28e4
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 20562
content:
"the seasonal cycle, we assess that there is medium confidence that \r\nCO2 fertilization is the main driver of the increase in the amplitude of \r\nthe seasonal cycle of atmospheric CO2. Based on available literature, \r\nCO2 fertilization has been the main driver of the observed greening \r\ntrend, but there is only low confidence in this assessment because \r\nof ongoing debate about the relative roles of CO2 fertilization, high \r\nlatitude warming, and land management, and the low number of \r\nmodels that represent the whole suite of processes involved."


id: 196a72de2066a811f7f6ee1d58d9b1a9
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
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index: climate_gpt_only_giec
vector_id: 1483
content:
"Since CMIP5, there has been a general increase in ocean horizontal and \r\nvertical grid resolution in ocean model components (Arora et al., 2020; \r\nSeferian et al., 2020). The latter of these developments is particularly \r\nsignificant for projections of ocean stressors as it directly affects the \r\nrepresentation of stratification. Updates in the representation of ocean \r\nbiogeochemical processes between CMIP5 and CMIP6 have typically \r\ninvolved an increase in model complexity. Specific developments have \r\nbeen the more widespread inclusion of micronutrients, such as iron, \r\nvariable stoichiometric ratios, more detailed representation of lower \r\ntrophic levels including bacteria and the cycling and sinking of organic \r\nmatter. CMIP6 biogeochemical model performance is generally an \r\nimprovement on that of the parent CMIP5 generation of models \r\n(Seferian et al., 2020). The global representation of present-day air-sea "


id: 7a6b57bda457cb1419c3b7fe29e59fdf
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 16833
content:
"(Perez et al., 2018). There has also been considerable improvement in \r\ndetection and attribution of anthropogenic CO2 versus eutrophication\u0002based acidification in coastal waters (Wallace et al., 2014)."


id: a674367e27410e265761153260b2eed7
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 23717
content:
"deoxygenation. The spatial distribution of the ocean deoxygenation \r\nin the interior of the ocean as well as over coastal areas is further \r\nassessed in Section 5.3."


id: e705407226767dbaac874145d23ecff5
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 33836
content:
"The increased evidence in recent studies supports an assessment that \r\nit is virtually certain that the uptake of anthropogenic CO2 was the \r\nmain driver of the observed acidification of the global surface open \r\nocean. The observed increase in acidification over the North Atlantic \r\nsubtropical and equatorial regions since 2000 is likely associated \r\nin part with an increase in ocean temperature, a response which \r\ncorresponds to the expected weakening of the ocean carbon sink with \r\nwarming. Due to strong internal variability, systematic changes in \r\ncarbon uptake in response to climate warming have not been observed \r\nin most other ocean basins at present. We further assess, consistent \r\nwith AR5 and SROCC, that deoxygenation in the upper ocean is due \r\nin part to anthropogenic forcing, with medium confidence. There is \r\nhigh confidence that Earth system models simulate a realistic time \r\nevolution of the global mean ocean carbon sink."


id: 92b45429081b2acfe8fdf54479ca4fc
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 20595
content:
"This section assesses model evaluation and attribution of changes \r\nin the modes of climate variability listed in Cross-Chapter Box 2.2, \r\nTable 2. The structure of the modes is described in Annex IV, observed \r\nchanges in the modes and associated teleconnections are assessed \r\nin Section 2.4, and the role of the modes in shaping regional climate \r\nis assessed in Section 10.1.3.2."


id: c733ee17fd0f2da859bd64d645953476
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 28929
content:
"Section 5.2.1.3 assesses that both observational reconstructions \r\nbased on the partial pressure of CO2 and ocean biogeochemical models \r\nshow a quasi-linear increase in the ocean sink of anthropogenic CO2\r\nfrom 1.0 +- 0.3 PgC yr-1 to 2.5 +- 0.6 PgC yr -1 between 1960-1969 and \r\n2010-2019 in response to global CO2 emissions (high confidence). \r\nDuring the 1990s, the global net flux of CO2 into the ocean is \r\nestimated to have weakened to 0.8  +-  0.5  PgC yr -1 while in 2000 \r\nand thereafter, it is estimated to have strengthened considerably \r\nto rates of 2.0 +- 0.5 PgC yr -1, associated with changes in SST, the \r\nsurface concentration of dissolved inorganic carbon and alkalinity, \r\nand decadal variations in atmospheric forcing (Landschutzer et al., \r\n2016, see also Section 5.2)."


id: 783f0e3b6288313025227baf8f517c28
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 16484
content:
"The Northern Annular Mode (NAM; also known as the Arctic \r\nOscillation) is an oscillation of atmospheric mass between the Arctic \r\nand northern mid-latitudes, analogous to the Southern Annular Mode \r\n(SAM; Section 3.7.2). It is the leading mode of variability of sea-level \r\npressure in the northern extratropics but also has a clear fingerprint \r\nthrough the troposphere up to the lower stratosphere, with maximum \r\nexpression in boreal winter (Kidston et al., 2015). The North Atlantic \r\nOscillation (NAO) can be interpreted as the regional expression of the \r\nNAM and captures most of the related variance in the troposphere over \r\na broad North Atlantic/Europe domain. Indices measuring the state of \r\nthe NAO correlate highly with those of the NAM, and teleconnection \r\npatterns for both modes are rather similar (Feldstein and Franzke, \r\n2006). A detailed description of the NAM and the NAO as well as \r\ntheir associated teleconnection over land is given in Annex IV.2.1."


id: 37d42271f7646fb686cb8754d0308027
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
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vector_id: 6156
content:
"AR5 found that while models simulated correctly most of the \r\nspatial properties of the NAM, substantial inter-model differences \r\nremained in the details of the associated teleconnection patterns \r\nover land (Flato et al., 2013). The AR5 reported that most models \r\ndid not reproduce the observed positive trend of the NAO/NAM \r\nindices during the second half of the 20th century. It was unclear \r\nto what extent this failure reflected model shortcomings and/or if \r\nthe observed trend could be simply related to pronounced internal "


id: 4ee86f507e0c4713d40a6674c4331f2e
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 9852
content:
"climate variability. The AR5 accordingly did not make an attribution \r\nassessment for the NAO/NAM."


id: ee2740dce8946fcba9acf733bb0700fa
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 34941
content:
"of trends in the CMIP6 historical simulations, and the observed NAM \r\ntrends over the same period lie above the 90th percentile. There is \r\na tendency for the CMIP5 models to systematically underestimate \r\nthe level of multi-decadal versus interannual variability of the winter \r\nNAO and jet stream compared to observations (X. Wang et al., 2017; \r\nBracegirdle et al., 2018; Simpson et al., 2018). Results from CMIP6 \r\n(Figure 3.33j,k) and over the 1958-2019 period (Figure 3.34a) confirm \r\nthis conclusion and seriously question the ability of the models to \r\nsimulate long-term fluctuations of the NAO/NAM, independently of \r\nits forced or internal origins."


id: 6978d1da549b9bc7e4748b951acd3ab2
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 14188
content:
"Dedicated SST-forced stand-alone atmospheric model experiments \r\n(AMIP) suggest that ocean forcing appears to play a role in decadal \r\nvariability of the NAO and associated fluctuations in the strength \r\nof the jet (Woollings et al., 2015). In particular, Atlantic and Indian \r\nOcean SST anomalies (Fletcher and Cassou, 2015; Baker et al., 2019; \r\nDouville et al., 2019; Dhame et al., 2020) may have contributed \r\nto the long-term positive trend of the winter NAO/NAM over the \r\n20th  century, but there is only low confidence in such a causal \r\nrelationship because of the limitation of the imposed SST approach \r\nin AMIP and the uncertainties in observed SST trends among datasets \r\nused as forcing of the atmospheric model. The representation of \r\nthe NAM and NAO spatial structure is slightly improved in AMIP \r\nensembles (Figure 3.33g,h), which also produce slightly larger trends \r\nthan the historical simulations for the NAO, but not for the NAM."


id: 68992da51c992998ed6593d3731fc70b
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 14048
content:
"When calculated over the most recent two decades, the wintertime \r\nNAM/NAO trend is weakly negative since the mid-1990s (Hanna \r\net al., 2015). Recent studies based on observations (Gastineau and \r\nFrankignoul, 2015) and dedicated modelling experiments (Davini \r\net al., 2015; Peings and Magnusdottir, 2016) suggest that the recent \r\ndominance of negative NAM/NAO could be partly related to the latest \r\nshift of the Atlantic Multi-decadal Variability (AMV) to a warm phase \r\n(Sections 2.4.4 and 3.7.7). Some recent modelling studies also find \r\nthat the Arctic sea ice decline might be partly responsible for more \r\nrecurrent negative NAM/NAO (Peings and Magnusdottir, 2013; B.M. \r\nKim et al., 2014; Nakamura et al., 2015), while other studies do not \r\nrobustly identify such responses in models (see also Cross-Chapter \r\nBox 10.1)."


id: 4fa3ed93a6242ffc4bda469782611271
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 9962
content:
"In contrast to winter, the observed trend of the NAO index over \r\n1958-2014 is overall negative in summer and is associated with \r\nmore recurrent blocking conditions over Greenland, in particular \r\nsince the mid-1990s, thus contributing to the acceleration of melting \r\nof the Arctic sea ice (Section 3.4.1.1) and Greenland Ice Sheet \r\n(Section 3.4.3.2; Fettweis et al., 2013; Hanna et al., 2015; Ding et al., \r\n2017). The origin of the negative trend of the summer NAO has \r\nnot been clearly identified, and is hypothesized to be the result of \r\ncombined influences (Lim et al., 2019), though trends in summertime \r\nNAO should also be interpreted with caution because of the presence \r\nof strong multi-decadal variability. The recent observed negative NAO \r\nprevalence and related blocking over Greenland is not present in any \r\nof the CMIP5 models (Hanna et al., 2018)."


id: c963cb4630d1c62d9a9d59d556743fbd
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 29247
content:
"The observed trend of the NAM and NAO indices is positive in \r\nwinter when calculated from the 1960s (Section 2.4.1.1) but it \r\nincludes large multi-decadal variability, which means that the \r\nnature of the trend should be interpreted with caution (Gillett et al., \r\n2013). The multi-model multi-member ensemble mean of the trend \r\nestimated from historical simulations over that period is very close \r\nto zero for both CMIP5 and CMIP6 (Figures 3.33j,k and 3.34a). Even \r\nif one cannot rule out that 1958-2014 was an exceptional period \r\nof variability, the observational estimates of the wintertime NAO \r\ntrend lie outside the 5th-95th percentile range of the distribution "


id: 90209aaed1d9cedb70e00556f88aa3a6
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 20209
content:
"Regarding the influence of external forcings since pre-industrial \r\ntimes, AR5 noted that CMIP5 models tend to show an increase in the \r\nNAM in response to greenhouse gas increases (Bindoff et al., 2013). "


id: 309663efb0e5dabe0994bba010dfe238
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 5066
content:
"Based on the CMIP5 historical ensemble, Gillett and Fyfe (2013) \r\nhowever showed that such a trend is not significant in all seasons. \r\nA multi-model assessment of eight CMIP5 models found a NAM \r\nincrease in response to greenhouse gases, but no robust influence of \r\naerosol changes (Gillett et al., 2013). As for ozone depletion, there is \r\nno robust detectable influence on long-term trends of the NAO/NAM \r\n(Karpechko et al., 2018) in contrast to the SAM (Section 3.7.2), but \r\nthere are indications that extreme Arctic ozone depletion events and \r\ntheir surface expression are linked to an anomalously strong NAM \r\nepisodes (Calvo et al., 2015; Ivy et al., 2017). However, the direction \r\nof causality here is not clear."


id: e37b803d4de356f77519f661f7991e9f
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 33269
content:
"Conclusions on external forcing influences on the NAM are supported \r\nby CMIP6 results based on single forcing ensembles (Figure 3.34a). \r\nPositive trends are found in historical simulations over 1958-2019 \r\nin boreal winter and are mainly driven by greenhouse gas increases. \r\nNo significant trends are simulated in response to anthropogenic \r\naerosols, stratospheric ozone or natural forcing. Albeit weak and "


id: edbc18aaf0f8ae0a1eb7c8aef527a5a5
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 34866
content:
"The Southern Annular Mode (SAM) consists of a meridional \r\nredistribution of atmospheric mass around Antarctica (Figure 3.33c,f), \r\nassociated with a meridional shift of the jet and surface westerlies \r\nover the Southern Ocean. SAM indices are variously defined as the \r\ndifference in zonal-mean sea level pressure or geopotential height \r\nbetween middle and high latitudes or via a principal-component \r\nanalysis (Annex IV.2.2). Observational aspects of the SAM are \r\nassessed in Section 2.4.1.2."


id: 166be329541beab3dca7eb1e33d87d8d
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 1052
content:
"AR5 assessed that CMIP5 models have medium performance in \r\nreproducing the SAM with biases in pattern (Flato et al., 2013). It \r\nalso concluded that the trend of the SAM toward its positive phase in \r\naustral summer since the mid-20th century is likely to be due in part \r\nto stratospheric ozone depletion, and there was medium confidence \r\nthat greenhouse gases have also played a role (Bindoff et al., 2013). \r\nBased on proxy reconstructions, AR5 found with medium confidence \r\nthat the positive SAM trend since 1950 was anomalous compared \r\nto the last 400 years (Masson-Delmotte et al., 2013)."


id: 7f2556f252860c797e29c66d46b87d0b
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 17555
content:
"Finally, there is some evidence of an apparent signal-to-noise \r\nproblem referred to as 'paradox' in seasonal and decadal hindcasts \r\nof the NAO over the period 1979-2018 (Scaife and Smith, 2018), \r\nwhich suggests that the NAO response to external forcing, SST or \r\nsea ice anomalies could be too weak in models. The weakness of the \r\nsignal has been related to troposphere-stratosphere coupling which \r\nis too intermittent (O'Reilly et al., 2019b) and to chronic model biases \r\nin the persistence of NAO/NAM daily regimes, which is critically \r\nunderestimated in coupled models (Strommen and Palmer, 2019; \r\nZhang and Kirtman, 2019), and which does not exhibit significant \r\nimprovement when model resolution is increased (Fabiano et al., \r\n2020). Note, however, that the apparent signal-to-noise problem may \r\nbe dependent on the period analysed over the 20th century, which \r\nquestions its interpretation as a general characteristic of coupled \r\nmodels (Weisheimer et al., 2020)."


id: 1147aef9fd4e3faa3920f07e3bdb3207
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 197
content:
"In summary, CMIP5 and CMIP6 models are skilful in simulating the \r\nspatial features and the variance of the NAM/NAO and associated \r\nteleconnections (high confidence). There is limited evidence for \r\na significant role for anthropogenic forcings in driving the observed \r\nmulti-decadal variations of the NAM/NAO from the mid 20th century. \r\nConfidence in attribution is low: (i) because there is a large spread in the \r\nmodelled forced responses which is overwhelmed anyway by internal \r\nvariability; (ii) because of the apparent signal-to-noise problem; and (iii) \r\nbecause of the chronic inability of models to produce a range of trends \r\nwhich encompasses the observed estimates over the last 60 years."


id: b7b5f1a86e01f46ebab0db947eeeb99c
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 26436
content:
"CMIP6 historical simulations capture the observed positive trend of \r\nthe summertime SAM when calculated from the 1970s to the 2010s \r\n(Figure 3.34b). J.L. Thomas et al. (2015) found that the chance of the \r\nobserved 1980-2004 trend occurring only due to internal variability is \r\nless than 10% in many of the CMIP5 models, and results from CMIP6 \r\nmodels suggest that the chance of the 1979-2019 trend being due "


id: 447ab2adbae3dfe1cfa13567cf9a1428
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 8197
content:
"such as variations in the imposed insolation may be too weak, whether \r\nmodels are insufficiently sensitive to such variations, or whether internal \r\nvariability including that associated with tropical Pacific variability \r\nis under-represented (Abram et al., 2014). The explanation could be \r\na combination of all these factors. However, despite the aforementioned \r\nlimitations of the reconstructions, Section 2.4.1.2 assesses that \r\nthe recent positive trend in the SAM is likely unprecedented in at \r\nleast the past millennium (medium confidence). CMIP5 and CMIP6 \r\nlast-millennium simulations only capture the present anomalous state \r\nduring the final decades of the simulations which are dominated by \r\nhuman influence; this state is also outside the range of simulated \r\nvariability characteristic of pre-industrial times."


id: 98447ac24581681aa6e31e99a0a3d6b5
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 21469
content:
"In summary, it is very likely that anthropogenic forcings have \r\ncontributed to the observed trend of the summer SAM toward its \r\npositive phase since the 1970s. This assessment is supported by \r\nfurther model studies that confirm the human influence on the \r\nsummertime SAM with improved models since AR5. While ozone \r\ndepletion contributed to the trend from the 1970s to the 1990s \r\n(medium confidence), its influence has been small since 2000, \r\nleading to a weaker summertime SAM trend over 2000-2019 \r\n(medium confidence). Climate models reproduce the spatial structure \r\nof the summertime SAM observed since the late 1970s well (high \r\nconfidence). CMIP6 models reproduce the spatiotemporal features \r\nand recent multi-decadal trend of the summertime SAM better than \r\nCMIP5 models (medium confidence). However, there is a large spread \r\nin the intensity of the SAM response to ozone and greenhouse gas \r\nchanges in both CMIP5 and CMIP6 models (high confidence), which "


id: 9136400481c72ae0e201e1c0f3a238c6
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 20386
content:
"On longer time scales, last millennium experiments from CMIP5 \r\nmodels fail to capture multicentennial variability evident in the \r\nreconstructions for the pre-industrial era (Abram et al., 2014; Datwyler \r\net al., 2018), which is also the case in those from available CMIP6 \r\nmodels (Figure  3.35). However, there is large uncertainty among \r\nreconstructions (Section  2.4.1.2). It is therefore unclear whether this \r\ndisagreement reflects this observational uncertainty, whether forcings "


id: 16e855b4d33afdbf71ff0df5f7b82e17
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 1129
content:
"limits the confidence in the assessment of the ozone contribution \r\nto the observed trends. CMIP5 and CMIP6 models do not capture \r\nmulticentennial variability of the SAM found in proxy reconstructions \r\n(low confidence). This confidence level reflects that it is unclear \r\nwhether this is due to a model or an observational shortcoming."


id: a8fb41c45178b7f9ae6265a940bd2173
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 24109
content:
"The El  Nino-Southern Oscillation (ENSO), which is generated via \r\nseasonally modulated interactions between the tropical Pacific ocean \r\nand atmosphere, influences severe weather, rainfall, river flow and \r\nagricultural production over large parts of the world (McPhaden \r\net al., 2006). In fact, the remote climate influence of ENSO is so large \r\nthat knowledge of its current phase and forecasts of its future phase \r\nlargely underpin many seasonal rainfall and temperature forecasts \r\nworldwide (Annex IV.2.3)."


id: 85f96ef39151a0d6941bd0a471db60b1
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 18617
content:
"AR5 noted that there have been clear improvements in the simulation of \r\nENSO through previous generations of CMIP models (Flato et al., 2013), \r\nsuch that many CMIP5 models displayed behaviour that was qualitatively \r\nsimilar to that of the observed ENSO (Guilyardi et al., 2012). However, \r\nsystematic errors were identified in the models' representation of the \r\ntropical Pacific mean state and aspects of their interannual variability \r\nthat affect quantitative comparisons. The AR5 assessment of ENSO \r\nconcluded that the considerable observed inter-decadal modulations \r\nin ENSO amplitude and spatial pattern were largely consistent with \r\nunforced model simulations. Thus, there was low confidence in the role \r\nof a human-induced influence in these (Bindoff et al., 2013)."


id: 627e587ff67bd7a296be4c9455ac769
created_at: 2023-03-16 14:00:40
updated_at: 2023-03-16 14:00:40
content_type: text
index: climate_gpt_only_giec
vector_id: 13063
content:
"Observed ENSO amplitude, which is measured by the standard \r\ndeviation of SST anomalies in a central equatorial Pacific region often \r\nreferred to as the Nino 3.4 region, along with the lifecycle of events, are \r\nboth reasonably well reproduced by most CMIP5 and CMIP6 models \r\n(Figure 3.36; Bellenger et al., 2014; Planton et al., 2021). The average \r\nCMIP5 model ENSO amplitude is slightly lower than that observed, \r\nwhile the average CMIP6 model ENSO amplitude is slightly higher than \r\nobserved (Figure 3.36). The ENSO amplitude of the individual models, \r\nhowever, is highly variable across CMIP5 and CMIP6 models with many \r\ndisplaying either more or less variability than observed (Stevenson, \r\n2012; Grose et al., 2020; Planton et al., 2021)."


