Antarctica & Greenland Combined Added
0.59 Of An Inch To Sea Levels Since 1958
Graph Source: Grinsted et al., 2009
In a newly published paper, oceanographers estimate that global sea levels rose at a rate of ~1.42 mm per year−1 (1.32 to 1.52 mm/yr−1) between 1958 and 2014, a 56-year span that directly coincides with an unprecedented rise in anthropogenic CO2 emissions.
“For the first time, it is shown that for most basins the reconstructed sea level trend and acceleration can be explained by the sum of contributors, as well as a large part of the decadal variability. The global-mean sea level reconstruction shows a trend of 1.5 ± 0.2 mm yr−1 over 1958–2014 (1σ), compared to 1.3 ± 0.1 mm yr−1 for the sum of contributors.”
This rate (which scores between the estimated sum of sea level rise contributors and a reconstruction from tide gauge and satellite measurements) is similar to the reconstructed rate for 1954-2003 (1.45 mm/yr−1) estimated by Dr. Simon Holgate (2007).
“The rate of sea level change was found to be larger in the early part of last century (2.03 ± 0.35 mm/yr 1904–1953), in comparison with the latter part (1.45 ± 0.34 mm/yr 1954–2003).”
Extrapolating the annual rate of rise over the 56-year period (1958-2014), global sea levels rose 7.95 centimeters (cm) in total, or 3.13 inches during the Anthropogenic Global Warming (AGW) era.
Negligible Polar Ice Sheet Melt Contribution To Sea Level Rise Since 1958
Of those 7.95 cm, just 1.17 cm (0.46 of an inch) of meltwater was contributed by Greenland Ice Sheet in 56 years, and the Antarctic ice sheet contributed just 0.37 of a cm (0.13 of an inch).
1958-2014 Sea Level Rise Neither Unusual Or Unprecedented
If 3.1 inches of sea level rise over a 56-year span does not appear to be either alarming or unprecedented, perhaps it’s because they are indeed neither — especially when one considers longer-term contexts.
As Holgate (2007) summarizes above, the ~50-year global rate of sea level rise was substantially higher (2.03 mm/yr−1) during the first half of the 20th century (1904-1953) compared to the post-1950s period (1.45 mm/yr−1 1954-2003).
In other words, since the 1950s, global sea level rise has decelerated.
The 1920 to 1950 period had rates of rise that were either higher or rivaled the rates of the more recent decades (using satellite altimetry modeling [3.4 mm/yr−1 ]). In fact, when the anomalous decadal variability is removed, the fastest rates of sea level rise occurred during the 1920 to 1950 period.
“The fastest sea level rise, estimated from the time variable trend with decadal variability removed, during the past 300 years was observed between 1920– 1950 with maximum of 2.5 mm/yr.”
“The fastest sea level rise during the 20th century was between 1920 – 50 and appears to be a combination of peaking of the 60– 65 years cycle with a period of low volcanic activity (Jevrejeva et al., 2006; Church and White, 2006).”
Glacier Melt Contribution To Sea Level Rise Much Greater Before 1950
A graphical reconstruction featured in a new paper (Treat and Jones, 2018) affirms that the glacier melt percentage (and contribution to sea level rise) in the Canadian Arctic was significantly greater during most of the last several thousand years compared to the modern era.
“Rates of permafrost aggradation in peatlands generally increased after 3000 BP and were greatest between 750 and 0 BP, corresponding with neoglacial cooling and the Little Ice Age (LIA), respectively.”
The ice sheet record for the 20th century also reveals that the glacier melt contribution to sea level rise was significantly greater during the 1920 to 1950 period than it has been since the ice melt contribution began decelerating (after the 1950s).
“The abrupt climatic transition of the early 20th century and the 25-year warm period 1925–1950 triggered the main retreat and volume loss of these glaciers since the end of the ‘Little Ice Age’. Meanwhile, cooling during the 1960s, 1970s and 1980s altered the trend, with advances of the glacier snouts.”
“By 1946, this glacier had retreated almost 90% of the total recorded between the LIA maximum (1868) and 2005. … Just as in the glaciers described above, the retreat of the Eastern Tungnahryggsjökull from its LIA position was more intense during the first half of the 20th century, and in 1946 its snout was only 200 m from its current position.”
4 New Papers: Sea Levels Were Much Higher Than Now In Past Millennia
As the introductory global sea level graph above and several dozen sea level reconstructions published in scientific journals every year (2016 and 2017) demonstrate, global sea levels were about 1 to 3 meters higher than they are now during the Middle Holocene, or when CO2 concentrations were significantly lower (~270 parts per million).
These non-correlations between sea level rise and CO2 concentration would not appear to be consistent with the popular conceptualization that CO2 concentration variations are significant drivers of temperatures, glacier melt, and/or sea level rise.
After all, the 3.1 inches of sea level rise since 1958 does not even fall outside the range of natural variability.
“With sea level stabilization a few metres above the present around 5.5 ka cal yr BP (Hein et al., 2016), the longshore drift system was reestablished and sediment accumulation in the littoral zone recommenced.”