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Global Projections for Temperature
Earth’s average surface temperature has increased from the 1860s to the year 2000, the period of instrumental record. In the 1900s the increase was 0.6 ¼C±0.2. Proxy data for the northern hemisphere indicates that over the past 1000 years, the twentieth century temperature increase was the largest of any century and the 1990s were the warmest decade. There is not enough proxy data for the southern hemisphere to make a similar comparison.
Since 1950, the sea surface temperature increase has been about half of the average land surface temperature increase. The nighttime land daily minimums have increased by about 0.2 ¼C per decade. This is twice the rate of increase in daily maximum surface temperatures. As a result, frost-free seasons are longer in many mid- and high latitude regions.
Figure 1. Variations of the Earth’s surface temperature: years 1000 to 2100.
Over the period 1000 to 1860, observations are shown of variations in average surface temperature of the Northern Hemisphere constructed from proxy data (tree rings, corals, ice cores, and historical records). The line shows the 50-year average, and the grey region the 95% confidence limit in the annual data. From the years 1860 to 2000, observations are shown of variations of global and annual averaged surface temperature from the instrumental record. The line shows the ten-year average. Over the period 2000 to 2100, projections are shown of globally averaged surface temperature for the six SRES scenarios and IS92a as estimated by a model with average climate sensitivity. The grey region labeled “several models all SRES envelope”, shows the range of results from the full range of 35 SRES scenarios. For a description of the 6 scenarios, see the section at the end of this article called “Socio-Economic Scenarios”.
Source: Adapted from Climate Change 2001 Synthesis Report p. 140
ACTIVITY 1 Questions: (Refer to Figure 1)
1. What does the horizontal line at 0.0 ¼ C represent?
2. What is the temperature difference increase between 1000 and 1860? Why was this year the chosen?
3. What is the temperature difference increase from 1860 to 2000?
4. What is the range (¼C) of the entire envelope which includes all scenarios at 2100?
5. What is the range (¼C) of increases which is the narrowest, yet includes the six SRES scenarios?
6. Why would the B2 Scenario have the smallest increase in temperature change? (See section “Socio-economic Scenarios” at the end of this article)
7. What do you notice about the size of the temperature increase to 2000 compared to the projected temperature increases with each scenario?
As the climate system changes, the land warms faster than the ocean. There is also greater warming at high latitudes. Climate models project a smaller surface air temperature increase in the North Atlantic and in the circumpolar southern ocean compared with the global average. (See Figure 2.)
Models also predict that in many areas, night-time lows will increase more than daytime highs (which will still increase). This will decrease the daily temperature range.
In the northern hemisphere land areas, there will be decreased daily variability in winter and increased daily variability in summer.
What will this look like? (See Projections for Extreme Weather)
Figure 2. The annual mean change of the temperature (colour shading) and its range (isolines) (Unit: oC) for the SRES scenario A2 (upper panel) and the SRES scenario B2 (lower panel). Both SRES scenarios show the period 2071 to 2100 relative to the period 1961 to 1990 and were performed by OAGCMs.
Source: IPCC Climate Change 2001 Synthesis Report p. 207
ACTIVITY 2 Questions (Refer to Figure 2.)
1. What time periods are being compared to determine the temperature change on these maps?
2. Are there any areas that show cooling?
3. Where is the least warming going to happen? How much will this area warm?
4. Where is the greatest warming? How much will this area warm?
5. What differences do you see between the maps for the two SRES scenarios, A2 and B2? What do you think is the reason for these differences? (See “Socio-economic Scenarios” at the end of this article)
Figure 3. Analysis of regional warming of two different SRES models. The background shows the annual mean change of temperature (color shading) for (a) the SRES scenario A2 and (b) the SRES scenario B2. Both SRES scenarios show the period 2071 to 2100 relative to the period 1961 to 1990. The warming is relative to the global average warming for that model.
Source: IPCC Climate Change 2001 Synthesis Report p. 65
In Figure 3, regions are classified as showing either
- agreement on warming in excess of 40% above the global average (‘Much greater than average warming’),
- agreement on warming greater than the global average (‘Greater than average warming’),
- agreement on warming less than the global average (‘Less than average warming’), or
- disagreement amongst models on the magnitude of regional relative warming (‘Inconsistent magnitude of warming’).
ACTIVITY 3 Questions (Refer to Figure 3.)
1. Refer to the legend. What two seasons are being compared in each of the boxes?
2. Where will winters be warmer than the global average warming by 40%?
3. Where will summers be warmer than the global average warming by 40%?
4. Where do both models consistently show less warming than the global average? In what seasons is this the case?
Figure 4. Surface Temperature Change Projection from 1990 to 2100
Source: Henry Hengeveld, Environment Canada, Canadian Centre for Climate Modeling and Analysis
5. What do you notice about the warming over land areas compared to ocean surfaces?
6. Compare the warming in high latitudes with low latitudes.
7. Describe warming in Canada, and the Arctic.
Source: Climate Change 2001 Synthesis Report, page 10
B = balanced
FI = fossil-intensive
T = non-fossil
A1 – very rapid economic growth and introduction of new technologies, global population peaking 2050.
Subset (A1Fl= fossil-fuel intensive, A1T= non-fossil energy A1B =balanced different energy sources)
A2 – world emphasizing self-reliance and preservation of local identities and economic growth, with global population slowly increasing continuously, and slower, more fragmented technological change.
B1 – rapid change to service and information economy, cleaner, more efficient technologies, global population peaking 2050, emphasizing global solutions to sustainability, improved equity.
B2 – local solutions to economic, social, environmental sustainability, intermediate levels of economic development, less rapid technological change, global population continuously increasing.
Global Projections for Precipitation
Globally averaged annual precipitation is projected to increase during the twenty-first century, typically 5 to 20%.
It is likely that precipitation will increase
- over high latitude regions in both summer and winter.
- over northern mid-latitudes, tropical Africa and Antarctica in winter
- in southern and eastern Asia in summer.
Australia, Central America, and southern Africa show consistent decreases in winter rainfall. Larger year-to-year variations in precipitation are very likely over most areas where an increase in mean precipitation is projected.
Figure 1. Analysis of regional annual mean change in rainfall of 2 different SRES models. The background shows the annual mean change of rainfall (color shading) for (a) SRES scenario A2 and (b) SRES scenario B2. Both SRES scenarios show the period 2071 to 2100 relative to the period 1961 to 1990. The boxes show agreement within the models on regional precipitation change.
Source: IPCC Climate Change 2001 Synthesis Report p. 66
The changes in precipitation in Figure 1 are classified as follows:
- agreement on increase with an average change of greater than 20% ( large increase),
- agreement on increase with an average change between 5 and 20% ( small increase),
- agreement on a change between -5 and +5% or agreement with an average change between -5 and +5% ( no change),
- agreement on decrease with an average change between -5 and -20% ( small decrease),
- agreement on decrease with an average change of more than -20% ( large decrease), or disagreement ( inconsistent sign).
A consistent result from at least seven of the nine models is defined as being necessary for agreement.
ACTIVITY 4 Questions
1. What two seasons are represented by the two boxes in each region?
2. In general what latitudes show increased precipitation in both summer and winter?
3. What regions show increased precipitation only in winter?
4. What regions show increased precipitation only in summer?
5. What regions show consistent decreases in winter?
Northern Hemisphere Projections for Precipitation
The CGCM (Canadian Global Climate Model) suggests a modest increase in global precipitation and an El Nino-like change in precipitation pattern under warmer climates.
By about 2050, precipitation changes in this projection are generally relatively small across medium to high latitudes, but show large increases for the tropical Pacific and west American coastline, and large decreases over south-eastern US and southern Europe.
Figure 2. CGCM Northern Hemisphere Winter Changes in Precipitation from 2080 – 2100
Source: MSC Climate Research Branch
By 2080-2100, the CGCM model predicts significant increases in winter precipitation across most high to mid latitude regions of the northern hemisphere, a very large increase over parts of the tropical oceans, and continued intense drying over south-eastern USA, Mexico, the Mediterranean, and eastern Asia. However, the change over much of Canada remains modest.
Figure 3. CGCM Northern Hemisphere Summer Changes in Precipitation from 2080 2100
Source: MSC Climate Research Branch
ACTIVITY 5 Questions (Refer to Figures 2 and 3.)
1. Where is the largest increase in summer precipitation predicted?
2. Compare the winter and summer increases over the western U.S. and central Canada. In which season is the precipitation increase greater?
3. What areas of the world are projected to experience a decrease in summer rainfall?
4. Observe the projected increases in summer precipitation over Arctic regions. Will the summer increase be greater or less than in winter?