Synthesis Report - Question 3

Climate Change 2001: Synthesis Report

Other reports in this collection


Globally averaged annual precipitation is projected to increase during the 21st century. Globally averaged water vapor and evaporation are also projected to increase.

WGI TAR Section 9.3.1
3.9 Global mean sea level is projected to rise by 0.09 to 0.88 m between the years 1990 and 2100, for the full range of SRES scenarios (see Figure 3-1). For the periods 1990 to 2025 and 1990 to 2050, the projected rises are 0.03 to 0.14 m and 0.05 to 0.32 m, respectively. This is due primarily to thermal expansion and loss of mass from glaciers and ice caps. The range of sea-level rise presented in the SAR was 0.13 to 0.94 m, based on the IS92 scenarios. Despite the higher temperature change projections in this assessment, the sea-level projections are slightly lower, primarily due to the use of improved models, which give a smaller contribution from glaciers and ice sheets.

WGI TAR Section 11.5.1
3.10 Substantial differences are projected in regional changes in climate and sea level, compared to the global mean change.

3.11 It is very likely that nearly all land areas will warm more rapidly than the global average, particularly those at northern high latitudes in winter. Most notable of these is the warming in the northern regions of North America, and northern and central Asia, which exceeds global mean warming in each model by more than 40%. In contrast, the warming is less than the global mean change in south and southeast Asia in summer and in southern South America in winter (see Figure 3-2).

WGI TAR Section 10.3.2
3.12 At the regional scale, both increases and decreases in precipitation are projected, typically of 5 to 20%. It is likely that precipitation will increase over high latitude regions in both summer and winter. Increases are also projected over northern mid-latitudes, tropical Africa and Antarctica in winter, and 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 (see Figure 3-3).

WGI TAR Section 10.3.2
3.13 The projected range of regional variation in sea-level change is substantial compared to projected global average sea-level rise, because the level of the sea at the shoreline is determined by many factors (see Figure 3-4). Confidence in the regional distribution of sea-level change from complex models is low because there is little similarity between model results, although nearly all models project greater than average rise in the Arctic Ocean and less than average rise in the Southern Ocean.

WGI TAR Section 11.5.2
3.14 Glaciers and ice caps are projected to continue their widespread retreat during the 21st century. Northern Hemisphere snow cover, permafrost, and sea-ice extent are projected to decrease further. The Antarctic ice sheet is likely to gain mass because of greater precipitation, while the Greenland ice sheet is likely to lose mass because the increase in runoff will exceed the precipitation increase. Concerns that have been expressed about the stability of the West Antarctic ice sheet are covered in Question 4. WGI TAR Section 11.5.4
Figure 3-2: 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, and were performed by AOGCMs. Scenarios A2 and B2 are shown as no AOGCM runs were available for the other SRES scenarios. The boxes show an analysis of inter-model consistency in regional relative warming (i.e., warming relative to each model's global average warming) for the same scenarios. Regions are classified as showing either agreement on warming in excess of 40% above the global mean annual average (much greater than average warming), agreement on warming greater than the global mean annual average (greater than average warming), agreement on warming less than the global mean annual average (less than average warming), or disagreement amongst models on the magnitude of regional relative warming (inconsistent magnitude of warming). There is also a category for agreement on cooling (this category never occurs). A consistent result from at least seven of the nine models is defined as being necessary for agreement. The global mean annual average warming of the models used span 1.2 to 4.5°C for A2 and 0.9 tO3.4°C for B2, and therefore a regional 40% amplification represents warming ranges of 1.7 to 6.3°C for A2 and 1.3 to 4.7°C for B2.
WGI TAR Figures 9.10d & 9.10e, & WGI TAR Box 10.1 (Figure 1)

Other reports in this collection

IPCC Homepage