Climate Change 2001:
Working Group II: Impacts, Adaptation and Vulnerability
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11.1.3.1. Surface Air Temperature


Figure 11-5:
Future trends in area-averaged annual mean temperature increase over land regions of Asia as simulated by CCSR/NIES AOGCM for IS92a and SRES emission scenarios. Because the climate sensitivity of model versions used for the new (SRES) and old (IS92a) sets of simulations are different, temperature trends shown are scaled so they can be compared directly; trends for IS92a scenarios are scaled by a factor of 1.56, which is the ratio of climate sensitivity averaged over Asia of new model version to that of old version. Also note that only the direct effect of sulfate aerosols is considered in the IS92a GHG+Aerosols simulation, whereas the direct and indirect effects of sulfate and carbon aerosols are considered in SRES simulations.

Climate change scenarios that are based on an ensemble of results as inferred from skilled AOGCMs for Asia and its subregions on annual and seasonal mean basis are presented in Table 11-2. Three future time periods centered around the 2020s (2010-2029), the 2050s (2040-2069), and the 2080s (2070-2099) have been considered here for developing scenarios of changes in surface air temperature and precipitation relative to the baseline period of 1961-1990. The projected area-averaged annual mean warming is 1.6±0.2°C in the 2020s, 3.1±0.3°C in the 2050s, and 4.6±0.4°C in the 2080s over land regions of Asia as a result of increases in the atmospheric concentration of GHGs. Under the combined influence of GHGs and sulfate aerosols, surface warming will be restricted to 1.4±0.3°C in the 2020s, 2.5±0.4°C in the 2050s, and 3.8±0.5°C in the 2080s. In general, projected warming over Asia is higher during NH winter than during summer for all time periods (see also Giorgi and Francisco, 2000). The area-averaged increase in surface air temperature is likely to be most pronounced over boreal Asia and least in southeast Asia in all seasons (Lal and Harasawa, 2001). It is evident from Table 11-2 that even though aerosol forcing reduces surface warming, the magnitude of projected warming is still considerable and could substantially impact the Asian region.

In December 1998, the writing team for the IPCC Special Report on Emission Scenarios (SRES) released a preliminary set of four SRES "marker" scenarios: A1, A2, B1, and B2 (Nakicenovic et al., 1998). Scenario B1 projects the most conservative future emissions of GHGs from Asia; scenario A2 is characteristic of scenarios with higher rates of GHG emissions in combination with higher sulfate and other aerosol emissions. The A1 scenario family has since been further divided into three groups that describe alternative directions of technological change in the energy system (IPCC, 2000). The three A1 groups are distinguished by their technological emphasis: fossil fuel-intensive (A1FI), nonfossil energy sources (A1T), or a balance across all sources (A1B). Projections of future aerosol loading as envisaged in SRES marker scenarios are significantly lower compared to the IS92a scenario.

Figure 11-5 illustrates the trends in area-averaged annual mean surface air temperature increase over land regions of Asia as simulated with CCSR/NIES AOGCMs for the IS92a scenario (GHG only and GHG + aerosols) and for the new SRES "marker" emission scenarios. Projections of future sulfate aerosol loading in SRES scenarios are significantly lower. Because the treatment of aerosol and GHG radiative effects in the old and new sets of scenario experiments is different, quantitative comparison of the results should be made with care. Nonetheless, the generally higher projected surface warming trend for SRES scenarios in the latter half of the 21st century is partially a result of intensive reduction of aerosol emissions. Projected surface warming trends for the IS92a and B1 emission pathways are close to each other. Maximum warming is simulated for the A1 emission scenario during the first half of the 21st century but is carried forward to the A2 emission scenario in the latter half of the 21st century. Projections of regional climate change that use these newer sets of emission scenarios for GHGs have not yet been thoroughly assessed for their applications in impact assessment studies.

Table 11-2: Plausible changes in area-averaged surface air temperature (top) and precipitation (bottom) over Asia and its subregions as a result of future increases in greenhouse gases (under IS92a emission scenarios), as inferred from an ensemble of data generated in experiments with CCSR/NIES, CSIRO, ECHAM4, and HadCM2 AOGCMs. Numbers in parentheses are area-averaged changes when direct effects of sulfate aerosols are included.
  Precipitation Change (%)
  2020s
2050s
2080s
Regions Annual Winter Summer Annual Winter Summer Annual Winter Summer
Asia
1.58
1.71
1.45
3.14
3.43
2.87
4.61
5.07
4.23
 
(1.36)
(1.52)
(1.23)
(2.49)
(2.77)
(2.23)
(3.78)
(4.05)
(3.49)
Boreal
2.17
2.66
1.71
4.32
5.52
3.29
6.24
8.04
4.82
 
(1.88)
(2.21)
(1.47)
(3.52)
(4.46)
(2.83)
(5.30)
(6.83)
(4.24)
                   
Arid/Semi-Arid                  
- Central Asia
1.61
1.56
1.77
3.18
2.81
3.55
4.83
4.41
5.34
 
(1.47)
(1.55)
(1.49)
(2.69)
(2.61)
(2.59)
(4.15)
(3.78)
(4.36)
- Tibet
1.77
1.90
1.62
3.38
3.55
3.19
5.04
5.39
4.69
 
(1.56)
(1.83)
(1.40)
(2.62)
(2.94)
(2.27)
(4.06)
(4.32)
(3.73)
                   
Temperate
1.49
1.74
1.23
2.86
3.26
2.48
4.34
5.11
3.67
 
(1.19)
(1.50)
(0.99)
(2.10)
(2.40)
(1.72)
(3.31)
(3.83)
(2.77)
                   
Tropical                  
- South Asia
1.36
1.62
1.13
2.69
3.25
2.19
3.84
4.52
3.20
 
(1.06)
(1.19)
(0.97)
(1.92)
(2.08)
(1.81)
(2.98)
(3.25)
(2.67)
- SE Asia
1.05
1.12
1.01
2.15
2.28
2.01
3.03
3.23
2.82
 
(0.96)
(0.94)
(0.96)
(1.72)
(1.73)
(1.61)
(2.49)
(2.51)
(2.34)
  Precipitation Change (%)
  2020s
2050s
2080s
Regions Annual Winter Summer Annual Winter Summer Annual Winter Summer
Asia
3.6
5.6
2.4
7.1
10.9
4.1
11.3
18.0
5.5
 
(2.3)
(4.3)
(1.8)
(2.9)
(6.5)
(1.5)
(7.0)
(12.1)
(3.5)
Boreal
6.1
11.1
2.6
12.8
23.8
5.1
20.7
39.5
7.7
 
(6.7)
(10.7)
(3.3)
(12.0)
(19.7)
(7.1)
(18.9)
(31.5)
(10.3)
                   
Arid/Semi-Arid                  
- Central Asia
1.3
3.0
-2.1
1.3
6.9
-2.3
-1.3
6.9
-4.0
 
(1.1)
(2.7)
(5.9)
(0.6)
(1.4)
(0.7)
(-3.6)
(1.0)
(-1.8)
- Tibet
5.9
8.9
4.4
9.0
19.2
4.7
12.8
25.6
5.7
 
(3.4)
(7.4)
(1.7)
(7.5)
(14.8)
(1.7)
(11.5)
(18.8)
(3.8)
                   
Temperate
3.9
4.2
3.7
7.9
13.3
5.4
10.9
20.1
7.8
 
(0.9)
(0.4)
(1.2)
(1.3)
(4.3)
(0.7)
(4.8)
(7.1)
(3.1)
                   
Tropical                  
- South Asia
2.9
2.7
2.5
6.8
-2.1
6.6
11.0
5.3
7.9
 
(1.0)
(-10.1)
(2.8)
(-2.4)
(-14.8)
(0.1)
(-0.1)
(-11.2)
(2.5)
- SE Asia
2.4
1.4
2.1
4.6
3.5
3.4
8.5
7.3
6.1
 
(1.7)
(3.3)
(1.2)
(1.0)
(2.9)
(2.6)
(5.1)
(5.9)
(4.9)


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