Climate Change 2001:
Working Group I: The Scientific Basis
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6.15.2 SRES Scenarios

6.15.2.1 Well-mixed greenhouse gases

Emissions from the SRES scenarios (Nakic´enovic´ et al., 2000) were used in Chapter 4 to simulate the concentrations of well-mixed greenhouse gases and O3 in the atmosphere for the period 2000 to 2100. Here we compute the associated radiative forcing due to well-mixed greenhouse gases using the simplified expressions given in Table 6.2 (for CO2, the expression in the first row of that Table is employed). The numbers displayed in Table 6.14 represent the radiative forcings in 2050 and 2100 with respect to the year 2000. For the gases relevant to radiative forcing only, the SRES scenarios give a wide range of radiative forcings for the various compounds. Note that the CO2 forcing increases substantially in the future. All the SRES scenarios give positive radiative forcing values for the well-mixed greenhouse gases (except for the radiative forcing by CH4 in the B1 scenario for 2100). The scenario for gases relevant to radiative forcing and ozone depletion yields negative values of the radiative forcing, reflecting the reductions in atmospheric concentrations of ozone depleting gases due to emission control.

From Table 6.11, the radiative forcing due to CO2 is at present slightly larger than 50% of the total greenhouse gas forcing (including tropospheric O3). In 2050 and 2100 the SRES scenarios indicate a stronger dominance of CO2 on the total greenhouse gas forcing (including tropospheric O3), at about 70 to 80% of the total forcing. The SRES scenarios indicate that HFC-134a will give the largest radiative forcing amongst the HFCs.

Table 6.14: Future (2050 and 2100) radiative forcings due to gases that are relevant for radiative forcing only (based on SRES scenarios), and due to gases that are relevant for radiative forcing and ozone depletion (based on WMO (1999) scenarios). For some gases the results for the IS92a emission scenario, with updated model calculations, are also shown (see Chapter 4 for further details). The radiative forcings presented here are with respect to the year 2000. They may be added to the approximately present day (1998) total radiative forcing given in Table 6.1 to obtain the approximate radiative forcings with respect to pre-industrial times (1750).
Gas
Radiative forcing (Wm-2)
 
2050
 
A1b
A1t
A1fi
A2
B1
B2
A1p
A2p
B1p
B2p
IS92a
Gases relevant to radiative forcing only
CO2
1.90
1.62
2.24
1.90
1.46
1.37
1.97
1.93
1.30
1.45
1.66
CH4
0.22
0.25
0.30
0.27
0.04
0.20
0.31
0.26
0.09
0.24
0.25
N2O
0.10
0.08
0.18
0.17
0.12
0.08
0.10
0.17
0.12
0.09
0.14
Tropospheric O3
0.24
0.37
0.66
0.43
0.04
0.28
0.32
0.42
0.15
0.28
0.32
HFC-23
0.003
0.003
0.003
0.003
0.003
0.003
0.003
0.003
0.003
0.003
  
HFC-125
0.013
0.013
0.013
0.008
0.008
0.008
0.013
0.007
0.008
0.009
0.020
HFC-32
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
  
HFC-134a
0.079
0.078
0.076
0.043
0.042
0.048
0.111
0.054
0.057
0.070
0.079
HFC-143a
0.009
0.009
0.009
0.006
0.006
0.006
0.010
0.006
0.006
0.007
  
HFC-152a
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.005
HFC-227ea
0.010
0.010
0.010
0.006
0.006
0.007
0.010
0.005
0.006
0.007
  
HFC-245ca
0.017
0.017
0.016
0.008
0.009
0.010
0.017
0.008
0.009
0.011
  
HFC-43-10mee
0.002
0.002
0.002
0.001
0.001
0.001
0.002
0.001
0.001
0.001
  
CF4
0.007
0.007
0.007
0.007
0.004
0.008
0.013
0.010
0.008
0.012
  
C2F6
0.002
0.002
0.002
0.002
0.001
0.002
0.003
0.002
0.002
0.002
  
C4 F10
0.000
0.000
0.000
0.000
0.000
0.000
0.007
0.005
0.005
0.005
  
SF6
0.010
0.010
0.010
0.011
0.007
0.009
0.011
0.011
0.008
0.011
  
Gases relevant to radiative forcing and ozone depletion
CFC-11          
-0.04
          
CFC-12          
-0.06
          
CFC-113          
-0.01
          
CFC-114          
-0.002
          
CFC-115          
0.000
          
CCl4          
-0.009
          
CH3 CCl3          
-0.004
          
HCFC-22          
-0.020
          
HCFC-141b          
-0.001
          
HCFC-142b          
0.000
          
HCFC-123          
0.000
          
Halon-1211          
-0.001
          
Halon-1301          
0.000
          
Gas
Radiative forcing (Wm-2)
 
2100
 
A1b
A1t
A1fi
A2
B1
B2
A1p
A2p
B1p
B2p
IS92a
Gases relevant to radiative forcing only
CO2
3.48
2.39
5.15
4.42
2.06
2.73
3.46
4.42
2.34
2.79
3.48
CH4
0.08
0.14
0.51
0.59
-0.07
0.39
0.15
0.58
0.10
0.27
0.43
N2 O
0.16
0.11
0.40
0.36
0.17
0.14
0.13
0.36
0.21
0.12
0.25
Tropospheric O3
0.15
0.11
0.89
0.87
-0.16
0.43
0.21
0.87
0.05
0.37
0.55
HFC-23
0.003
0.003
0.003
0.003
0.003
0.003
0.002
0.002
0.002
0.002
  
HFC-125
0.031
0.032
0.031
0.025
0.013
0.023
0.030
0.023
0.013
0.023
  
HFC-32
0.002
0.002
0.002
0.002
0.001
0.002
0.002
0.002
0.001
0.001
  
HFC-134a
0.129
0.142
0.133
0.130
0.055
0.123
0.172
0.168
0.076
0.154
  
HFC-143a
0.026
0.027
0.026
0.020
0.012
0.018
0.026
0.020
0.012
0.019
  
HFC-152a
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.007
HFC-227ea
0.021
0.022
0.021
0.018
0.011
0.020
0.020
0.016
0.010
0.018
  
HFC-245ca
0.021
0.023
0.022
0.024
0.009
0.024
0.020
0.023
0.009
0.020
  
HFC-43-10mee
0.004
0.005
0.004
0.003
0.002
0.003
0.004
0.002
0.002
0.002
  
CF4
0.021
0.021
0.021
0.025
0.010
0.024
0.028
0.034
0.015
0.033
  
C2 F6
0.004
0.004
0.004
0.005
0.002
0.005
0.006
0.007
0.003
0.007
  
C4 F10
0.000
0.000
0.000
0.000
0.000
0.000
0.022
0.016
0.013
0.017
  
SF6
0.027
0.027
0.027
0.031
0.016
0.020
0.027
0.032
0.017
0.034
  
Gases relevant to radiative forcing and ozone depletion
CFC-11          
-0.06
          
CFC-12          
-0.10
          
CFC-113          
-0.02
          
CFC-114          
-0.003
          
CFC-115          
0.000
          
CCl4          
-0.010
          
CH3 CCl3          
-0.004
          
HCFC-22          
-0.030
          
HCFC-141b          
-0.001
          
HCFC-142b          
-0.002
          
HCFC-123          
0.000
          
Halon-1211          
-0.001
          
Halon-1301          
-0.001
          

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