315
Source
CO2
CH4
N20
CFCs
(time period)
IPCC'94
(1750-1990)
1.56
0.47
0.14
0.28
ECHAM4
(1750-1990)
1.55
0.57
0.15
0.30
(2)ECHAM4
(1860-1990)
1.37
0.47
0.13
0.30
(1750-1860)
0.18
0.10
0.02
0.00
IPCC/IS92a
(1990-2100)
4.50
0.76
0.37
0.15
ECHAM4/1S92a
(1990-2100)
4.72
0.69
0.40
0.10(3)
(1) In IPCC, overlap is included already in the individual components
(2) year 1860: Start of the scenario experiment
(3) updated CFC-scenario according to IPCC'95
Total:
L(1)
including
band overlap
2.45
2.45
2.57
2.56
2.27
2.26
0.30
0.30
5.78
5.78
5.91
5.86
Table 3: Greenhouse gas radiative forcing (W/m 2 ) at the tropopause leve1. The years
1860-1990 are based on observational data. 1990-2100 according to IPCC scenario IS92a.
distribution (averaged between 1979 and 1988), the coupled control experiment can be considered as a simulation of the present climate. In addition
to the coupled control experiments, two Atmospheric Model Intercomparison Project (AMIP) -type experiments (Gates, 1992) have been performed
with the atmospheric component (ECHAM4). In these experiments, observed monthly mean SSTs and sea ice extents are prescribed according to
an extended AMIP SST data set and sea ice data set (Jan. 79 through
May 94). Operational ECMWF analyses (1980-1994) of sea level pressure,
geopotential height, wind and temperature are used as an observational
reference.
The climate change experiment started in Jan. 1860. However since the
model has been initialized with present SSTs, and present greenhouse gas
concentrations, we have to assume that these data were also valid initially.
The concentrations of greenhouse gases are therefore systematically higher
than in the present climate. This is not likely to be of any significance
since we have used the actual changes in the direct forcing that have taken
place up to 1990 and estimated increases after that date (Table 3). An
actual initialization of the initial conditions of the coupled system at 1860
is presently not feasible due to lack of relevant observations. It could of
Source
CO2
CH4
N20
CFCs
(time period)
IPCC'94
(1750-1990)
1.56
0.47
0.14
0.28
ECHAM4
(1750-1990)
1.55
0.57
0.15
0.30
(2)ECHAM4
(1860-1990)
1.37
0.47
0.13
0.30
(1750-1860)
0.18
0.10
0.02
0.00
IPCC/IS92a
(1990-2100)
4.50
0.76
0.37
0.15
ECHAM4/1S92a
(1990-2100)
4.72
0.69
0.40
0.10(3)
(1) In IPCC, overlap is included already in the individual components
(2) year 1860: Start of the scenario experiment
(3) updated CFC-scenario according to IPCC'95
Total:
L(1)
including
band overlap
2.45
2.45
2.57
2.56
2.27
2.26
0.30
0.30
5.78
5.78
5.91
5.86
Table 3: Greenhouse gas radiative forcing (W/m 2 ) at the tropopause leve1. The years
1860-1990 are based on observational data. 1990-2100 according to IPCC scenario IS92a.
distribution (averaged between 1979 and 1988), the coupled control experiment can be considered as a simulation of the present climate. In addition
to the coupled control experiments, two Atmospheric Model Intercomparison Project (AMIP) -type experiments (Gates, 1992) have been performed
with the atmospheric component (ECHAM4). In these experiments, observed monthly mean SSTs and sea ice extents are prescribed according to
an extended AMIP SST data set and sea ice data set (Jan. 79 through
May 94). Operational ECMWF analyses (1980-1994) of sea level pressure,
geopotential height, wind and temperature are used as an observational
reference.
The climate change experiment started in Jan. 1860. However since the
model has been initialized with present SSTs, and present greenhouse gas
concentrations, we have to assume that these data were also valid initially.
The concentrations of greenhouse gases are therefore systematically higher
than in the present climate. This is not likely to be of any significance
since we have used the actual changes in the direct forcing that have taken
place up to 1990 and estimated increases after that date (Table 3). An
actual initialization of the initial conditions of the coupled system at 1860
is presently not feasible due to lack of relevant observations. It could of