Simulations used for the U.S. National Assessment

 1.   CGCM1

Canadian Centre for Climate Modelling and Analysis (CCCma):  First generation Coupled General Circulation Model (CGCM1)

Simulations:
3 ensemble (ensembles have different initial conditions but similar boundary conditions) runs from 1850 - 2100 using:

• 1% equivalent CO2 increase per year + sulfate aerosols (IS92a):  Core scenario for the National Assessment is GHG+A Ensemble  # 1.   Daily and monthly 0.5o gridded time series available for the U. S. from VEMAP.

Optional additional scenarios for the National Assessment (1 run each).

• 1% equivalent CO2 increase per year (IS92a) [GHG]

• control simulation with present concentration of greenhouse gases [Control]

time series: 1850, scenarios start 1990

2.    HADCM2

United Kingdom Meteorological Office/ Hadley Centre for Climate Prediction and Research: HADCM2

Simulations:
4 ensemble runs from 1860 - 2099  (scenarios start 1990) using

• 1% equivalent CO2 increase per year + sulfate aerosols (IS92a):  Use Ensemble # 1.  Daily and monthly 0.5o gridded time series available for the U. S. from VEMAP.

Optional additional scenarios for the National Assessment (4 ensembles each).

•  1% equivalent CO2 increase per year (IS92a)

• IS92d CO2 + IS92d sulfate aerosols

•  IS92d CO2

1 control simulation

time series: 1860, scenarios start 1990
 

3.   ECHAM4/OPYC3

• IS92a CO2 + IS92a sulfate aerosols

4.    NCAR CSM  (Climate System Model)

• Business as usual

• stabilization at 550 ppm CO2

These scenarios (1 run each) are run from 1980-2100, and they don't start diverging until after 2010.  NCAR also has run a 20th century scenario (from 1870-1998) and an unforced control, but these simulations are not publicly available. 

GFDL 

• 1% equivalent CO2 increase per year + sulfate aerosols (IS92a)

•  IS92d CO2 + IS92d sulfate aerosols

DOE PCM (Department of Energy Parallel Climate Model, at NCAR)

 Emission Scenarios

 Figure 1a:  The 1% equivalent CO2 increase per year case is scenario IS92a before present and 1% per year compounded increase of CO2 into the future.  Equivalent CO2 is a way of increasing the CO2 concentration to account for the radiative effects of the other greenhouse gases (N2O, CH4, O3, Halogenated compounds).  The figure shows IS92a for CO2 alone (red) and equivalent CO2 (black).  The CO2 concentration by 2100 is about 700 ppmv, but increases to about 1050 ppmv when the effects of the other greenhouse gases are included.  The 1% increase per year scenario (blue) leads to a slightly larger increase than the IS92a equivalent CO2 scenario, resulting in around 1250 ppmv by 2100.  The 0.5% equivalent CO2 increase per year case is actually just IS92d.  The CO2 alone concentration for IS92d (light blue) results in 540 ppmv by 2100, whereas the equivalent CO2 (green) case actually used in the scenarios results in 730 ppmv CO2 by 2100.  These concentrations were calculated from the radiative forcings developed for IPCC from upwelling diffusion energy balance models (T. Wigley, personal communication), using the radiative forcing functions in IPCC Technical Paper II (Houghton et al., 1997).
 

Figure 1b:  Radiative forcing used to derive the concentrations in Figure 1a.

Figure 1c:  The IS92a and IS92d total sulfate emissions scenarios.  Only direct effects of sulfate aerosols have been considered in these scenarios.  These emissions were calculated from the radiative forcings developed for IPCC from upwelling diffusion energy balance models (T. Wigley, personal communication) , using the radiative forcing functions in IPCC Technical Paper II (Houghton et al., 1997).  The HADCM2 experiments used these emission values (TgS = teragrams of sulphur) in the form of surface albedos.

Figure 2a:  The actual equivalent CO2 concentration used in the HADCM2 experiments.  The values from the historical period are based on the IPCC estimated greenhouse gas forcings from 1765-1990 (Shine et al., 1990, Table 2.6; Mitchell and Johns, 1997), calculated as equivalent CO2.  After 1990, CO2 is increased at the rate of 1%/year.

Figure 2b:  Equivalent CO2 radiative forcings computed from the HADCM2 GCM.





 

Figure 2c:  SO4 (total) radiative forcings computed from the HADCM2 GCM (note that actual emission values were not used in HADCM2, which does not have a sulfate chemistry model).  The values from the historical period are scaled from present-day values to correspond with historical estimates (Mitchell and Johns, 1997).  Present and future sulfate loadings were derived using the sulfur cycle model of Langner and Rodhe (1991) and IS92a estimates for the future (Mitchell and Johns, 1997).

For a complete description of the NCAR CSM forcing scenarios, go to NCAR CSM.

Note:  The CGCM1 experiments used the same forcing as the HADCM2 experiments (for the 1% case).

References

Houghton, J. T., Filho, L. G. M., Griggs, D. J., and K. Maskell, Eds., 1997, An introduction to simple climate models used in the IPCC second assessment report, IPCC, 47 pp.

Langner, J. and H. Rodhe, 1991, "A global three-dimensional model of the tropospheric sulfur cycle", J. Atmos. Chem., 13, 225-263.

Mitchell, J. F. B. and T. C. Johns, 1997, "On modification of global warming by sulfate aerosols", J. Climate, 10(2): 245-267.

Shine, K. P. , Derwent, R. G., Wuebbles, D. J., and J. J. Morcrette, 1990, "Radiative forcing of climate", Climate Change. The IPCC Scientific Assessment, J. T. Houghton, G. J. Jenkins, and J. J. Ephraums, Eds., Cambridge University Press, 41-68.