The model used here is a coupled ocean-atmosphere model that consists of the CCSR/NIES atmospheric GCM, the CCSR ocean GCM, a thermodynamic sea-ice model, and a river routing model (Abe-Ouchi et al., 1996). The spatial resolution is T21 spectral truncation (roughly 5.6º latitude/longitude) and 20 vertical levels for the atmospheric part, and roughly 2.8º horizontal grid and 17 vertical levels for the oceanic part. Flux adjustment for atmosphere-ocean heat and water exchange is applied to prevent a drift of the modelled climate.
Three integrations are made for 200 model years (1890-2090). In the control experiment, the globally uniform concentration of greenhouse gases is kept constant at 345 ppmv CO2-equivalent and the concentration of sulphate is set to zero. In the experiment used here in SCENGEN, the concentration of greenhouse gases is gradually increased, while that of sulphate is set to zero. In the third experiment, the increase in anthropogenic sulphate as well as that in greenhouse gases is given and the aerosol scattering (the direct effect of aerosol) is explicitly represented. The indirect effect of aerosol is not included in any experiment. The scenario of atmospheric concentrations of greenhouse gases and sulphate aerosols is given in accordance with Mitchell and Johns (1997). The increase in greenhouse gases is based on the historical record from 1890 to 1990 and is increased by 1% / yr (compound) after 1990. Discussion on the results of the experiments will be found in Emori et al. (1999).
We acquired the results from this experiment from the IPCC Data Distribution Centre in 1999. The greenhouse gas only change fields used in SCENGEN are calculated as the difference in climate between the 30-year means of years 2071-2100 and 1961-90 in the greenhouse gas only forced simulation. The global warming by 2071-2100, with respect to 1961-90, was 3.0deg C and the increase in global precipitation was 2.92%, yielding a global precipitation sensitivity of 1.0% per degree Celsius warming. The climate sensitivity of the same atmospheric model, coupled to a mixed-layer ocean, was estimated to be 3.5deg C.
Mean monthly precipitation pattern correlation coefficient = 0.59
Abe-Ouchi,A. et al. (1996) Outline of CCSR-98 coupled atmosphere and ocean model and experiment Internal report, Centre for Climate System Research, University of Tokyo, Japan.
Emori,S., Nozawa,T., Abe-Ouchi,A., Numaguti,A., Kimoto,M. and Nakajima,T. (1999) Coupled ocean-atmosphere model experiments of future climate change with an explicit representation of sulfate aerosol scattering J.Meteor. Soc. Japan (submitted)
Mitchell,J.F.B. and Johns,T.C. (1997) On modification of global warming by sulphate aerosols J.Climate, 10, 245-267.