Coupled ocean-atmosphere model experiments of future climate change with an explicit representation of sulfate aerosol scattering

The transient response of a coupled ocean-atmosphere model to increasing concentrations of greenhouse gases and sulfate aerosols, is investigated with an explicit representation of aerosol scattering. Experiments with an implicit representation of aerosol scattering, through the modification of surface albedo with the same parameter values as used in previous climate projections, are also conducted for comparison. The indirect effect of aerosol is yet to be included. As suggested by previous radiation computation studies, the estimated radiative forcing due to the direct effect of sulfate aerosol is significantly smaller with the explicit representation, than with the implicit one. A principal source of the overestimation by the implicit method is the neglect of the dependence of aerosol scattering on near-surface humidity. The projected surface air temperature change due to the addition of sulfate aerosols is considerably smaller in magnitude especially over dry regions with the explicit method, than with the implicit one. It is also suggested that the change in the Asian summer monsoon precipitation due to an increase in sulfate aerosols is particularly sensitive to the representation of sulfate aerosol scattering.