Climate response to increasing levels of greenhouse gases and sulphate aerosols

Abstract

CLIMATE models suggest that increases in greenhouse-gas concentrations in the atmosphere should have produced a larger global mean warming than has been observed in recent decades, unless the climate is less sensitive than is predicted by the present generation of coupled general circulation models^1,2. After greenhouse gases, sulphate aerosols probably exert the next largest anthropogenic radiative forcing of the atmosphere³, but their influence on global mean warming has not been assessed using such models. Here we use a coupled oceaná¤-atmosphere general circulation model to simulate past and future climate since the beginning of the near-global instrumental surface-temperature record⁴, and include the effects of the scattering of radiation by sulphate aerosols. The inclusion of sulphate aerosols significantly improves the agreement with observed global mean and large-scale patterns of temperature in recent decades, although the improvement in simulations of specific regions is equivocal. We predict a future global mean warming of 0.3 K per decade for greenhouse gases alone, or 0.2 K per decade with sulphate aerosol forcing included. By 2050, all land areas have warmed in our simulations, despite strong negative radiative forcing in some regions. These model results suggest that global warming could accelerate as greenhouse-gas forcing begins to dominate over sulphate aerosol forcing.