The Mechanisms of Summer Dryness Induced by Greenhouse Warming

Abstract

Abstract To improve understanding of the mechanisms responsible for CO2-induced, midcontinental summer dryness obtained by earlier modeling studies, several integrations were performed using a GCM with idealized geography. The simulated reduction of soil moisture in middle latitudes begins in late spring and is caused by the excess of evaporation over precipitation. The increase of carbon dioxide and the associated increase of atmospheric water vapor enhances the downward flux of terrestrial radiation at the continental surface at all latitudes. However, due mainly to the CO2-induced change in midtropospheric relative humidity, the increase in the downward flux of terrestrial radiation is larger in the equatorward side of the rain belt, making more energy available there for both sensible and latent heat. Since the saturation vapor pressure at the surface increases nonlinearly with surface temperature, a greater fraction of the additional radiative energy is realized as latent heat flux at the expense of ...