Climate Studies with a Multi-Layer Energy Balance Model. Part II: The Role of Feedback Mechanisms in the CO2Problem

Abstract

The sensitivity of climate to a doubling of the atmospheric CO₂, content has been studied using the GLAS multi-layer energy balance model. In response to a doubled CO₂ content, tropospheric temperature lapse rate decreases at low latitudes but increases at high latitudes. Averaged over the Northern Hemisphere, the change is +2.3°C in the surface temperature and +0.47°C in the earth's brightness temperature. The increase, in surface temperature is mainly caused by the intensified downward IR radiation in the water vapor bands at all latitudes and by the increased absorption of solar radiation at high latitudes due to the reduction of ice/snow cover. The effects of some feedback mechanisms on the climate sensitivity to a doubled CO₂ content have also been studied. It is found that the sensitivity of surface temperature is approximately doubled at all latitudes due to the change in water vapor content. There are two important, yet offsetting, effects of ice/snow cover on the climate sensitivity. As the ice/snow cover decreases due to an increased surface temperature, both the absorption of solar radiation and evaporation increase greatly. The effect of allowing the ice/snow cover to change with temperature is to enhance the global sensitivity by 40%. Other feedback mechanisms studied include meridional transport of latent heat and e-type absorption.