An Investigation with a General Circulation Model of the Climatic Effects of Cloud Albedo Changes Caused by Atmospheric Pollution

Abstract

A hemispheric general circulation model, with fixed zonally averaged cloud cover, was used to investigate the climatic impact of increased albedo of low-level clouds caused by atmospheric pollution. The albedo of these clouds was increased from 0.69 to 0.87, corresponding to rather high levels of pollution. The albedo was modified in the midlatitudes and subtropics of the model in two separate experiments. In the midlatitude experiment, a cooling of 2.5 K at the surface occurred. The cooling was confined to the zone of the albedo increase. The subtropical experiment had a maximum surface cooling of only 1 K, but it extended beyond the immediate zone of the albedo increase. These coolings were much less than those produced by radiative-convective models. Time series plots of surface temperature at an individual point indicated that it would be difficult to detect this cooling against the day-to-day variability of the model atmosphere. A number of other perturbations to the model's climate occurred, which could be related to the cooling. These included variations in convective activity, precipitation and evaporation. Dynamical changes were also identified, including stronger mean zonal winds in midlatitudes, variations in eddy kinetic energy, and modifications to the mean meridional streamfunction. Despite the perturbations induced by the cloud albedo increases, no systematic changes in the synoptic properties of the model atmosphere were detected.