CLIMATE RESPONSE TO INDIRECT ANTHROPOGENIC SULFATE FORCING

A general circulation model (GCM) has been used to conduct sensitivity tests of the climatic influence imparted by a cloud albedo change hyp othesized to result from anthropogenic increases in atmospheric sulfur , The global distribution of anthropogenic sulfate aerosols is compute d with a simplified 3-D transport model. The NCAR CCM1 has been run wi th a cloud albedo perturbation that is a function of the distribution of anthropogenic sulfur particles. We report climate statistics from t he last 20 years of 30 year GCM control and experiment runs. The clima te response is strongest in the northern hemisphere winter, with cooli ng over the North Atlantic and North Pacific oceans on the order of 2- 6 degrees C. The 500 mb geopotential height field shows a significant deepening over the Canadian provinces, enhancing the northerly flow ov er the North American and North Atlantic regions during boreal winter. The equilibrium climate does not, however, cool over central Europe i n northern hemisphere winter, despite this region being one of the mos t heavily impacted areas in the world by sulfate aerosol. The anthropo genic sulfate 'indirect' forcing elicits a highly non-linear climate r esponse that ban be explained through changes in the hemispheric wave train. These results may assist in explaining the long-standing climat e change issue of what causes the cooling over the North Atlantic and North Pacific over the last decades, a feature that is not explained b y increases in greenhouse gases alone.