GLOBAL COMPARISON OF THE REGIONAL RAINFALL RESULTS OF ENHANCED GREENHOUSE COUPLED AND MIXED-LAYER OCEAN EXPERIMENTS - IMPLICATIONS FOR CLIMATE-CHANGE SCENARIO DEVELOPMENT

The extent of agreement amongst current global climate models (GCMs) o n the global pattern of rainfall change simulated under enhanced green house conditions is assessed. We consider the results of five experime nts which use a simple mixed layer ocean formulation and five which us e a fully dynamic ocean model ('coupled experiments'). For many region s of the northern hemisphere there is strong agreement amongst both mi xed layer and coupled experiments on the sign of simulated rainfall ch ange. However, in the southern hemisphere there are large, and apparen tly systematic, differences between the coupled and mixed layer experi ments. In particular, whereas the mixed layer experiments agree on sim ulated rainfall increase in summer in the tropics and subtropics of th e Australian sector, the coupled experiments agree (although more weak ly) on rainfall decreases. These differences appear to relate to the m uch reduced warming simulated by the coupled experiments in the high l atitudes of the southern hemisphere. However, recent oceanographic evi dence suggests that this suppressed warming may be considerably overes timated. We conclude therefore that despite the in-principle advantage s of coupled models, it may be too soon to base some regionally specif ic climate change scenarios solely on the results of coupled experimen ts.