CLIMATE RESPONSE TO RADIATIVE FORCINGS BY SULFATE AEROSOLS AND GREENHOUSE GASES

The annual, global mean radiative forcing for the troposphere-surface system has been used to rank the global warming influences of atmosphe ric trace gases. The approach was also used recently to compare the co oling influence of tropospheric sulfate aerosols with the warming infl uence of greenhouse gases. However, the spatial inhomogeneity of sulfa te aerosols (concentrated mainly in the continental Northern Hemispher e) may induce climate responses which differ other than just in sign f rom those induced by increased concentrations of the more homogeneousl y distributed greenhouse gases. Here we use a general circulation mode l to further examine the suitability of global mean radiative forcing as a predictor of differences in global, hemispheric, and regional cli mate responses to differing spatial and temporal forcing patterns. The calculated responses indicate that changes of the global and annual m ean surface air temperature depend only on global average net forcing and are not highly sensitive either to the details of the spatial and seasonal patterns in forcing or to the nature of the forcing (shortwav e vs. longwave). Thus in global and annual mean the negative aerosol f orcing may be viewed as a scaleable anti-greenhouse forcing. However s ubstantial responses to nonuniformly distributed aerosol forcing were observed at hemispheric and regional scales. Further, the patterns of response differ from the patterns of forcing, leading to the conclusio n that the spatial distribution of all significant forcings must be ac curately represented when studying regional climate changes.