CLIMATE-CHANGE FROM INCREASED CO2 AND DIRECT AND INDIRECT EFFECTS OF SULFATE AEROSOLS

A global coupled ocean-atmosphere general circulation model without fl ux correction is integrated in a set of 75 year sensitivity experiment s where the indirect forcing effect of sulfate aerosols is included fo r the first time in combination with transient greenhouse gas forcing and the direct effect of sulfate aerosols. Sulfate aerosol forcing inc reases from zero to present-day estimates in the first 30 years of the integrations while equivalent CO2 forcing increases by 1% per year re lative to the control experiment, similar to the rate of increase of o bserved greenhouse gas forcing over the period 1960-1990. Annual mean averages around year 30, analogous to present-day conditions, indicate better agreement with recent observed geographic and zonal mean tempe rature anomaly patterns in the sulfate aerosol experiments and less wa rming in northern summer than winter. Sulfate aerosols then are increa sed following the IS92a scenario, while CO2 continues to increase a 1% per year. Averages around year 65, analogous to conditions roughly 35 years in the future, indicate warming almost everywhere in the tropos phere over the globe as the CO2 forcing overwhelms the negative radiat ive forcing from the sulfate aerosols. There is also a general indicat ion of weakening of the south Asian monsoon in the sulfate aerosol exp eriments. There is qualitative agreement in the patterns of the temper ature changes, both geographic and zonal, between the different sulfat e aerosol experiments, with the magnitude of the changes a function of the size of the forcing.