SEASONAL, LATITUDINAL, AND SECULAR VARIATIONS IN TEMPERATURE TREND - EVIDENCE FOR INFLUENCE OF ANTHROPOGENIC SULFATE

Tropospheric aerosols increase the shortwave reflectivity of the Earth -atmosphere system both by scattering light directly, in the absence o f clouds, and by enhancing cloud reflectivity. The radiative forcing o f climate exerted by anthropogenic sulfate aerosols, derived mainly fr om SO2 emitted from fossil fuel combustion, is opposite that due to an thropogenic greenhouse gases and is estimated to be of comparable aver age magnitude in Northern Hemisphere midlatitudes. However, persuasive evidence of climate response to this forcing has thus far been lackin g. Here we examine patterns of seasonal and latitudinal variations in temperature anomaly trend for evidence of such a response. Pronounced minima in the rate of temperature increase in summer months in Norther n Hemisphere midlatitudes are consistent with the latitudinal distribu tion of anthropogenic sulfate and changes in the rate of SO2 emissions over the industrial era.