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Tuesday, May 24, 2011

"Sulfate aerosol control of Tropical Atlantic climate over the Twentieth Century" by C.-Y. Chang et al., J. Climate 24 (May 15, 2011)

Journal of Climate, Vol. 24 (May 15 2011), pp. 2540-2555; doi: 10.1175/2010JCLI4065.1

Sulfate aerosol control of Tropical Atlantic climate over the Twentieth Century

C.-Y. Chang and J. C. H. Chiang (Department of Geography and Center for Atmopsheric Sciences, University of California, Berkeley, Berkeley, CA, U.S.A.), M. F. Wehner (Lawrence Berkeley National Laboratory, Berkeley, CA, U.S.A.), A. R. Friedman (Department of Geography and Center for Atmospheric Sciences, University of California, Berkeley, Berkeley, CA, U.S.A.) and R. Ruedy (NASA Goddard Institute for Space Studies, New York, NY, U.S.A.)

(Manuscript received 9 September 2010, in final form 2 December 2010)


The tropical Atlantic interhemispheric gradient in sea surface temperature significantly influences the rainfall climate of the tropical Atlantic sector, including droughts over West Africa and Northeast Brazil. This gradient exhibits a secular trend from the beginning of the twentieth century until the 1980s, with stronger warming in the south relative to the north. This trend behavior is on top of a multidecadal variation associated with the Atlantic multidecadal oscillation. A similar long-term forced trend is found in a multimodel ensemble of forced twentieth-century climate simulations. Through examining the distribution of the trend slopes in the multimodel twentieth-century and preindustrial models, the authors conclude that the observed trend in the gradient is unlikely to arise purely from natural variations; this study suggests that at least half the observed trend is a forced response to twentieth-century climate forcings. Further analysis using twentieth century single-forcing runs indicates that sulfate aerosol forcing is the predominant cause of the multimodel trend. The authors conclude that anthropogenic sulfate aerosol emissions, originating predominantly from the Northern Hemisphere, may have significantly altered the tropical Atlantic rainfall climate over the twentieth century.

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