Contrasting the Effects of the 1850–1975 Increase in Sulphate Aerosols from North America and Europe on the Atlantic in the CESM

Abstract

AbstractThe extent and mechanisms of the Atlantic response to the historical (1850–1975) increase of sulphate aerosol emissions from North America and Europe as simulated in eight‐member ensemble experiments with the coupled Community Earth System Model (CESM1)‐Community Atmosphere Model version 5.3 are contrasted. The results show that aerosols from either source cause a long‐term cooling of North Atlantic sea surface temperatures, with the patterns a combination of atmospheric aerosol effects and an aerosol‐induced strengthening of the Atlantic Meridional Overturning Circulation. The response to North American emissions is larger since prevailing winds cause wider aerosol spread over the Atlantic, collocated with climatological cloud cover. The Intertropical Convergence Zone shifts southward affecting tropical precipitation globally. The simulated (multi)decadal components of sea surface temperature and Atlantic Meridional Overturning Circulation variability are furthermore primarily externally forced. The analysis provides novel insights into the mechanisms of aerosol impact on the Atlantic. It suggests that projected further emission reductions will lead to opposite changes.