Aerosol Impacts on Climate and Biogeochemistry

Aerosols are suspensions of solid and/or liquid particles in the atmosphere andmodify atmospheric radiative fluxes and chemistry. Aerosols move mass from one part of the earth system to other parts of the earth system, thereby modifying biogeochemistry and the snow surface albedo. This paper reviews our understanding of the impacts of aerosols on climate through direct radiative changes, aerosol-cloud interactions (indirect effects), atmospheric chemistry, snow albedo, and land and ocean biogeochemistry. Aerosols play an important role in the preindustrial (natural) climate system and have been perturbed substantially over the anthropocene, often directly by human activity. The most important impacts of aerosols, in terms of climate forcing, are from the direct and indirect effects, with large uncertainties. Similarly large impacts of aerosols on land and ocean biogeochemistry have been estimated, but these have larger uncertainties. 45 A nn u. R ev . E nv ir on . R es ou rc . 2 01 1. 36 :4 574 . D ow nl oa de d fr om w w w .a nn ua lr ev ie w s. or g by 6 8. 62 .1 8. 60 o n 11 /0 5/ 11 . F or p er so na l u se o nl y. EG36CH03-Mahowald-NEW ARI 29 October 2011 14:11 Aerosols: liquids or solids suspended in the atmosphere Climate sensitivity: the change in equilibrium surface temperature in response to a doubling of carbon dioxide Radiative forcing: the change in the radiation budget (both short and longwave) owing to the addition of a constituent, either natural or anthropogenic