Aerosol Effects on Cloud Emissivity and Surface Longwave Heating in the Arctic

Increases in anthropogenic aerosols in the atmosphere tend to increase the reflectance of solar (shortwave) radiation from water clouds, which can lead to lower surface temperatures. Here an opposing effect whereby aerosols increase the longwave emissivity of thin clouds that adds to the warming of the earth’s surface, is discussed. The latter effect may be particularly important in the Arctic, especially during the winter and early spring when thin stratus clouds are ubiquitous, relatively high levels of anthropogenic pollution are common, and there is little solar radiation.