When modeling climate, scientists must account for a large number of variables. One of the most challenging is the effect of small particulates suspended in the atmosphere, which can either reflect or absorb incoming radiation from the sun and thus alter its influence. The most common types of aerosols are soot, ash and other man-made particles as well as naturally derived dust and salt. Until now, plants and animals have been considered a small source of particulate pollution. But a new study suggests that up to 25 percent of aerosols worldwide could be coming from biological sources, including fur, skin, pollen and bacteria...