Threat Watch: Atmospheric Brown Clouds

The danger of Atmospheric Brown Clouds, in a new report by the United Nations scientists, threatens a range of human and ecological activity, and also serves to mask the effects of greenhouse warming.

The byproduct of automobiles, slash-and-burn agriculture, wood-burning kitchen stoves and coal-fired power plants, these plumes of carbon dust rise over southern Africa, the Amazon basin and North America. But they are most pronounced in Asia, where so-called atmospheric brown clouds are dramatically reducing sunlight in many Chinese cities and leading to decreased crop yields in swaths of rural India, say a team of more than a dozen scientists who have been studying the problem since 2002. [un report on brown clouds]