China and India are among the world's top polluters, with countless cars, factories and households belching more than 2 million metric tons of carbon soot and other dark pollutants into the air every year.
A new study reveals that the pollutants can affect climate thousands of miles away, warming the United States, cooling other countries.
Light-colored aerosols such as sulfates that spew from power plants and volcanoes scatter light back into space, cooling Earth. But dark aerosols, such as soot from diesel engines and power plants, absorb more sunlight, gaining heat and warming the air around them.
The pall hanging over rapidly developing countries, especially China, India and those in southeastern Asia, has come to be known as "the Asian brown cloud." It weakens winds during the Asian summer monsoon and changes the timing and location of monsoon rainfall. Some studies show dark aerosol emissions from China alone doubled between 2000 and 2006.
Haiyan Teng, at the National Center for Atmospheric Research in Boulder, Colo., and colleagues used a detailed climate model that evaluated the interactions among land, sea, atmosphere, and sea ice.