By Sid Perkins
The murky clouds of smoke and soot that blanket many regions of Asia have heated the lower atmosphere there in recent decades as much as increases in carbon dioxide and other greenhouse gases have, a new field study suggests.
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Scientists have long argued about the net climatic effect of aerosols such as dust, smoke, and soot. Light-colored aerosols scatter much of the light that strikes them, some of it back to space, says V. Ram Ramanathan, a climate scientist at the Scripps Institution of Oceanography in La Jolla, Calif. However, dark aerosols such as soot can absorb much of the incoming radiation, warming themselves and the air around them. Current estimates of the overall effect of light-dark mixtures—including the so-called atmospheric brown clouds of pollution found in parts of Asia—are based largely on computer simulations, says Ramanathan.