for National Geographic News
Soot-filled "brown clouds" over the Indian subcontinent warm the lower atmosphere just as much as greenhouse gases do, a recent study reports.
Such clouds contain aerosols—tiny particles suspended in the air that are known to create a general cooling effect that could mitigate global warming.
But the latest study suggests that aerosols can be responsible for regional warming. Specifically, the clouds of aerosols over India enhance atmospheric warming there by 50 percent.
"We found this brown cloud can cover the entire North Indian Ocean, an area the size of the continental United States," said lead author Veerabhadran Ramanathan, a climate scientist at Scripps Institution of Oceanography at the University of California, San Diego.
The haze of brown clouds over the region can be up to two miles (three kilometers) thick, Ramanathan said.
And the haze touches the lower parts of the glaciers in the Himalaya mountain range, said study co-author David Winker, principal investigator of the CALIPSO satellite at NASA's Langley Research Center.
This suggests that the brown clouds may be contributing to glacial melting in the Himalaya.
(Related: "Mountain Glaciers Melting Faster Than Ever, Expert Says" [February 16, 2007].)
How Now Brown Cloud?
Brown clouds contain dark aerosols such as soot that are released into the atmosphere by burning organic matter.
These particles absorb solar energy and then release it to the surrounding air as heat.
Natural forces such as forest fires can create soot, but so can human actions such as burning fossil fuels.
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