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Pollution, Greenhouse Gases and Climate Clash in South Asia

Earth climate in delicate balance between natural, man-made forces

A new analysis by atmospheric scientists shows how air pollution, global climate change-producing gases and natural fluctuations in climate impact the world's most populous regions.

In a study funded by the U.S. National Science Foundation (NSF) and NASA, scientists Chul Eddy Chung and V. Ramanathan of the Scripps Institution of Oceanography in California describe their analysis of sea-surface temperatures and other data from the Indian Ocean region, according to a May 11 NSF press release.

They found that cooler-than-normal temperatures in the northern part of the ocean have weakened the natural climate circulation and monsoon conditions in the region, resulting in reduced rainfall over India and increased rainfall over the Sahel area south of the Sahara Desert in Africa.

As the tropical Indian Ocean heats up due to climate change, the authors said, the northern Indian Ocean, which is next to highly populated regions, is not warming as quickly as the rest of the ocean, causing increased drought conditions that could affect more than 2 billion people in South Asia.

Such conditions affect a range of industries and resources, from agriculture to fresh water availability.

The culprit behind the changes, the authors said, is an ongoing and intricate clash among air pollution, greenhouse gases and naturally produced climate changes.

In previous studies, these scientists and an international group of colleagues found that pollution particles called aerosols are "masking" warming effects from greenhouse gases.

The same is true in the current study, says Ramanathan, director of the Center for Clouds, Chemistry and Climate at Scripps.

"It appears that this whole tropical area is being pulled in different directions," he said. "The greenhouse gases are pushing in one direction, warming the ocean and trying to make more rain, and the aerosols are pushing in another direction, toward a cooler ocean and less rain."

The net effect is to drive the monsoon rain system away from South Asia into the equatorial and southern oceans.

"Some years the aerosols might win, and some years the greenhouse effect may win," Ramanathan added. "We're concerned that in coming decades the variability between the two will become large and it will be difficult to cope with rapid changes from year to year."

"This study is a demonstration that Earth's climate hangs in delicate balance between natural and man-made forces," said Jay Fein, director of the NSF climate dynamics program. "Understanding the processes that can throw climate out of balance is among the most challenging issues facing us today."

Similar pollution clouds, or brown-haze clouds, can be seen in regions around the world, including over major urban locations such as Los Angeles and Denver in the United States.

Five to 10 years ago, scientists thought about pollution as solely an urban problem, Ramanathan said. "Now we have discovered that these pollution clouds travel quickly and can cover an entire ocean." Scientists have shown that in a matter of five days, airborne pollutants can travel from China to the United States, and in a matter of three to four days, they can travel from the United States to Europe.

Source: U.S. Department of State

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