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  • Asian soot fuels global warming

Large amounts of black soot are disrupting weather patterns over China and may have contributed to the severe flooding and droughts that the country has seen in recent decades, according to a new study.

The research, published in this week's Science, suggests that soot — produced by diesel engines, cooking fires and other sources — could have nearly as much impact on climate change as carbon dioxide, which has long been considered the primary culprit in global warming.

A group of US and Chinese researchers used a global climate model to simulate how black carbon affects weather patterns. They found that soot can influence regional climate by absorbing sunlight, heating the air and affecting rainfall.

Emissions of soot are particularly large in China because cooking and heating are done with wood, cow dung and coal at low temperatures that do not allow for complete combustion.

"If our interpretation is correct, then reducing the amount of black carbon or soot may help diminish the intensity of floods in the south and droughts in the northern areas of China, in addition to having human health benefits," says one of the authors of the study, James Hansen, a leading climate change scientist and director of NASA's Goddard Institute for Space Studies. Currently research is being conducted to verify a similar pattern over India.

The findings raise important policy issues, according to Michael Bergin, assistant professor at Georgia Tech's School of Earth and Atmospheric Sciences. "In the past, researchers have felt that soot didn't really have a significant warming effect," he says. "But as we've learned more about the amount of black carbon emitted by countries like China and India, it appears now that soot could have important climate effects."

Climate change control measures aimed at reducing emissions of soot could have relatively quick effects. Soot particles are removed from the atmosphere on time scales of weeks to months, while carbon dioxide lingers for hundreds of years.

"From a policy standpoint, the payoff for controlling soot could be on the scale of years rather than centuries," Bergin says.

He adds that the research also calls into question the accuracy of global climate change models, which have not considered the effects of black carbon. "This creates some opportunities for climate modelers to revise their approaches," he says.

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