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Asia Pollution Changing World's Weather, Scientists Say

Anne Minard
for National Geographic News
March 6, 2007
 
Pollution in Asia is altering global weather patterns by creating larger clouds and more intense storms, a new study says.

The findings are the first definitive link between human activities and significant shifts in storm patterns that influence weather worldwide, the researchers write.

The affected weather system, known as the Pacific storm track, spins off tropical cyclones and typhoons, the authors point out. (Related photo: 'Supertyphoon' Batters China Coast [August 11, 2006].)

Even more significantly, the storms affect global air and heat circulation and may be linked to warming in the polar regions. (Related: "Arctic Summers Ice Free by 2040, Study Predicts" [December 12, 2006].)

"The intensified Pacific storm track likely has profound implications on climate," said lead researcher Renyi Zhang, an atmospheric scientist at Texas A&M University.

The research is presented in this week's online edition of the journal Proceedings of the National Academy of Sciences.

Fossil Fueled

Previous research has found that smoke from wildfires in the Amazon rain forest delays the onset of storms in the region. When the storms do arrive, they're fiercer.

And urban pollution has been blamed for intensified electricity and lightning in storms over cities.

So Zhang and his colleagues turned an eye to Asia, where rapid industrialization and population growth over the past two decades have spurred huge increases in pollution from the burning of fossil fuels.

The team studied the region's average cloudiness during the past 20 years, focusing on deep convective clouds, which start close to Earth and can tower about six miles (ten kilometers) or higher. Such clouds are associated with intense storm activity, such as the eye-walls of cyclones.

The researchers found that the clouds increased in frequency by 20 to 50 percent over that time frame, corresponding to an observed increase in soot, sulfur dioxide, and other aerosols from coal and oil burning.

"Profound Implications"

According to Zhang, more intense storms can affect atmospheric temperatures on a regional scale. But the activity likely also impacts the general circulation of air and heat worldwide.

In fact, the results are highly relevant to recent findings by the Intergovernmental Panel on Climate Change that show the highest levels of global warming are occurring over the polar regions, the research team writes. (Related: "Global Warming 'Very Likely' Caused by Humans, World Climate Experts" [February 2, 2007].)

The stronger storms could be pushing heat and aerosols out into the atmosphere and northward, the scientists point out, which could be contributing to shrinking ice caps in the Arctic and may cause sea levels to rise.

Zhanqing Li is an atmospheric and oceanic scientist at the University of Maryland, College Park.

Because of the magnitude of the influence of the pollution-climate interaction and its apparently far-reaching consequences, the new study "is of tremendous implication for climate studies," he said.

"While the underpinning cause for the linkage is not a completely new discovery, no one would have expected that the Asian pollution could influence such a mighty system so dramatically over such a short period and long distance," he wrote in a review of the paper.

Li says the paper may be as significant as a 2005 study of hurricanes led by Peter J. Webster of the Georgia Institute of Technology. That research suggested that warming oceans have been driving an increase in severe hurricanes.

Between 1970 and 2004, the average tropical sea surface temperature rose by almost 1 °F (0.6 °C), coinciding with an increase in the number of Category Four and Five storms.

Zhang, meanwhile, hopes his latest paper will pave the way for future research.

"This is the first work to establish the connection between a large-scale weather system and human pollution," he said.

"More studies are needed to investigate the interaction between aerosols, clouds, and climate."

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