Asian Pollution Cloud Changing Climate, Study Says

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Huebert headed the research team for the Aerosol Characterization Experiments, or ACE-Asia, which concentrated on aerosols—tiny solid or liquid particles suspended in the atmosphere. Some aerosols come from natural sources like dust from volcanoes and deserts. But most come from human activities like burning wood and coal. Asia is one of the largest sources of aerosols on the Earth.

Aerosols can harm human health by causing asthma and through exposure to the carcinogens they harbor, including arsenic, lead, chromium, selenium and other toxic materials.

Aerosols powerfully affect the environment and climate. They absorb the acids that create acid rain. They reflect sunlight and influence rainfall patterns, affecting weather and global climate change. Understanding the way they affect climate is one of the more perplexing problems for atmospheric scientists.

Atmospheric scientists are puzzling over the interaction of aerosols and other factors like greenhouse gases—carbon dioxide and other gases that trap the sun's heat and warm the Earth's atmosphere.

Altering Climate

"While many parts of Earth are warming up because of greenhouse gases, in places where there are huge concentrations of aerosols, there is actually cooling," said Huebert. In April, for example, the surface cooling effect of aerosols downwind of Asia is 10 percent higher than warming caused by greenhouse gases, Huebert notes.

When you increase temperature differences between places, it may increase the severity of storms, like hurricanes," Huebert says. "One possibility is that this could cause more severe storms, more droughts and more floods."

Although the climatic impact of this cooling is still being assessed, scientists do know that these temperature disparities have great impact on the water cycle. "When air is warmer than the Earth below it, you reduce evaporation and the formation of clouds—which reduces rainfall," explained Huebert.

Good and Bad News

Researchers presented good news as well as bad.

One study, Transport and Chemical Evolution over the Pacific (TRACE-P), "sniffed air coming out of China to learn what was being emitted," says project leader Daniel J. Jacob, an atmospheric chemist from Harvard University in Cambridge, Mass.

Jacob's team tested for about 100 different "species" of pollutants, including greenhouse gases, aerosols and ozone. Although nothing on the list had significantly improved since 1994, "there hasn't been the kind of explosive growth that was predicted," Jacob says.

An exception was soot and carbon, caused by low-tech polluters like wood- and dung-burning stoves and cooking fires, as well as dirty industries. "There was also a lot of biomass burning from forest fires in Cambodia and Thailand," Jacob says.

Asian Ozone Comes to California

Another study examined ozone levels reaching California from across the Pacific and discovered that they are 30 percent higher than levels detected in 1985.

"The increase in ozone is surprising," says David P. Parrish, an atmospheric chemist with the National Oceanic and Atmospheric Administration Aeronomy Lab in Boulder, Colo., and head of the Intercontinental Transport and Chemical Transformation study. "It was larger than we expected. It reduces the room we have to mess up our own air."

"To address the problem, we will need an international consortium of governments willing to make policy based on the best available scientific consensus," Huebert says.

In a world where prevailing winds can push pollution clouds like the Asian Express halfway around the world in a week's time, these new findings underscore how no nation is an island.



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