A Darkening Sky

A smoky shroud over Asia blocks both sun and rain

U.S. News & World Report

March 10, 2003

by Charles W. Petit

V. "Ram" Ramanathan sat on an airliner heading south from Bombay. Ahead were the Maldives, an archipelago near the equator, where the atmospheric scientist from the Scripps Institution of Oceanography near San Diego planned to set up instruments to study haze and weather. He expected that results from the international project would come slowly and be of interest only to specialists. He was not prepared for what he saw just gazing out the plane window.

As he took off from Bombay, the layers of brown gunk in the sky were no surprise. Pollution controls on factories and vehicles are rare in his native land. Hundreds of millions of its citzens burn low-quality coal, wood, and cow dung for cooking and heating. But nearly 1,000 miles later over the open sea, the dirty pall still had not given way to blue sky and white clouds. "The haze just kept going and going. It didn't even seem to thin out. I was thinking, this is something big."

It is. Since Ramanathan's 1998 flight, scientists have realized that the pall he saw is just part of a vast brown cloud that often extends thousands of miles east, across China. A stew of dust, ash, and smoke from fires and industry, the cloud threatens the health of the billions who live under it. The fine particles, or aerosols, also warm some areas and cool others, drying up storm clouds and perhaps even shifting India's life-givening monsoon. In many places the haze swamps greenhouse gases as a climate-changing force, say scientists. The atmospheric havoc in Asia may even play a role in El Nino, the climate cycle now drenching the southern United States.

Much of this picture is still fuzzy, but scientists are working to sharpen it. Ramanathan and his Scripps colleague Paul Crutzen, a chemist and Nobel laureate, made a start with their Indian Ocean Experiment in the late 1990s, which studied haze from a score of ground stations and from aircraft. Their glimpses of the cloud's extent and impacts helped set off an explosion of similar studies across India, off Japan and Korea, and in China, which has launched the largest single scientific project in the country's history to analyze aerosols and climate. And it has spawned a new United Nations effort called Project Asian Brown Cloud. Led by Ramanathan and Crutzen, it is organizing a massive study of the pollution's sources and effects, and what to do about it.

In a way, Asia with its dirty, fast-growing industry is repeating on a far vaster scale the smoky evolution of European and U.S. industry in the 19th and early 20th centuries. Coal consumption in China, for example, was 50 percent higher than in the United States in 1999 and could be twice as high by 2010. Across Asia, coal heats houses and cooks meals. Smoke from agricultural burning and wildfires adds to the brew. In China, the haze sometimes starts as dust blowing off western deserts, "but it picks up all kinds of toxic pollutants as it travels," says F. Sherwood Rowland, a University of California Irvine chemist who received a Nobel Prize for work on ozone. "We can detect Asian aerosols blowing all the way across the U.S."

Yet just five years ago, Ramanathan could be startled by the pall he saw from the plane window because experts still thought of smog outbreaks as local, covering a city or filling a river valley. Until recently nobody had seen the goop all in one glance. Cameras on early weather satellites were calibrated for clouds but not hazes. But new full-color satellite camera systems now send images of a nearly continous 2-mile thick blanket of sulfates, soot, organic compounds, dust, fly ash, and other crud draped across much of India, Bangladesh, and Southeast Asia, including the industrial heart of China.

The sand-colored air of Los Angeles is pristine by comparison. When Chinese scientists told U.S. colleagues about foul air back home, "we'd say we have smog here too," says Lorraine Remer, who analyzes satellite data at NASA's Goddard Space Flight Center. "Then we saw the extinction numbers" --satellite data on how much the brown cloud dims light. Across much of Asia, they were several times higher than anything ever seen in America smog. "We were standing there not believing it," she says. In and around India, the researcher found sunlight was reduced by 10 percent. Crop scientists say this is enough to reduce rice yields by 3 percent to 10 percent across much of the country.

Ground data in China show the same thing. In Beijing, airborne particulates are routinely five times as high as in Los Angeles. Donald Blake, an atmospheric chemist at the University of California Irvine, says that a colleague on a visit asked a group of kindergartners to draw the sky. They all reached for the gray crayon.

It's worse than unsightly. India has 23 cities of more than 1 million people; not one meets World Health Organization pollution standards. Indoor smoke from poorly vented fires is blamed for half a million premature deaths annually in India alone, mostly women and children. In southern China and Southeast Asia, as many as 1.4 million people die annually from pollution-related respiratory ills.

Disturbing effect. Researchers are coming to realize that, through a long chain of effects, the brown cloud may also be to blame for drought and flooding. Scientists' understanding of how aerosols shape climate is not nearly as well developed as it is for greenhouse gases like carbon dioxide, still No. 1 on any list of human impacts on climate. "But one common aspect," says Ramanathan, "is that the haze and its heating of the atmosphere is sufficient to disturb climate a lot."

Unlike the whitish sulfate particles from cleaner-burning power plants in the United States and Europe, the Asian hazes are dark with soot. As a result, they absorb sunlight and can double the rate at which it warms the atmosphere several thousand feet up, while shading and cooling the ground below. Some scientists think that the net effect is to boost global warming. But the more certain impact of the hazes is on rainfall, says Jeff Kiehl of the National Center for Atmospheric Research in Boulder, Colorado. "They are radically changing the temperature profile of the atmosphere in many areas, with a big impact on where rain falls and how much."

By cooling the nothern Indian Ocean, the haze reduces evaporation, cutting the water supply for rainfall. On land, the warm air aloft acts as a lid on cloud formation, quashing the convection that feeds thunderstorms. And the aerosols themselves seed the formation of tiny mist particles--so many that they suck water out of the air and choke off the growth of larger drops that would fall as rain. While the haze particles dry out the land, the rain does fall over the sea, where larger, natural sea-salt particles promote droplet growth. "We're shifting rain from land to the ocean," says Daniel Rosenfeld of the Hebrew University of Jerusalem.

At least that's the theory, and there are signs it may be happening. Some computer climate models predict that the hazes over India should displace the annual monsoon rains, leading to floods in the south and east of the country while drying the north and shrinking the vital Himalayan snowpack. "That's just the pattern we are starting to see emerge." says Surabi Menon of the Goddard Institute for Space Studies in New York City.

In southeastern China, where haze has cut sunlight by 2 percent to 3 percent every 10 years since the 1950s, temperatures are dropping, while rising elsewhere in the country, presumably because of greenhouse gases. The changed temperature patterns have rerouted storm tracks, one recent Chinese study said. The study blamed the shift for severe floods in the nation's south in recent years, coupled with drought in the north. It ranked the new weather pattern as the greatest sustained change in China's climate in more than 1,000 years.

Some scientists also suspect that the pollution cloud could be cooling the sea surface and slowing evaporation in the far western Pacific, off Asia. The effects could ripple across half the globe to the United States, because in western pacific is the breeding ground for El Ninos, the bouts of Pacific warming that change rainfall across the Americas and beyond.

All of this is enough to make Asia'a brown cloud, and the sparser hazes eleswhere, into a global climate threat. Fortunately, hazes are far easier to counter than greenhouse gases like carbon dioxide. Clean up industry and smother the fires, and in a few weeks rain would wash the skies clean. Carbon dioxide, in contrast, lingers for centuries, and ordinary pollution controls can't touch it.

Going after hazes. Some scientists, distressed at the reluctance of the U.S. government and many developing nations to tackle greenhouse gases, hope that the relatively easier task of curbing fine particles could kick-start international efforts to address climate change. Going after hazes, particularly those heavy with soot, is "a no-lose situation as far as I'm concerned," says Stanford University atmospheric researcher Mark Jacobson.

The Chinese government, rattled by the data on the country's polluted air, is doing just that. For both health and weather reasons, it has largely replaced home use of coal with cleaner-burning natural gas in big cities and is starting to require catalytic converters on vehicles. China also hopes to restore blue skies to Beijing in time for the 2008 Olympics.

At the same time, some scientists worry that major assaults on aerosols might divert attention from the far tougher problem of carbon dioxide and other culprits in global warming. Jacobson laments that President Bush cited the climate impact of soot as one reason to abandon the Kyoto climate change agreement, which deals with greenhouse gases. "You can't stop with aerosols," Jacobson says. "You definitely have to go after the greenhouse gases, too."

But the lesson of the Asian brown cloud, says Ramanathan, is that there's more to global change than greenhouse warming. "If all you deal with is CO2, then you don't understand climate at all."