A Darkening Sky
A smoky shroud over Asia blocks both sun and rain
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 continuous, 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 American smog. "We were standing there not believing it," she says. In and around India, the researchers 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, Colo. "They are radically changing the temperature profile of the atmosphere in many areas, with a big impact on where rain falls and how much."
advertisement
