Haze alert over the Indian Ocean
New Straits Times
June 20, 1999
A vast haze caused by human activity has been found to cover the Indian Ocean during winter and scientists are still trying to determine whether it will have a cooling or warming effect on the region.
Scientists have discovered that a haze of air pollution about the size of the United States covers the Indian Ocean during winter.
The phenomenon, they say, may have important implications for global climate and the regional environment of both Asia and the tropical ocean.
The brownish haze is composed of several kinds of minute by-products from the burning of fossil fuels for industry and transportation.
These elements, including soot and sulphur droplets, are blown out over the ocean from the Indian subcontinent, China and Southeast Asia during the winder monsoon when prevailing winds sweep down from the Himalayas and out to sea.
In late spring and summer, the winds reverse as part of the summer monsoon and blow the haze back across the land, where it combines with monsoon rains and falls out of the atmosphere as acid rain.
The summer monsoon is now under way, although the scientists said they had no direct evidence of how the haze was currently being affected.
They do know it persisted over the ocean, from the Bay of Bengal and the Arabian Sea southward past the Equator, throughout six weeks of intensive surveillance by aircraft, ships, balloons, satellites and land stations in February and March.
The results were announced on June 8 by the US National Science Foundation, which sponsored the US$25 million (RM95 million) project in part, and the Scripps Institution of Oceanography in San Diego.
"It appeared as if the whole Indian sub-continent was surrounded by a mountain of pollution." said Veerabhadran Ramanathan, the director of Scripps' Centre for Clouds, Chemistry and Climate, which coordinated the project.
Veerabhadran and Paul J. Crutzen, director of the Max Planck Institute for Chemistry, in Germany, are the co-chiefs of the research project.
The cloud of atmospheric aerosols, as the tiny particles and droplets of pollution are called, has at least two important implications for the environment: The acid rain it produces may harm both terrestrial and marine life, and the aerosols alter the Earth's climate by reflecting solar radiation and thereby cooling the part of the Earth beneath the haze.
The new findings are sure to complicate experts' efforts to pin down whatever influence human activity is having on global climate.
Industrial aerosols have long been known to affect North America and Europe, where most of the earth's industries have been concentrated.
Scientists believe that aerosols are diminishing over those two continents as a result of environmental controls, but aerosol emissions have been increasing in Asia as industry grows there, and that growth is expected to continue.
Globally, the cooling aerosols have combined with heat-trapping greenhouse gases like carbon dioxide to help produce a crazy-quilt pattern of human-induced climate change.
Like the aerosols, greenhouse gases are produced by industrial and transportation combustion, and scientists say they tend to warm the planet as a whole while aerosols cool some regions.
Greenhouse gases generally persist in the atmosphere for decades or even centuries, while aerosols can rain out of the atmosphere for decades or even centuries, while aerosols can rain out of the atmosphere in only a few days.
While industrial aerosols in Europe and America are generally confined to within 2,000 feet of the Earth's surface, Veerabhadran said, those observed above the Indian Ocean rose to about 10,000 feet, far higher although still below, say, the cruising altitude of commercial airliners.
Preliminary results of measurements, he said, indicate that the aerosols reflected enough sunlight to reduce the amount of solar energy absorbed by the ocean by about 10 percent. This, in turn, means that less water will evaporate from the sea, producing less rainfall.
In addition, some of the aerosols are sucked up by huge thunderstorms that characterize the equatorial region and are then mixed with water and deposited in the ocean as acid rain, which could affect marine life.
Some of these equatorial aerosols may also be transported by high-level winds to other parts of the world, he said, but this has not been established.
A complicating factor, he said, is that because of incomplete combustion, the haze has an unusually high proportion of soot.
Soot is dark, and absorbs solar radiation. This would tend to counteract the cooling effect of lighter, liquid aerosols that reflect sunlight.
"So," Veerabhadran said, "it is just too early to say at this point whether the net effect is one of cooling or warming." — NYT