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|June 12, 2000|
Carbon dioxide has competition in global warming game
Beej Jasani in San Francisco
Soot, it's been found, does more than just pollute.
Scientists have recently discovered that the large quantity of airborne soot over the Indian Ocean has the alarming ability to raise atmospheric temperatures and quicken global warming.
These latest findings are based on observations made during the Indian Ocean Experiment (INDOEX). Dr V Ramanathan, director of the Center for Clouds, Chemistry and Climate at the Scripps Institution of Oceanography, San Diego, and Dr Paul J Crutzen, Nobel Prize winner in Chemistry (1995) and Director of the Max Planck Institute for Chemistry, Germany, led the project.
Headquartered in the Maldives, INDOEX lasted four years and cost $25 million. Over 150 scientists from around the world employed ships, satellites and aircraft for this major project.
During the main six-week long experiment last February, scientists discovered a dense, dark haze, three kilometers thick and the size of the United States, cover much of the northern part of the Indian Ocean, the Arabian Sea and the Bay of Bengal, all the way up to China.
Haze is caused by a high concentration of aerosols, tiny particles of pollution. These particles are primarily made of sulphates, nitrates, soot, fly ash and mineral dust. It is, however, only a winter phenomenon (December - April), when the north-east monsoon winds blow pollutants from the mainland onto the Indian Ocean.
Up until now, scientists believed that in the daytime, these haze particles reflect sunlight back into space, allowing less solar radiation to reach Earth's surface, thus cooling it. Also, droplets form on these particles, which increases cloud cover and makes them brighter as well.
"We went there [to the Indian Ocean] expecting to find the clouds brighter than they would be if it were less polluted. But in fact, we didn't find many clouds at all," said Andy Ackerman, scientist at NASA's Ames Research Center in Moffett Field, California and a part of the INDOEX team.
This mysterious lack of cloud cover prompted them to focus their study on the soot particles present in the haze. And this new discovery, reported in a paper that was published last month in the journal Science, has caused quite a stir in the scientific world.
It notes that soot is an exception to the rule, behaving in a manner opposite to what other aerosols are known to do. A darker aerosol, soot absorbs sunlight and consequently, heats up the atmosphere. This phenomenon causes clouds to burn off and evaporate.
Andy Ackerman, who is lead author of the paper, warns that the soot measured over the Indian Ocean in 1998 and 1999 warms the surrounding area, and this effect is three to five times stronger than the global warming due to carbon dioxide.
As alarming as this sounds, the heat inducing trend of the darker aerosol, soot, versus the climate cooling trend of the lighter-colored aerosols may somewhat balance out in the end. "Different constituents of the aerosols are doing different things to the clouds," says Andy Ackerman.
Another paper published in Nature calculates that due to the absorption of sunlight by soot, the Earth receives three times less solar energy than what the atmosphere does. The authors of this paper, Dr V Ramanathan and S K Satheesh, a researcher at Scripps, predict that this reduction in sunlight reaching the ocean is likely to affect the marine ecosystem, and may also alter the monsoon cycle of the Indian subcontinent. Dr Ramanathan, who co-authored the Science paper, says it will take several years to understand fully these complicated mechanisms.
Aerosol pollution exists in most industrialized regions of the world. However, in Asia and the Indian subcontinent, the haze is unusually darker. Larger amounts of combustion-derived soot pollute the air, with a heavy population of over two billion and less stringent environmental laws sharing the blame.
Dr Ramanathan believes that studying the cloud-aerosol-climate interaction in the Indian Ocean is necessary in the light of the economic development in India and the surrounding region. "We wanted to understand how it [development] was modifying the environment," he explained.
INDOEX originally started out as a small study. As other scientists began to get interested and excited, they joined in, eventually transforming it into a major international experiment that involved the governments of the United States, some European countries, India and the Maldives.
Dr Ramanathan, who has been awarded the Volvo Environment Prize (1997) for his valuable contribution to the global warming issue, hopes the new research will do good. "Being a person of Indian origin, I'm very interested to see what's happening in our part of the world; see if we can help out, do research... give advance warning..."
He expects that over 40 papers will be published in the near future, based on observations made during INDOEX. "It started out as an exciting scientific enterprise," he added, "but then the results are quite sobering."
Besides Andy Ackerman and V Ramanathan, O B Toon, D E Stevens, A J Heymsfield and E J Welton were the others who contributed to the Science paper.
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