Feb. 1, 1999 Pollutants known as aerosols play a role in cooling the planet and mitigating the effects of global warming. Scientists from around the world are now trying to find out how; the intensive field phase of an experiment sponsored in part by the National Science Foundation (NSF) is beginning this week.
The $25-million Indian Ocean Experiment, or INDOEX, will be coordinated by the Center for Clouds, Chemistry and Climate (C4) at the Scripps Institution of Oceanography (SIO). "C4", an NSF Science and Technology Center, is based at the University of California at San Diego. Paul J. Crutzen, director of the Max Planck Institute for Chemistry and a 1995 Nobel Laureate in Chemistry, and V. Ramanathan, director of C4 at the Scripps Institution of Oceanography, will serve as INDOEX co-chief scientists.
Aerosol cooling is one of the largest remaining sources of uncertainty in predicting future climate. Data collected during INDOEX will provide scientists with crucial information needed to develop more accurate global climate prediction models.
"INDOEX scientists will document the chemical and physical properties of natural and human-produced atmospheric aerosols and use these observations to study and model the complex interactions among atmospheric aerosols, clouds and climate," says Jay Fein, program director in NSF's division of atmospheric sciences, which funds INDOEX. "The project is addressing one of the key remaining issues regarding potential climate change. This knowledge is essential to improve climate forecasts."
Aerosols are tiny particles of about a micron (one millionth of a meter) or so in diameter that scatter sunlight back to space and, thus, cause a regional cooling effect. The particles also can have an indirect cooling effect on climate by acting as seeds for cloud condensation and, thus, increasing the reflectivity, or albedo, of clouds. The effect of sulfate aerosols is equivalent to that of trillions of tiny mirrors floating in the sky, reflecting sunlight back to space. Concentrated predominantly over the industrial areas of the northern hemisphere, sulfates contribute to acid rain and haziness. In addition to sulfates, aerosols also include pollutants such as soot, organic carbon and mineral dust, and are produced both naturally and by human activities.
"This is one of the first comprehensive experiments aimed at understanding the magnitude of the cooling effect of sulfates and other aerosols on climate," says Ramanathan. "We hope to learn the extent to which aerosol cooling has offset global warming due to human-produced greenhouse gases, and how that may change with increased regulation of aerosol emissions in the United States and Europe."
The scientists chose the Indian Ocean region as the site for INDOEX because the Indian subcontinent and surrounding nations are rich sources for many kinds of aerosols, including those produced from industrial and auto emissions, biomass burning and soil dust. With Asia's population rising at a dramatic rate, the amount of sulfur dioxide released is expected to increase.
The Republic of Maldives will serve as headquarters for the intensive field investigation. Scientists will use ships, aircraft and land stations to collect data from the sea surface through the lower stratosphere on aerosol composition, reactive atmospheric gases, solar radiation fluxes, winds and water vapor distribution.
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