One of the primary goals of INDOEX is to determine the role that aerosols play in global climate change. Early results indicate that the pollutants play a dual role in that they have both warming and cooling effects. The tiny particles produce a cooling effect in that they scatter sunlight back to space. By acting as seeds for cloud condensation, they also produce an indirect cooling effect by increasing both the longevity and reflectivity, or albedo, of clouds. The pollutants have a warming effect, however, in that they absorb a large amount of sunlight. The airborne particles over the northern Indian Ocean are unusually dark because they contain large amounts of soot and other materials from incompletely burned fuels and wastes. Dark aerosols lead to the increased absorption of solar radiation. "The soot contributes a substantial amount of heating of the atmosphere, but it also reduces the amount of sunlight reaching the ocean," Ramanathan said. "So, it is just too early to say at this point whether the net effect is one of cooling or warming."

The dark airborne particles over the Indian Ocean appear to be markedly different from those over North America and Europe, where advanced pollution control technologies remove much of the dark material and yield particles that are relatively brighter. Thus, the impact on climate processes of pollution particles stemming from Asia appears to be fundamentally different from those originating in the United States and Europe. The measurements taken in the Indian Ocean are also important because they characterize emissions from the rapidly emerging economies in this region. Emissions of pollutants are expected to increase over the Indian Ocean and in other parts of the globe as similar economies grow.

The INDOEX scientists were surprised to find that such a dense pollution layer in the Indian Ocean was caused by sources at least a th
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Contact: Cheryl Dybas
cdybas@nsf.gov
703-306-1070
National Science Foundation
8-Jun-1999