Scientists from around the world will begin the intensive field phase in February 1999 of an international experiment sponsored in part by the National Science Foundation to determine the role that pollutants known as aerosols play in cooling the planet and mitigating the effects of global warming.

The $25 million experiment called the Indian Ocean Experiment, or INDOEX, will be coordinated by the Center for Clouds, Chemistry and Climate (C4) at Scripps Institution of Oceanography, a National Science Foundation Science and Technology Center at the University of California, 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 co-chief scientists and lead an international team of scientists from England, France, Germany, India, Maldives, Mauritius, the Netherlands, Sweden, and the United States.

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.

"This is one of the first comprehensive experiments aimed at understanding the magnitude of the cooling effect of sulfates and other aerosols on climate," Ramanathan said. "One fundamental thing we hope to learn is to what extent the aerosol cooling
has offset the 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."

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.

"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 radiative forcing of climate," said Jay Fein, program director in NSF's division of atmospheric sciences, which funds INDOEX. "The project is, thus, addressing one of the key remaining issues regarding potential climate change and will shed light on the effects of aerosols on climate. This knowledge is essential for improved climate forecasts."

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 region is also a perfect natural laboratory. Continental air laden with man-made aerosols collides with pristine air from the southern Indian Ocean in a region near the equator called the Intertropical Convergence Zone (ITCZ). This mingling of polluted and clean air is particularly evident from January to April of each year during
the winter monsoon. The main INDOEX field experiments will occur during this time frame to learn whether the ITCZ may be transporting sulfates and other aerosols to other parts of the globe.

Some scientists now contemplate whether the cooling effect of aerosols may explain why a buildup of greenhouse gases in the atmosphere has not caused the planet to warm as much as predicted by climate models. Similarly, the increased concentration of atmospheric aerosols over industrial areas may help to explain why the warming trend in North America does not appear to be following the pattern seen in other parts of the world.

INDOEX aims to provide new insights on whether the regional cooling effect from aerosols may mitigate global warming from greenhouse gases.

"Until about five years ago, we thought that greenhouse warming was the dominant effect in the atmosphere. Now, new research has shown that the aerosol effect could dominate the greenhouse effect over the continents," Ramanathan said. "If aerosols reach the ITCZ, the thunderstorm clouds can transport them into the upper atmosphere where fast winds can in turn circulate them around the globe."

Malé island in the Republic of Maldives will serve as headquarters for the intensive field investigation to begin in February. A pilot phase of the experiment was completed last year. 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. The field data will be used to calibrate NASA Earth Observing System satellites to obtain a regional map of the cooling effect by aerosols. The field and satellite data also will be used to calculate the effects of aerosols in global warming prediction models.

Scientists participating in the project come from more than 50 institutions around the world, including the Max-Planck Institute for Chemistry in Mainz; the Laboratoire de Meterologie Dynamique du CNRS in Paris; the University of Utrecht in the Netherlands; the Indian Space Research Organization; the National Physical Laboratory, New Delhi; the National Institute of Oceanography, Goa; the National
Center for Atmospheric Research in Boulder, Colo.; the University of Miami; the University of Hawaii; Oregon State University at Corvallis, and NOAA's Aeronomy Laboratory in Boulder, Colo. The INDOEX International Project Office and the US INDOEX Office is located at the C4 Center at Scripps at the University of California, San Diego.

The Center for Clouds, Chemistry and Climate was established at Scripps Institution of Oceanography in 1991. The goal of this National Science Foundation Science and Technology Center is to improve our understanding of cloud-chemistry-climate interactions, thereby enhancing our knowledge of the climate system and improving our ability to predict how it will respond to human and other influences. The center brings together research groups in the United States, Europe, and Asia that have made fundamental contributions in the areas of the greenhouse effect, atmospheric chemistry, climate and global change. Recently, the center's funding was renewed for another five years beginning July 1997.

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