Aerosols, clouds, climate get $25 million study

In a model simulation of sulfate aerosol visible optical depth, January, above, shows little sulfate is transported from the subcontinent. By April, below, there is significant transport of sulfate aerosol over the Indian Ocean

February 3, 1999
Web posted at: 4:20 PM EST

By Environmental News Network staff

(ENN) -- There seems to be a general consensus that humans are changing global climate, but are we heating it up, cooling it down or both?

Atmospheric interaction between greenhouse gases, which are causing global warming, and aerosol pollutants, which are known to cool the planet, have made building climate prediction models a tad difficult. An international study is now under way to try to determine how the aerosols work.

Aerosol cooling is one of the largest remaining sources of uncertainty in predicting future climate. A $25 million study, known as the Indian Ocean Experiment or INDOEX, is designed to collect data that will provide scientists with crucial information needed to develop more accurate global climate prediction models.

"The project is addressing one of the key remaining issues regarding potential climate change. This knowledge is essential to improve climate forecasts," says Jay Fein, program director in the National Science Foundation Division of Atmospheric Sciences, which funds INDOEX.

Aerosols are tiny particles about a micron (one millionth of a meter) or so in diameter that scatter sunlight back to space, causing a regional cooling effect. The particles also can have an indirect cooling effect on climate by acting as seeds for cloud condensation, thereby increasing the reflectivity of clouds. Think of the tiny particles as trillions of tiny mirrors floating in the sky, reflecting sunlight back to space.

Concentrated predominantly over the industrial areas of the Northern Hemisphere, aerosols include sulfates, soot, organic carbon and mineral dust, and are produced both naturally and by human activities. Sulfate aerosols also contribute to acid rain and haziness.

"This is one of the first comprehensive experiments aimed at understanding the magnitude of the cooling effect of sulfates and other aerosols on climate," said V. Ramanathan, director of the Center for Clouds, Chemistry and Climate at the Scripps Institution of Oceanography, which is coordinating the study.

"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," he said.

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.

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