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Solar radiation is absorbed by the earth and is subsequently reemitted. The buildup of carbon dioxide and certain other gases in the earth's atmosphere traps some of that radiation. This is known as the greenhouse effect and is believed to contribute to a warming of the earth's climate. Concerns are growing that, in addition to carbon dioxide and other conventional greenhouse gases, certain air pollutants may affect the climate. GAO was asked to examine (1) the extent of agreement among scientists regarding the effect on the climate of three air pollutants--black carbon (soot), ground-level ozone, and sulfate aerosols--and (2) seven countries' efforts to control these pollutants, trends in these substances in these countries over the past 2 decades, and estimates for the next decade. GAO was also asked to summarize the relationship between economic growth and environmental pollution. The seven countries include four that are economically developed--Germany, Japan, the United Kingdom, and the United States--and three that are developing--China, India, and Mexico. These countries were chosen because they have large economies with a high potential to emit these pollutants. The two federal agencies asked to comment generally agreed with the information presented in this report.

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