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Seasonal signs of pollutant cooling.

Seasonal signs of pollutant cooling

Though greenhouse gases are rapidly accumulating in the atmosphere, the global average temperature has not risen as quickly as computer models suggested it would. Over the last few years, climate researchers have come to suspect that sulfur pollution - emitted by the combustion of fossil fuels - has exerted a cooling effect, counteracting part of the expected warming over some regions of the globe (SN: 4/11/92, p.232).

Researchers at the Brookhaven National Laboratory in Upton, N.Y., now report finding temperature trends that support the sulfur theory. David E. Hunter and his colleagues focused their attention on the middle latitudes of the northern hemisphere. Scientists believe sulfur pollution wields its greatest cooling effect in the middle latitudes because this heavily industrialized belt - which includes the United States, most of Europe, Russia and China - emits approximately 90 percent of the world's sulfur pollution. The Brookhaven team divided the temperature records by season, expecting that the light-reflecting pollution would show the most influence during summer, when sunlight is most intense.

Hunter and his colleagues found that from 1854 to 1910, the record shows a strong cooling in this region of the northern hemisphere during summer. That cooling does not appear in other regions or seasons. From 1910 to 1945, the trend reversed: The northern middle latitudes showed a strong summertime warming. Then from 1945 through 1989, they continued to warm in summer but at a much slower rate than other regions.

The researchers correlate the climate trends with changes in sulfur emissions. From 1854 to 1910, records show a dramatic rise in emissions, says Hunter, consistent with a cooling over the middle latitudes at that time. From 1910 to 1945, sulfur emissions remained relatively constant, while levels of greenhouse gases rose, a relationship that matches the observed warming over the northern middle latitudes. Around 1945, sulfur emissions began rising sharply - again consistent with the slower rate of warming over that part of the globe.

Hunter says the findings suggest the possibility that the cooling from sulfur pollution - at its strongest - has roughly canceled the warming from greenhouse gases over some parts of the globe.
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Publication:Science News
Article Type:Brief Article
Date:May 30, 1992
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