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Global Climate Change Digest

A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

Cooling of the Upper Atmosphere (JUNE 1999)

Item #d99jun39

In its May 1, 1999, issue, the New Scientist reported on a meeting of specialists in the upper atmosphere in Pune, India, in February of this year. The conference participants had found that the mesosphere, between 50 and 90 km up, beyond the troposphere and the stratosphere, has been cooling as much as one degree per year for the past 30 years, a rate that is ten times what had been predicted. As radiatively active gases in the lower atmosphere trap the heat reflected from the Earth’s surface, radiative cooling, perhaps amplified by changes in atmospheric circulation, occurs in the upper atmosphere. As it cools, the upper atmosphere appears to be shrinking, also. Over Antarctica, the top of the mesosphere has descended about 8 km during the past 40 years. Similar observations have been made over Europe. Calculations indicate that a doubling of carbon dioxide in the atmosphere will bring the edge of space 20 km closer and that the highest reaches of the atmosphere will become less dense. These observations were cited by the scientists gathered at Pune as the latest and most unequivocal sign that global climate is changing.

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