Altostratus clouds
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Courtesy of Ronald L. Holle

Clouds, Climate and Cosmic Rays
News story originally written on September 4, 2002

It is well known that our planet is becoming globally warmer, but scientists have long been perplexed why higher levels in the atmosphere have remained cool while the Earth's surface is warming.

Clouds are likely responsible for this phenomenon. "A systematic change in global cloud cover will change the atmospheric heating profile," said Fangqun Yu of the State University of New York at Albany, author of a new study. High clouds reflect sunlight and low clouds retain surface energy, so, increases in amounts of thick, low clouds can warm the surface of the Earth, but not higher levels in the atmosphere.

How might worldwide cloud cover change? Cosmic rays are partially responsible for changes in the patterns of cloudiness in the Earth's atmosphere, warming Earth's surface by generating a blanket of low, thick clouds. With increases in cosmic rays, there are increases in low clouds that warm the surface. Greenhouse gases, whose quantities have been steadily increasing in our atmosphere, increase the impact of cosmic rays. This means that with increased greenhouse gases even more low clouds are produced by the cosmic rays. Said Fangqun Yu, "the cosmic ray-induced global cloud changes could be the long sought mechanism connecting solar and climate variability".

Last modified September 4, 2002 by Lisa Gardiner.

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