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Desert Diary
Climate/Dimmer Earth


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As everyone knows, our desert is famous for its clear skies and bright sunlight. What is not known by everyone, though, is that those skies are not as clear nor as bright as they were 50 years ago. This is not limited to deserts, though. Measurements of the strength of sunlight at the earth's surface shows decreases nearly everywhere, though varying from place to place. Perhaps an average value of around a 10% decrease from the 1950s to the 1990s would be fair, but with higher values in places such as the United States.

The observations and the pattern of variation indicate that, once more, human intervention on a global scale is involved. Satellite readings show that it's not a matter of a dimmer sun. This leaves air pollution as the likely culprit. Particulates in the air not only reflect sunlight back into space, but also act as nuclei for the formation of water droplets. And water droplets, of course, are the stuff of which clouds are made—clouds that reflect solar radiation into the blackness of space.
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listen to the>Audio (mp3 format) as recorded by KTEP, Public Radio for the Southwest.


Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.

Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.