Enormously long “megadroughts” lasting thousands of years (African Agriculture)

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http://www.africanagricultureblog.com/2011/03/ancient-mega-droughts-are-sign-of-dry.html

Ancient mega droughts are sign of dry times to come

by John D. Cox

Across the American Southwest, the idea of drought never seems very far away. There are good years and bad, of course, but it only takes a 10 percent loss of rainfall to bring on severe water-supply trouble. They don’t call it desert for nothing.

Now a a team of federal and university researchers have published a remarkably detailed record of the region’s distant hydrological past that is a must-read for anyone contemplating the populous region’s future. Their analysis of ancient lakebed sediments is published in the current issue of the journal Nature.

The team took an 80-meter-long sediment core drilled from the volcanic lakebed of Valles Caldera in northern New Mexico. The core exposed laminations that give scientists roughly 200,000 years of climate history, between 370,000 and 550,000 years ago. Temperature and precipitation patterns rise and fall over such a great expanse of time, in response to periodic changes in Earth’s orbit and atmospheric circulation. But the most striking features in the core are enormously long “megadroughts” lasting thousands of years.

Especially interesting to researchers is a 50,000-year warm period that began about 435,000 years ago when Earth’s orbital and climate conditions were pretty close to the way they are now. Within this period are two cool-wet phases and three warm-dry phases — including a southwestern drought lasting several thousand years that began and ended abruptly.

The team “found that the driest conditions occurred during the warmest phases” of the warm periods, when average annual temperature “was comparable to or higher” than modern temperatures, reported lead author paleoclimatologist Peter Fawcett of the University of New Mexico in the paper’s abstract.

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About Willem Van Cotthem

Honorary Professor of Botany, University of Ghent (Belgium). Scientific Consultant for Desertification and Sustainable Development.
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