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quarta-feira, 11 de maio de 2011

@BreakingScience #climate record suggests severe tropical droughts

2,300-year record suggests severe tropical droughts as northern temperatures rise via @

The study compared the record in the Pumacocha sediment core (PC) to various geological records from South America -- Cascayunga Cave (CC), the Quelccaya ice Cap (QIC), and the Cariaco Basin (CB) -- as well as the annual position of the Intertropical Convergence Zone (ITCZ). Credit: U. of Pittsburgh

A 2,300-year climate record University of Pittsburgh researchers recovered from an Andes Mountains lake reveals that as temperatures in the Northern Hemisphere rise, the planet's densely populated tropical regions will most likely experience severe water shortages as the crucial summer monsoons become drier. The Pitt team found that equatorial regions of South America already are receiving less rainfall than at any point in the past millennium.

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The researchers report in the (PNAS) that a nearly 6-foot-long from Laguna Pumacocha in Peru contains the most detailed geochemical record of fluctuations yet uncovered. The core shows pronounced dry and wet phases of the South American summer monsoons and corresponds with existing geological data of precipitation changes in the surrounding regions.

Paired with these sources, the sediment record illustrated that during the South American summer monsoon has dropped sharply since 1900—exhibiting the greatest shift in precipitation since around 300 BCE—while the Northern Hemisphere has experienced warmer temperatures.

Study coauthor Mark Abbott, a professor of geology and planetary science in Pitt's School of Arts and Sciences who also codesigned the project, said that he and his colleagues did not anticipate the rapid decrease in 20th-century rainfall that they observed. Abbott worked with lead author and recent Pitt graduate Broxton Bird; Don Rodbell, study codesigner and a geology professor at Union College in Schenectady, N.Y.; recent Pitt graduate Nathan Stansell; Pitt professor of geology and planetary science Mike Rosenmeier; and Mathias Vuille, a professor of atmospheric and environmental science at the State University of New York at Albany. Both Bird and Stansell received their PhD degrees in geology from Pitt in 2009.