ClimateSevere tropical droughts as northern temperatures rise

Published 16 May 2011

A sediment core from a South American lake revealed a steady, sharp drop in crucial monsoon rainfall since 1900, leading to the driest conditions in 1,000 years as of 2007 and threatening tropical populations with water shortages; a 2,300-year climate record 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

A sediment core from a South American lake revealed a steady, sharp drop in crucial monsoon rainfall since 1900, leading to the driest conditions in 1,000 years as of 2007 and threatening tropical populations with water shortages, a team from the University of Pittsburgh, Union College, and SUNY-Albany reports in PNAS

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.

The researchers report in the Proceedings of the National Academy of Sciences(PNAS) that a nearly 6-foot-long sediment core from Laguna Pumacocha in Peru contains the most detailed geochemical record of tropical climate 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.

A University of Pittsburgh release reports that paired with these sources, the sediment record illustrated that rainfall 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 twentieth-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, New York; 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 Ph.D. degrees in geology from Pitt in 2009.

“This model suggests that tropical regions are dry to a point we would not have predicted,” Abbott said. “If the monsoons that are so critical to the water supply in tropical areas continue to diminish at this pace, it will have devastating implications for the water resources of a huge swath of the planet.”

The sediment core shows regular fluctuations in rainfall from