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Is Global Warming Making Tibet Dustier?

January 6, 2011

by Eli Kintisch on 5 January 2011, 2:05 PM | http://news.sciencemag.org/

SAN FRANCISCO, CALIFORNIA - Sediments taken from the bottom of a lake on
the Tibetan Plateau suggest that changes in wind patterns caused by
global warming may be making the area dustier. That trend could
accelerate the melting of crucial glaciers in the Himalayas and affect
already imperiled water supplies.

Jessica Conroy, a graduate student in paleoclimatology at the University
of Arizona in Tucson, and colleagues collected sediment cores from the
bottom of Kiang Lake in southwestern Tibet using equipment suspended
from rafts. The cores track the history of climate in the region back to
1050 C.E. According to Conroy, who presented the data here at the fall
meeting of the American Geophysical Union on 15 December, the amount of
fine-grained dust in the lake sediment increased over the 20th century.
Finer dust arrives from distant desert regions hundreds of kilometers
away, suggesting stronger winds with the power to deliver the material.

Scientists have previously noted the rise of dust in the region but
attributed it to the increase in agriculture, grazing, and other
relatively local developments. Data Conroy presented showed that dusty
periods coincide with summers when a Northern Hemisphere atmospheric
phenomenon called the Arctic Oscillation is in a "positive phase." A
positive phase of this pattern in the summer leads to stronger winds in
desert areas to the north of the lake as well as south of the Himalayas.

Global warming seems to be keeping the Arctic Oscillation in its
positive phase more often, which Conroy says could mean that climate,
not just changes in the local landscape caused by human activity, could
be making southwestern Tibet dustier. Lonnie Thompson, a
paleoclimatologist at Ohio State University in Columbus, who did the
earlier work noting the rise of dust, says he was "impressed" with the
data and called the work "thoughtful." The findings mirrored patterns he
had documented within ice in a Himalayan glacier called Dasuopu,
"particularly the increase in the past century or so of dust," he says.
Conroy's hypothesized link between dust levels and the Arctic
Oscillation "probably warrants more investigation," Thompson says.

"It's going to continue to be dusty in this region, and dust can
accelerate the melting of the glaciers in the Himalayas," says Conroy.
That's because the dust lands on the white ice and makes it darker,
absorbing radiation and accelerating melting in the Himalayas. These
glaciers, which provide water for hundreds of millions of people across
Asia, are in serious danger - although a well-documented typographic
error in the 2007 IPCC report exaggerated the rate of their
disappearance. Dust also warms the air above the Tibetan Plateau,
enhancing monsoon circulation patterns, which could affect rain and
alter rainfall patterns across the southern Asia.
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