Climate Change Could Worsen African 'Megadroughts'
Date: 17-Apr-09
Country: US
Author: Deborah Zabarenko, Environment Correspondent
Climate Change Could Worsen African 'Megadroughts' Photo: Antony Njuguna
A
Kenyan Maasai herdsman walks with his cattle in search of water in Kajiado
District some 110 km (68 miles) from Nairobi February 22, 2006.
Photo: Antony Njuguna
WASHINGTON - The recent decades-long drought that killed 100,000 people in
Africa's Sahel may be a small foretaste of monstrous "megadroughts" that
could grip the region as global climate change worsens, scientists reported
on Thursday.
Droughts, some lasting for centuries, are part of the normal pattern in
sub-Saharan Africa. But the added stress of a warming world will make these
dry periods more severe and more difficult for the people who live there,
the scientists said.
"Clearly, much of West Africa is already on the edge of sustainability, and
the situation could become much more dire in the future with increased
global warming," said University of Arizona climatologist Jonathan Overpeck,
a co-author of the study published in the journal Science.
The Sahel is an area between the Sahara desert and the wetter parts of
equatorial Africa that stretches across the continent from the Atlantic
Ocean in the west to the Red Sea in the east.
Overpeck and his colleagues studied sediments beneath Lake Bosumtwi in Ghana
that gave an almost year-by-year record of droughts in the area going back
3,000 years. Until now, the instrumental climate record in this region
stretched back only 100 years or so.
The researchers found a pattern of decades-long droughts like the one that
began in the Sahel in the 1960s that killed at least 100,000 people, as well
as centuries-long "megadroughts" throughout this long period, with the most
recent lasting from 1400 to 1750.
The scientists also described signs of submerged forests that grew around
the lake when it dried up for hundreds of years. The tops of some of these
tropical trees can still be seen poking up from the lake water.
RISING TEMPERATURES, NASTIER DROUGHTS
During the recent Sahel drought, the lake's water level dropped perhaps 4.6
metres (5 yards). By contrast, during megadroughts the level fell by as much
as 27.5 metres (30 yards).
"What's disconcerting about this record is that it suggests that the most
recent drought was relatively minor in the context of the West African
drought history," said Timothy Shanahan of the University of Texas, a
co-author of the study.
The most recent decades of data culled from Lake Bosumtwi show that droughts
there appear to be linked to fluctuations in sea surface temperatures, a
pattern known as the Atlantic Multidecadal Oscillation, or AMO, the
researchers said.
"One of the scary aspects of our record is how the Atlantic ... changes the
water balance over West Africa on multidecadal time scales," Overpeck said
in a telephone briefing.
The cause of centuries-long megadroughts is not known, but he said the added
burden of climate change could make this kind of drought more devastating.
Temperatures in this region are expected to rise by 5 to 10 degrees F (2.77
to 5.55 degrees C) this century, the scientists said, even if there is some
curbing of the greenhouse emissions that spur climate change.
"We might actually proceed into the future ... we could cross a threshold
driving the (climate) system into one of those big droughts without even
knowing it's coming," Overpeck said.
(Editing by Will Dunham)
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