Global warming, drought linked
2009-03-26 14:02
Singapore - Global warming is more than a third to blame for a major drop in rainfall that includes a decade-long drought in Australia and a lengthy dry spell in the United States, a scientist said on Wednesday.
Peter Baines of Melbourne University in Australia analysed
global rainfall observations, sea surface temperature data as
well as a reconstruction of how the atmosphere has behaved over
the past 50 years to reveal rainfall winners and losers.
What he found was an underlying trend where rainfall over
the past 15 years or so has been steadily decreasing, with
global warming 37% responsible for the drop.
"The 37% is probably going to increase if global warming continues," Baines told Reuters from Perth in Western Australia, where he presented his findings at a major climate change conference.
Rainfall declining
Baines' analysis revealed four regions where rainfall has
been declining. The affected areas were the continental United
States, southeastern Australia, a large region of equatorial
Africa and the Altiplano in South America.
But there were two areas in the tropics where rainfall has
been increasing - northwestern Australia and the Amazon Basin.
"This is all part of a global pattern where the rainfall is
generally increasing in the equatorial tropics and decreasing
in the sub-tropics in mid-latitudes," Baines said.
"This is a little bit like the pattern that the (computer)
models predict for global warming but this is coming out of the
rainfall observations of the past 30 years," added Baines, of
Melbourne University's civil and environmental engineering
department.
Sea surface temperatures
The rainfall trend was also accompanied by a trend in
global sea surface temperatures (SST), he said, adding he used
temperature data going back to 1910.
Sea surface temperatures have been rising as the atmosphere
warms.
"If you take the SST data and analyse that over a long
period you can break that up into a variety of components, such
a global warming component," he said.
He also looked at the influence on rainfall of major ocean
circulation patterns that have a major impact on the world's
weather such as the Atlantic conveyor belt that brings warm
temperatures to northern Europe.
Two Pacific circulation patterns, including the Pacific
Decadal Oscillation, were also studied for their influence on
rainfall.
The key in the analysis was to strip out the influence of
the El Nino ocean-climate pattern which causes drought in
Southeast Asia and Australia and floods in Chile and Peru.
Baines, who also works for the Department of Earth Sciences
at the University of Bristol in England, said the Atlantic
conveyor belt was 27 percent to blame for the decreased
rainfall, while the two Pacific ocean circulation patterns were
30% responsible.