Peter Baines of Melbourne University in Australia analyzed 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 per cent is probably going to increase if global warming continues," Baines said as he presented his findings at a major climate change conference in Perth Australia.
Four major regions has seen a large decline in rainfall. The affected areas are the continental United States, southeastern Australia, a large region of equatorial Africa and the Altiplano in South America.
At the same time there is 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.
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 also 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 Niño ocean-climate pattern which routinely causes drought in Southeast Asia and Australia and floods in Chile and Peru.
Baines says the Atlantic conveyor belt was 27% to blame for the decreased rainfall, while the two Pacific ocean circulation patterns were 30% responsible.
See Also:
Global Warming in Russia & the North Atlantic
Global Warming: Hurricanes in Europe?
Australian Drought
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