PARIS, Sept 24, 2009 (AFP) - Global warming periodically shifts El Nino thousands of miles to the west, potentially intensifying Asian droughts and weakening its dampening effect on Atlantic hurricanes, reports a study published Thursday.
Up to now, the tropical weather phenomenon, which strikes on average every four or five years, has generally occurred along a wide stretch of the equator in the eastern Pacific.
Such is the case with the current El Nino, which is likely to remain in place well into next year, the World Meteorological Organisation said last month.
El Nino disrupts weather patterns around the world, causing drought in Indonesia, Australia, India and eastern Brazil, and unusually heavy rainfall in the US Gulf Coast and parts of South America.
It also lowers sea surface temperatures in the Caribbean and Atlantic, which helps prevent the formation and intensity of hurricanes in that region.
But climate change has apparently given rise to an alternate form of El Nino that is likely to become more frequent over the coming decades, according to the new research, published in Nature.
"There are two El Ninos," said Ben Kirtman, a professor at the University of Miami and a co-author of the study.
"In addition to the eastern Pacific El Nino ... a second El Nino in the central Pacific is on the increase," he said in a communique. The two do not occur at the same time, he added.
This could be bad news on at least two fronts, the researchers said.
In Asia, it could intensify droughts that have already wreaked havoc in recent decades. And in the Atlantic, it could weaken the positive effect it has had up to now in mitigating the intensity of hurricanes that strike the Caribbean and the US east coast.
Researchers led by Sang-Wook Yeh of the Korea Ocean Research and Development Institute in Ansan, Korea matched sea surface temperature data from the last 150 years against future global warming scenarios laid out by the UN Intergovernmental Panel for Climate Change (IPCC).
Most of the models showed that global warming will boost the frequency of the central Pacific El Nino.
The findings are bolstered by observation: half of the most recent El Nino occurrences have been in the central rather than the eastern Pacific, compared to only one-out-of-five before that.
During a strong eastern Pacific El Nino, ocean temperatures can average 2.0 to 3.5 degrees Celsius (4.0 to 6.0 degrees Fahrenheit) above normal between the international dateline and the west coast of South America.
The warm water region also coincides with above average tropical rainfall.