Extreme versions of the El Nino weather phenomenon - which can bring torrential rains and flooding to one part of the world and catastrophic drought and forest fires to another - could double in frequency in the next 100 years because of global warming, a study has found.
Scientists have for the first time detected a possible link between increasing global temperatures and the more extreme versions of El Nino, when rainfall patterns across the Pacific shift dramatically from their normal range.
They believe that the frequency of extreme conditions could double, increasing their occurrence from once every 20 years to once every 10 years.
The last extreme El Nino occurred in 1997-1998 and killed as many as 23,000 people worldwide.
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El Nino causes intense rainfall in the eastern equatorial Pacific, where cold, dry conditions normally prevail, and intense drought in the western equatorial regions of the Pacific, including Australia. A change in the direction of ocean currents in the equatorial Pacific is a signature feature of El Nino, where changes to the sea surface are intimately linked with variations in wind patterns and rainfall distribution.
Extreme El Ninos occur when the sea surface temperatures exceed 28C in the normally cold waters of the eastern equatorial Pacific.
Until now, climate scientists were unable to establish any association between the size and frequency of El Nino and rising global temperatures.
However, findings based on analysing 20 different computer models of the global climate have now found a statistically significant link between global temperatures and El Nino.
"Our research ... found a doubling of events from the present day through the next century in response to greenhouse warming," said Dr Wenju Cai of Australia's Commonwealth Scientific and Industrial Research Organisation and lead author of the study.