Climate change could spawn more frequent El Ninos

Some of the worst El Niños, the infamous climate patterns that shakeup weather around the world, could double in frequency in upcomingdecades due to global warming, says a new study out Sunday in thejournal Nature Climate Change.

During an El Niño, watertemperatures in the central and eastern equatorial Pacific Ocean tend tobe warmer-than-average for an extended period of time - typically atleast three to five months. This warm water brings about significantchanges in global weather patterns.

The most powerful El Niños --such as the ones that developed in 1982-83 and 1997-98 -- are forecastto occur once every 10 years throughout the rest of this century,according to study lead author Wenju Cai of the Commonwealth Scientificand Industrial Research Organisation, Australia's national scienceagency. Over the past 100 years or so, however these "extreme" El Niñosoccurred only once every 20 years, he said.

This means that theextreme weather events fueled by El Niños - such as droughts andwildfires in Australia, floods in South America, and powerful rainstormsalong the U.S. West Coast -- will occur more often.

The most recent El Niño ended in 2010.

Theresearch results came from an aggregation of 20 climate models (thatwere used in the Intergovernmental Panel on Climate Change report)

Themodels found that this doubling of extreme El Niño episodes is causedby increased surface warming of the eastern equatorial Pacific Oceanbecause of climate change. This area of the ocean warms faster than thesurrounding waters, the researchers found.

But Caiacknowledges.those findings stand in contrast.to previous studies thatfound no solid consensus on how El Niños will change because of globalwarming.

"The question of how global warming will change thefrequency of extreme El Niño events has challenged scientists for morethan 20 years," said study co-author Mike McPhaden of the NationalOceanic and Atmospheric Administration. "This research is the firstcomprehensive examination of the issue to produce robust and convincingresults."

"It looks like a solid study," said meteorologistMichael Mann of Penn State University, who was not involved in theresearch. "The authors appear to provide reasonably convincing evidencethat El Niño events are likely to become more extreme as the climatecontinues to warm, in turn implying greater future regionalclimate/weather extremes than past studies."

However, anotherexpert, senior scientist Kevin Trenberth of the National Center forAtmospheric Research in Boulder, Colo, said that some aspects of thestudy are not really new, although it is cast in a new way. He notesthat there remain issues in how well models simulate El Niño events,which means uncertainty remains on just how El Niño and the climate ofthe tropical Pacific will actually change.

He suggests that a way forward is to also look at the atmospheric component of El Niño and how that is changing.

"Evenif the projection for this increased frequency of extreme El Ninos iscorrect, there will still be extended periods of infrequent and weak ElNinos, such as has been experienced since the late 1990s (since the lastbig event of 1997-98)," said Lisa Goddard, director of theInternational Research Institute for Climate and Society with ColumbiaUniversity.

"This is likely the result of decadal variability,which is something the climate community is actively researching atpresent," she added.

A separate study published in Nature Climate Change in2013 found that El Niños appeared to occur a lot more than normal overthe last 50 years, just as temperatures worldwide rose because of globalwarming, also suggesting a connection.


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