Some of the worst El Niños, the infamous climate patterns that shake up weather around the world, could double in frequency in upcoming decades due to global warming, says a new study out Sunday in the journal Nature Climate Change.
During an El Niño, water temperatures in the central and eastern equatorial Pacific Ocean tend to be warmer-than-average for an extended period of time – typically at least three to five months. This warm water brings about significant changes in global weather patterns.
The most powerful El Niños – such as the ones that developed in 1982-83 and 1997-98 – are forecast to occur once every 10 years throughout the rest of this century, according to study lead author Wenju Cai of the Commonwealth Scientific and Industrial Research Organisation, Australia's national science agency. Over the past 100 years or so, however these "extreme" El Niños occurred only once every 20 years, he said.
This means that the extreme weather events fueled by El Niños – such as droughts and wildfires in Australia, floods in South America and powerful rainstorms along the U.S. West Coast – will occur more often.
The most recent El Niño ended in 2010.
The research results came from an aggregation of 20 climate models, which were used in the Intergovernmental Panel on Climate Change report.
The models found that this doubling of extreme El Niño episodes is caused by increased surface warming of the eastern equatorial Pacific Ocean because of climate change. This area of the ocean warms faster than the surrounding waters, the researchers found.
But Cai acknowledges those findings stand in contrast.to previous studies that found no solid consensus on how El Niños will change because of global warming.
"The question of how global warming will change the frequency of extreme El Niño events has challenged scientists for more than 20 years," said study co-author Mike McPhaden of the National Oceanic and Atmospheric Administration. "This research is the first comprehensive examination of the issue to produce robust and convincing results."
"It looks like a solid study," said meteorologist Michael Mann of Penn State University, who was not involved in the research. "The authors appear to provide reasonably convincing evidence that El Niño events are likely to become more extreme as the climate continues to warm, in turn implying greater future regional climate/weather extremes than past studies."
However, another expert, senior scientist Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colo, said that some aspects of the study are not really new, although it is cast in a new way. He notes that there remain issues in how well models simulate El Niño events, which means uncertainty remains on just how El Niño and the climate of the 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.
"Even if the projection for this increased frequency of extreme El Ninos is correct, there will still be extended periods of infrequent and weak El Ninos, such as has been experienced since the late 1990s (since the last big event of 1997-98)," said Lisa Goddard, director of the International Research Institute for Climate and Society with Columbia University.
"This is likely the result of decadal variability, which is something the climate community is actively researching at present," she added.
A separate study published in Nature Climate Change in 2013 found that El Niños appeared to occur a lot more than normal over the last 50 years, just as temperatures worldwide rose because of global warming, also suggesting a connection.