It's well understood that climate change is expected to increase the number of extreme weather events. What new research shows is how more warming will increase the number of a specific event: extreme El Niño seasons, which affect much of the Pacific. Looking at 20 climate models, a team of researchers from Australia and the United States found that, by the end of this century extreme El Niños could happen on average once every decade, twice as often as they currently occur.
El Niño is characterized by warmer surface waters in the Pacific, which tends to increase rainfall in the southern US and Peru, while causing drought in the western Pacific. Extreme El Niño events involve large temperature differentials across the Pacific, with some sea surface temperatures topping 82°F in the western part of the ocean, with the eastern part as many as 10 degrees cooler. The result is extreme drought conditions in Australia and islands in the western Pacific, accompanied by flooding in Ecuador and northern Peru.
The researchers point out that the 1997-98 El Niño, the strongest in 50 years, alone caused $35 billion in damage and killed 23,000 people. During that event, rainfall in central Ecuador and Peru was 10 times higher than normal. The heavy rain damaged 10 percent of Peru's health facilities, further increasing the death and disease toll.
At the same time, drought and forest fires hit Malaysia, Indonesia, and Brazil. Other research has shown that El Niño events can cause civil strife in the tropics to double, increase the rates of malaria, dengue fever, and Rift Valley fever.
Curiously, though the study shows the number of extreme El Niño events increasing, it does not show an increase in the frequency of overall El Niños. This average increase in intensity is already apparent: Over the 20th century, El Niño intensity increased by roughly 20 percent.
Considering the ramifications—the authors say such events affect "ecosystems, agriculture, tropical cyclones, drought, bushfires, floods and other extreme weather events worldwide"—how certain is this research?
Climate Central argues that some of the models used in the study have overestimated the past number of El Niños “by a wide margin,” as well as not always taking into account other climate patterns that also influence El Niño and how this might change as the climate continues to change. Conversely, Dr. Myles Allen of Oxford University, quoted by University Herald, characterized the research as being “very reasonable” and a “very sensible approach.”
That means the oft-heard scientific caveat that more research is needed applies here, although the only debate appears to be over how much extreme El Niño frequency will increase, and not whether they'll increase at all. As a singular piece of research fitting into the larger picture, it stands as yet more evidence that climate change will produce more extreme weather.