El Niños/La Niñas: More severe with climate change?

Twenty-five or more years ago — long before computer modeling and sophisticated global weather monitoring systems — any discussion of the El Niño and La Niña phenomena was like as not to result in snickers and eye rolling.

As climate knowledge and data have increased, both have become accepted as significant influences on weather variability, responsible for both droughts and flooding over wide reaches of the earth.

Across much of the Southeast, an El Niño is generally associated with wetter/cooler-than-normal conditions and La Niña with drier/warmer-than-normal weather.

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When they are particularly strong, the impact can be severe, as with back-to-back El Niño and La Niña systems in the 1997-99 period. Both were the strongest ever recorded.

Among the impacts, the U.S. Southwest experienced one of the most severe droughts in history; Venezuela had flash flooding and landslides that killed 25,000 to 50,000 people; river floods and storms in China led to the death of thousands and displaced more than 200 million people; and Bangladesh had the most destructive flooding in modern history, with more than 50 percent of the country's land area flooded, leading to severe food shortages and the spread of waterborne epidemic diseases that affected more than 30 million people.

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The 1998 North Atlantic hurricane season also spawned one of the deadliest and strongest hurricanes on record, Mitch, which claimed more than 11,000 lives in Honduras and Nicaragua.

Economic damages from the two systems were estimated at more than $45 billion. An average El Niño is estimated to result in U.S. agricultural losses of about $2 billion, or nearly 1 percent to 2 percent of total crop output.

While El Niños and La Niñas — caused by fluctuations in ocean temperatures in the equatorial Pacific — occur with reasonably predictable regularity, every five years or so, extreme events have been rare, occurring only every 20-23 years in the last century.

But thanks to climate change, the severe versions are likely to occur with greater frequency, weather scientists say. Their number could, in fact, double.

New research published in Nature Climate Change indicates that the frequency of the strongest El Niños and La Niñas could change from once every 23 years to once every 13 years by the end of this century.

Wenju Cai, whose team at Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) ran the climate models, says 17 of 21 models point to the greater frequency for “devastating weather events with profound socio-economic consequences.”

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The study covered 200 years, using historical data for 1900-2005 and Intergovernmental Panel on Climate Change forecasts of greenhouse emissions for 2006-2099

The result was 2,100 years of virtual climate, in which only four of the 21 models didn’t predict an increase.

El Niño’s impacts are far-reaching, influencing rainfall and temperature patterns across the globe. In agriculture, these impacts are felt primary through the cycle’s effect on precipitation, particularly in the developing world where 80% of farmland is rainfed. But not all impacts are bad — while some areas may suffer from drought, others enjoy above average rainfall and good harvests.  

"Many people associate El Nino with a bad year, with drought and disasters. The truth is, in an El Nino year, there will be winners and losers in agriculture and food security." – Walter Baegthen, International Research Institute for Climate and Society

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