Stories

El Niño may make a comeback this fall and winter

Note: Temperature anomalies are relative to the 1985 to 2012 average; Data: National Oceanic and Atmospheric Administration; Map: Chris Canipe/Axios

Odds favor a return this year of the climate phenomenon known as El Niño — above-average sea surface temperatures in the equatorial tropical Pacific Ocean and related changes in weather patterns.

Why it matters: Depending on their intensity and exact location, El Niño events can alter global weather patterns — favoring above average precipitation in the parched state of California, for example, while inducing drought elsewhere. Typically, such events develop sometime in late summer or early fall, and peak during the winter.

Such events also can provide a natural pulse of heat released from the ocean to the atmosphere, boosting the odds that 2018 and possibly 2019 could be among the top five warmest years on record.

The big picture: The last El Niño event took place in 2015 and 2016, and it was one of the strongest on record. Michelle L’Heureux, a meteorologist at NOAA's Climate Prediction Center in Maryland, tells Axios that the upcoming event — which has about a 70% likelihood of occurring by the upcoming winter — is unlikely to be as potent.

"If something forms it’s likely to be on the weaker side of things," she said. "In general, weaker events tend to be a bit tougher to predict than stronger events.”

For signs of El Niño, scientists like L'Heureux look at sea surface temperatures in specific parts of the tropical Pacific, known as El Niño regions. These are the boxed areas on the sea surface temperature chart. In recent weeks, ocean temperatures have increased in parts of these areas.

But the formation of El Niño is a complicated dance between air and sea, and now, L'Heureux says, it's the atmosphere's turn to alter trade winds in a way that reinforces the changes in the water. These air and ocean feedbacks are what really get an El Niño going.