Read our COVID-19 research and news.

Trouble ahead? A pool of warm water (in red) is moving east in the tropical Pacific Ocean. If it reaches the surface, it could trigger El Niño.

Trouble ahead? A pool of warm water (in red) is moving east in the tropical Pacific Ocean. If it reaches the surface, it could trigger El Niño.

Dan Pisut/NOAA; (data) GODAS/CPC

El Niño Is Coming Back

The little boy could soon be back. El Niño, a periodic warming in the waters of the eastern tropical Pacific Ocean, will probably emerge in the coming months, according to a forecast issued yesterday by the Climate Prediction Center (CPC) of the National Oceanic and Atmospheric Administration (NOAA). If strong, the El Niño event could not only wreak havoc on weather around the world, but could also trigger a resumption of global warming that has been seemingly stalled for the last 15 years.

The prediction center found that there is a 58% chance that El Niño will emerge within the next 3 months. By the early fall, that probability rises to 78%. “We’re more confident than we ever have been,” says Michelle L’Heureux, a climate scientist at the prediction center, located in College Park, Maryland.

El Niño is defined as a temperature anomaly of at least half a degree Celsius in the waters of a region of the equatorial Pacific. Once the warm water reaches the surface, it interacts with the atmosphere, creating weather patterns that can cause droughts, storms, fires, and floods throughout the world. The last El Niño occurred in 2009 to 2010, and the last big one, in 1997 to 1998, caused billions of dollars of damage around the globe.

Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research in Boulder, Colorado, says the coming event could rival the one from 1997. He has been monitoring sea levels with satellite altimetry data and has noticed about a 20-centimeter difference between the western and eastern tropical Pacific.

In the past 15 years, Trenberth says, winds associated with La Niña—El Niño’s sister effect—have piled up warm water in the western Pacific, near the Philippines. Those winds have largely collapsed this year, and so those waters are moving back east. “It’s been waiting to slop back, and is now doing so, and will be very hard to stop,” he says. He also points out that NOAA based its prediction mostly on data from April—and says more recent data show strong signs that waters off the coast of Peru are continuing to warm. “I don’t think we’ve seen anything like this before,” he says.

For Anthony Barnston, it’s still too early to say how strong the event could be. Barnston is a climate scientist at Columbia University’s International Research Institute for Climate and Society in Palisades, New York, which jointly issues the El Niño forecasts with NOAA’s CPC. He says that May is an uncertain time for tropical weather systems and that unstable winds could as easily undermine the gathering El Niño as they could strengthen it. “There’s been a lot of buzz in the media about a superstrong event and I think that has been premature,” Barnston says.

The impacts of El Niño vary across the globe, by season and location—and they are not all bad. In southern California, for example, El Niño typically brings heavy rains—and that could be a blessing for a region suffering from severe drought.

For climate scientists, a major question is whether the coming event will be big enough to flip the world into the warm phase of the Pacific Decadal Oscillation (PDO), a 20- to 30-year climate cycle that is related to El Niño or La Niña conditions. For nearly the past 20 years—probably since 1997 to 1998—the PDO has been in a cool phase, and La Niña conditions have typically prevailed. There is tenuous evidence that a strong El Niño event could push the PDO back into a warm phase—one in which El Niño events would be more common. That could allow heat from the ocean to be released into the atmosphere—causing a jump in atmospheric global warming, Trenberth says: “This could be a very important year.”