El Niños to strengthen because of global warming, will cause 'more extreme weather', study says

El Niños will be stronger and more frequent in the decades ahead  because of global warming, causing “more extreme events” in the United States and around the world, a news study says.

A natural phenomenon marked by warmer-than-average seawater in the tropical Pacific Ocean, El Niño is Earth’s most influential climate pattern. A weak one is forecast to form at some point this winter, federal scientists have said.

Rather than once every 15 years, powerful El Niños will occur roughly once every 10 years, said study lead author Wenju Cai, a scientist with the Commonwealth Scientific and Industrial Research Organization in Australia.

Researchers used 17 climate models to determine how ocean temperatures will increase by 2100 as levels of carbon dioxide and other greenhouse gases increase in Earth's atmosphere. 

They found that the physical processes in the ocean and atmosphere that produce strong El Niños will be supercharged by human-caused climate change. 

The study was published in Nature, a peer-reviewed British journal.

What does this mean for California?

Strong El Niño events often bring pummeling rains across the state.

“This adds to the evidence that what we’ve experienced in California over the last several years is consistent with what we can expect from global warming,” said Noah Diffenbaugh, a climate scientist at Stanford University who was not involved in the study.

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In general, El Niño affects California weather by influencing whether a ridge of high pressure sets up in the atmosphere and blocks storms from hitting the state, Diffenbaugh says. If that ridge is absent, a few intense events — in which so-called atmospheric rivers deliver huge amounts of precipitation in the span of a few days — often account for most of the state’s annual rainfall.

“Are those atmospheric rivers getting blocked or not?” Diffenbaugh said. “That’s essentially what makes a wet year or dry year in California.”

Strong La Niñas, which usually follow, contribute to drought.

The new results square with other recent studies that foreshadow a future of increased water extremes for California under climate change.

Work by Diffenbaugh and others suggests that atmospheric patterns that block storms will become more common, and that these dry spells will still be punctuated by very wet years. This will present real challenges for water managers, Diffenbaugh said.

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California’s water infrastructure relies on the state’s snowpack, which gradually melts in the spring and summer, and on dams that provide both flood control and water storage. But projected changes will increasingly bring these goals into conflict.

Intense storms, and an increase in the proportion of precipitation that falls as rain rather than snow, raise the risk of floods.

As in the 2017 Oroville Dam crisis, managers will have to release water to prevent reservoirs from overflowing — or collapsing. But that reduces the supply of water available later, after the rain stops. And that supply will become increasingly critical as climate change amplifies droughts.

What’s ahead for California?

Experts say the state must take a new approach to managing water in the future.

One part of the solution may be to store more water underground, rather than in reservoirs, Diffenbaugh said. Projects to replenish groundwater have already sprung up from Sacramento to Los Angeles, where managers use spreading ponds to let surface water percolate down through the soil, or inject it directly into aquifers.

Efforts like the Central Valley Flood Protection Plan also call for restoring riparian ecosystems to limit the damage from intense runoff.

California’s water treatment plants and storm water system will be stressed by increasingly volatile weather too, said Jamesine Rogers Gibson, a climate analyst at the Union of Concerned Scientists who studies California.

Rogers Gibson said California is at a crossroads.

“Our existing infrastructure is reaching the end of its useful life and needs to be replaced,” she said. “We have the opportunity to build for the future.”

From reports by Doyle Rice of USA TODAY and Julia Rosen of the Los Angeles Times via Tribune Content Agency