The current El Niño could become the strongest ever, according the World Meteorological Organization – but are El Niños in general getting stronger due to climate change? New evidence suggests.. maybe.
The Pacific El Niño–Southern Oscillation (ENSO) generates climate extremes that endanger ecosystems, infrastructure, and human well-being worldwide. The response of this system to climate warming is poorly constrained, due both to data scarcity and uncertainties in climate models. The geochemistry of Galápagos coral skeletons across the past millennium reveals a large recent increase in interannual variability of sea surface temperature in the eastern equatorial Pacific compared to existing paleorecords that exceeds simulated natural variability. This increase parallels rising global temperature and results from stronger El Niño events. Central Pacific coral data also show increased variability, although less distinctly than in the Galápagos. Our results provide long-term context for understanding ENSO variability trends, with troubling implications for climate extremes.
The vibrant biodiversity of the Galápagos Islands has helped biologists from Charles Darwin onward unlock the mysteries of evolution. Now, corals growing around the archipelago in the tropical Pacific Ocean are providing clues to another enduring puzzle: whether global warming is changing El Niño, the recurring Pacific climate cycle that drives extreme weather around the world.
Climate models have offered conflicting answers so far. Historical El Niño records are too short to reveal a clear trend. And El Niño’s own large natural swings have made it difficult to tease out any human influence.
But a 1000-year archive preserved in fossil corals from the Galápagos offers some of the strongest evidence yet that global warming is already making El Niño stronger. Reporting today online in Science, researchers found that temperature swings recorded in Galápagos corals—a place where the El Niño signal is strong—have intensified by 36% over the past 4 decades, far beyond anything seen in previous centuries. Along with other coral results elsewhere in the Pacific, the findings suggest “there’s something about this important source of climate extremes that has already changed in recent decades,” says Kim Cobb, a climate scientist at Brown University who was not part of the study.
The study doesn’t prove climate change is the culprit. But because the intensification coincides with rapid postindustrial warming and exceeds El Niño’s natural variability, the authors argue that human-driven warming is the leading explanation. “That’s the thing that has changed over that time,” says Julia Cole, a paleoclimatologist at the University of Michigan who led the study. “So if I get pushback on that, I would like to know what the alternative is.”
The stakes are enormous, as Cole herself witnessed when she first visited the Galápagos in 1989 and saw the devastation that spiking ocean temperatures during a 1982–83 El Niño inflicted on the islands’ coral reefs. Beyond ecological damage, the extreme weather during large El Niño events can cause trillions of dollars of economic losses. As forecasters warnthat this year’s El Niño could end up the strongest in nearly a century, understanding whether climate change itself is strengthening the events has taken on new urgency.
“This system is the largest source of climate extremes on our planet,” Cobb says. “And if it is in itself becoming more extreme, that has some very serious implications for society, and it’s information that we should be acting on.”
El Niño events develop every 2 to 7 years, when weaker trade winds allow warmer waters from the western Pacific to flow east and pile up near the Galápagos. Through “teleconnections” in the atmosphere, the events have far-flung effects, for example causing flooding in South America and devastating droughts in some parts of Africa.
Diagnosing how the events might be changing has proved difficult. El Niño depends on subtle interactions among winds, ocean currents, and sea-surface temperatures that climate models struggle to reproduce. In many simulations, the eastern tropical Pacific starts out too cold. Those kinds of errors can ripple through the feedbacks that generate El Niño, causing models to disagree on how the phenomenon will respond to greenhouse warming. “Those can create uncertainty,” says Agus Santoso, a climate scientist at the Laoshan Laboratory.
Historical records haven’t delivered a clear verdict either. El Niño records span little more than a century, and satellite observations of the Pacific, critical to watching the events unfold, extend back only to the 1980s. But in ancient corals scientists can trace the phenomenon over centuries. “Corals are one of the best games in town for El Niño,” says Judson Partin, a geophysicist at the University of Texas at Austin who has been teasing El Niño signals from corals in Vanuatu, an archipelago in the southwestern Pacific.
Corals build their skeletons from calcium carbonate precipitated from the surrounding water, adding a band of new growth each year. In the Galápagos, Cole and her colleagues drilled cores from corals—both on the beach and underwater. Back in the lab, the researchers measured trace amounts of strontium trapped in each carbonate layer. During El Niño events, when the Galápagos waters warm, the carbonate captures fewer of the large strontium atoms from the water.
The researchers also measured the carbonate’s ratio of heavy oxygen, O18, to ordinary O16. Warmer water favors the incorporation of lighter oxygen, lowering the ratio. Together, the signals provided a record of El Niño–driven temperature swings stretching back centuries. The team found those swings grew significantly stronger after global warming took off—far stronger than natural variability could explain.
The new findings echo an analysis of fossil corals from Kirimati in the central Pacific that Cobb and her colleagues reported in 2019, which found a 25% increase in El Niño variability. But the signal is even stronger in the Galápagos, where the warming effects from El Niño are the most extreme.
That observation is based on a reconstruction by Cole and her colleagues of sea surface temperatures in the eastern Pacific Ocean in the millennium before the Industrial Revolution, published today in Science1. According to the analysis of coral skeletons from the Galapagos Islands, the past century has seen strong El Niño events happening more frequently than in the 1,000 years before human-generated greenhouse-gas emissions began to warm the planet.
Many climate models project that this trend towards more-frequent strong El Niños will continue with climate change this century. These events lead to a temporary surge in global average temperatures, and influence the weather in particular places around the globe, with consequences for ecosystemsand economies. “We need to think about how to prepare better so that these aren’t as catastrophic for us,” says Cole, who is at the University of Michigan in Ann Arbor.
However, the interactions between the ocean and the atmosphere that drive El Niño events are complex, so there is still uncertainty about how cycles of Pacific temperature will change this century. “Corals give us a time machine to look into the past,” says Cole. “They don’t give us a time machine to look into the future.”
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Below, “America’s Meteorologist” Ryan Hall never says the word “climate” to his decidedly MAGA audience, but he gives a rundown here on what to expect with this year’s pattern.