Is climate change supercharging El Nino? Scientists don't agree.

It’s a vigorous debate taking place right now among scientists around the world, with far-reaching implications for extreme weather and costly disasters: Is climate change making El Nino more intense?

El Nino, the natural phenomenon that occurs every few years and pushes up global temperatures, has just begun and is expected to continue through 2027. Scientists say this latest version is likely to be especially potent and could smash records.

As greenhouse gasses heat the planet, El Nino events over the past few decades have been comparatively strong. The run of powerful El Ninos since the 1980s stands out when measured against the past 600 years.

That’s led some scientists to suggest that climate change is supercharging El Nino. Others say there is no clear evidence to support that theory.

“It’s highly contested, because it’s such an important question to get right,” said Kim Cobb, a climate scientist and the director of the Institute at Brown for Environment and Society.

It’s a mystery that might not become clearer until years into the future, as more data piles up.

The question is crucial, because El Ninos disrupt weather patterns globally, often in devastating ways -- driving temperatures higher, increasing the likelihood of drought in some places and flooding in others. The events are essentially ocean anomalies, and if climate change makes these anomalies larger in size, that means more chaos and damage.

But the debate shows that there are limits to how fully scientists can understand some of the most complicated consequences of rising greenhouse gas emissions, which result primarily from the burning of fossil fuels.

El Nino events are notoriously complex. They are driven not by a single cause, but by a series of feedback loops in the ocean and atmosphere. The National Oceanic and Atmospheric Administration once described El Nino, and its cool Pacific counterpart known as La Nina, as a cycle “controlled by hundreds of dimmer switches.” Climate change can fiddle with those switches, turning some up and others down. But does that lead to a stronger or weaker signal?

“El Nino is the noisiest part of the climate system,” said Axel Timmermann, the director of the IBS Center for Climate Physics in Busan, South Korea. “We’re trying to look for a change in the noise.”

Of 16 scientists who spoke with the Times, eight said they see compelling evidence that climate change is likely increasing the intensity of El Nino events. Among them is Michael McPhaden, a senior scientist at NOAA, who cautioned that the science is “very uncertain,” but said the development of another strong El Nino this year would be “pretty remarkable.”

If the current El Nino reaches the proportions that many forecast, it would mean three of the six strongest events since 1950 have come in the last 11 years.

El Nino events are measured by looking at changes in sea surface temperatures in a vast rectangular zone in the central Pacific, where temperatures are currently soaring. Many forecasts indicate that temperatures there this year could rise more than 5.4 degrees Fahrenheit, or 3 degrees Celsius, above the longer-term average, giving rise to an El Nino of unprecedented amplitude.

“It could be evidence that a climate change signal in today’s ENSO cycle is beginning to emerge from the background noise,” McPhaden said, using the acronym for the cycle of El Ninos and La Ninas.

Perhaps the most assertive case is made by Wenju Cai, a scientist at the Ocean University of China, who has spent more than 20 years running climate models and trying to tease out a potential link between rising emissions and more powerful El Ninos. In a 2023 study published in Nature, Cai and other scientists simulated hundreds of years of El Nino and La Nina events in an imaginary world where greenhouse gas concentrations remained at the low levels of before the Industrial Revolution. The odds of such a world producing a 60-year run of strong events comparable to modern times: 2.5%.

“It’s almost impossible to have this without climate change,” Cai said.

Many future-looking models also project El Nino intensity to increase.

Still, other scientists caution that models can have flaws. They note that there are limits in the historic record. Precise oceanic readings date back to the 1950s. A decent account of ocean temperatures, from sailors’ logbooks, extends into the 1800s. Beyond that, scientists have tried to understand El Nino’s fluctuations by looking for signatures of weather and temperature change left in corals and tree rings. That provides a meaningful estimate about the amplitude and frequency of past events, but not certainty.

Clara Deser, a senior scientist at the National Center for Atmospheric Research, said the El Ninos of recent decades might be “just a random signal.”

“I’m the skeptical scientist,” Deser said. “How much is just due to the chaos in the climate system that can give you a whole string of heads -- or tails -- for no apparent reason?”

Because there is no consensus, scientific groups have tended to move carefully. In 2021, the Intergovernmental Panel on Climate Change, the world’s preeminent climate science body, wrote that there was “low confidence” that human-caused climate change had influenced the changes in El Nino and La Nina. Earlier this month, the World Meteorological Organization, in an advisory about the developing El Nino, said there was “no evidence that climate change increases the frequency or intensity of El Nino events.”

Responding to a question from the Times, the WMO stated that its position reflects “the current assessed state of the science.”

“However, it is important also to acknowledge the ongoing scientific debate,” the organization said. “This is not a settled scientific question.”

Cobb, an IPCC lead author, said she personally thinks that climate change is intensifying the pattern. In 2019, she coauthored a research paper, based on coral analysis, that concluded modern day El Nino extremes were “significantly stronger than those of the preindustrial era in the central tropical Pacific.”

There is widespread agreement that any El Nino occurring now, compared with preindustrial times, will yield more extremes around the world, with a moister atmosphere supercharging floods and hotter temperatures amplifying droughts.

“El Nino conditions will pour fuel on the fire of a warming world,” United Nations Secretary-General António Guterres said this month. “Impacts will hit even harder.”

This article originally appeared in The New York Times.

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