“The majority of climate models say that El Nino amplitude shall go up in a warming climate, and all of our paleoclimate records say that we're currently in a more active period of El Niño than the last several 1,000 years,” Callahan says.

Research published in August uses data collected from ancient coral, and provides that 1,000-year glimpse Callahan mentions. (He wasn’t involved with the study.) The scientists found an uptick in El Niño amplitude that neatly mirrors when humans started pumping greenhouse gases into the atmosphere, though they didn’t attempt to attribute the shift to climate change.

This year’s El Niño will provide another data point to help researchers suss things out.

How Is El Niño Impacting Climate Change?

But as Callahan notes, there’s also an important question about how El Niño is layering on top of climate change.

“Even if climate change has not made the event itself stronger, even if the [sea surface temperature] anomalies are totally natural, the presence of those SSTs in a climate that has been changed by global warming might produce unprecedented impacts,” he says.

El Niño’s impacts on weather—known as teleconnections—are well known, from increasing the odds of drought in the Amazon and Indonesia to juicing precipitation in the Southwest US and lowering the odds of Atlantic hurricanes.

Such an extreme event layered on top of climate change doesn’t mean teleconnections get thrown out the window, though. In fact, some of them may be even more intense.

“We can no longer place as much confidence in the knowledge we’ve gathered from data regarding how El Niño manifests in terms of weather and climate in different parts of the planet,” says Estrada.

What El Niño Means for Climate Risk

From a risk perspective, Estrada believes it’s important to understand how the two phenomena interact and how that combination will affect societies.

He and Callahan’s main concern is not merely whether this El Niño will be the most intense on record but rather the combination of an exceptional event with a climate that has warmed significantly.

“Surprises are the last thing you want when you’re trying to manage risk,” Estrada says.

Callahan’s work shows that the impacts of El Niño on society are extreme, with the most severe events knocking off trillions of dollars from the global GDP. Ecosystems also suffer greatly, particularly coral reefs, which are facing a mass bleaching event.

Given this scenario, the United Nations and other international organizations have called for urgent adaptation measures to safeguard the well-being of the at-risk populations and ecosystems. Some places are already doing that: California preemptively declared a state of emergency last month.

“El Niño conditions will pour fuel on the fire of a warming world. Impacts will hit even harder, travel even farther, and cross borders with devastating speed,” UN Secretary-General António Guterres said last month.

Additional reporting by Brian Kahn.