What an exceptionally powerful El Niño could mean for hurricanes, drought and flooding

Rachel Feltman: For Scientific American’s Science Quickly, I’m Rachel Feltman.

You’ve probably heard by now, possibly even on this very podcast, that this year’s El Niño is on track to be one of the strongest ever recorded. But what does that mean for our weather forecasts?

Scientific American’s senior editor for Earth and environment Andrea Thompson is here to demystify this atmospheric phenomenon.

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Thanks so much for coming on to chat with us.

Andrea Thompson: Thanks for having me.

Feltman: So we’ve talked, briefly, about this year’s El Niño in a couple other episodes. But let’s start with the basics just to refresh our listeners’ memories. What exactly is El Niño?

Thompson: Right. So it’s this, sort of, cyclical climate phenomenon. Its epicenter is in the tropical Pacific Ocean. And so basically in, sort of, normal times or on average, trade winds blow from east to west and across the tropical Pacific, and that, sort of, piles warm water up around Indonesia.

But in El Niño times, those winds weaken or can even reverse, and that means all of that warm water, sort of, sloshes back over toward the eastern tropical Pacific. And that can have really big impacts because that heat isn’t just limited to the ocean; it’s releasing out into the atmosphere. And that changes where clouds and storms form, which has, sort of, this domino effect in the atmosphere that can change major weather circulation patterns.

And, for example, it tends to quash hurricane activity in the Atlantic because you get a lot of what we call wind shear, so sort of cross-cutting winds, whereas in the Pacific Ocean, it tends to ramp up hurricane activity, which we’ve seen both of those play out over this hurricane season with really not a lot happening in the Atlantic and then whole bunch of flurry of storms in the Pacific.

And this particular El Niño is really, really strong; so the, the warm waters in the Eastern Pacific right now are just record-breakingly hot in terms of basically any El Niño we’ve seen in our lifetimes.

Feltman: Well and we’ve heard a lot about how this year’s El Niño is so intense. So I guess, a few questions there that we can tackle one at a time. How intense is it? How do we know? And then: What kinds of impacts are we gonna see because of that? So let’s start with just, you know, what do we mean by saying this is such a powerful El Niño, and how does it compare to previous years?

Thompson: Right. So we mainly measure that based on the sea surface temperatures in a specific part of the Pacific Ocean. And we, sort of, monitor what those temperatures are doing. If they reach a certain threshold, that’s when we say, “We’re in an El Niño,” and then if they get, you know, really high, then you could say, “This is a very strong El Niño.”

And these have been breaking records since September. I talk to climate scientists who are, kind of, just aghast at how strong this one is. Right now, temperatures in the, sort of, core part of the Pacific where we monitor El Niño are about 3.5 degrees Celsius above normal. That is astounding. They could reach four degrees Celsius above normal, when this event, sort of, peaks, which typically happens in the November-December timeframe for El Niños. And those just, sort of, absolutely smash any heat records we have, at least with direct temperature measurements. Those go back to, into the 19th century, and the, sort of, the record we have was set by an El Niño in 1877.

We can also estimate sea surface temperatures going further back than, you know, direct temperature measurements based on things like tree growth rings, coral growth rings, and those tree rings tell us how El Niño–related precipitation changes happened. And then coral growth rings are actually a little bit more direct. How the coral grows is related to sea surface temperatures. And so those we can build out an estimate going back to around the year 1100, and this would probably set records even going back that far. So this is a truly astounding event.

Feltman: Wow. And do we know why this is happening?

Thompson: It can be hard to say. So, you know, El Niño and especially really big El Niños are still relatively rare events, and so you don’t quite have enough data to really be able to piece out why they happen when they happen. Anytime data is rare, it’s very hard to find a trend. There is some new research that indicates that climate change may be pushing us more toward these really strong El Niños. That’s based also in coral records. So it could be that we’re seeing more of these in part because of climate change.

But some of it’s also probably just the chaos of the Earth’s system that, you know, sometimes you’re gonna get one, and sometimes you aren’t. And of course, there’s a baseline warming of the world’s oceans that’s feeding into this a little bit, but even, sort of, subtracting that from the ocean temperatures, this El Niño is still outstanding.

Feltman: Right. Well, and so segueing into the impacts we can expect, you know, even though we can’t necessarily pin this on climate change, the fact that climate change is happening and global temperatures are already warmer and weather is already weirder probably means that a really extreme El Niño is maybe more worrying than it would’ve been a couple decades ago. Would you say that that’s correct?

Thompson: Definitely can, because for an example, El Niño tends to bring drought conditions to the Amazon. And the Amazon is already in a weakened state, both in part because of a previous strong El Niño that caused drought and contributed to wildfires as well as climate change acting on that and exacerbating those droughts. And then other, of course, land-use change happening in parts of the Amazon. So you don’t just have the effects of this El Niño, you have all those other things playing in.

And then we have various what are called teleconnections in scientific parlance, where El Niño has certain effects in certain places. And generally these are more robust when you have a very strong El Niño just because you have more input into the system from the El Niño. So, you know, you have the effects on hurricanes in the Atlantic and the Pacific, where we’ve seen almost no hurricane activity in the Atlantic this year and a flurry of storms especially around Hawaii and the Pacific. You’ve also seen a major drought and wildfires in Indonesia. That is a hallmark of El Niños.

And generally, the closer places are to where El Niño is, sort of, happening, the stronger the impacts are, which makes sense. But they can reach really far afield too, so you know, there are teleconnections in Africa. You tend to have more rainfall and flooding in the Horn of Africa but less rainfall and drought in, sort of, South Africa. And it’s going to be particularly interesting to watch this winter.

So, you know, with the climate being warmer than it was in the past, you know, it’s unclear how much of the precipitation from these storms may fall as rain instead of snow when what you want in the West is snow because that snowpack is, sort of, what gives you the water that lasts you through spring, summer and fall.

These storms also bring a lot of coastal waves, we already have exceptionally high sea levels off the coast of California right now ’cause it’s very warm there, too, and we have these, sort of, pulses of warm water that can come up from the main El Niño region called Kelvin waves, which I know we talked about before. And so all of that together could mean we have a lot of major coastal flooding in California this winter.

Feltman: Right. So how much do we know about how long the El Niño is gonna last?

Thompson: So we have a pretty good understanding of, sort of, the cadence of El Niño. It tends to always peak in the November/December/January timeframe. This one has ramped up a lot faster than ones we’ve seen in the past, so it got warm very quickly.

It’s a little unclear exactly how high it’s going to peak, and that might determine how long temperatures stay really elevated. If it peaks higher, it may take longer for them to come down. After it peaks, it’ll, sort of, slowly come down through the winter.

But winter is typically the time where we see the biggest impacts, at least in the Northern Hemisphere, in the U.S. It’s gonna last several more months. Eventually it will, sort of, exhaust itself, and ocean temperatures will get back to, sort of, more typical levels, and then we’ll be in what’s called, sort of, neutral conditions.

But the heat of an El Niño in the atmosphere always lags the heat in the ocean, the heat in the ocean peaks November/December-ish. Heat in the atmosphere follows a few months behind. So we’re going to see global temperatures stay elevated for longer. Right now it’s a little unclear if 2026 is going to be the hottest year on record. Very well could be. It’s definitely going to be up there, which is pretty remarkable because we started this year in, sort of, a weak La Niña state, so ...

Feltman: Which brings temperatures down?

Thompson: Down, yeah. So no one was expecting that this was going to be a contender. It will definitely be 1.5 degrees Celsius above preindustrial this year, which would be the second year that’s ever happened after 2024.

[The year] 2027 [is] almost certainly going to be the warmest year on record because of that heat lag. And it will also be warmer than 1.5 C. And one thing I’ve talked to with some scientists is the question of: Do we come back down from that, or are we, sort of, at 1.5 C from now on? Now, that still wouldn’t technically breach the climate agreement ’cause that’s considered an average over many, many years, but it’s possible.

Now, if we swing over to La Niña, maybe we come back down below 1.5 C above preindustrial. It’s a little hard to tell. But, you know, this is definitely not going in the direction we want things to go in, for sure

Feltman: Yeah. I remember years ago, at this point, an expert I talked to said, you know, “We’re on an escalator. El Niño is us getting up on our tippy-toes, and La Niña is us ducking down, but the escalator keeps going up.” And that has really stuck with me all these years.

Thompson: Right. Yeah, and typically, sort of, El Niño’s temperature effects on the globe are temporary. Eventually that heat is radiated back to space. But what a couple climate scientists pointed out to me is that the same, sort of, feedbacks that happen with climate change, where you have sea ice melts or permafrost thawings that can, sort of, exacerbate it, those are sort of agnostic to where that additional heat comes from. So if you have more heat coming from El Niño, those might also ramp up those feedbacks and, sort of, effectively lock some of the El Niño heat into the system instead of it just being temporary.

Feltman: Well, not necessarily the most fun topic to discuss but always a pleasure to have you on. Thanks for talking us through this.

Thompson: Yeah, absolutely. Thanks for having me.

Feltman: That’s all for today’s episode. If you’ve got any burning weather-related questions that you’d like Andrea to help us answer for you, send them on over to sciencequickly@sciam.com. We’ll be back on Friday to dig into some surprising new perspectives on the science of stuttering.

Science Quickly is produced by me, Rachel Feltman, along with Fonda Mwangi, Sushmita Pathak, Allison Rodgers and Jeff DelViscio. This episode was edited by Alex Sugiura. Marielle Issa and Aaron Shattuck fact-check our show. Our theme music was composed by Dominic Smith. Subscribe to Scientific American for more up-to-date and in-depth science news.

For Scientific American’s Science Quickly, this is Rachel Feltman. See you next time!