How El Niño shapes the world’s weather trends

[MUSIC PLAYING] IRA FLATOW: Hi, Ira here. And you’re listening to Science Friday. Scientists studying climate models say that this year has a good chance of shaping up to be an El Niño year. And not just any El Niño, but a super El Niño.

So what is that? Why does it happen? Why should we care? Joining me is Dr. Dillon Amaya. He’s a Research Scientist at the NOAA Physical Sciences Laboratory in Boulder, Colorado. Welcome to Science Friday.

DILLON AMAYA: Hi. Thanks for having me.

IRA FLATOW: Nice to have you. OK, first, refresh our memory for exactly what is an El Niño.

DILLON AMAYA: At its most basic level, an El Niño is just simply a warming of the eastern equatorial Pacific Ocean. Typically, we define it as a period of time where that pocket of ocean gets more than about half a degree Celsius for five consecutive three-month averages.

IRA FLATOW: And how often do they happen? Do they have a cycle?

DILLON AMAYA: Yeah. Typically, El Niños occur about every three to five years. And they’re often paired with La Niña events, which is the cold phase of what we call the El Niño Southern Oscillation, which is the total package.

IRA FLATOW: So with climate change, does that make them more likely to happen?

DILLON AMAYA: That’s a really, really interesting science question. It’s something that we’re actively trying to understand better as climate models get better and better. Right now, we do know that every El Niño is going to be warmer than the last, and that’s primarily because of something like global warming.

IRA FLATOW: OK, so why are they calling this a super-duper El Niño this year?

DILLON AMAYA: Yeah. Primarily because we expect this event to be really big. And by big, we mean something like 2 degrees Celsius warmer than normal. And that may not sound like a lot. Jumping into the ocean in that part of the world, you may not be able to notice the difference on your skin. But the atmosphere and the broader climate system definitely will notice a difference.

IRA FLATOW: Mm-hmm. So what are the models saying about this year? What are the odds?

DILLON AMAYA: Right now, the models give it about a 25% chance of a very strong, strong, or moderate-strength El Niño developing this summer and into the fall and winter.

IRA FLATOW: Mm-hmm. Let’s talk through the mechanics here. How does one get started? What are the warning signals?

DILLON AMAYA: Well, to understand exactly how an El Niño happens, you kind of have to have a sense for what are normal conditions along the equatorial Pacific. Generally speaking, we have what are called the trade winds, which are these east-to-west winds along the surface of the ocean, and that pushes warm water from the eastern equatorial Pacific all the way to the western equatorial Pacific. I’m talking over by Indonesia.

And if those winds were to relax for long enough periods of time, a lot of that warm water sloshes all the way back to the eastern equatorial Pacific, over by the coast of places like Peru. And that can cause dramatic increases in temperature in that part of the world.

IRA FLATOW: All right. Let’s talk about the dramatic increases in other things. What happens when the temperatures rise, and what are some of the effects that may cause?

DILLON AMAYA: In short, El Niño can drive wholesale changes in atmospheric circulation and precipitation patterns all over the world. And the reason for that is because it’s really dragging rainfall from places where it normally happens, like the western equatorial Pacific, to the eastern equatorial Pacific, in a part of the world where you don’t typically get a lot of rain.

And in the atmosphere, rain is energy. It creates a lot of heat and a lot of energy that has to go somewhere, and that creates ripples that create atmospheric waves that propagate all over the world. And that can push around the jet stream around places like North America. And that can shift where storms are starting to make landfall on places like the US West Coast.

IRA FLATOW: And what effect would that have on the weather for this coming year?

DILLON AMAYA: Typically, we think of El Niño driving wetter than normal conditions in places like the American Southwest. So places like Southern California, Arizona, New Mexico, Texas, and even to some extent in the Southeast, places like Florida and Georgia. And we also tend to think that El Niños drive drier conditions in the Pacific Northwest. And this is all typically during the wettest part of the year for places like the American Southwest and during boreal winter. So sort of November, December, January. Ultimately, there’s a wholesale shift in the jet stream, and that could affect weather for as far north as New York.

IRA FLATOW: Are there places elsewhere in the world that would be especially impacted?

DILLON AMAYA: Yeah. El Niño is a global phenomenon. In the climate system, on these sort of seasonal to year-to-year timescales, El Niño is king. It will redistribute rainfall all over the world. I tend to think about these impacts in the United States, but we also see impacts in places like Australia, South America, the Sahel region of Africa. Yeah. No place will be left untouched by a really strong El Niño event.

IRA FLATOW: And I guess I’d ask then, what is the opposite? What does La Niña do?

DILLON AMAYA: La Niña you can think of as just the polar opposite of El Niño. It’s a colder than normal condition in the equatorial Pacific. And typically, its impacts on the global climate are opposite. So again, I’ll return to that Southwest US example. During El Niño, we would tend to get wet conditions. During La Niña, we’d expect dry conditions.

IRA FLATOW: Mm-hmm. What is it that makes it super El Niño this year and not just a regular El Niño?

DILLON AMAYA: Yeah. That’s, again, a great, really, really good research question. I think, typically, we get really strong El Niños like this when we get a critical mass of subsurface ocean heat content in places like the western equatorial Pacific. You get a lot build up of warm water over the years. And then once those winds relax along the equatorial Pacific, that water sloshes back all at once and can lead to these really massive and sustained events.

IRA FLATOW: Does a stronger El Niño means stronger weather or the places where it happens shift more?

DILLON AMAYA: Typically, a stronger El Niño will just mean a stronger signal. So really, the climate system is a distribution. I think that’s the most important thing to understand. You can get drier than normal conditions. You can get wetter than normal conditions. And that’s all, in part, driven by random noise in the climate and weather system.

What El Niño does is it pushes that distribution towards drier or wetter depending on where you’re at. So take LA for example. Take Los Angeles for example. During El Niño, you push that distribution towards wetter conditions. That doesn’t mean that drier conditions aren’t possible. But during a particularly strong El Niño, that push, it’s much stronger. You’re really going to shift that distribution towards wetter conditions. Makes it more likely.

IRA FLATOW: OK. We’ve had stronger El Niños, super-duper El Niños before. What were those effects, and what might we expect given that?

DILLON AMAYA: I mean, I think there’s going to be both positive and negative impacts for big, big, strong El Niños like this. For one thing, right now, a lot of the American Southwest is experiencing anything from moderate to exceptional drought. And so in this case, a really strong El Niño that’s going to bring a lot of rain to places like New Mexico, Arizona, Southern California, that is a reprieve. That could be a drought buster. That could help us get over the hump in terms of managing really sensitive water resources.

On the negative side of things, though, we are currently experiencing a really strong marine heatwave right now in the ocean along the US West Coast. And that’s exactly what it sounds like. That is a heatwave that’s happening in the ocean. And that can have really negative marine ecosystem impacts. And El Niños have been known to exacerbate these sorts of events and help them stick around for a lot longer.

So that could be the negative side of this event. There’s this massive marine heatwave off the coast of Southern California, and there’s a lot of fisheries that are on alert right now thinking about the impacts of this El Niño on very sensitive marine ecosystems.

IRA FLATOW: Now we know that corals are affected by ocean temperatures, right?

DILLON AMAYA: Yeah, absolutely. Corals are super sensitive to the temperature of the water.

IRA FLATOW: And so should we expect coral bleaching in this season?

DILLON AMAYA: Potentially. El Niños do tend to drive marine heatwaves around the globe. And if a marine heatwave were to persist or exacerbate in places like off the coast of Florida and the Keys region, where you have these really strong corals, it could lead to severe bleaching events.

IRA FLATOW: Now I know you study ocean heatwaves. You mentioned ocean heatwaves. What do you study? What do you need to know about them? What impact do they have?

DILLON AMAYA: Yeah. Ocean heatwaves are really interesting. They are these subsurface boiling of the water, so to speak. It’s not quite literally boiling, but to maybe a passing fish or a seagrass or a coral, it’s really uncomfortable. You can get strong heatwaves that are something like 2 to 3 degrees Celsius warmer than average.

And the difference, I think, between an atmospheric heatwave and an ocean heatwave that people might be interested in is that an ocean heatwave lasts a lot longer. It can last months, seasons, possibly even years, whereas on land, we might experience a heatwave for a few days.

IRA FLATOW: Mm-hmm. How does an El Niño change the ocean ecosystems? I mean, when it’s done, do they adapt, or are they permanently changed?

DILLON AMAYA: It really depends. There are some fish that are highly mobile. They can get out of the way. They can go to their preferred thermal habitat, and they’ll be fine. They have high adaptation capability. But then there are other things that are more rooted to the spot, things like corals or seagrasses, or what we call demersal or benthic fish species, things that live on the seafloor, like crabs or lobsters. These things aren’t mobile or aren’t particularly mobile. And they could really be impacted by strong ocean heating driven by El Niño.

IRA FLATOW: We’ve heard about various Earth systems that are close to what we call ecological tipping points. Is there a chance that a very strong El Niño could push some system over the edge, something there’s no coming back from?

DILLON AMAYA: That’s a really interesting question. Certainly, climate tipping points are something that we’re concerned about in terms of how climate change could irreversibly impact the way that we live our lives. I would say that, right now, this El Niño is probably not going to be the primary driver that gets us over the edge on some of these tipping points. But as climate continues to change, a really big signal, a really big shock to the system, like a future strong El Niño event, potentially could be the thing that pushes that ball over the hump.

IRA FLATOW: People should not be thinking of this as a storm that is coming, right?

DILLON AMAYA: No, definitely not. It’s not a weather phenomenon. It’s not that– I always go back to thinking about that Chris Farley skit from Saturday Night Live in the late ’90s, where he refers to El Niño as this big tropical storm. And it’s not like that. It’s not a hurricane. It’s not something that we can watch coming from afar. It’s this massive shift in the way that climate is going to unfold over the next year and a half or so, and that can affect the way that weather is felt in your day-to-day life.

IRA FLATOW: Hmm. So my last question is, when will we know? How long for the models to firm up the prediction?

DILLON AMAYA: The models are very confident that El Niño is coming. I would say 80% to 90% to 100% confident that El Niño is coming. Right now, the uncertainty lies in how strong that El Niño event is, whether it’s moderate, very strong, extreme. And that’s kind of where the models are starting to firm up. Give us another month or two, and I think the models will start to agree.

IRA FLATOW: Do they tell us a date when it might be coming?

DILLON AMAYA: Typically, the models don’t decide a specific date when an El Niño arrives. It’s not a weather pattern in that way. It’s more of a slow-moving transition. So I would expect El Niño to be declared officially, I would say, come this fall.

IRA FLATOW: Wow. Well, Dr. Amaya, thank you for taking time to be with us today. Fascinating stuff.

DILLON AMAYA: Yeah. Thank you so much. This was a lot of fun. Thanks for having me.

IRA FLATOW: Dr. Dillon Amaya is a research scientist at the NOAA Physical Science Lab in Boulder, Colorado. This episode was produced by Rasha Aridi and Charles Bergquist. And if you’ve got a question about the way the world works, like how warm water near Indonesia can make more snow near California, give us a call, 877-4-SCIFRI. 877, number 4, SCIFRI. Thanks for listening. I’m Ira Flatow.

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