Chapter 1: What is El Niño and why is it significant?
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 Nino year, and not just any El Nino, but a super El Nino. So what is that? Why does it happen? Why should we care? Joining me is Dr. Dylan Amaya. He's a research scientist at the NOAA Physical Sciences Laboratory in Boulder, Colorado.
Welcome to Science Friday.
Hi, thanks for having me.
Nice to have you.
Chapter 2: How often does El Niño occur and what influences its frequency?
Okay, first refresh our memory for exactly what is an El Nino?
At its most basic level, an El Nino 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.
And how often do they happen? Do they have a cycle?
Yeah, typically El Niños occur about every three to five years, and they're often paired with La Niña events, which is sort of the cold phase of what we call the El Niño-Southern Oscillation, which is sort of the total package.
So with climate change, does that make them more likely to happen?
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.
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Chapter 3: What makes this year’s El Niño a 'super' event?
Okay, so why are they calling this a super-duper El Nino this year?
Yeah, primarily because we expect this event to be really big. By big, we mean something like 2 degrees Celsius warmer than normal. And that may not sound like a lot, you know, 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 the difference.
Mm-hmm. So what are the models saying about this year? What are the odds?
Right now, the models give it about a 25% chance of a very strong, strong or moderate strength El Nino developing this summer and into the fall and winter.
Mm-hmm. Let's talk through the mechanics here. How does one get started? What are the warning signals?
Well, to understand exactly how an El Nino happens, you kind of have to have a sense for, you know, 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.
All right.
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Chapter 4: What are the global weather impacts of El Niño?
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?
In short, El Nino 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 U.S. West Coast.
And what effect would that have on the weather for this coming year?
Typically, we think of El Nino 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 Ninos 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 during boreal winter, so sort of November, December, January. Ultimately, there's sort of a wholesale shift in the jet stream, and that could affect weather for as far north as New York.
Are there places elsewhere in the world that would be especially impacted?
Yeah, El Nino was a global phenomenon. In the climate system, you know, on these sort of seasonal to year-to-year timescales, El Nino is king. It will redistribute rainfall all over the world.
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Chapter 5: How does El Niño affect marine ecosystems?
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 Nino event.
And I guess I'd ask then, what is the opposite? What does La Nina do?
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 U.S. example. During El Niño, we would tend to get wet conditions. During La Niña, we'd expect dry conditions.
What is it that makes it super El Niño this year and not just a regular El Niño?
Yeah, it's again a great, really, really good research question. I think typically we get really strong El Ninos like this when we get sort of a critical mass of subsurface ocean heat content in places like the western equatorial Pacific. You get a lot of buildup 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.
Does a stronger El Nino mean stronger weather or the places where it happens shift more?
Typically, a stronger El Nino 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 know, you can get drier than normal conditions.
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Chapter 6: What are the potential positive and negative impacts of a strong El Niño?
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 Nino does is it pushes that distribution towards weather. you know, drier or wetter, depending on where you're at. So take LA, for example, take Los Angeles, for example. Right. During El Nino, you push that distribution towards wetter conditions.
That doesn't mean that drier conditions aren't possible, but during a particularly strong El Nino, that push is, you know, it's much stronger, right? You're really going to shift that distribution towards wetter conditions, makes it more likely.
Okay. We've had stronger El Ninos, super duper El Ninos before. What were those effects and how, what might we expect given that?
I mean, I think there's going to be both positive and negative impacts for big, big, strong El Ninos 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 Nino 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 heat wave right now in the ocean along the U.S. west coast. And that's exactly what it sounds like.
That is a heat wave that's happening in the ocean, and that can have really negative marine ecosystem impacts.
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Chapter 7: How do ocean heat waves relate to El Niño?
And El Ninos have been known to exacerbate these sorts of events and help them stick around for a lot longer. So that could be sort of the negative side of this event. There's this massive marine heat wave 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 Nino on very sensitive marine ecosystems.
Now, we know that corals are affected by ocean temperatures, right?
Yeah, absolutely. Corals are super sensitive to the temperature of the water.
And so should we expect coral bleaching in this season?
Potentially. You know, El Ninos do tend to drive marine heat waves around the globe. And if a marine heat wave 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.
Now, I know you study ocean heat waves. You mentioned ocean heat waves. What do you study? What do you need to know about them? What impact do they have?
Ocean heat waves 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 heat waves that are something like two to three degrees Celsius warmer than average and
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Chapter 8: What can we expect from El Niño in the upcoming months?
The difference, I think, between an atmospheric heat wave and an ocean heat wave that people might be interested in is that, you know, an ocean heat wave lasts a lot longer. It can last months, seasons, possibly even years. You know, whereas on land, we might experience a heat wave for a few days.
How does an El Nino change the ocean ecosystems? I mean, when it's done, do they adapt or are they permanently changed?
It really depends, right? 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 Nino.
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 Nino could push some system over the edge, something there's no coming back from?
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 Nino 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, you know, a really big signal, a really big shock to the system, like a future strong El Nino event, you know, potentially could be the thing that pushes that ball over the hump.
People should not be thinking of this as like a storm that is coming, right?
No, definitely not. It's not a weather phenomenon. I always go back to thinking about that Chris Farley skit from Saturday Night Live in the late 90s, where he refers to El Nino 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.
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