Short Wave - Sea Camp: Why Are Ocean Currents Shifting?

Episode Date: July 7, 2025

A warming climate doesn't just affect dry land — it affects the ocean, too. For years, Earth's ocean has acted as a heat sink for climate change: A large part of the heat generated by human use of fossil fuels is being absorbed by the ocean. And while the deep sea is largely unaffected by this heat absorption, oceanographers have discovered that the upper ocean currents are accelerating. That acceleration has the potential for huge knock-on effects, including sea level rise, changing fish migration cycles, shifting storm patterns, and more.This is the first episode of Sea Camp, Short Wave's summer series exploring the intriguing and otherworldly depths of the ocean. Follow us every Monday through August as we travel from the sunlit zone to the sea floor.Interested in more stories about the ocean? Email us your question at [e-mail] to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shorewave from NPR. Hey, ShoreWavers, it's Regina Barber and Emily Kwong. And we are excited to announce the launch of Seeky. Every Monday for the next eight weeks, we'll be traveling deeper and farther into the depths of the ocean. From the sunlit zone to the twilight zone to the sea floor. And we're going to start today right on the surface. Sitting beside us on a metaphorical boogie board is producer Hannah Chin. Hi, Hannah.

Hi, Emily. Hi, Gina. Today, we're focused on how the atmosphere and the ocean affect each other. I got to say, though, even though I grew up on the West Coast, going to the ocean every summer, hunting in tide pools, watching sea lions, I didn't realize until recently that that same ocean is also constantly affecting how we experience life on land. Anyone who lives along the West Coast, the U.S., for instance, knows that we have really mild winters, and that's a result of the fact that we have the ocean kind of mediating the weather

there. So this is Matt Luongo. He's climate scientists and a physical oceanographer at the University of Washington in Seattle. In the northern hemisphere, the weather moves from the west to the east, and they're pretty strongly moderated by the ocean. Yeah, I mean, I grew up in Washington State and California, and he's right. Like, we do have very mild winters, but I never like put together. It's because of the Pacific Ocean. Yeah. And you know, when I think of the ocean, ocean and the atmosphere. I also think about how humans have trapped on Earth with greenhouse gases, heat. And that heat is getting absorbed by the ocean. Like if oceans didn't exist, climate change would have cooked us a long time ago. Totally. And I think it's easy to be like, oh, like great, the ocean saved us.

We're fine. But Emily, all that heat in the atmosphere is still slowly affecting the ocean's surface. And scientific models are indicating that these surface level changes, that heat could have big, lasting effects on the ocean's currents, their location, their stability, as well as on this kind of feedback loop of ocean atmosphere interaction. So today on the show, we're talking about the surface of the sea and the complex movements of the currents in it. How those currents are shifting in response to a warming planet and why that might spell disaster.

You're listening to Shortwave, the science podcast from NPR. Okay, Hannah, let's start with like what are ocean currents and why are they important. Yeah, so ocean currents are the continuous movement of water within the ocean along a particular path. So they can be deep and they can be shallow. They're kind of like rivers and streams, but they're winding through the ocean instead of the land and they're taking things with them. They affect fish migration. They distribute heat and nutrients which support ecosystems. They help drive weather. And these surface currents can help shape human travel, which is why sailors have been mapping the surface currents of the ocean for a long, long time.

People have needed to know surface currents ever since they were sailing, you know, back in, you know, thousands of years ago. It's very, very important for navigation. This is physical oceanographer Lynn Talley. She's a professor at the Scripps Institution of Oceanography at the University of California, San Diego. She told me that one of the oldest ocean current maps we have comes courtesy of Benjamin Franklin. The Benjamin Franklin? Of course. He did so many things. Yeah. Turns out, in addition to being an inventor and a scientist, scientist and a diplomat. He was also the postmaster general of Philadelphia. He opened a post office in Philadelphia, and that was to get the mail back and forth between England and Philadelphia. Wow. Airmail was not an option at the time. So all these letters had to come via a boat over the Atlantic

Ocean. He noticed that his cousin in Rhode Island, he was a whaling captain, could get across the Atlantic Ocean a whole lot faster than the British official postmaster ships. And that's because Because his cousin in Rhode Island knew about the Gulf Stream. Because the Gulf Stream, right, that's that big current that flows from the Gulf of Mexico and goes north along the eastern coastline and then towards Northern Europe. It's like a perfect route if you want to cross the Atlantic. Yeah, and it's also a huge feeding ground for whales, which is probably why Benjamin Franklin's cousin knew about it.

And at the time, the average postal ship took two weeks longer to cross the Atlantic Ocean than Benjamin Franklin's cousin, the whaling captain, did, because the postal ship wasn't taking advantage of the Gulf Stream. This is so fascinating. It's kind of like Benjamin Franklin's cousin was like standing on an escalator, just like relaxing. And like the other guy, this other ship was like trying to go down the up escalator. Like it's not even a race at all.

A fair race, no. And get this. In 1978, a scientist from the Woods Hole Oceanographic Institution found several copies of Ben Franklin's Gulf Stream map, and he realized nothing had really changed. And he was went, oh my goodness, because the map was so accurate. And it was exactly where it is now. Oh, so she's saying the Gulfstream was the same as it was in the 1760s?

Yeah, basically the same. And that's personally because these surface currents remain so consistent over time. Lynn told me they can meander back and forth a little. They're not set in a stream bed or a riverbed the way that our currents on land are. But this main envelope, she called it, that Benjamin Franklin, Drew is basically the same map as what we use now. Hmm. That is so cool. Wait, Hank, can you tell us, like, what's driving these surface currents?

Like, what exactly in the ocean is keeping them going? Yeah, it's really a number of things. There's temperature, there's salinity, coastlines, overall global wind patterns. Like, even the rotation of the Earth can drive these currents because of something that's called the Coriolis Effect. Good old Coriolis effect. I remember my students, like, hating this subject. Okay, so because the Earth is spinning, it affects air currents.

So, like, this makes air flow, like, slightly deflect to the right in the northern hemisphere, and it slightly deflects to the left in the southern hemisphere. And it makes these, like, curved paths of air, and this, in turn, like, affects the ocean currents. Yeah, exactly. And that's essentially what Lynn and Matt told me to. The surface currents are primarily driven by winds. So those are really the currents that we know and love and we see, you know, these are the Gulf Stream, the California current, the Curitio. And the things that we see day to day that we think about with currents are really these kind of wind-driven surface currents.

For a long time, these wind-driven surface currents have stayed pretty consistent. But now they're changing. Why? Is it us? Is it climate change? Okay. So the scientist you're going to hear from next is Shang Fing Shia. He's a climate scientist as well as an oceanographer.

And a few years ago, he and his team did a study using predictive models to show that in a warming climate, service currents across the globe will significantly accelerate. Like, will they speed up everywhere? In more than three quarters of the world's oceans, yes, but the surface current specifically, not the deep ocean ones. This is because of like heat transfer, right? Like heat doesn't go through water very quickly. Again, I'm going to push more physics.

I'm so sorry. No, I love physics. It's right. It's kind of like, I don't know if either of you have ever been to an outdoor swimming pool in the summer. Yes. Shang Ping told me it's kind of like that. If you swim during the sunny afternoon in summer, you will feel like the surface water is a lot warmer than below.

It's definitely bringing me back to like swim team. Like if you're swimming along the surface, it's going to be pretty warm. You go even just a little bit, it's going to be cooler. But if you sit on the bottom, it's pretty cold. Yeah, exactly. But Hannah, our ocean is so much bigger than a swimming pool. So how does this apply to us on planet Earth? Well, it's kind of the same idea that it'll take a really long time for the deep.

ocean to warm, but the top layer is warming much faster. In the ocean, it's a layer of warm water floating over a body of a deeper cold water. And as this surface water warms, its molecules move faster and further apart, meaning that it's all going to take up more space. That'll result in intensified pressure differences, basically pushing parts of the ocean, like the currents of the surface, to move faster. Oh, that's why you said earlier so many surface currents are expected to speed up. Exactly. And this is already happening. For example, scientists know from satellite measurements and observational floats that the Antarctic circumpolar current, which is the eastward ocean current kind of encircling Antarctica, it sped up significantly over the past few decades. And Shang Ping said this overall acceleration could really change ocean life as we know it.

Yeah, so fish definitely is going to tell the difference because a lot of fish, they migrate, sports. burning and feeding and the nursery grounds. So they do rely on the kind of a temperature structure. So phytoplankton and also the fish migration is certainly going to change tremendously. And it's not just fish in plankton. Lynn told me that as these currents speed up, they could end up shifting their location and their effects as well. When the current speed up, they're going to move. nutrients, they're going to move heat.

If you speed a current up, it might not want to stay where it started. It might try to push itself a little farther towards the pole. And it will carry things farther and faster. There is one key exception to this overall surface acceleration trend, and that's the AMOC. Okay. So this stands for the Atlantic meridional overturning circulation. Cool. And it's a system of surface acceleration.

currents and deep currents, kind of like an Atlantic Ocean conveyor belt that moves warm water north and cold water south. And this helps redistribute energy and kind of moderate heat around the world. Got it. Okay. So what's happening to the AMOC, right? Yes. Under climate change. Well, for decades, scientists have been worried that it's begun to slow down.

And Shang Ping's team's models supported this. They said that along with multiple currents in the deeper ocean, it'll continue to decelerate. Which could change a whole host of things. It could increase storm severity and cause sea level rise along the north part of the east coast. It could make Western Europe and a lot of the northern hemisphere way colder or change monsoon season and rainfall near the equator. Scientists don't know all of the potential effects yet. That's like a choose-your-own-adventure game, but bad. Yeah, but unlike a choose-your-one adventure game where you can restart it whenever, we humans only get one shot.

And for Matt Luongo, who's the oceanographer you heard from at the beginning of this episode, that means we should act now so that we can curb this climate disaster. We understand a lot of the basic building blocks. So I think it then becomes kind of a political and social decision on how much we want to not emit CO2, for instance. It's kind of what we decide to do. Gahan, thank you so much for bringing us this story and kicking off Sea Camp. Yes. The surface, but with great depth.

Oh, no problem. Thanks for having me. And good luck with the rest of CCAM. Thanks, Han. This episode was produced by Hannah Chin and Rachel Carlson. It was edited by our showrunner, Rebecca Ramirez, and fact-checked by Tyler Jones. Jimmy Keely was the audio engineer. Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Regina Barber. I'm Emily Kwong. Thank you for listening to Shortwave. And Seacamp from NPR.