Sea Camp: Why Are Ocean Currents Shifting?

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 https://www.npr.org/series/g-s1-75877/short-wave-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 [email protected] mailto:[email protected]. Listen 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 http://plus.npr.org/shortwave. See pcm.adswizz.com https://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 https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Speaker 00

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• 0:16Emily Kwong?

  You're listening to Short Wave from NPR.

• 0:23Regina Barber?

  Hey, Shortwavers. It's Regina Barber.

• 0:24Emily Kwong?

  And Emily Kwong.

• 0:25Regina Barber?

  And we are excited to announce the launch of Sea Camp.

• 0:31Emily Kwong?

  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 seafloor.

• 0:44Emily Kwong?

  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.

• 0:53Speaker 03

  Hi, Emily. Hi, Gina. Today, we're focused on how the atmosphere and the ocean affect each other. I gotta 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.

• 1:13Speaker 04

  Anyone who lives along the West Coast, the US, 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.

• 1:22Speaker 03

  So this is Matt Luongo. He's a climate scientist and a physical oceanographer at the University of Washington in Seattle.

• 1:29Speaker 04

  In the northern hemisphere, the weather moves from the west to the east, and they're pretty strongly moderated by the ocean.

• 1:36Regina Barber?

  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.

• 1:45Emily Kwong?

  Yeah. And you know, when I think of the 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.

• 2:01Speaker 03

  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.

• 2:27Regina Barber?

  So today on the show, we're talking about the surface of the sea and the complex movements of the currents in it.

• 2:33Speaker 03

  How those currents are shifting in response to a warming planet.

• 2:36Regina Barber?

  And why that might spell disaster.

• 2:39Speaker 03

  You're listening to Short Wave, the science podcast from NPR.

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• 4:04Regina Barber?

  Okay, Hannah, let's start with like, what are ocean currents and why are they important?

• 4:09Speaker 03

  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.

• 4:39Speaker 05

  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.

• 4:47Speaker 03

  This is physical oceanographer Lynn Tally. 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.

• 5:01Emily Kwong?

  The Benjamin Franklin?

• 5:02Regina Barber?

  Of course, like, he did so many things.

• 5:04Speaker 03

  Yeah. Turns out, in addition to being an inventor and a scientist and a diplomat, he was also the postmaster general of Philadelphia.

• 5:13Speaker 05

  He opened a post office in Philadelphia, and that was to get the mail back and forth between England and Philadelphia.

• 5:20Speaker 03

  Wow. Airmail was not an option at the time, so all these letters had to come via boat, over the Atlantic Ocean.

• 5:26Speaker 05

  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 his cousin in Rhode Island knew about the Gulf Stream.

• 5:43Emily Kwong?

  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.

• 5:53Speaker 03

  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.

• 6:11Regina Barber?

  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.

• 6:24Speaker 03

  Not 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.

• 6:37Speaker 05

  And he was like, oh my goodness, because the map was so accurate. And it was exactly where it is now.

• 6:45Regina Barber?

  Oh, so she's saying the Gulf Stream was the same as it was in the 1760s?

• 6:50Speaker 03

  Yeah, basically the same. And that's partially 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 river bed, 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.

• 7:10Regina Barber?

  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?

• 7:17Speaker 03

  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.

• 7:29Regina Barber?

  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 airflow 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.

• 7:50Speaker 03

  Yeah, exactly. And that's essentially what Lynn and Matt told me, too.

• 7:53Speaker 04

  The surface currents are primarily driven by winds. So those are really the, uh, the currents that we know and love and we see. You know, these are the Gulf Stream, the California Current, the Curacao. And the things that we see day to day that we think about with currents are really these kind of wind-driven surface currents.

• 8:12Speaker 03

  For a long time, these wind-driven surface currents have stayed pretty consistent. But now, they're changing.

• 8:19Emily Kwong?

  Why? Is it us? Is it climate change?

• 8:22Speaker 03

  Okay, so the scientist you're gonna hear from next is Shang Ping Xia. 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, surface currents across the globe will significantly accelerate.

• 8:40Regina Barber?

  Like, will they speed up everywhere?

• 8:41Speaker 03

  In more than three quarters of the world's oceans, yes. But the surface currents specifically, not the deep ocean ones.

• 8:47Regina Barber?

  This is because of like, heat transfer, right? Like, heat doesn't go through water very quickly. Again, I'm gonna push more physics, I'm so sorry.

• 8:55Speaker 03

  No, I love physics. It's right. It's kind of like, uh, I don't know if either of you have ever been to an outdoor swimming pool in the summer.

• 9:02Regina Barber?

  Yes.

• 9:03Speaker 03

  Shangping told me it's kind of like that.

• 9:04Speaker 06

  If you swim during the sunny afternoon in summer, you will feel like the surface water is a lot warmer than below.

• 9:14Regina Barber?

  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.

• 9:24Speaker 03

  Yeah, exactly.

• 9:25Emily Kwong?

  But Hannah, our ocean is so much bigger than a swimming pool. So how does this apply to us on planet Earth?

• 9:30Speaker 03

  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.

• 9:38Speaker 06

  You know, ocean is a layer of warm water floating over a body of a deep cold water.

• 9:46Speaker 03

  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 at the surface, to move faster.

• 10:01Emily Kwong?

  Oh, that's why you said earlier so many surface currents are expected to speed up.

• 10:04Speaker 03

  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 Shangping said this overall acceleration could really change ocean life as we know it.

• 10:27Speaker 06

  Yeah, so fish definitely is going to tell the difference. Because, you know, a lot of fish, they migrate, spawning and feeding and the nursery grounds. So they do rely on the kind of a temperature structure. So phytoplankton and also the fish migration.

• 10:47Speaker 06

  Is certainly going to change tremendously.

• 10:52Speaker 03

  And it's not just fish and plankton. Lynn told me that as these currents speed up, they could end up shifting their location and their effects as well.

• 11:00Speaker 05

  When the currents 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.

• 11:17Speaker 05

  And it will carry things farther and faster.

• 11:21Speaker 03

  There is one key exception to this overall surface acceleration trend, and that's the AMOC.

• 11:27Regina Barber?

  OK.

• 11:28Speaker 03

  So this stands for the Atlantic meridional overturning circulation.

• 11:32Regina Barber?

  Cool.

• 11:33Speaker 03

  And it's a system of surface 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.

• 11:46Regina Barber?

  Got it. OK, so what's happening to the AMOC, right?

• 11:50Speaker 03

  Yes.

• 11:51Regina Barber?

  Under climate change?

• 11:52Speaker 03

  Well, for decades, scientists have been worried that it's begun to slow down. And Shangping'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.

• 12:17Regina Barber?

  What?

• 12:18Speaker 03

  Scientists don't know all the potential effects yet.

• 12:21Regina Barber?

  Huh.

• 12:21Emily Kwong?

  That's like a choose your own adventure game, but bad.

• 12:25Speaker 03

  Yeah, but unlike a choose your own 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.

• 12:41Speaker 04

  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.

• 12:56Emily Kwong?

  Hannah, thank you so much for bringing us this story and kicking off Sea Camp.

• 12:59Regina Barber?

  Yes.

• 12:59Emily Kwong?

  Surface, but with great depth.

• 13:02Speaker 03

  No problem. Thanks for having me. And good luck with the rest of Sea Camp.

• 13:05Regina Barber?

  Thanks, Hannah.

• 13:08Emily Kwong?

  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 Keeley was the audio engineer.

• 13:17Regina Barber?

  Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Regina Barber.

• 13:23Emily Kwong?

  I'm Emily Kwong.

• 13:24Regina Barber?

  Thank you for listening to Short Wave. And C. Camp from NPR.

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