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A new robot could help fight climate change by sinking stinky seaweed


This week, NPR is doing something new - we're dedicating an entire week to stories and conversations about the search for climate solutions. This next one is about a robot and sargassum. It's a seaweed that floats around the North Atlantic Ocean and Caribbean Sea. Since 2011, the overall amount of sargassum has been increasing. And NPR's Emily Olson reports that when it comes too close to the shores, it can wreak havoc.

EMILY OLSON, BYLINE: When sargassum comes into shallow waters, it starts to smother local coral reefs, mangroves, seagrasses. It can alter pH levels in the water, and that can suffocate marine life. And that's not all. Like, if you're a human on a boat, algae might get into your motor or your propeller. You might get stuck for a while. And if you fish for a living, you could lose a lot of money. And in some places, it's even mucked up basic life necessities. Once, sargassum clogged a desalination plant in the U.S. Virgin Islands, and people didn't have safe drinking water.

SHAPIRO: Emily's been looking into a robot built by the company Seaweed Generation. Its creators hope it will one day sink sargassum before it reaches the shore and, in doing so, actually fight climate change. She spoke with Aaron Scott of NPR's Short Wave podcast.


OLSON: It's a rainy September morning, and there's a few engineers standing around an above-ground swimming pool.


OLSON: You know, like, the hard, plastic kind you might find in someone's backyard.


OLSON: All along the top of the water are rubber duckies.

AARON SCOTT, BYLINE: (Laughter) You mean like the bath toys?

OLSON: Yeah. These ducks are an important part of testing this robot called the AlgaRay.


PADDY ESTRIDGE: The AlgaRay is our submersible, and it's designed to be a fully independent glider.

OLSON: That's Paddy Estridge. She's the CEO of Seaweed Generation and the woman who had the idea to create this thing. Right now, the AlgaRay - you can picture it. It's just a wire-framed metal box. But one day, it'll have wings on the side, hence the name AlgaRay - it'll be in the shape of a manta ray - and it'll be over 30 feet long.


OLSON: It's so heavy that the team has to use ropes and pulleys to heave it into the water. But once it's in the water, they can take it through a series of tests.

UNIDENTIFIED PERSON: So I'm just going to test the operation of the thrusters now.

OLSON: Most importantly, they check that they can scoop up the rubber duckies and sink them, like, down to the bottom of the pool. See, the ducks are just a stand-in for what will be the AlgaRay's eventual target - sargassum.

SCOTT: OK, Emily, let's take a step back. Why is sargassum taking over the Atlantic Ocean now?

OLSON: Well, Aaron, we don't know.

SCOTT: (Laughter).

OLSON: These monster blooms are relatively new, so it's still early days for zeroing in on the causes. What we do know is that more studies are showing sargassum may contain heavy metals, like arsenic, so it could be really harmful for humans. Back in 2018, there was a period of intense buildup on the islands of Guadeloupe and Martinique. Doctors there reported more than 8,000 cases of something they were calling acute sargassum toxicity. I mean, here's how one teacher described sargassum season in Saint Lucia and what it does for her students.

UNIDENTIFIED TEACHER: They start fidgeting, and many, if not all of them, become very unsettled, making complaints that they're not feeling well, that they have headaches. Some even say that they have to throw up.

OLSON: She was one of dozens of people who came to a sargassum conference this year to raise awareness about what it's doing. And other speakers mentioned that they were losing sleep, feeling dizzy, developing rashes.

SCOTT: It sounds horrible. Are communities able to clean the sargassum up when it's piling up on the beach to prevent all these problems, then?

OLSON: A lot of them try to. But remember, this is thick and clumpy. It's not easy to move. That means they usually have to bring in heavy equipment, and that costs a lot of money. And some places can't afford to get, you know, a dozen bulldozers for a month, let alone every year again and again.

SCOTT: Yeah. And beaches probably aren't the best place to be driving bulldozers around anyway.

OLSON: Exactly. They can worsen shoreline erosion, plus they can squash turtle nests.

SCOTT: Poor turtles. Is this where our rubber-ducky-scooping robot comes in?

OLSON: Bingo. As Paddy puts it...

ESTRIDGE: The AlgaRay is a bit like a Pac-Man meets a Roomba for sargassum.

SCOTT: (Laughter) I love that image - sold. So I guess the next question is who's going to pay for this?

OLSON: Right now, Seaweed Generation - it's a startup, so it's funded by venture capitalists. And the company says they've seen a lot of interest from local governments and hotel groups that might want to buy and operate their own AlgaRays in the future. But Paddy told me, you know, there's also another stream of revenue that they could see working out in the long-term future.

ESTRIDGE: We are selling carbon dioxide removal credits for sinking sargassum to corporations with net-zero goals.

SCOTT: Right, right, right, carbon credits - this, of course, is one way that some corporations are trying to limit the warming of our atmosphere to 1.5 degrees Celsius above preindustrial levels in order to avoid the most catastrophic effects of climate change.

OLSON: Yeah.

SCOTT: Is the idea here that the AlgaRay will sink the sargassum, and then that is basically pulling all the carbon inside of that algae down to the bottom of the ocean and leaving it there?

OLSON: Yeah, that's the idea. And when I talked to Ajit Sabaraman (ph) - he's an oceanographer with Columbia University, and he says the ocean is already pretty good at storing carbon.

AJIT SUBRAMANIAM: Our current models of ocean circulation basically tell us that if you go below about 2,000 meters, then you are not going to come back to the atmosphere for at least 100 years.

SCOTT: How much sargassum can one AlgaRay sink?

OLSON: So the company says, when it's fully up and running, if one AlgaRay is working three months out of the year, 12 hours every day, that alone could sink about 80,000 tons of sargassum a year.


OLSON: And that translates to 8,000 tons of carbon dioxide.

SCOTT: Is that a lot?

OLSON: Well, let's compare it to the world's largest direct carbon capture facility. That's in Iceland. It's still being built. But right now, when it's up and running, that facility is only capturing about half of what this company is saying that the AlgaRay could potentially do.

SCOTT: Which is not bad for one little sargassum Roomba.

OLSON: Totally. But let's level-set here. I mean, even that big, fancy Iceland facility - that will just capture one-ten-thousandth of 1% of what humans emit annually.


OLSON: I mean, one AlgaRay can't reverse climate change. But, of course, there could be more AlgaRays working together, but we don't know what could happen if we start sinking, you know, half or even one-tenth of all the sargassum that's in the wild. That much might start to be harmful to all the marine life that's starting to take up a home, you know, there in those patches.

SCOTT: So still a lot of questions unresolved.

OLSON: Yeah. And to be fair, I think Seaweed Generation is very clear-eyed about the unknowns, and they're fine with being a test case. They want to see this as a window into researching sinking biomass as a whole.

ESTRIDGE: To help us understand whether seaweed, as a larger concept, could be viable for large-scale carbon dioxide removal. But we're pretty excited about just being able to alleviate the problems on the coast and solve some of the ecological problems that are being caused by the influxes at the moment.

OLSON: And they still got some time. I mean, she thinks it'll be about 18 months until this prototype will be even ready to work reliably in the wild. So like everything else in this climate emergency - even figuring out the solutions - it takes time.

SHAPIRO: That's Emily Olson and Aaron Scott with NPR's Short Wave podcast. To hear more stories exploring climate solutions, go to

(SOUNDBITE OF LILY MOORE SONG, "BEAUTIFUL LIE") Transcript provided by NPR, Copyright NPR.

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Emily Olson
Emily Olson is on a three-month assignment as a news writer and live blog editor, helping shape NPR's digital breaking news strategy.