How Sinking Carbon-storing Seaweed Can Help Fight Climate Change

pull to refresh — The carbon in sargassum seaweed is eventually released in the form of methane, a much more dangerous and potent greenhouse gas than carbon dioxide. Zen Rial/Getty Images

Climate change, driven primarily by human activity that pumps large amounts of carbon dioxide into the atmosphere, already is having observable effects all over the planet, and scientists fear it will have catastrophic impacts by the end of this century, from increasingly violent storms and brutal heat waves to rising sea levels that will inundate coastlines.

But as climate activists and politicians grapple over how aggressively carbon emissions need to be reduced to stave off what many see as an existential threat, a group of volunteer visionaries called Pull to Refresh is proposing an ingenious alternative solution. They want to use seaweed — specifically, the vast quantities of macroscopic algae such as kelp and sargassum which occur naturally in our oceans — to absorb carbon emissions from the atmosphere and store the carbon.

The Pull to Refresh Plan

Pull to Refresh — which cleverly takes its name from a familiar touch-screen gesture — would do this by deploying a fleet of robotic, solar-powered vessels to roam the oceans. In the Caribbean, the autonomous craft would sink the existing, plentiful masses of sargassum, so that the carbon would be stored on the ocean bottom, explains Arin Crumley, filmmaker, entrepreneur and CEO of Pull to Refresh. In the Pacific, similar robots could cultivate kelp forests in remote areas, growing the carbon-absorbing algae on trellises and eventually sinking it in the deep ocean, as this 2021 Technology Review article describes.

Crumley, who in addition to directing and producing films has imported parts for electric skateboards, says that Pull to Refresh grew out of a discussion group on Clubhouse, a social media app, which brought together a bunch of climate-minded talent from a variety of fields, ranging from creative media types to engineers.

"All of the people who came together have been wanting to do something about climate change for a long time, but weren't sure what that could be," Crumley explains via Zoom. They coalesced around a goal of entering in the XPrize Carbon Removal competition, which offers $100 million in funding for the competitor with the best idea for fighting climate change.

Initially, Crumley and the others looked at finding a way to capture carbon directly from the air, until they hit upon the idea of seaweed as a carbon storage medium. "It just turned out that you can get so much farther by utilizing photosynthesis and the open ocean," Crumley says. Eventually, the team realized that "we just need a thing that floats around and can go out to do the stuff that needs to be done."

For Crumley, it all clicked. "It's basically a giant electric skateboard," he says. Relatively giant, that is — Crumley says the robotic vessels might start in size at 8 meters (26 feet) in length by 6.6 feet (2 meters) across. "It has all the same components. You've got a main battery pack, the main electronic components, a couple of different motors. And it's just a kind of blown-up enlarged version of what I was pretty familiar with already."

Unmanned Vessels Are Key

"My background is not in electronics or mechanical engineering, or any of these specific realms of expertise, but just in understanding how it all works," he continues. "What all the components are, what different talents are involved, what kind of teams get certain things done. It became clear that there was no reason we couldn't design an unmanned vessel that would do the work."

Using unmanned vessels is key, Crumley says, because they eliminate the need to have "huge crews out really far from the coastline. Because you need to get to where there's enough depth. So you can't operate anywhere near the coast. So now you're talking danger, you're talking very high salaries, you're talking about people missing their loved ones for months and months."

From Growing Kelp to Harvesting Sargassum

Initially, Pull to Refresh focused upon the idea of growing kelp in the Pacific. "So that was kind of our initial prototyping and development that we did," explains Laurel Tincher, another of the organization's leaders. But the focus recently has shifted from kelp to Caribbean sargassum, in part because it provids an opportunity to have an impact not just on climate change, but upon another environmental problem as well.

"We also came across this really massive issue of invasive sargassum in the Caribbean," Tincher says. "Really, in the past 10 years it has become a huge problem. And we thought, well, there's already all of this seaweed out there, this is already carbon that's been captured. Let's do something with this. And so we kind of pivoted to create this stepping stone where we have a vessel that can drive around and gather up that sargassum and sink that. So that can really help us to prove out a lot of different aspects of our technology that will ultimately be used in both systems but can also help solve this forgotten problem."

If the sargassum is allowed to wash up on beaches, it not only is an eyesore, but the carbon in the sargassum eventually can be released in the form of methane, a much more potent greenhouse gas than carbon dioxide. Instead, by lowering the sargassum into the water, the algae eventually becomes compressed and loses its buoyancy, so that it can sink to the bottom, according to Crumley.

To actually make a serious dent in the Earth's atmospheric carbon, Pull to Refresh would have to put a lot of robotic vessels out in the world's oceans — perhaps as many as a billion. "I understand that's a crazy number," Crumley says. But he also notes that it's the equivalent of a decade's worth of production in the global automobile industry. With a sufficiently broad base of support, "it's doable," he insists.

But before Pull to Refresh can attract funders to scale up to that size, it has to prove that its technology works and that it can reduce atmospheric carbon. In the meantime, the organization is operating on a shoestring, dependent upon pro bono labor and donations from its members. Pull to Refresh recently rented a house on the water in Panama, where it plans to conduct research on prototypes.

"We're crowdsourcing to a group of over 50 volunteers and growing," notes Crumley, who also says that a major industrial design software firm has helped out by providing "seats," i.e., user access, to some of its products. Eventually, Pull to Refresh hopes to attract backing from companies who want to offset their own carbon output, as well as individual contributors.

Crumley says that Pull to Refresh is aware of potential downsides to sequestering carbon on the ocean floor, such as possibly changing the content of the "Marine snow" that life in the oceans depends upon for nutrients. For that reason, Pull to Refresh would "follow it down and carefully monitor it," and look for ways to mitigate any negative effects.

In the meantime, as Pull to Refresh develops its technology, it's also working to find creative ways to get the word out about its alternative method for reducing atmospheric carbon.

"There's such a big storytelling element to what we're trying to do, because it's such a large scale that we need to get to, and we really need to get everybody on board and people don't even really know about carbon removal that much yet," Tincher says. "So we're trying to figure out ways of how do we show, how do we tell the story in a visual way, or what audio are we using? How do we simplify it down, so that people really get it?"