Kelp Is Weirdly Great at Sucking Carbon Out of the Sky

The start-up Running Tide wants to use kelp buoys to fight climate change. The plan might not work, but it’s still a preview of our climate future.

A man in a kelp hatchery
A Running Tide employee works inside a kelp hatchery. Because kelp grows as fast as two feet a day, it absorbs a huge amount of carbon through photosynthesis. (Jamie Walter / Running Tide)

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Last month, somewhere off the coast of Maine, a small group of researchers and engineers released a series of tiny, floating objects into the water. The team called them “buoys,” but they looked more like a packet of uncooked ramen noodles glued to a green party streamer than anything of the navigational or weather-observing variety. These odd jellyfish had one role in life: to go away and never be seen again. With any luck, their successors would soon be released into the open ocean, where they would float away, absorb a small amount of carbon from the atmosphere, then sink to the bottom of the seafloor, where their residue would remain for thousands of years.

That is not only the goal. That is also the business model. The team worked for Running Tide, a Portland, Maine–based start-up that claims it can remove carbon dioxide from the ocean and atmosphere through the magic of kelp. Running Tide is one of a series of carbon-removal companies that have burst onto the market over the past few years with the hope of whisking heat-trapping pollution out of the atmosphere and locking it away for centuries. The most famous companies, such as Switzerland’s Climeworks or Canada’s Carbon Engineering, perform direct air capture, using common industrial processes to chemically clean carbon from the air. But this is not the only approach: Some firms have tried to store carbon in stone or concrete; others have tried to accelerate the rock-weathering process that normally takes thousands of years.

And then there’s kelp. Kelp grows as fast as two feet a day, which means it absorbs a huge amount of carbon through photosynthesis. That kelp could then be harvested, disposed of, or allowed to naturally drift to the bottom of the ocean. It has seemed like the perfect natural tool to sop up carbon from the ocean and atmosphere. But that has made me suspicious. The idea that humanity will remove carbon dioxide from the atmosphere by growing kelp smacks of the same naivete in the idea that we can solve climate change by growing trees or living in harmony with nature.

So I was pleasantly surprised when I met the leaders of Running Tide earlier this month. Far from having a hippie-dippie-ish enthusiasm about kelp, they spoke like engineers, aware of the immense scale of carbon removal that stands before them. While much of Running Tide's science remains unvetted, the researchers seem to be thinking about all the right problems in all the right ways—approaching carbon removal as an organization-level problem rather than a one-off process.

At its core, carbon removal is “a mass-transfer problem,” Marty Odlin, Running Tide’s CEO, told me. The key issue is how to move the hundreds of gigatons of carbon emitted by fossil fuels from the “fast cycle,” where carbon flits from fossil fuels to the air to plant matter, back to the “slow cycle,” where they remain locked away in geological storage for millennia. “How do you move that?” Odlin said. “What’s the most efficient way possible to accomplish that mass transfer?” The question is really, really important. The United Nations recently said that carbon removal is “essential” to remedying climate change, but so far, we don’t have the technology to do it cheaply and at scale.

An image of Running Tide's kelp buoy
Running Tide’s buoys are made of reclaimed waste wood, limestone, and kelp seedlings. (Jamie Walter / Running Tide)

Odlin, who comes from a Maine fishing family and went to college for robotics, founded Running Tide in 2017 on the theory that the ocean, which covers two-thirds of the planet’s surface, would be essential to carbon removal. At least for now, the key aspect of Running Tide’s system is its buoys. Each buoy is made of reclaimed waste wood, limestone, and kelp seedlings, materials that are meant to address the climate problem in some way: The wood represents forest carbon that would otherwise be thrown out or incinerated, the limestone helps reverse ocean acidification, and, most important, the kelp grows ultrafast, absorbing carbon from the land and sea. Eventually, the buoy is meant to break down, with the limestone dissolving and the wood and kelp drifting to the bottom of the seafloor.

The details of Running Tide’s buoy emerged after lots of brainstorming with fishermen, oceanologists, and marine biologists, Odlin said. “We ended up with this idea of a non-recoverable floating buoy,” he said. But what to make it out of? Odlin knew that he wanted materials that were plentiful enough that the company could make lots and lots of buoys to suck up “all the carbon,” if it had to. During the brainstorming process, he also became convinced that the buoys couldn’t be released in one place on the planet’s surface—the risk was too great that they would damage the fragile chemistry of one of the ocean’s crucial “Goldilocks zones,” where biodiversity is concentrated, he said. Because transportation is so carbon-intensive, that all but meant that the buoys’ production couldn’t happen in one factory: They’d have to be made out of cheap, floating, carbon-negative materials that are widely available across the world.

“What are you left with? It’s like, very quickly, there were not a lot of ways to do it.” Waste wood, limestone, and kelp became Running Tide’s building materials of choice. Odlin and the company’s leaders see the buoys as only one of their future products, preferring to cast their output as a set of interlocking systems that collectively remove carbon. “​This is hard for external communication, but, internally, we hold all possibilities at all times,” he said. “What we’re doing right now is trying to keep the ocean in a Goldilocks zone.”

At least in theory, the ocean allows them to shortcut some of the hardest aspects of carbon removal. A direct-air-capture (DAC) plant needs to operate giant cooling-tower-like fans in order to suck air into its industrial machinery. The sloshing ocean, meanwhile, is always depositing new material onto the surface of the buoy. Likewise, a DAC plant ends its process by pumping extracted carbon deep into the bedrock. Running Tide doesn’t need to expend energy on that process: Gravity and the current simply carry the waste wood and kelp to the bottom of the ocean.

So far, Running Tide has tested thousands of its buoys, although it estimates that they have removed less than 1,000 tons of carbon from the atmosphere. It will conduct its largest release ever later this year, off the coast of Iceland.

Although Running Tide’s plan is promising, it’s hardly a sure bet. Scientifically, the company faces at least two major obstacles, David Ho, an oceanography professor at the University of Hawaii, told me. First, it’s not clear that all the carbon captured by kelp remains in the plant as it sinks to the seafloor. Second, the choppy, complicated way that the ocean and sea interact means that not all carbon absorbed by kelp actually comes out of the air. Perhaps only 40 of every 100 tons of carbon sequestered by kelp is actually removed from the atmosphere in the long term, a recent draft study has found. “They think they might have a way to figure out” how to beat those problems, but Ho said he doubted it.

What’s more impressive is how Running Tide approaches the carbon-removal problem as an organization. Right now, it costs $250 to remove a ton of carbon using its technology, which is at the low end of current carbon-removal approaches. For society’s purposes, that’s still way too high: The Department of Energy hopes to get carbon removal to less than $100 a ton by 2030.

But the $250-a-ton number exerts a pull throughout Running Tide, because in order for the company to make sure that it does not accidentally put more carbon into the atmosphere than it’s removing, it has to remain carbon negative as an organization. That means it maintains an internal corporate carbon price that is equal to whatever its per-ton cost of carbon removal is.

The need to keep carbon costs low propagates through the company. It’s why many of Running Tide’s 70 employees work in Iceland: The county’s geothermal electricity means their local carbon costs are effectively $0. But not every part of the company’s chain is so low carbon: It still costs the firm $750 in carbon to get the buoys on a boat and release them off Iceland’s coast. That’s why Running Tide is looking into purchasing renewable biofuel from GoodFuels, a Danish start-up that sells low-carbon fuel for ships. The need to stay carbon negative “is a function of what carbon removal is, as an industry,” Jordan Breighner, Running Tide’s head of policy, told me. “All we are is a supply chain. And the attribute that we sell is tons of carbon removed. We partner with nature to make that happen … Instead of offloading ships at port, we’re offloading carbon at sea.”

In a way, Running Tide and other carbon-removal companies are discovering what it means to take carbon seriously. It’s still very possible that kelp itself won’t end up being a feasible approach to removing carbon from the atmosphere. Still, the company is a preview of a future in which “net zero” is something more than faraway corporate promises. The ideas that Running Tide is committing itself to will matter for much longer than its ramen-looking buoys do.