HALIFAX, Nova Scotia (AP) — Dozens of companies and academic groups are pitching the same theory: that sinking rocks, nutrients, crop waste or seaweed in the ocean could lock away climate-warming carbon dioxide for centuries or more. Nearly 50 field trials have taken place in the past four years, with startups raising hundreds of millions in early funds. But the field remains rife with debate over the consequences for the oceans if the strategies are deployed at large scale, and over the exact benefits for the climate. Critics say the efforts are moving too quickly and with too few guardrails.
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HALIFAX, Nova Scotia (AP) — From the grounds of a gas-fired power plant on the eastern shores of Canada, a little-known company is pumping a slurry of minerals into the ocean in the name of stopping climate change.
Whether it’s pollution or a silver bullet that will save the planet may depend on whom you ask.
From shore, a pipe releases a mixture of water and magnesium oxide — a powdery white mineral used in everything from construction to heartburn pills that Planetary Technologies, based in Nova Scotia, is betting will absorb more planet-warming gases into the sea.
“Restore the climate. Heal the ocean,” reads the motto stamped on a shipping container nearby.
Planetary is part of a growing industry racing to engineer a solution to global warming using the absorbent power of the oceans. It is backed by $1 million from Elon Musk’s foundation and competing for a prize of $50 million more.
Dozens of other companies and academic groups are pitching the same theory: that sinking rocks, nutrients, crop waste or seaweed in the ocean could lock away climate-warming carbon dioxide for centuries or more. Nearly 50 field trials have taken place in the past four years, with startups raising hundreds of millions in early funds.
But the field remains rife with debate over the consequences for the oceans if the strategies are deployed at large scale, and over the exact benefits for the climate. Critics say the efforts are moving too quickly and with too few guardrails.
“It’s like the Wild West. Everybody is on the bandwagon, everybody wants to do something,” said Adina Paytan, who teaches earth and ocean science at the University of California, Santa Cruz.
Planetary, like most of the ocean startups, is financing its work by selling carbon credits — or tokens representing one metric ton of carbon dioxide removed from the air. Largely unregulated and widely debated, carbon credits have become popular this century as a way for companies to purchase offsets rather than reduce emissions themselves. Most credits are priced at several hundred dollars apiece.
The industry sold more than 340,000 marine carbon credits last year, up from just 2,000 credits four years ago, according to the tracking site CDR.fyi. But that amount of carbon removal is a tiny fraction of what scientists say will be required to keep the planet livable for centuries to come.
Those leading the efforts, including Will Burt, Planetary’s chief ocean scientist, acknowledge they’re entering uncharted territory — but say the bigger danger for the planet and the oceans is not moving quickly enough.
“We need to understand if it’s going to work or not. The faster we do, the better.”
Vacuuming carbon into the sea
Efforts to capture carbon dioxide have exploded in recent years.
Most climate models now show that cutting emissions won’t be enough to curb global warming, according to the United Nations’ Intergovernmental Panel on Climate Change. The world needs to actively remove heat-trapping gases, as well — and the ocean could be a logical place to capture them.
Money has already poured into different strategies on land — among them, pumping carbon dioxide from the air, developing sites to store carbon underground and replanting forests, which naturally store CO2. But many of those projects are limited by space and could impact nearby communities. The ocean already regulates Earth’s climate by absorbing heat and carbon, and by comparison, it seems limitless.
“Is that huge surface area an option to help us deal with and mitigate the worst effects of climate change?” asked Adam Subhas, who is leading a carbon removal project with the Woods Hole Oceanographic Institution, based on Cape Cod, Massachusetts.
On a Tuesday afternoon along the edge of Halifax Harbour, Burt stashed his bike helmet and donned a hard hat to give two engineering students a tour of Planetary’s site.
A detached truck trailer sat in a clearing, storing massive bags of magnesium oxide mined in Spain and shipped across the Atlantic to Canada.
Most companies looking offshore for climate solutions are trying to reduce or transform the carbon dioxide stored in the ocean. If they can achieve that, Burt said, the oceans will act “like a vacuum” to absorb more gases from the air.
Planetary is using magnesium oxide to create that vacuum. When dissolved into seawater, it transforms carbon dioxide from a gas to stable molecules that won’t interact with the atmosphere for thousands of years. Limestone, olivine and other alkaline rocks have the same effect.
Other companies are focused on growing seaweed and algae to capture the gas. These marine organisms act like plants on land, absorbing carbon dioxide from the ocean just as trees do from the air. The company Gigablue, for instance, has begun pouring nutrients in New Zealand waters to grow tiny organisms known as phytoplankton where they otherwise couldn’t survive.
Still others view the deepest parts of the ocean as a place to store organic material that would emit greenhouse gases if left on land.
Companies have sunk wood chips off the coast of Iceland and are planning to sink Sargassum, a yellowish-brown seaweed, to extreme depths. The startup Carboniferous is preparing a federal permit to place sugarcane pulp at the bottom of the Gulf of Mexico, also referred to as the Gulf of America as declared by President Donald Trump.
Though Planetary’s work can sound like some “scary science experiment,” Burt said, the company’s testing so far suggests that magnesium oxide poses minimal risks to marine ecosystems, plankton or fish. The mineral has long been used at water treatment plants and industrial facilities to de-acidify water.
Halifax Harbour is just one location where Planetary hopes to operate. The company has set up another site at a wastewater treatment plant in coastal Virginia and plans to begin testing in Vancouver later this year.
According to the National Academies of Sciences, Engineering, and Medicine, the industry needs to remove billions of tons of carbon dioxide per year by mid-century to meet climate goals set nearly a decade ago during the Paris climate agreement.
“The whole point here is to mitigate against a rapidly accelerating climate crisis,” Burt said. “We have to act with safety and integrity, but we also have to act fast.”
‘Twisted in knots’
While there’s broad enthusiasm in the industry, coastal communities aren’t always quick to jump on board.
In North Carolina, a request to dump shiploads of olivine near the beachside town of Duck prompted questions that downsized the project by more than half.
The company Vesta, formed in 2021, promotes the greenish-hued mineral as a tool to draw down carbon into the ocean and create mounds that buffer coastal towns from storm surges and waves.
During the permitting process, officials at the state Wildlife Resources Commission, Division of Marine Fisheries and the U.S. Fish and Wildlife Service raised a long list of concerns.
“As proposed, the project is a short term study with the potential for long term impacts and no remediation plans,” a field supervisor for the Fish and Wildlife Service wrote. The agencies said olivine could smother the seafloor ecosystem and threaten a hotspot for sea turtles and Atlantic sturgeon.
Vesta CEO Tom Green said the company never expected its original application to be approved as written. “It’s more the start of a dialogue with regulators and the community,” he said.
The project went forward last summer with a much smaller scope, a restoration plan, and more detailed requirements to monitor deep-water species. Eight thousand metric tons of olivine shipped from Norway are now submerged beneath North Carolina’s waves.
Green said he understands why people are skeptical, and that he tries to remind them Vesta’s goal is to save the environment, not to harm it. It’s the company’s job, he says, “to show up in local communities, physically show up, and listen and share our data and build trust that way.”
Fishing communities have opposed another climate project led by Subhas of the Woods Hole research center that has generated 10 months of conversation and debate.
The project as proposed last spring would have poured 66,000 gallons of sodium hydroxide solution into ocean waters near Cape Cod. Woods Hole later proposed downsizing the project to use less than 17,000 gallons of the chemical, with federal approval still pending.
In two separate reviews, the Environmental Protection Agency said it believes the project’s scientific merit outweighs the environmental risks, and noted it doesn’t foresee “unacceptable impacts” on water quality or fishing.
But fifth-generation fisherman Jerry Leeman III wants to know what will happen to the lobster, pollock and flounder eggs that float in the water column and on the ocean surface if they are suddenly doused with the harsh chemical.
“Are you telling all the fishermen not to fish in this area while you’re doing this project? And who compensates these individuals for displacing everybody?” he said.
Subhas’ team expects the chemical’s most potent concentrations to last for less than two minutes in the ocean before it’s diluted. They’ve also agreed to delay or relocate the project if schools of fish or patches of fish eggs are visible in the surrounding waters.
Sarah Schumann, who fishes commercially for bluefish in Rhode Island and leads a campaign for “fishery friendly” climate action, said after attending four listening sessions she’s still unsure how to balance her support for the research with the apprehension she hears in the fishing community.
“If I was actually trying to decide where I land on this issue, I’d be twisted in knots,” she said.
And Planetary, which has seen little pushback from locals along Halifax Harbour, faced a series of protests against a climate project it proposed in Cornwall, England.
In April last year, more than a hundred people marched along a beach carrying signs that read “Keep our sea chemical free.”
Sue Sayer, who runs a research group studying seals, said she realized in discussions with Planetary that “they had no idea about what animals or plants or species live in St. Ives Bay.” The company’s initial release of magnesium hydroxide into the bay, she said, fired up a community that is “massively, scientifically passionate about the sea.”
David Santillo, a senior scientist with Greenpeace Research Laboratories at the University of Exeter, took issue with how Planetary proposed tracking the impact of its work. According to a recorded presentation viewed by AP, the company’s baseline measurements in Cornwall were drawn from just a few days.
“If you don’t have a baseline over a number of years and seasons,” Santillo said, “you don’t know whether you would even be able to detect any of your effects.”
An audit commissioned by the United Kingdom’s Environment Agency found that Planetary’s experiments posed a “very low” risk to marine life, and a potential for significant carbon removal.
Still, the company put its proposal to pump another 200 metric tons of minerals on pause. Following a government recommendation, Planetary said it would search for a source of magnesium hydroxide closer to the Cornwall site, rather than shipping it from China. It also assured locals that it wouldn’t sell carbon credits from its past chemical release.
Sara Nawaz, research director at American University’s Institute for Responsible Carbon Removal, said she understood why scientists sometimes struggle to connect with communities and gain their support. Early research shows the public is reluctant to the idea of “engineering” the climate.
Many people have a strong emotional connection to the ocean, she added. There’s a fear that once you put something in the ocean, “you can’t take it back.”
The great unknowns
It’s not just locals who have questions about whether these technologies will work. Scientists, too, have acknowledged major unknowns. But some of the principles behind the technologies have been studied for decades by now, and the laboratory can only simulate so much.
During a recent EPA listening session about the Woods Hole project, a chorus of oceanographers and industry supporters said it’s time for ocean-scale tests.
“There’s an urgency to move ahead and conduct this work,” said Ken Buesseler, another Woods Hole scientist who studies the carbon captured by algae.
Even so, the ocean is a dynamic, challenging landscape to work in. Scientists are still uncovering new details about how it absorbs and recycles carbon, and any materials they add to seawater are liable to sink, become diluted or wash away to other locations, challenging efforts to track how the ocean responds.
“It’s so hard to get the ocean to do what you want it to,” said Sarah Cooley, a carbon cycle scientist who has worked for the nonprofit Ocean Conservancy and the federal government.
Katja Fennel, chair of the oceanography department at Dalhousie University, works on modeling how much carbon Planetary has captured in Halifax Harbour— a number that comes with some uncertainty.
She co-leads a group of academics that monitors the company’s project using water samples, sensors and sediment cores taken from locations around the bay. Some days, her team adds a red dye to the pipes to watch how the minerals dissolve and flow out to sea.
The models are necessary to simulate what would happen if Planetary did nothing, Fennel said. They’re also necessary because the ocean is so large and deep it’s impossible to collect enough data to give a complete picture of it.
“We can’t measure everywhere all the time,” she said.
Questions also linger about how long the carbon capture will last.
It’s a point especially important to companies working with algae, wood chips, or other organic materials, because depending on where they decompose, they could release carbon dioxide back into the atmosphere.
The deeper the plants and algae sink, the longer the carbon stays locked away. But that’s no easy feat to ensure. Running Tide, a now-shuttered company that sank nearly 20,000 metric tons of wood chips in Icelandic waters, said carbon could be sequestered for as long as three millennia or as little as 50 years.
Even if these solutions do work long term, most companies are operating on too small of a scale to influence the climate. Expanding to meet current climate goals will take massive amounts of resources, energy and money.
“The question is, what happens when you scale it up to billions of tons every year?” said David Ho, co-founder and chief science officer of the nonprofit (C)Worthy, which works on verifying the impact of ocean-based carbon removal. “And that’s still to be determined.”
Planetary’s Burt imagines a future in which minerals are pumped out through power plants and water treatment facilities on every major coastline in the world. But that would require a large, steady volume of magnesium oxide or similar minerals, along with the energy to mine and transport them.
Seaweed and algae growth would need to expand exponentially. The National Academies of Sciences, Engineering, and Medicine has estimated that nearly two-thirds of the world’s coastline would need to be encircled by kelp to even begin to make a dent in global warming. The company Seafields, which is running tests in the Caribbean, says it envisions building a Sargassum farm between Brazil and West Africa more than 200 miles wide.
There’s the risk that these expansions exacerbate environmental harm that isn’t detectable in small trials, and because of global water circulation, could be felt around the world.
But the alternative to never trying, Ho said, is unabated climate change.
Running out of time
Late last year, Planetary announced that its Nova Scotia project successfully captured 138 metric tons of carbon – allowing it to deliver exactly 138 carbon credits to two of the company’s early investors, Shopify and Stripe.
Monetizing the work is uncomfortable for many who study the ocean.
“On one hand, it’s encouraging more research and more science, which is good. On the other hand, it’s opening doors for abuse of the system,” said Paytan, the Santa Cruz professor, who has been contacted by several startups asking to collaborate.
She pointed to companies that are accused of drastically overestimating the carbon they sequestered, though they bragged of restoring rainforests in Peru and replacing smoke-producing stoves in Africa.
But absent more government-funded research, several companies told AP there’s little way for the field to advance without selling credits.
“Unfortunately, that’s the way we’ve set things up now, is that we put it in the hands of these startups to develop the techniques,” said Ho.
Back in his shipping container office along Halifax Harbour, Burt said he understood the unease around selling credits, and said Planetary takes seriously the need to operate openly, responsibly and cautiously. But he also says there’s a need for startups that can move at a faster pace than academia.
“We cannot study this solution at the same rate that we’ve been studying the problems,” he said. He says there’s not enough time.
Last year marked the hottest year in Earth’s history, even as global carbon emissions are projected to reach another all-time high.
“We need to reduce emissions urgently, drastically,” said Fennel, the researcher studying Planetary’s project. “Any removal of CO2 from the atmosphere is much more difficult and costly than avoiding CO2 emissions to begin with.”
The industry continues to push forward. Planetary said in February that it had sequestered a total of 1,000 metric tons of carbon in the ocean, and Carboniferous completed its first test of sinking sugarcane to the seafloor. Early this year, Gigablue signed a deal for 200,000 carbon credits for dispersing nutrient-filled particles in the ocean.
A growing number of companies are also using electricity to alter seawater molecules, with the same goal of prompting the ocean to absorb more carbon dioxide. The startup Ebb Carbon recently struck a deal with Microsoft to provide up to 350,000 carbon credits, and Captura, which is funded in part by investors affiliated with oil and gas production, expanded its operations from California to Hawaii.
It’s unclear whether the U.S. government will stall or support ocean climate work going forward. The policy landscape continues to shift as the Trump administration seeks to roll back a wide range of environmental regulations and reconsider the scientific finding that greenhouse gases endanger public health.
Though White House adviser Musk has downplayed some of his past statements about global warming, four years ago his foundation committed $100 million to fund a competition for the best solution for carbon capture, of which Planetary is in the running for the top prize.
The winner will be announced April 23 — the day after Earth Day.
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