A Canadian company is testing ocean-based carbon removal, aiming to fight climate change, but critics warn of unknown risks and lack of oversight.
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| As companies test ocean-based carbon removal to combat climate change, scientists and communities remain divided over its safety and effectiveness. Image: Alkalign/ CH |
HALIFAX, CANADA, March 24, 2025:
A Canadian company is pumping mineral-rich slurry into the ocean, claiming it can fight climate change. Whether this is a climate breakthrough or an environmental risk depends on perspective.
On the grounds of a gas-fired power plant, Nova Scotia-based Planetary Technologies is releasing a magnesium oxide solution into seawater, hoping to enhance the ocean’s ability to absorb carbon dioxide. With a $1 million grant from Elon Musk’s foundation and a shot at a $50 million prize, the company is part of a growing industry betting on ocean-based carbon removal.
From sinking rocks to cultivating seaweed, nearly 50 field trials have taken place in recent years, with hundreds of millions of dollars pouring into startups. Yet, critics warn that scaling up these methods without regulation could have unintended ecological consequences.
“This industry is moving fast, but we still don’t fully understand the risks,” said Adina Paytan, an earth and ocean sciences professor at the University of California, Santa Cruz.
Planetary and other ocean startups finance their projects through carbon credits—certificates representing a ton of carbon dioxide removed from the air. These credits, though largely unregulated, are sold for hundreds of dollars each. Last year, the industry sold over 340,000 marine carbon credits—an exponential rise from 2,000 just four years ago, but still far from the scale needed to impact global warming.
The UN’s Intergovernmental Panel on Climate Change (IPCC) states that cutting emissions alone won’t be enough to curb global warming. Actively removing carbon dioxide from the air is essential, and the ocean—a natural climate regulator—is an attractive target.
Land-based methods like direct air capture and reforestation face space limitations and community concerns. The ocean, covering 70% of the planet, appears to offer more potential—if the risks can be managed.
"Can the ocean’s vast surface area help reverse climate change?" asked Adam Subhas, a scientist at the Woods Hole Oceanographic Institution in Massachusetts.
Planetary’s process dissolves magnesium oxide into seawater, which chemically binds to carbon dioxide, converting it into stable molecules that stay out of the atmosphere for centuries. Other companies are testing similar ideas using limestone, olivine, and even large-scale seaweed farming.
Some startups are exploring deep-sea storage, sinking organic materials like wood chips or agricultural waste to trap carbon indefinitely. New Zealand-based Gigablue is fertilizing phytoplankton growth, while Carboniferous is seeking approval to deposit sugarcane pulp in the Gulf of Mexico.
Planetary’s chief ocean scientist, Will Burt, acknowledges the uncertainties. "This may seem like an untested experiment, but early tests show minimal risks to marine life." Magnesium oxide, he points out, is already used in water treatment plants to reduce acidity.
Planetary operates at test sites in Halifax Harbour and Virginia, with plans to expand to Vancouver later this year.
Despite industry optimism, some coastal communities are skeptical.
In North Carolina, a project to spread olivine near the town of Duck faced environmental concerns, forcing the company to cut its plans by more than half. In Cornwall, England, protests against Planetary’s planned magnesium hydroxide release led the company to pause operations.
Even within the scientific community, uncertainties remain. While the core principles behind these technologies have been studied for decades, large-scale trials introduce unpredictable factors. Tracking how added materials behave—whether they disperse, sink, or alter ocean chemistry—is difficult.
Longevity is another issue. Organic materials like seaweed or wood chips could eventually decompose, re-releasing carbon. While some estimates predict storage lasting millennia, others suggest mere decades.
Scaling up ocean-based carbon removal to billions of tons per year would also require vast resources, energy, and investment.
Still, with carbon emissions at record highs, some argue that inaction poses a greater risk.
“The alternative to trying,” said David Ho, an oceanography professor at the University of Hawaii, “is letting climate change spiral further out of control.”