On the grounds of a gas-fired power plant on Canada’s eastern coast, an obscure company is pumping a mineral-rich slurry into the ocean, aiming to combat climate change.
Whether this is an act of pollution or a breakthrough in climate solutions depends on perspective.
A pipe along the shore releases a blend of water and magnesium oxide—a fine white powder commonly used in construction and antacids. Planetary Technologies, based in Nova Scotia, is betting that this mineral will help the ocean absorb more greenhouse gases.
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"Restore the climate. Heal the ocean," reads the slogan displayed on a nearby shipping container.
Planetary is one of many emerging companies exploring ways to harness the ocean’s natural ability to absorb carbon. With a $1 million grant from Elon Musk’s foundation, it is also in the running for a $50 million prize.
Numerous other companies and research groups are testing similar concepts—whether by sinking rocks, dispersing nutrients, submerging agricultural waste, or cultivating seaweed—to trap carbon dioxide for centuries. Over the past four years, nearly 50 field trials have been conducted, with startups securing hundreds of millions in funding.
However, debate surrounds the potential consequences of scaling these approaches and their true effectiveness in combating climate change. Critics argue the industry is advancing too hastily without sufficient oversight.
“It’s like the Wild West. Everyone is jumping on board, eager to contribute,” said Adina Paytan, a professor of earth and ocean sciences at the University of California, Santa Cruz.
Planetary, like many ocean startups, finances its projects by selling carbon credits—certificates representing one metric ton of carbon dioxide removed from the air. Though largely unregulated and widely debated, carbon credits have become a common way for businesses to offset emissions rather than reducing them directly. These credits often sell for several hundred dollars each.
Last year, the industry sold over 340,000 marine carbon credits—up from just 2,000 four years prior, according to tracking site CDR.fyi. Yet, this remains a minuscule fraction of what scientists estimate is necessary to maintain a habitable planet.
Despite the uncertainties, industry leaders like Will Burt, Planetary’s chief ocean scientist, acknowledge they are venturing into unknown territory. However, they argue that inaction poses an even greater risk to both the planet and the oceans.
“We need to determine if this approach works as quickly as possible. The sooner, the better.”
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Drawing Carbon into the Ocean
Carbon capture efforts have expanded significantly in recent years.
According to the United Nations’ Intergovernmental Panel on Climate Change, cutting emissions alone will not be sufficient to slow global warming. Actively removing heat-trapping gases is essential, and the ocean presents a vast and logical solution.
Significant investments have already been made in land-based approaches, including extracting carbon dioxide from the air, underground storage, and reforestation. However, these methods are often limited by space and potential disruptions to local communities. In contrast, the ocean, which already plays a crucial role in regulating the planet’s climate, appears nearly boundless.
“Can the ocean’s vast surface area help mitigate the worst effects of climate change?” asked Adam Subhas, who leads a carbon removal project at the Woods Hole Oceanographic Institution in Massachusetts.
On a recent afternoon along Halifax Harbour, Burt swapped his bike helmet for a hard hat as he guided two engineering students through Planetary’s site.
A detached truck trailer stored massive bags of magnesium oxide mined in Spain and shipped across the Atlantic to Canada.
Many companies exploring ocean-based climate solutions aim to reduce or transform the carbon dioxide stored in seawater. If successful, Burt explained, the ocean will act "like a vacuum," drawing in more carbon from the atmosphere.
Planetary’s approach involves dissolving magnesium oxide into seawater, which converts carbon dioxide from a gas into stable molecules that remain out of the atmosphere for millennia. Other alkaline minerals, like limestone and olivine, have a similar effect.
Other startups are focusing on cultivating seaweed and algae to absorb carbon dioxide, similar to how trees remove carbon from the air. Gigablue, for instance, is adding nutrients to New Zealand’s waters to stimulate the growth of phytoplankton, which would not otherwise thrive there.
Some companies see the ocean’s depths as a storage site for organic materials that would otherwise emit greenhouse gases on land. Startups have submerged wood chips off Iceland’s coast and are planning to sink Sargassum seaweed to extreme depths. Carboniferous is seeking federal approval to deposit sugarcane pulp in the Gulf of Mexico, also called the Gulf of America by President Donald Trump.
Burt acknowledges that Planetary’s work may seem like a “scary science experiment.” However, early tests indicate minimal risks to marine life. Magnesium oxide is already used in water treatment facilities to neutralise acidity.
Halifax Harbour is just one of Planetary’s testing locations. The company also operates at a wastewater treatment facility in Virginia and plans to launch trials in Vancouver later this year.
The National Academies of Sciences, Engineering, and Medicine estimate that to meet the climate goals set during the Paris Agreement, billions of tons of carbon dioxide must be removed from the atmosphere annually by mid-century.
“The goal is to counteract the rapidly worsening climate crisis,” Burt said. “We must act with caution and integrity, but we must also act swiftly.”
Balancing Enthusiasm and Caution
Despite industry optimism, not all coastal communities are eager to embrace these initiatives.
In North Carolina, plans to deposit large quantities of olivine near the town of Duck faced regulatory concerns, reducing the project’s scale by more than half. Vesta, the company behind the initiative, promotes olivine as a tool for absorbing carbon while reinforcing coastlines against erosion.
However, state and federal agencies raised concerns about potential harm to marine ecosystems, including habitats for sea turtles and Atlantic sturgeon.
Vesta CEO Tom Green acknowledged that the initial proposal was unlikely to be approved as submitted. “It’s about starting a dialogue with regulators and local communities,” he explained.
After incorporating a restoration plan and more detailed monitoring, a scaled-down version of the project proceeded last summer. Now, 8,000 metric tons of olivine from Norway lie beneath North Carolina’s waves.
Green understands the skepticism and emphasises that Vesta’s intent is to protect, not harm, the environment. “It’s our responsibility to engage with local communities, present our data, and build trust.”
Other projects have faced similar resistance. Fishing communities have voiced concerns over a Woods Hole project near Cape Cod that involves introducing sodium hydroxide into ocean waters. While the Environmental Protection Agency supports the project’s scientific merits, fishermen worry about potential impacts on marine life and local industries.
Planetary, too, encountered opposition in Cornwall, England, where a proposed magnesium hydroxide release sparked protests. Following community backlash and government recommendations, the company paused operations, pledging to source minerals closer to the site and abstain from selling carbon credits from previous releases.
The Unanswered Questions
Even among scientists, uncertainties remain. Some principles behind these technologies have been studied for decades, yet real-world trials are essential to understanding large-scale impacts.
Tracking how the ocean processes added materials is complex. Elements may sink, disperse, or alter in ways difficult to predict. “It’s incredibly challenging to control the ocean,” noted carbon cycle scientist Sarah Cooley.
Questions persist regarding how long carbon will remain sequestered. Organic material like seaweed and wood chips could eventually decompose, re-releasing carbon. While some estimates suggest centuries or millennia of storage, others predict mere decades.
Scaling these efforts to billions of tons annually presents further challenges, requiring vast resources, energy, and funding.
Despite uncertainties, many experts argue that waiting is not an option. With global temperatures breaking records and carbon emissions reaching new highs, the urgency to act grows stronger.
“The alternative to trying,” said David Ho, an oceanography professor at the University of Hawaii, “is allowing climate change to continue unchecked.”