Ocean carbon removal advances under a cautious global framework

By Olivia Hart

More than $500 million (£370 million) has been invested in ocean carbon removal since 2021, according to Ocean Carbon Removal Watch, a database launched by the Pulitzer Center that tracks marine carbon dioxide removal investments.

The spending has outrun the rulebook. In October, the International Maritime Organization adopted the first international framework for marine geoengineering, but it stopped short of clearing methods for wider deployment.

What is operating in Halifax Harbour?

Candy cane-striped smokestacks at Tufts Cove, Nova Scotia, overlook a marine carbon-removal operation. From a shipping container, Planetary Technologies runs ocean alkalinity enhancement five days a week.

The company adds its proprietary alkaline slurry to cooling water from a local power company. The odourless, milky composite enters Halifax Harbour, where Planetary Technologies monitors it with sensors.

Ocean alkalinity enhancement adds a chalk-like substance that allows seawater to absorb and store more atmospheric carbon than usual. It can also offset ocean acidification, which advocates call the climate crisis's evil twin and which is increasing sharply.

Planetary Technologies co-founder and senior scientist Greg Rau describes the method as acceleration of a natural carbon cycle that has rebalanced atmospheric and ocean chemistry over billions of years.

Proponents argue that reliance on an existing process means no harm to the harbour's mackerel, sunfish, harbour seals and sea turtles. Marine scientists counter that adding materials to a stressed ecosystem may hurt aquatic life and requires more research.

The pilot has a monitoring system, but its environmental case remains unsettled.

Who is buying the credits?

Planetary Technologies started with small government grants, venture funds and other private capital. It now generates revenue by selling carbon-removal credits worth millions of dollars to companies including JPMorgan Chase and Shopify.

The market has buyers now, while environmental proof remains incomplete.

What did the IMO decide?

After more than a decade of protracted negotiations among dozens of countries, the IMO adopted the first international framework to formally recognize three marine carbon-removal techniques in October.

• Ocean fertilisation.
• Ocean alkalinity enhancement.
• Biomass sinking.

The framework took shape at the annual London meeting of the London Convention and Protocol, the treaty governing dumping of waste at sea. The IMO set a research threshold: “Further scientific research is needed before any activities beyond the research stage can be considered.” It also noted that marine geoengineering was attracting increasing scientific, commercial and public attention.

Ocean Conservancy vice-president for climate Fatima Candace Vahlsing says the assessments signal government and industry priority, while businesses, academics and nonprofits all need a trusted system.

The IMO has named the methods, but has not cleared them for wider use.

Where are trials moving?

Nova Scotia, with its cod-fishing history and strong tides, now hosts the world's largest ocean alkalinity-enhancement centre. Dalhousie University's Ocean Frontier Institute anchors the hub, backed by Canadian government grants and partnerships with research institutions in Germany and Australia.

CarbonRun and pHathom Technologies operate there as private companies. Carbon to Sea, a nonprofit scientific research programme, runs a test site.

As Halifax grows, the wider sector proposes field trials in several settings:

• The Gulf of Mexico.
• The Gulf off Saudi Arabia.
• Norway's rivers.
• Singapore harbours.

Existing maritime laws do not clearly apply to the new activity, and their jurisdictional limits remain unsettled. New York-based Sabin Center for Climate Change Law deputy director Romany Webb says those gaps create opportunities for bad actors.

Ocean Visions chief executive Brad Ack calls for significant public investment to set rules and standards. He says private and academic work is not enough, while US government funding, in the country where the sector began, has increasingly dried up.

Nova Scotia supplies the test ground, not a settled rulebook.

What can the added material do?

Base materials for alkalinity enhancement do not share the same risk profile. Mining byproducts cost considerably less than other feedstocks, but their trace metals can have an outsized effect on marine ecosystems.

Jožef Stefan Institute senior scientist Nina Bednaršek warns that trace metals can produce toxic effects at very low concentrations, with particular risk for zooplankton at the base of marine food chains. She said: “Right now, there is no price on the biology. I think that’s wrong.”

Bednaršek works with the Intergovernmental Panel on Climate Change to develop a method for accounting for carbon removed through ocean alkalinity enhancement. The accounting work, like the IMO framework, could support environmental safeguards and regulatory oversight.

University of Gothenburg senior lecturer Sam Dupont compares deployment without adequate testing to jumping straight to a clinical trial for a new medicine rather than following its required steps.

Lisa Levin, professor emeritus at Scripps Institution of Oceanography, says most OAE research assesses ocean chemistry, which she does not consider an environmental-risk assessment. Scientists are studying marine impacts, but the field remains understudied globally.

Some scientists and conservation organisations fear the private market is moving too quickly and may damage the ocean or cloud the sector before genuine breakthroughs. Carbon-removal businesses counter that more legislation means more delay, although the ocean and planet have little time to spare.

Rau argues that conservation groups treat any unusual intervention as harmful. His view is that the ocean already suffers damage from warming and acidification, and fences around test areas cannot stop either process.

The next milestone is clear: governments must apply the IMO framework and define jurisdictional limits before commercial trials expand; until then, biology remains unpriced.