Ocean Carbon Removal Shows Promise, But Big Questions Remain – State of the Planet

A new report from the National Academies of Sciences, Engineering, and Medicine finds that marine carbon dioxide removal could play an important role in addressing climate change, but faces significant scientific, technical and governance challenges that could limit its development and deployment.

The report, “A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration,” is the first installment of an updated research strategy for marine carbon dioxide removal, or marine CDR. It updates and expands key sections of the National Academies’ 2022 report, addressing a broad range of governance considerations for marine CDR, and the specific technique of ocean alkalinity enhancement (OAE). The authors also published a new summary, “State of Marine CDR,” offering a broad overview of the field’s current status, challenges and opportunities.  

Two Columbia University researchers served on the standing committee that produced the report: Romany Webb, deputy director of the Sabin Center for Climate Change Law, and Galen McKinley, a professor in the Department of Earth and Environmental Sciences within the Faculty of Arts and Sciences and a researcher at Lamont-Doherty Earth Observatory, which is part of the Columbia Climate School.

“The ocean is too large a part of the carbon cycle to ignore, and we need every viable tool for addressing climate change,” McKinley said. “But the case for marine carbon dioxide removal at scale has to be built on evidence we do not yet have. OAE remains promising, but there are still major uncertainties about how it would work in the ocean, how much carbon it would actually remove and what it would take to scale responsibly.”

The need for additional carbon dioxide removal is becoming increasingly urgent. The U.N. Environment Programme’s recent Limiting Overshoot report warns that global temperatures are likely to exceed 1.5°C above pre-industrial levels within the next decade and calls for rapidly reducing emissions while scaling up carbon dioxide removal.

Marine CDR research has advanced significantly since the National Academies’ 2022 report, including through new in-ocean field trials, laboratory and mesocosm studies, and a growing body of modeling work. Private companies have also entered the field and begun selling marine CDR carbon credits, while governments and international bodies continue to debate how to regulate research and any future large-scale deployment.

Ocean alkalinity enhancement is one of the most actively studied marine CDR approaches. The technique involves adding alkalinity to seawater, shifting ocean chemistry so surface waters can absorb more carbon dioxide from the atmosphere; in theory, carbon stored this way could remain in the ocean for millennia. But the report finds major open questions remain about how alkaline materials dissolve, how quickly the ocean absorbs additional carbon dioxide, how to distinguish carbon removed by an intervention from the ocean’s much larger natural carbon sink and whether large-scale deployment would be net-negative once mining, processing, transportation and dispersal are accounted for. “Transparent, consistent life-cycle accounting has to be part of any carbon removal claim, and the report finds current practices inconsistent enough to make approaches hard to compare,” said McKinley. 

The report also emphasizes that governance gaps could limit near-term progress. Marine CDR presents unique regulatory challenges because it involves deliberate interventions in the ocean, a global commons shared by all countries. Existing international agreements and national environmental laws may apply to some activities, but many were designed for other purposes, creating gaps and uncertainties.

“Marine CDR involves perturbing the ocean, a global commons that all countries and all people have an interest in protecting,” Webb said. “Existing legal frameworks were largely developed with other activities in mind, and they often fit awkwardly around approaches that may pose environmental risks but are ultimately intended to deliver climate benefits. Unless clearer governance frameworks are put in place, advancing marine CDR may prove impossible.”

The new report concludes that governance gaps “directly constrain the near-term scalability” of ocean alkalinity enhancement and calls for further work to advance marine CDR governance at the international, national and subnational levels. It emphasizes that governance should support responsible research and development while maintaining robust environmental and social safeguards.

The authors stress that marine CDR should be considered only as a complement to rapid emissions reductions, not a substitute for them. The report calls for a research agenda that can help determine whether marine CDR approaches can be effective, durable, verifiable, environmentally responsible and socially acceptable at meaningful scales.