Rapidly reducing greenhouse gas emissions is the world’s top priority for combatting climate change. But scientists agree that we must also remove significant amounts of carbon from the atmosphere to meet global climate goals and keep warming to safer levels. This carbon dioxide removal (CDR) can come from many different approaches — including emerging methods based in the ocean.

The ocean covers 70% of the earth and holds 42 times more carbon than the atmosphere. Proposed ocean CDR approaches seek to leverage this capacity to safely store more carbon. Such methods could potentially remove up to billions of tons of CO2 per year. But this potential is paired with a lot of uncertainty. More funding is needed for research and at-sea testing to understand both how effective ocean CDR approaches are at removing carbon and storing it over time, and what impacts they could have on people and the environment.

The United States can and should lead on developing research in this area.

As the world’s largest historical greenhouse gas emitter, the U.S. has a responsibility to drive early research and development of CDR technologies that are needed to address the climate crisis. The U.S. also specifically mentions ocean CDR in its long-term low-emissions development strategy. This charts the course to net-zero emissions by 2050 and includes roughly 1 billion metric tons of carbon removal across all types of approaches. Yet, while the U.S. has already directed billions toward the development of land-based carbon removal, little funding has gone to ocean CDR.

Scaling up funding for ocean CDR research and testing can help build a knowledge base to inform decisions on which approaches are suitable for large-scale deployment. This will ultimately help reach not just U.S. but global climate goals.

Opportunities and Risks for Ocean-based Carbon Removal in the U.S.

Just as on land, there are a wide range of ways the ocean could be used to increase carbon removal. These can generally be grouped into methods that leverage biological processes and those that leverage non-biological processes, otherwise known as “biotic” and “abiotic” approaches.

One example of biological ocean-based carbon removal is the cultivation and intentional sinking of seaweed. This can include the harvesting and sinking of nuisance seaweed, which has become an increasing issue on the United States’ Gulf Coast and Florida’s Atlantic coast in recent years. Seaweed takes up dissolved carbon dioxide (CO2) from surface waters as it grows and transforms that CO2 into its carbon tissues. That embodied carbon is sequestered when the seaweed is sunk. The seawater depleted of CO2 then re-equilibrates with the atmosphere by taking up some of its carbon dioxide, resulting in atmospheric carbon removal.

On the abiotic side are techniques such as ocean alkalinity enhancement, which involves applying ground-up alkaline rock to seawater. The ground material reacts with dissolved CO2 in surface waters to form solid bicarbonates and carbonates that lock away carbon. As with seaweed cultivation, ocean alkalinity enhancement seeks to reduce the amount of dissolved CO2 in surface waters so that they can remove more CO2 from the air.

Graphic showing types of biotic and abiotic ocean-based carbon removal approaches.

These approaches remain largely untested and all involve risks and tradeoffs. Scientists and researchers are uncertain about how effective they are at removing carbon in different locations and under different circumstances. They’re also unsure of how long it takes for sequestration to happen and the duration of carbon storage. Moreover, these results can be difficult to measure given that the ocean is always moving and transboundary.

Each approach also presents potential ecological and environmental impacts. For example, large-scale cultivation of seaweed can reduce light penetration and deplete nutrients and oxygen in the water. This can affect the growth of other species such as phytoplankton. For ocean alkalinity enhancement, ground alkaline minerals may contain trace amounts of toxic minerals that can harm marine organisms. Accessing this alkaline material can also require increasing mining and transport on land, which comes with its own social and environmental risks.

The magnitude and severity of these impacts on the environment and coastal communities depend on the scale, location and many other factors associated with a project. More research and testing are needed to better characterize them.

What Has the U.S. Government Done So Far to Support Ocean CDR?

U.S. government action related to ocean CDR is at an earlier stage than its support for land-based CDR approaches, where funding has increased significantly in the past five or so years. However, momentum is growing. There’s been meaningful progress on both strategy and policy support for ocean CDR recently.

In 2021, the National Academies of Science, Engineering, and Medicine released a landmark report on a federal research strategy for ocean carbon dioxide removal and sequestration. It laid out the state of knowledge across approaches, highlighted knowledge gaps and recommended more than $1 billion in federal funding to be invested over 10 years. This report helped raise the profile of ocean CDR and highlight its research funding needs. It was followed by a research strategy from the National Oceanographic and Atmospheric Administration (NOAA) outlining their motivation for working on ocean CDR, their capacities relevant to advancing it, and what they would need to help assess the efficacy and risks of different approaches.

2023 saw the release of a federal Ocean Climate Action Plan by the Ocean Policy Committee, which convenes leads from the White House Office of Science and Technology Policy and the Council on Environmental Quality. The plan put forth a whole-of-government approach to leverage the ocean for climate mitigation. It includes specific goals related to ocean CDR, including building a sufficient knowledge base around efficacy and tradeoffs and developing a robust regulatory framework. A Fast-Track Action Committee on Marine Carbon Dioxide Removal was also created to evaluate the tradeoffs of different types of marine CDR to help shape policy and research decisions.

Two fishermen in Oregon collect sea urchins from kelp beds.
Fishermen harvest sea urchins from kelp beds in Depoe Bay, Oregon. Kelp cultivation is one way the ocean can be leveraged to remove carbon dioxide from the atmosphere. Photo by gchapel/iStock

A few agencies have begun to fund ocean CDR research. The Department of Energy has $10 million in 2024 for research and development of biological ocean CDR, $250,000 for clarifying regulatory processes and $20 million to continue a CDR purchase pilot prize. This pilot prize is the first government initiative to directly purchase CDR credits, and ocean CDR is eligible. In 2023, the National Oceanic Partnership Program provided $24 million for 17 project teams working on CDR research. DOE has also funded work on macroalgal cultivation since 2017 (though with a focus on utilization rather than removal).

Finally, Congress has introduced, but not yet passed, several bills to support the scale-up of carbon dioxide removal approaches, including ocean CDR. The Carbon Dioxide Removal Research and Development Act of 2023 lays out a comprehensive, 10-year research and development agenda for CDR, including more than $1 billion over 10 years for ocean CDR. The CREST Act of 2023 and the Federal Carbon Dioxide Removal Leadership Act of 2024 both aim to increase government procurement of CDR from various approaches. And the CREATE Act would set up inter-agency working groups to support CDR research and development across agencies.

This early funding and policy support is an important first step. But much more is needed to address scientific and governance uncertainties and move forward in an informed manner.

Is Anyone in the U.S. Already Working on Ocean CDR?

Some U.S.-based companies are already attracting investment for development, at-sea testing and ultimately deployment of their ocean CDR approaches and technologies. These early movers can help address research gaps if their data and learnings are shared. But they do not have the capacity to build a comprehensive knowledge base on their own. This growing private sector momentum underscores the need for greater public funding to build a strong foundation of knowledge around ocean CDR efficacy and impacts.

U.S. companies working on ocean CDR include, for example, Running Tide, which combines biomass sinking and ocean alkalinity enhancement. Others, like Captura, Ebb Carbon and Equatic, use electricity to strip CO2 out of the water directly or to create alkalinity, which is then added to seawater to indirectly remove carbon. Vesta applies alkaline material to coastlines. Several of these companies spun out of universities and continue to collaborate with academic researchers. Many are beginning at-sea testing and/or project deployment both inside and outside of the U.S.

In addition, companies like Shopify and Microsoft are purchasing tons of ocean carbon removal to support the industry and help meet their climate commitments. So are advance market commitments like Frontier, a group of companies, including Shopify and others, that has committed to purchasing $1 billion of durable carbon removal by 2030. Frontier is already purchasing from several ocean CDR companies.

Nonprofit initiatives have also sprung up to address knowledge and research gaps associated with ocean CDR. These include the Carbon to Sea Initiative, which is focused on evaluating ocean alkalinity enhancement; Ocean Visions, which has compiled a database of known at-sea trials for ocean CDR among other resources; and [C]Worthy, which is developing modeling and data resources to support ocean CDR. Research initiatives are ongoing at universities and within national science institutions like the National Academy of Sciences, Engineering, and Medicine.

How is Ocean Carbon Removal Regulated in the U.S.?

Despite growing private sector activity, ocean-based carbon removal is not clearly or comprehensively regulated either within U.S. national waters or in the high seas.

In the U.S., at-sea research and deployment for ocean CDR projects are subject to existing safety and permitting regulations for activities at sea. U.S. regulations apply to projects located within 200 nautical miles of a coastline that fall under national jurisdiction. (This is the country’s exclusive economic zone, or EEZ). Projects located within three miles of the U.S. coast (or 9 miles for Florida, Texas and Puerto Rico) fall within that state’s laws and regulations.

Illustration of the United States' maritime jurisdiction boundaries.

Current permitting regimes for ocean CDR are based on existing regulations for activities like marine dumping or wastewater discharge. In other words, ocean CDR activities are being slotted into regulatory frameworks that were not designed for them. This means that ocean CDR might be subject to overlapping or unnecessary regulations, which can stifle at-sea research, while at the same time not being comprehensively regulated.

In early 2024, the EPA clarified how existing regulation — either under the Clean Water Act or the Marine Protection Research and Sanctuaries Act — is to be applied to ocean CDR approaches. This provides clarity on how to navigate current regulation, but it does not address the need for proactive and comprehensive governance that is focused on ocean CDR.

While it is not a replacement for more robust and fit-for-purpose regulation, non-governmental groups, such as the Aspen Institute and American Geophysical Union, have published proposed codes of conduct for ocean CDR research. These “soft law” guidelines can help ensure research projects are done responsibly. They include guidance on following relevant laws and regulations as well as on managing environmental impacts, transparency, community engagement and more. Columbia University’s Sabin Center for Climate Change Law also proposed a model law for ocean CDR research permitting in the United States. It includes ocean CDR research zones with expedited permitting processes and safeguards to ensure research minimizes environmental and societal risks. These resources could be built upon or integrated into a national policy and regulatory framework specific to ocean CDR.

What Are the Next Steps for Responsibly Developing Ocean CDR?

Growing interest and investment in ocean CDR, combined with uncertainties around the science and governance, underscore the need for greater government support. Developing and deploying ocean CDR responsibly will require increased funding for research and testing, a more comprehensive governance framework that ensures stringent environmental protections, careful evaluation of potential tradeoffs and engagement with coastal communities, among other things.

Public funding will be critical to resolving scientific uncertainties in this space and helping determine which approaches are suitable for scaling and under what conditions. Just as federal funding for CDR approaches on land went from almost nothing five years ago to billions today, a similar increase for ocean CDR approaches can help ensure there is a solid foundation of scientific understanding from which to operate.