The ocean plays a key role in regulating our climate, absorbing 30% of carbon dioxide emissions and 90% of excess heat. With scientific consensus that carbon dioxide removal is needed to complement deeper emissions reductions, there’s growing interest in leveraging the ocean’s natural processes to pull more carbon dioxide out of the atmosphere.
This is possible through marine carbon dioxide removal (mCDR) approaches, such as seaweed cultivation, ocean alkalinity enhancement and nutrient fertilization. Estimates indicate that mCDR could remove billions of tons of carbon per year by midcentury. But this massive potential is paired with an equally large uncertainty about both the efficacy of proposed approaches and the possibility of ecological and social impacts.
Marine CDR approaches are in early stages of development today, with all tested close to countries’ coastlines in national waters and very few tested at sea. However, as interest in mCDR grows from countries and companies looking to meet net zero and other climate commitments, at-sea testing and deployment of approaches proven safe and effective will likely move into international waters. These waters, known as the high seas, make up around two-thirds of the world’s ocean.
For any marine carbon dioxide removal activity in the high seas, clear and comprehensive governance will be needed to ensure environmental safety, scientific integrity and compliance with international law. Today, mCDR is governed by the existing international treaties and agreements that protect the ocean and marine life. But because they generally were not written with marine CDR in mind, comprehensive and proactive regulation of marine carbon removal activities may require more specific governance frameworks.
The State of mCDR Development and At-Sea Testing
Interest and investment in marine carbon removal have been growing over the past few years both in the United States and other countries, like Germany, Iceland and Singapore.
In 2023, the U.S. published the Ocean Climate Action Plan, a government-wide roadmap to leverage the ocean for climate mitigation. And in late 2024, it released a national mCDR research strategy to address the objectives in the Ocean Climate Action Plan, including building a sufficient knowledge base about the efficacy and tradeoffs of different marine CDR approaches and developing a robust regulatory framework for their use. The federal government provided an initial $24 million for mCDR research projects in 2023; whether and how this work will continue under the Trump administration is uncertain.
In Germany, the CDRmare project, which runs through 2027, is working to assess if and how mCDR can play a role in removing CO2 from the atmosphere. In the EU, the SEAO2-CDR project, which also runs through 2027, is funded by the EU’s Horizon Europe, a research and innovation program, and includes interdisciplinary work to develop tools and guidelines to help ensure mCDR is developed responsibly and transparently.
Apart from national and supranational governments, interdisciplinary researchers have developed codes of conduct to ensure responsible research. Groups like Carbon to Sea Initiative and Ocean Visions are supporting mCDR research with funding and other resources.
Projects are also beginning to move out of the lab and into the marine environment for testing along national coastlines. One mCDR project led by Woods Hole Oceanographic Institute in Massachusetts is in the process of applying for EPA permits to do ocean alkalinity enhancement testing off the state’s coast. Another project received a permit from the Army Corps of Engineers to add carbon-removing alkaline sand offshore in North Carolina. In total, Ocean Visions identifies 45 research trials that are either in operation or concluded around the world, and six more than are approved to move forward.
As for projects in the high seas, a non-profit coalition of researchers has announced its intention to start research trials for ocean iron fertilization in international waters of the Pacific as early as 2026. The coalition plans to request approval from the U.S. Environmental Protection Agency, which administers the Marine Protection Research and Sanctuaries Act, the relevant domestic legal framework for this activity.
Parties to the London Convention and Protocol — two international legal frameworks that govern activity on the high seas — have been meeting to discuss governance of mCDR activity. In 2023, parties released a non-binding statement recommending that OAE and biomass sinking be treated similarly to ocean iron fertilization – namely that activity outside of legitimate scientific research be deferred. A November 2024 meeting presented various ways to make this statement stronger, but none moved forward due to parties’ disagreement over the role of commercial interests in mCDR development.
How the High Seas Are Currently Governed
The location of mCDR activity will determine how it is governed. In the vast majority of cases, mCDR activities conducted within 200 nautical miles from the shore are within a country’s exclusive economic zone (EEZ) and are governed by that country’s domestic laws and regulations. Beyond a country’s EEZ is the high seas, which is open access to all countries and is governed by international legal frameworks.
Several international legal frameworks govern activity in the high seas but do not explicitly regulate mCDR, as they were written before mCDR activities existed or had been proposed. As a result, they are now being interpreted and applied with varying levels of clarity.
Major international legal frameworks governing activity in the high seas
| Agreement | Year adopted; year entered into force | Number of parties | General intent of agreement |
|---|---|---|---|
| United Nations Convention on the Law of the Sea (UNCLOS) | 1982; 1994 | 169 countries and the EU | Establishes a legal framework for all use and management activities in the ocean, including defining maritime boundaries, cooperating in transboundary waters, managing mineral exploitation and protecting freedom of scientific research. |
| Convention on Biological Diversity (CBD) | 1992; 1993 | 195 countries and the EU | Focuses on the conservation of biological diversity, the sustainable use of its components and the fair and equitable sharing of genetic resources. |
| London Convention (LC) | 1972; 1975 | 87 countries | Promotes the effective control of the deliberate disposal, or dumping, of wastes and other matter at sea. Parties must regulate dumping and prohibit dumping of certain substances |
| London Protocol (LP) | 1996; 2006 | 55 countries | Protects and preserves the marine environment from all sources of pollution more comprehensively than the LC (which it is intended to modernize and eventually replace) Parties must prohibit dumping of all substances except those listed. Member states can be Contracting Parties to the LC, the LC/LP or neither the LC/LP. |
| Biodiversity Beyond National Jurisdiction (BBNJ; also known as High Seas Treaty; Global Ocean Treaty) | 2023; not yet in force | 15 (60 needed to enter into force) | Provides the legal framework and process under UNCLOS to protect marine life and biodiversity in the high seas. Allows for creation of marine protected areas in international waters and requires environmental impact assessments for certain activities. |
Sources: UN Law of the Sea; Convention on Biological Diversity; London Convention; London Protocol; LC/LP Status, BBNJ
Each framework addresses different, but related, aspects of ocean governance, and coordinating across multiple agreements helps address shared goals for protecting biodiversity, reducing pollution and responding to climate impacts. For example, the Convention on Biological Diversity’s (CBD) intergovernmental scientific advisory body provides guidance on alignment with Biodiversity Beyond National Jurisdiction (BBNJ) for meeting biodiversity goals in areas beyond national jurisdiction. Countries rely on global organizations like the International Maritime Organization (IMO), a specialized UN agency, and the CBD Secretariat for support coordinating policy alignment and enforcement measures.
How Does mCDR Fit into These Legal Frameworks?
Under the United Nations Convention on the Law of the Sea, all parties are free to conduct marine scientific research in the high seas, if it is done peacefully and following “appropriate scientific methods.” However, UNCLOS does not define what constitutes marine scientific research and fails to differentiate research conducted to expand knowledge from research that enables future commercial activity. (This is the case for other international law, too.) UNCLOS also includes general obligations for all parties to protect and preserve the marine environment — for example, by, for example, limiting marine pollution and avoiding the introduction of invasive species.
General provisions of the Convention on Biological Diversity relevant to mCDR include identification and monitoring for activities likely to have a significant adverse effect on the conservation and sustainable use of biodiversity and a requirement for environmental impact assessments for certain activities. The CBD initially adopted a resolution to ban commercial application of iron fertilization in 2008, and then expanded that in 2010 to ban all climate-related geoengineering activities except for small-scale scientific research studies in a controlled setting. While the resolution is nonbinding, it’s supported by 196 countries and was reaffirmed at the UN Biodiversity Summit (COP16), an indication of the strong lack of support for projects that are not “small scale” or “in a controlled setting.”
The London Convention and the London Protocol focus on limiting dumping or disposal of material into marine waters. Whether mCDR approaches that add material to the ocean for carbon removal are considered dumping is a topic of continued debate. The Convention includes a list of materials that cannot be dumped. The Protocol is stricter and includes a list of material that can be dumped (with a permit) and prohibits dumping everything else, with limited carve-outs.
Following the 2008 CBD resolution, the parties to both the London Convention and the London Protocol passed a resolution agreeing that iron fertilization is within scope for both agreements, but that only legitimate scientific research is allowed. In 2010 the parties adopted a tool to determine if an activity constitutes legitimate scientific research. And in 2013, an amendment to the Protocol officially banned iron fertilization except for legitimate scientific research, and an annex to that amendment determined that additional marine geoengineering techniques could fall under the scope of the amendment in the future. Only six of the LP’s 55 parties have ratified the amendment so far — fewer than the two-thirds needed to enforce it. This amendment is one of few examples of governance specific to certain mCDR techniques, but the Protocol’s ability to more comprehensively govern mCDR is limited by its overall aim of limiting ocean dumping.
Biodiversity Beyond National Jurisdiction is an agreement ratified under UNCLOS that opened for signature in 2023 and has not yet entered into force. Its objective is to create a comprehensive framework under UNCLOS to address sustainable use of biodiversity and conservation in areas beyond national jurisdiction. It does this through two mechanisms: environmental impact assessment and area-based management tools, such as marine protected areas that could be used to preclude mCDR testing in areas where no other existing international body has competency.
For environmental impact assessments, BBNJ includes more specific requirements than UNCLOS, such as assessing whether the planned activity will have “more than a minor…effect” on the marine environment and determining if the effects are not well understood. If either criterion is met, a screening process would determine whether an environmental impact assessment is needed. Since most mCDR methods have not been well studied, they would likely trigger this screening. Under BBNJ, a full environmental impact assessment would include the monitoring and reporting of economic, social, cultural and human health impacts. Following public comment of potentially affected parties, it would then up to the state party with jurisdiction over the project to decide if it could go forward.
Aside from these legal frameworks, customary international law arises from established international practices and is generally binding on all states (unlike earlier frameworks which just apply to countries that are party to each agreement). Some aspects of customary international law are also enshrined in legal frameworks. For example, the “no harm rule” is included in the CBD, so parties to that agreement must adopt measures to enact these treaties domestically. The “no harm rule” means that all countries are obligated to prevent activities under their jurisdiction from causing significant harm to the territory of other countries and areas beyond the individual jurisdiction and control of countries, such as the high seas.
These legal frameworks are primarily designed to minimize harm, and mCDR approaches are intended to provide a net benefit to the climate while minimizing local harms. However, current legal frameworks are not designed to weigh that benefit against any harms introduced by the mCDR activity. In this way, current legal frameworks are not well suited to governing mCDR activities.
Applying International Legal Frameworks to mCDR in the High Seas
Marine CDR activities in the high seas will be governed by the country that registered the vessel performing those activities or the country where it is loaded with material for the activities. Countries that are parties to international legal frameworks are obligated to create mechanisms to enforce them domestically. And in some cases, countries that are not parties also have domestic laws implementing these frameworks. For example, the United States is not a party to the London Protocol, but the U.S. EPA’s Marine Protection, Research and Sanctuaries Act is a domestic application of the London Protocol’s anti-dumping aims. While the regulation of activities in the high seas would fall under relevant national laws, how the regulation is approached would likely be influenced by ongoing discussions among parties to each legal framework.
International framework governance of selected mCDR approaches
| Approach | UNCLOS | LC/LP | CBD | BBNJ |
|---|---|---|---|---|
| All approaches | General provisions around protection of the marine environment and marine scientific research. | General obligation of employing a precautionary approach. mCDR activities could be permissible if deemed to be for purposes other than mere disposal, to not run contrary to the aims of the LC/LP and to constitute “legitimate scientific research.” | General provisions on identification and monitoring, and environmental impact assessments. |
If passed, all approaches will be subject to spatial regulations established through area-based management tools and could be evaluated through environmental impact assessments. |
| Seaweed cultivation | Regulates the introduction of new or alien species. Relevant if using non-native species. | Likely permissible, provided sinking of seaweed or any added nutrients to grow seaweed are not considered dumping. | Could be considered “climate geoengineering,” but ban is non-binding and excludes small-scale scientific research. | |
| Nutrient fertilization | Field tests for research could be permissible, but potential downstream impacts may violate “no-harm” principle under customary international law. | Small-scale research could be permitted under the LC/LP if it doesn’t risk harming the marine environment. Large-scale application would likely be prohibited under the LP. | Could be considered “climate geoengineering” but the ban is non-binding and excludes small-scale scientific research; requires case-by-case assessment. | |
| Ocean alkalinity enhancement | Field tests would be permissible if general obligations are met. | Research projects could be permitted if they don’t risk harming the marine environment. Large-scale application would likely be prohibited under the LP. | Activities would be permissible if general obligations of the CBD are met. |
What’s Next for International Governance of Marine CDR
Marine CDR has the potential to provide large-scale carbon removal if, along with increased funding to address scientific knowledge gaps, governance frameworks can comprehensively regulate the new sector. This potential coincides with growing demand for legal clarity on country obligations to address climate change under international law. The International Tribunal for the Law of the Sea released an advisory opinion in May 2024 emphasizing the responsibility of countries under UNCLOS to prevent, reduce and control greenhouse gas emissions to protect the marine environment, and the International Court of Justice is likely to clarify similar obligations under broader treaties sometime this year. These opinions will dually guide countries’ responsibility to climate action and appropriate caution in mCDR implementation.
In 2025, discussions about these issues will continue under the London Protocol and the London Convention, scientific experts under the United Nations will propose a new framework to assess projects, and global forums like the UN Ocean Conference and Our Ocean Conference will convene ocean experts on topics including mCDR. The coming years will see countries advancing interdisciplinary research, including on the evaluation of social and environmental impacts, informed by emerging data-sharing and management guidelines. And, as individual projects move forward, transparent communication within and among countries on the impacts and benefits will provide a greater shared understanding for updating the relevant international governance frameworks to consider this potential climate solution.