Wondering whether marine carbon dioxide removal can really help with climate change? It could supplement emission cuts if proven feasible and responsible, but scale, measurement and environmental effects remain open questions.
This guide is part of the site’s wider coverage of ocean climate solutions.
| Item | Value |
|---|---|
| Approaches assessed in the December 2021 National Academies release | 6 approaches |
| Recommended U.S. research program | $125 million over 10 years |
| CO2 removal needed per year by 2050 (2019 report) | Roughly 10 gigatons |
| Priority research estimate, electrochemical processes | $350 million |
| Priority research estimate, artificial upwelling and downwelling | $25 million |
These figures come from the National Academies’ December 2021 news release. Estimates can change as research moves on, so check the source before you rely on them.
What marine carbon dioxide removal means
Marine CDR covers ocean-based methods that aim to pull carbon dioxide out of the atmosphere and keep it out. A National Academies report released in December 2021 said current CO2 emissions greatly exceed nature’s ability to remove it, and that reducing emissions alone may not be enough to stabilize the climate, according to the release.
The same release cites a 2019 National Academies finding that carbon dioxide removal would need to take out roughly 10 gigatons of CO2 every year by 2050 to meet climate goals. It adds that some land-based strategies may be ready for deployment, while less is known about the risks, benefits and trade-offs of ocean-based ones.
The ocean is the obvious place to look. A Woods Hole Oceanographic Institution feature from February 2022 describes it as a carbon reservoir more than 50 times bigger than the atmosphere, absorbing roughly one-third of the fossil fuel emissions humans produce each year.
The six approaches the National Academies assessed
The committee behind the 2021 report assessed six approaches, a set the National Academies’ digital report page says was identified by the study sponsor. The release describes them like this:
- Nutrient fertilization: adds nutrients such as phosphorus or nitrogen to the ocean surface to increase photosynthesis by phytoplankton.
- Artificial upwelling and downwelling: upwelling moves cooler, nutrient- and CO2-rich deep water to the surface, while downwelling moves surface water and carbon to the deep ocean.
- Seaweed cultivation: large-scale farming that transports carbon to the deep ocean or into sediments.
- Ecosystem recovery: protecting and restoring coastal ecosystems and helping fish, whales and other marine wildlife recover.
- Ocean alkalinity enhancement: chemically alters ocean water to increase its alkalinity and so enhance reactions that take up atmospheric CO2.
- Electrochemical processes: pass an electric current through water to change its acidity or alkalinity so that CO2 is released or retained.
A closer look at one coastal habitat is in the guide to mangrove carbon storage. The chemistry-based route is covered in the guide to ocean alkalinity enhancement.
How the approaches compare
The committee rated each approach on efficacy, durability, scalability, environmental risk and what is already known. The table below restates the 2021 ratings and research cost estimates as the release reports them.
| Approach | Reported assessment | Priority research estimate |
|---|---|---|
| Nutrient fertilization | Medium to high confidence it is effective and scalable; medium environmental risks | $290 million |
| Artificial upwelling and downwelling | Low confidence in efficacy and scalability; medium to high environmental risks | $25 million |
| Seaweed cultivation | Medium efficacy, medium to high durability; medium to high environmental risks | $130 million |
| Ecosystem recovery | Low to medium efficacy; lowest environmental risks of the six | $220 million |
| Ocean alkalinity enhancement | High confidence in efficacy; medium environmental risks | $125 million to $200 million |
| Electrochemical processes | High confidence in efficacy; highest scale-up cost of the six | $350 million |
The ratings and research estimates in this table come from the National Academies’ December 2021 news release, and they can change, so check the source before you rely on them.
Read the table as a snapshot, not a ranking. The release says the research should aim to build an unbiased knowledge base, not to advocate for or lock in deployment of any specific approach. The cost figures are for research priorities, not for running a project at scale, and they differ widely because the approaches are at very different stages of understanding.
Some of these ratings have aged. According to the National Academies Press report page, as of the 2026 update the modules on nutrient fertilization, seaweed cultivation, artificial upwelling and downwelling, ecosystem recovery and electrochemical approaches had not yet been updated and still reflect the 2022 report. The alkalinity module was updated, so check it for the newer view.
Open questions that remain
The National Academies’ news release dated September 16, 2026 says marine CDR has advanced, with growing research, technology development, private-sector involvement and movement toward field testing. It also says major questions remain. They fall into four groups:
- Scale: whether these approaches can remove carbon dioxide at meaningful scales, since significant scale-up would be needed to contribute to climate targets.
- Measurement: how net carbon removal can be reliably measured and verified.
- Environmental effects: especially long-term and ecosystem-scale effects.
- Governance: regulation will be needed at local, national and global levels and will have to evolve alongside the science.
The release adds that viability cannot be settled by technology alone. It will also depend on public acceptance, political and regulatory decisions, community considerations, and the environmental and social characteristics of the places where research or deployment occurs.
The National Academies’ December 2021 release made a similar point about process. It says the recommended research program should develop and adhere to a common code of conduct that emphasizes transparency and public engagement. The Woods Hole feature lists policy support, permitting for test sites and long-term monitoring among the most pervasive hurdles beyond funding, as noted in its February 2022 piece.
What the 2026 update changed
The report page explains that the National Academies established a standing committee in 2025 to keep the 2022 report current. The first update, released in 2026, changed four parts of the series:
- A new State of Marine CDR module covering recent advances, emerging trends and remaining knowledge gaps.
- An updated introduction and assessment framework.
- An updated and expanded module on governance and social considerations.
- An updated and expanded module on ocean alkalinity enhancement, which now also covers electrochemical processes that modify seawater alkalinity.
Sponsors are public record. The December 2021 release says the original study was sponsored by ClimateWorks Foundation. The September 2026 release says the update was sponsored by Carbon to Sea Initiative and the National Academy of Sciences’ George and Cynthia Mitchell Endowment for Sustainability Science Fund.
Frequently asked questions
Is marine carbon dioxide removal ready to be deployed?
Show answer
Not according to the National Academies’ September 2026 release, which says major questions remain about removal at meaningful scales, measurement, environmental effects and governance. It does note movement toward field testing.
Would it replace cutting emissions?
Show answer
The September 2026 release says marine CDR, if demonstrated to be feasible and responsible, could supplement reductions in greenhouse gas emissions. It does not describe it as a substitute for them.
Which approach had the lowest environmental risk in the 2021 assessment?
Show answer
Ecosystem recovery, which the December 2021 release says carries the lowest environmental risks of the six, with low to medium efficacy. Electrochemical processes carried the highest scale-up cost.
How much research did the National Academies recommend?
Show answer
The December 2021 release recommended a $125 million U.S. research program over the next 10 years, in addition to approach-specific research estimates ranging from $25 million to $350 million.
