Wondering whether the ocean could help pull carbon from the air? Ocean alkalinity enhancement chemically raises seawater alkalinity so it takes up more CO2. A 2021 National Academies report had high confidence in its efficacy, but real-world questions remain.
This page sits within the wider topic of ocean climate solutions, which compares the ways the sea might help with the climate problem.
| Item | Value |
|---|---|
| Confidence in efficacy (National Academies, 2021) | High confidence |
| Environmental risk | Medium |
| Scale-up cost | Medium to high |
| Estimated cost of priority research | $125 million to $200 million |
| CO2 removal needed from all methods by 2050 (2019 report) | Roughly 10 gigatons of CO2 per year |
The figures come from the National Academies news release of December 8, 2021. These values reflect that release’s date, so check the source for newer assessments before you rely on them.
How does ocean alkalinity enhancement work?
The National Academies describe the approach as one that chemically alters ocean water to increase its alkalinity. The goal is to enhance the reactions that take up atmospheric CO2, so the sea absorbs more carbon dioxide from the air.
A related route uses electricity. According to the same release, passing an electric current through water can either increase the acidity of seawater to release CO2, or increase its alkalinity to enhance its ability to retain CO2. The report assessed these electrochemical processes as a separate approach.
Why are scientists looking at it at all?
The 2021 report said current levels of CO2 emissions greatly exceed the ability of nature to remove it, and that reducing emissions alone may not be enough to stabilize the climate. You can read that framing in the National Academies release.
The same release cites a 2019 National Academies report. It found that carbon dioxide removal technologies and strategies will need to remove roughly 10 gigatons of CO2 every year by 2050 to meet climate goals.
Several land-based strategies, such as storing carbon in agricultural soil or changing forest management, may be ready for deployment. Less is known about the risks, benefits and trade-offs of ocean-based strategies, which is why the ocean options are framed as a research question first.
How did it compare with other ocean approaches in 2021?
The committee behind the report assessed six approaches. It looked at efficacy, durability, scalability, potential environmental risks, social considerations, and how much is known about each so far, as described in the National Academies release.
| Approach | Confidence or efficacy finding | Estimated research cost |
|---|---|---|
| Ocean alkalinity enhancement | High confidence in efficacy | $125 million to $200 million |
| Electrochemical processes | High confidence in efficacy | $350 million |
| Nutrient fertilization | Medium to high confidence it is effective and scalable | $290 million |
| Seaweed cultivation | Medium efficacy | $130 million |
| Ecosystem recovery | Low to medium efficacy | $220 million |
| Artificial upwelling and downwelling | Low confidence in efficacy and scalability | $25 million |
The confidence ratings and research cost estimates in this table come from the National Academies news release of December 8, 2021. Later National Academies work may have updated these ratings, so check the source before you rely on them.
Read the table as a list of research priorities, not a ranking of what to build. The research was meant to give the public, stakeholders and policymakers an unbiased base of knowledge, not to advocate for or lock in deployment of any specific approach.
What risks and costs come with it?
For this method, the 2021 report found medium environmental risks and medium to high scale-up costs. These are the main points from the release:
- Efficacy: high confidence.
- Environmental risk: medium.
- Scale-up cost: medium to high.
- Research priorities: field and laboratory experiments to explore the impact on marine organisms, estimated at $125 million to $200 million.
The electrochemical route was rated differently on cost. The report said it carries the highest scale-up cost of any approach assessed, with medium to high environmental risks.
Scott Doney, chair of the committee, put the gap plainly in 2021: society and policymakers did not have the information they needed to evaluate the impacts and trade-offs of these climate responses. That is why the report pushes research before deployment.
What changed in the 2026 National Academies update?
A Woods Hole Oceanographic Institution press release dated September 17, 2026 describes a new digital report from the National Academies. It includes updated and expanded modules on governance and social dimensions and on ocean alkalinity enhancement.
The release says marine carbon dioxide removal has advanced, with growing research activity and movement toward field testing. Major questions remain, though:
- Whether these approaches can remove carbon dioxide at meaningful scales.
- How that removal can be reliably measured and verified.
- What the potential environmental effects are.
- How marine carbon dioxide removal should be governed.
The report also says viability cannot be settled by technological performance alone. It will depend on public acceptance, political and regulatory decisions, community considerations, and the character of the places where research or deployment occurs, per the same release.
A field example: LOC-NESS
The same release names the Locking Ocean Carbon in the Northeast Shelf and Slope (LOC-NESS) project as one effort studying this method. It examines effectiveness and environmental impacts through field experiments, ocean modeling, laboratory studies and monitoring.
According to the release, the team completed a field trial in the Gulf of Maine in August 2025 and reported preliminary findings at the Ocean Sciences Meeting. The release gives no final results, so treat the outcome as still open.
Where does it fit among ocean-based options?
You can place this method in context in the guide to marine carbon dioxide removal, which covers the wider family of approaches. The 2026 report says such approaches, if demonstrated to be feasible and responsible, could supplement reductions in greenhouse gas emissions, according to the WHOI release.
A very different option is covered in the guide to artificial upwelling. The 2021 report gave that approach low confidence in efficacy and scalability, as the National Academies release explains.
The 2026 report also notes that significant scale-up would be needed for marine carbon dioxide removal to contribute meaningfully to climate targets. Uncertainties remain about monitoring and measuring net carbon removal.
Frequently asked questions
What is ocean alkalinity enhancement?
Show answer
It is an approach that chemically alters ocean water to increase its alkalinity, in order to enhance reactions that take up atmospheric CO2, as described in the National Academies release of December 8, 2021.
How confident were experts that it works?
Show answer
The 2021 National Academies report expressed high confidence in its efficacy. It also found medium environmental risks and medium to high scale-up costs, per the release.
Has it been tested in the ocean?
Show answer
The LOC-NESS team completed a field trial in the Gulf of Maine in August 2025 and reported preliminary findings, according to a September 17, 2026 WHOI release. That release also says major questions remain about scale, measurement, environmental effects and governance.
Could it replace cutting emissions?
Show answer
The National Academies’ 2026 report frames it as an addition, not a substitute. It says marine carbon dioxide removal, if demonstrated to be feasible and responsible, could supplement reductions in greenhouse gas emissions, according to the WHOI release of September 17, 2026.
