New report reveals major risks in turning oceans into carbon sinks

According to an expert panel reporting to the European Union, the answer is no.

At least, not yet — not until there are strong safeguards proving that these methods, known as marine carbon dioxide removal technologies, function as intended and do not create new environmental problems.

Marine carbon dioxide removal approaches rely on the ocean’s natural capacity to absorb carbon. Some strategies use biological processes, such as increasing plankton or seaweed growth so they can take up carbon dioxide as they develop. Others rely on chemical or physical techniques, including systems that directly remove carbon dioxide from seawater.

Once carbon is extracted from the upper layers of the ocean, it can be stored in deep-sea sediments, on the ocean floor, in the deep ocean, in geological formations, or in products designed to last for long periods.

Protecting the Ocean While Exploring New Climate Tools

“This is about safeguarding the oceans for a common good. The oceans can be part of the climate solution, but we need to strengthen the way we safeguard them before we scale things up,” said Helene Muri, a senior researcher at NILU, the Norwegian Institute for Air Research and the Norwegian University of Science and Technology (NTNU).

Muri led an expert group formed by the European Marine Board to evaluate the issue.

The group’s findings appear in a new report, “Monitoring, Reporting and Verification for Marine Carbon Dioxide Removal,” released during COP30, the UN climate conference now taking place in Brazil.

Rising Temperatures and the 1.5°C Threshold

Earth’s temperature is rising more quickly than countries expected when they agreed in Paris to keep global warming within 1.5°C above “pre-industrial levels.”

During his opening remarks at the COP30 Leaders’ Summit on November 6, UN General Secretary António Guterres called attention to the seriousness of the climate outlook.

“Science now tells us that a temporary overshoot beyond the 1.5°C limit — starting at the latest in the early 2030s — is inevitable,” he said. “Let us be clear: the 1.5°C limit is a red line for humanity. It must be kept within reach. And scientists also tell us that this is still possible.”

The European Marine Board report stresses that immediate action must focus on approaches already known to work — namely cutting emissions. “We know how to cut emissions, and we have lots of methods that work,” Muri said. “That has to take top priority.”

Why Carbon Removal Is Still Needed

If the main goal is to reduce emissions to zero, why consider removing carbon dioxide from the ocean at all?

The answer lies in the reality that some sectors are far harder to make carbon free. Although shifting away from fossil fuels toward solar and wind power is achievable, certain technologies and products remain difficult to decarbonize. Air travel is one example. Despite extensive research, carbon-free flight is still out of reach, and some travel cannot be avoided.

To meet climate targets, countries aim to reach net zero by 2050. This means any remaining emissions must be balanced by removing an equivalent amount of carbon dioxide.

Reaching the 1.5°C target requires going further to achieve net negative emissions. Societies would need to eliminate all emissions they reasonably can, then counterbalance the “residual” emissions that cannot be removed.

“We must have a net removal of carbon dioxide from the atmosphere to get to 1.5°C and that means that you will likely have some residual emissions from some sectors, such as shipping and aviation, and some industries,” Muri said. “And then you will have relatively large scale removal of carbon dioxide from the atmosphere as well, so that the net is at about between 5 to 10 gigatons of CO2 removed per year towards the end of the century, according to scenarios by the IPCC.”

For context, global CO2 emissions were 42.4 gigatons in 2024, according to CICERO, the Oslo-based Center for International Climate Research.

Land-based approaches for handling this residual carbon already exist. The most established method is afforestation. Another example is the Climeworks direct air capture facility in Iceland, where air is drawn through filters that trap CO2. The captured CO2 is then mixed with water and injected into bedrock, where it turns into stone.

Marine Carbon Removal Is Still in Early Stages

A number of field trials have tested different marine carbon removal techniques, but many remain in the early development stage. Others are advancing more quickly. This is why establishing standards for monitoring, reporting, and verifying results is essential.

Technical and Scientific Challenges

Some ocean-based carbon removal methods resemble familiar land-based efforts. Planting trees or protecting forests to capture carbon has long been used on land. Similarly, certain marine strategies focus on restoring or protecting coastal ecosystems such as mangrove swamps.

Other approaches involve more direct intervention, such as adding iron or other nutrients to stimulate plankton growth. These large blooms absorb carbon dioxide, and when they sink, they carry carbon deep into the ocean. That is the expectation, at least.

The challenge, Muri says, is determining how well these methods actually perform.

How can a company prove how much extra carbon dioxide its technology removes?

If carbon is stored in the deep ocean, how long will it stay there?

And with many agencies, treaties, and protocols involved internationally, which organization should be responsible for oversight, and how should verification be handled?

Ideally, “you monitor what is the background state of carbon (in the ocean) and then you implement your project and make sure that you have removed carbon from the atmosphere. And you try to monitor how much carbon that you have removed and how long it is staying away from the atmosphere. And then you report that to some independent party and then it verifies that what you’re saying is correct,” Muri said.

The Ocean Is Constantly Changing

The complication, she says, is that storing carbon in the ocean itself makes tracking and management far more difficult.

“If you’re storing it in the ocean, in some form or another, not in a geological reservoir, it’s a lot harder to to govern it and also monitor it. The ocean doesn’t stay put,” she said.

Carbon Credits and Environmental Considerations

These challenges become even more important as technologies advance to the point where companies or governments may seek credit for removing carbon dioxide.

Some companies have already started moving in this direction, Muri says.

“None of these methods are mature to use if you cannot verify impacts or where the carbon goes, or how long it stays away from the atmosphere,” Muri said.

“If we want to be serious about figuring out if you can do marine carbon dioxide removal in responsible ways that can make meaningful contributions, then we have to get serious about the monitoring, reporting and verification aspects,” she added.

“The credit part of it also has to work right. You have to have reliable and transparent and scientifically defensible crediting systems.”

Environmental impacts must also be thoroughly reported, Muri said.

Looking Ahead

Despite the uncertainties surrounding marine carbon removal, “all future scenarios are showing us that we will need carbon dioxide removal in order to reach our most ambitious temperature goal,” Muri said. This conclusion appears repeatedly in IPCC assessments, particularly the 2018 special report on Global Warming of 1.5°C.

“We don’t know all the threats of these immature methods yet, but it’s a bit hard to just take them off the table because they’re uncomfortable to think about,” she said.

Even so, she stressed that marine carbon removal is not a “miracle ocean fix to climate change.” As she put it, “Some people are really hoping to find an answer in the ocean, but in our opinion, we’re not there yet.”

“And there’s a question of whether it can be a scientifically governed climate solution, and we don’t have the answer to that yet. But if we want to go in that direction, then we need to clear up all of these standards and establish these properly before we can scale things up,” she said.