Can we tap the ocean’s power to capture carbon?

(Press-News.org) The oceans have to play a role in helping humanity remove carbon dioxide from the atmosphere to curb dangerous climate warming. But are we ready to scale up the technologies that will do the job?

The answer, according to an expert group reporting to the European Union, is no.

At least, not yet – not until there are measures in place to ensure these technologies, called marine carbon dioxide removal technologies, are doing what they are supposed to do and won’t do more harm than good.

Marine carbon dioxide removal technologies build on the ocean’s ability to absorb carbon. They can be biological, like encouraging the growth of plankton or seaweed that take up carbon dioxide as they grow, or they can be chemical or physical, such as directly removing carbon dioxide from the ocean.

After these technologies remove the carbon from the upper parts of the ocean, it can be stored at the ocean floor and sediments, or the deep ocean, or in geological reservoirs or long-lived products.

“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 was chair of an expert group commissioned by the European Marine Board to study the issue.

Their new report, “Monitoring, Reporting and Verification for Marine Carbon Dioxide Removal,” is released in conjunction with the UN’s climate change meeting, COP30, currently being held in Brazil.

Emissions cuts first priority The Earth is getting warmer, and much faster than the nations of the world had hoped a decade ago when they pledged in Paris to limit global temperature increases to 1.5°C above “pre-industrial levels”.

In his opening remarks to the COP30 Leaders’ Summit on November 6, UN General Secretary António Guterres confronted his audience with the urgency of the situation.

“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 underscores the need to act now with tools that are 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.”

Net zero and residual carbon So why talk about removing carbon dioxide from the ocean at all, if the goal is to cut carbon dioxide emissions to zero?

Here’s where reality comes in. Cutting emissions from burning fossil fuels for energy, while difficult, is doable because we have alternative energy sources, such as solar and wind energy, that can do the job.

However, some products and technologies we rely on are difficult to make carbon free. There’s plenty of research being done to reduce carbon emissions from air travel, for example, but carbon-free flight has proved elusive. And even as people are encouraged to fly less, there are still times when air travel is the only option.

Societies across the globe need to achieve something called net zero by 2050. That’s when all the CO2 emissions are zeroed out by removing the exact same amount of emissions.

Reaching the 1.5°C level requires reaching net negative emissions. That’s where societies cut all emissions that are possible to cut but then find ways to compensate for “residual” emissions, those that simply can’t be eliminated.

“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.”

To put those numbers into context: Total global CO2 emissions were 42.4 gigatons of CO2 in 2024, according to CICERO, the Oslo-based Center for International Climate Research.

Land-based technologies to remove this “residual” carbon are already underway – the main method is through afforestation. Another example are the Climeworks direct air capture plants in Iceland, where giant fans suck air through a filter that removes the CO2, which is then mixed with water and injected into bedrock, where it turns to stone.

There have been quite a few field tests of different kinds of marine carbon dioxide removal, but many of the technologies remain in their infancy. Others are gaining more traction. Here is why setting standards now, for monitoring, reporting and verifying what is being done, is important.

The challenge Some marine based approaches to removing carbon dioxide from the ocean are similar to land-based mitigation options. Planting lots of trees or protecting rainforests because they soak up carbon are two examples of land-based mitigation. In the same way, some marine carbon dioxide removal technologies involve protecting and enhancing coastal areas, such as mangrove swamps.

Other approaches are more interventionist, such as fertilizing the ocean with iron or other nutrients to fuel plankton growth. These huge plankton blooms absorb carbon dioxide. When they die, they carry the carbon into the deep ocean, far from the atmosphere.That’s the theory, at least. 

The problem, Muri says, is knowing how well these different technologies actually work.

For example, how does a company actually prove how much excess carbon dioxide is being removed by the technology in question?

If we send carbon to the deep ocean, do we know how long it will stay there?

And while there are a number of different government and international agencies, along with international treaties and protocols, which ones should take the lead role? And how do they verify what is actually being done?

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 twist?

“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.

Credits and environmental impacts Addressing these issues will be critical as technologies mature to the point where they are used by governments or companies to claim credit for removing carbon dioxide.

Some companies have already begun to do so, 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.”

Reporting will also have to include any environmental impacts, Muri said.

The way forward In spite of the many uncertainties surrounding marine carbon dioxide 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.That’s the conclusion of the IPCC from any number of the organization’s reports, but particularly in a special report from 2018 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.

Nevertheless, marine carbon dioxide removal will not be a “miracle ocean fix to climate change,” she said.  “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.

Reference: Muri, H., Sulpis, O., Argüello, G., Baker, C. A., Böettcher, M., García-Ibáñez, M. I., Kuliński, K., Landolfi, A., Landschützer, P., McGovern, E., Ninčević Gladan, Ž., Oschlies, A., Yfantis, E. A. (2025) Monitoring, Reporting and Verification for Marine Carbon Dioxide Removal. Muñiz Piniella, A., Rodríguez Perez, A., Kellett, P., Alexander, B., Bayo Ruiz, F., Heymans, J. J. [Eds.] Future Science Brief N°. 13 of the European Marine Board, Ostend, Belgium. ISSN: 2593-5232.ISBN: 9789464206388. DOI: https://doi.org/10.5281/zenodo.17435116

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