A new expert report warns that marine carbon dioxide removal technologies are not ready for large-scale use without robust safeguards. Released during COP30 in Brazil, the findings emphasize prioritizing emissions cuts over unproven ocean-based methods. Researchers stress the need for better monitoring to avoid environmental harm.
The European Marine Board's report, titled 'Monitoring, Reporting and Verification for Marine Carbon Dioxide Removal,' was released on November 17, 2025, during the UN climate conference COP30 in Brazil. Led by Helene Muri, a senior researcher at the Norwegian Institute for Air Research (NILU) and the Norwegian University of Science and Technology (NTNU), the panel evaluated ocean-based strategies to absorb carbon dioxide.
Oceans are expected to help draw CO2 from the atmosphere to limit warming, using biological methods like boosting plankton or seaweed growth, or chemical and physical techniques to remove CO2 from seawater. Extracted carbon could be stored in deep-sea sediments, the ocean floor, deep ocean waters, geological formations, or durable products.
However, the experts conclude these technologies are too uncertain for expansion without strong monitoring, reporting, and verification (MRV) systems. '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,' Muri said.
The report aligns with urgent climate warnings. At COP30's Leaders' Summit on November 6, UN Secretary-General António Guterres noted that a temporary overshoot of the 1.5°C limit is inevitable by the early 2030s, but still achievable with action. Global CO2 emissions reached 42.4 gigatons in 2024, per CICERO.
To meet 1.5°C goals, net negative emissions are needed, requiring 5 to 10 gigatons of CO2 removal annually by century's end, according to IPCC scenarios. Sectors like aviation and shipping will have residual emissions that ocean methods might offset, but Muri stressed: 'We know how to cut emissions, and we have lots of methods that work. That has to take top priority.'
Challenges include verifying carbon removal amounts, storage duration in the dynamic ocean, and environmental impacts. Many techniques, like nutrient addition for plankton blooms, remain in early trials. Without reliable MRV and crediting systems, scaling risks unintended harm. 'None of these methods are mature to use if you cannot verify impacts or where the carbon goes,' Muri added.
The report urges focusing on proven emissions reductions first, while developing ocean safeguards. As Muri put it, marine removal is not a 'miracle ocean fix' yet.