As the world grapples with the accelerating impacts of climate change, the oceans emerge as a crucial arena for climate intervention strategies aimed at curbing carbon dioxide concentrations in the atmosphere. Marine carbon dioxide removal (mCDR) technologies, which leverage the ocean’s natural capacity to sequester carbon, have garnered increasing attention for their potential to supplement emission reduction efforts. However, as an expert report released by the European Marine Board underscores, the present state of readiness to upscale such interventions remains preliminary and fraught with scientific and governance uncertainties that must be addressed to ensure efficacy and avoid unintended ecological harms.
The ocean acts as one of the planet’s largest carbon sinks, absorbing approximately a quarter of anthropogenic CO2 emissions annually. Building on this natural process, marine carbon removal techniques explore diverse approaches, ranging from biological amplification—such as stimulating phytoplankton blooms or cultivating seaweed farms—to more engineered solutions involving chemical absorption and physical extraction of dissolved CO2. These captured carbons can then be sequestered either in ocean depths or geological formations, theoretically isolating them from atmospheric exchange for extended periods.
Yet despite promising theoretical frameworks, the empirical assessment of these strategies remains in nascent stages. During field studies such as those conducted by GEOMAR on the North Sea’s plankton communities, researchers utilize mesocosms—large enclosed water columns capable of simulating natural ocean conditions—to monitor the ecological and biogeochemical responses to carbonate manipulation. These studies are vital for understanding the fate of carbon post-removal and the resilience of associated marine ecosystems, which remain poorly characterized at present.
Critically, according to Dr. Helene Muri of the Norwegian Institute for Air Research (NILU) and NTNU, embedding robust monitoring, reporting, and verification (MRV) frameworks is paramount. It is insufficient merely to demonstrate carbon removal; stakeholders must scientifically quantify how much carbon has been taken up, the duration it remains sequestered, and verify that this process does not induce adverse ecological feedbacks. This challenge is compounded when sequestration occurs within dynamic ocean systems, where currents and mixing complicate traceability and permanence.
Carbon removal innovation must also contend with the overarching imperative to prioritize emission reductions. The climate science community, including the Intergovernmental Panel on Climate Change (IPCC), emphasizes that imminent and ambitious cuts to greenhouse gas emissions remain the foundational pillar to avoid catastrophic warming. Marine CDR technologies, as reflected in the European Marine Board’s recent report issued alongside COP30, should be viewed as complementary tools to address residual emissions—those unavoidable carbon outputs from sectors such as aviation and shipping that currently defy clean alternatives.
Achieving global net zero by mid-century necessitates balancing emissions with equivalent removals. Yet to stabilize global temperature rise near 1.5°C, net negative emissions—actively removing more carbon than is being emitted—will be essential. Projections estimate that by century’s end, atmospheric carbon extraction on the order of 5 to 10 gigatons annually will be required, a monumental scale that currently no marine technology can deliver independently. Land-based solutions such as afforestation and direct air capture are advancing, but marine approaches may offer symbiotic or supplemental pathways if matured responsibly.
Technologies involving nutrient fertilization, for instance, inject iron or other trace elements to stimulate phytoplankton productivity, thereby enhancing the biological pump that transports carbon from surface waters to the deep ocean. However, the ecological consequence of large-scale bloom induction remains a concern, including potential hypoxia, altered food webs, and biogeochemical imbalances. Without credible MRV mechanisms, verifying the long-term sequestration efficacy and environmental safety of such interventions remains impossible.
The governance landscape for marine carbon sequestration is likewise unsettled. Numerous international treaties and ocean governance bodies exist, but none currently provide a comprehensive framework for licensing, monitoring, and enforcing regulations surrounding mCDR deployment. The ocean’s fluidity complicates territorial jurisdiction and the tracking of carbon flows; thus, developing transparent protocols that mandate independent validation of outcomes is a critical next step.
In addition to quantifying carbon removal efficacy, the issue of ‘crediting’ those activities poses significant challenges. Carbon credits—tradable certificates representing quantified carbon storage—must be grounded in verifiable data and rigorous accounting standards to avoid greenwashing or unintentional enhancement of emissions elsewhere. The report cautions that premature market reliance on unproven marine CDR methods risks undermining climate integrity.
Environmental integrity further demands that potential side effects receive thorough assessment before technologies scale. For example, disrupting plankton dynamics may ripple through marine food webs, while altering alkalinity or pH balance can affect sensitive species. Reporting mechanisms must integrate comprehensive environmental impact assessments alongside carbon accounting to ensure balanced decision-making.
Despite the complexities, the consensus among climate experts is clear: the ocean’s role as a carbon sink is indispensable, and marine carbon dioxide removal, while not a panacea, represents a critical frontier for research and potential deployment. The field mandates careful, science-based progression, with robust international collaboration to establish standards and protocols that prioritize ecological stewardship and transparency.
As COP30 advances global climate negotiations, this new European Marine Board report serves as a timely call for measured, evidence-based development of marine carbon removal technologies. Avoiding premature deployment without standardized MRV frameworks is essential, as is aligning with the broader climate imperative of emissions reduction. The ocean, a shared global resource, must be safeguarded even as we innovate solutions to mitigate climate change’s immense challenges.
Ultimately, navigating the scientific, technical, and political complexities of marine carbon removal demands humility and rigorous inquiry. Current knowledge gaps necessitate sustained investment in multidisciplinary research, pilot projects, and governance mechanisms. Only through such deliberate efforts can marine carbon dioxide removal move from conceptual promise to a credible component of an integrated climate strategy, one capable of meaningfully contributing to humanity’s stewardship of a warming planet.
Subject of Research: Not applicable
Article Title: Monitoring, Reporting and Verification for Marine Carbon Dioxide Removal
News Publication Date: 17-Nov-2025
Web References:
- European Marine Board: https://www.marineboard.eu
- Climeworks direct air capture plants: https://climeworks.com/plant-mammoth
- CICERO – Center for International Climate Research: https://cicero.oslo.no/en/articles/global-fossil-co2-emissions-continue-a-persistent-rise
- UNFCCC COP30 address by António Guterres: https://unfccc.int/news/this-cop-must-ignite-a-decade-of-acceleration-and-delivery-un-secretary-general-address-to-belem
References:
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.
Image Credits: Photo: Michael Sswat, GEOMAR
Keywords: marine carbon dioxide removal, ocean alkalinity enhancement, carbon sequestration, climate mitigation, monitoring reporting verification, carbon removal technologies, marine ecosystems, COP30, net zero emissions, IPCC, climate change solutions
