Advancing Monitoring Reporting and Verification for marine Carbon Dioxide Removal

Carbon dioxide removal (CDR) is becoming increasingly relevant as a complement to rapid and sustained greenhouse gas emission reductions in overshoot pathways and pathways that limit warming to 1.5–2°C. Marine CDR (mCDR) could contribute by enhancing ocean uptake and storage of carbon, but only if Monitoring, Reporting, and Verification (MRV) can robustly quantify net removals and detect impacts. Ensuring that such interventions are effective, verifiable, and environmentally sustainable requires robust MRV systems that enable transparent carbon accounting and early detection of impacts. Yet MRV for mCDR faces a fundamental challenge because the ocean is highly variable and strongly advective, and carbon and tracers can be rapidly redistributed across space, depth, and jurisdictional boundaries.Building on the European Marine Board Future Science Brief on MRV for mCDR, which synthesises the state-of-the-art in MRV for mCDR and provides actionable recommendations for policymakers, practitioners, and research funders, this presentation highlights key scientific and operational priorities. We present a practical six-pillar MRV framework centred on baselines, additionality, detection and attribution, durability, non-CO2 greenhouse gases, and environmental and biodiversity indicators. The framework is designed to demonstrate that observed changes exceed natural variability and can be translated into net atmospheric CO2 removal with decision-relevant uncertainty.We argue that fit-for-purpose MRV must integrate targeted in situ observations and autonomous platforms with mechanistic, regional, and Earth system modelling, supported by model–data fusion and machine learning where direct high-frequency or long-term measurements are not feasible. MRV should expand beyond net CO2 uptake to include indicators of impacts and side effects such as carbonate chemistry, oxygen, nutrients, and ecosystem responses, with monitoring intensity scaled to project ambition and risk and linked to adaptive management levers. We conclude with recommendations on standardised MRV requirements, sustained carbonate-system observing, stronger model validation against observations, and clear limits on scaling or co-deployment until MRV protocols are demonstrated, while rapid reductions in CO2 emissions remain the top priority.