Photo by Ekaterina Boltaga
A major new report from the Intergovernmental Oceanographic Commission (IOC) of UNESCO has identified critical gaps in scientific understanding of the ocean’s carbon cycle that could be significantly undermining global climate predictions and the policies built upon them.
The Integrated Ocean Carbon Research Report, prepared by 72 authors across 23 countries, reveals that current scientific models disagree by 10 to 20% globally, and by even greater margins in certain regions, on how much carbon the ocean absorbs. The ocean currently stores around 25% of all CO₂ emissions generated by human activity, making it by far the largest active carbon sink on the planet. Yet the report finds that the processes governing this uptake remain poorly understood, with limited long-term data and major unresolved questions about how the sink will respond to continued warming.
UNESCO Director-General Khaled El-Enany said: “The ocean is one of our strongest climate allies, absorbing a large share of the carbon we emit. Yet we still lack a full understanding of how this natural defence functions – or how long it can endure. Coordinated global monitoring of ocean carbon absorption is therefore essential and urgent.”
The discrepancies identified in the report stem from several interrelated problems: a shortage of sustained long-term datasets, insufficient understanding of how ocean warming and changing circulation patterns affect carbon uptake, and gaps in knowledge about how shifts in plankton communities and microbial life influence how long carbon is stored. Coastal and polar regions, which play a disproportionately important role in the global carbon exchange, are particularly under-observed.
The implications for climate planning are serious. If the ocean begins to absorb less carbon than current models assume, larger volumes of CO₂ will remain in the atmosphere, accelerating warming beyond projected levels. This would force revisions to national emissions targets and climate adaptation plans, and could alter assessments of the carbon budgets that underpin the Paris Agreement. The report also cautions that industrial activities and proposed ocean-based climate engineering interventions may further alter the ocean’s natural absorption capacity – and that decisions about these must be grounded in more robust evidence than currently exists.
The report sets out a coordinated roadmap for closing these knowledge gaps. Its core recommendation is the development of a global ocean carbon observing system combining satellite monitoring, autonomous platforms and continuous measurements from the surface to the deep ocean. It also calls for improved climate modelling that incorporates ocean carbon dynamics more rigorously, and for significantly expanded capacity development in under-represented regions, particularly across the Global South, to ensure that monitoring is genuinely global rather than concentrated in the North Atlantic and a handful of other well-studied areas.
Since the launch of the UN Decade of Ocean Science for Sustainable Development in 2021, IOC-UNESCO has initiated more than 500 projects worldwide and mobilised over one billion dollars to advance ocean knowledge. The full report is available via the IOC-UNESCO digital library.