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A new report by the Intergovernmental Oceanographic Commission (IOC) of UNESCO reveals a critical lack of understanding of how the ocean absorbs and stores carbon. This uncertainty about our planet’s largest carbon sink threatens to skew current climate predictions and hamper our ability to develop effective mitigation and adaptation strategies in the coming decades.
The report also lays out a roadmap to bolster international cooperation, strengthen ocean carbon monitoring and update climate models accordingly.
“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 defense functions – or how long it can endure. Coordinated global monitoring of ocean carbon absorption is therefore essential and urgent. This report reaffirms UNESCO’s commitment to supporting Member States in developing climate policies based on robust science to advance this goal,” said Khaled El-Enany, UNESCO Director-General.
The ocean is storing around 25% of global CO₂ emissions. But, according to the new report coordinated by the IOC of UNESCO, major blind spots remain in our scientific understanding of this process, with variations large enough to considerably affect how governments plan climate mitigation and adaptation strategies.
Climate models built on incomplete data
The Integrated Ocean Carbon Research Report finds that scientific models differ widely in estimating how much carbon the ocean absorbs, with discrepancies of 10-20% globally and even greater in certain regions.
These differences stem from limited availability of long-term data, and gaps in understanding how key processes respond to climate change. This means quantifying how changes in ocean warming and circulation affect carbon uptake, how shifts in plankton and microbial life influence long-term storage, and how coastal and polar regions exchange carbon with the atmosphere. Industrial activities today, and the risks associated with climate engineering in the future may also alter the ocean’s natural ability to absorb carbon.
Major implications for climate targets and adaptation
All of this indicates that we are making climate decisions without knowing how the ocean will behave. If the ocean absorbs less carbon in the future, more CO₂ will remain in the atmosphere and accelerate global warming. This would have a direct impact on future emissions targets and national climate plans.
Greater uncertainty in ocean carbon uptake also complicates adaptation planning, especially for coastal communities already vulnerable to storms, sea-level rise and warming waters. Decisions about potential carbon removal strategies and ocean-based climate interventions must also be grounded in more robust scientific evidence.
From uncertainty to action
Prepared by 72 authors across 23 countries, the Integrated Ocean Carbon Research Report offers the most comprehensive synthesis to date of the uncertainties affecting our ocean carbon sink estimates.
Beyond identifying research needs, the report also lays out a coordinated roadmap to strengthen monitoring, modelling and international cooperation so that ocean carbon science can more directly inform climate policy. To close these knowledge gaps, the report calls for a global ocean carbon observing system, combining satellites, autonomous platforms and sustained measurements from the surface to the deep ocean – while improved ocean and climate modelling should also include stronger capacity development in under-represented regions to ensure truly global monitoring coverage.
Reducing carbon emissions remains the only long-term solution to protect the ocean and the climate. But without a clearer understanding of how the ocean carbon sink is changing, global mitigation and adaptation strategies risk being built on incomplete information.
Since the start of the UN Decade of Ocean Science for Sustainable Development (2021–2030), more than 500 projects have been launched worldwide, and over $1 billion have been mobilised to advance ocean knowledge and transform it into measurable action.
From strengthening global ocean observing systems and advancing seabed mapping to improving early warning for coastal hazards and supporting ecosystem-based climate solutions, IOC of UNESCO is helping build the scientific foundations required to protect ocean biodiversity and enhance climate resilience worldwide.
