The ocean absorbs about 25% of human CO₂ emissions, but its future capacity to store carbon remains uncertain under a changing climate. A recent UNESCO report highlights critical knowledge gaps in ocean carbon dynamics, while CMCC research is working to address them through integrated and interdisciplinary approaches that improve models, observations, and climate solutions. “Considering that the ocean covers about 70% of the planet’s surface, these uncertainties are especially significant,” says CMCC scientist Annalisa Bracco.

The ocean plays a crucial role in regulating the Earth’s climate, acting as a major carbon sink that absorbs roughly a quarter of anthropogenic CO₂ emissions. Yet, despite its importance, how the ocean takes up, transports and stores carbon remains only partially understood.

“Considering that the ocean covers about 70% of the planet’s surface, these knowledge gaps are especially significant and is urgent to tackle them,” says CMCC scientist Annalisa Bracco, who contributed to a recent report on integrated ocean carbon research, coordinated by UNESCO’s Intergovernmental Oceanographic Commission. “Improving both process understanding and model representation is therefore essential.”

The report describes a significant blind spot in current knowledge of ocean carbon dynamics, a key research area in which CMCC is a global leader and is actively advancing new research directions. While the ocean currently absorbs around 25% of global emissions, estimates vary considerably – by 10–20% at the global scale and even more regionally – due to limited observations and incomplete representation of key processes in climate models.

The ocean represents one of the largest sources of uncertainty in the global carbon cycle. A key open question concerns the relative role of physical and biological processes in ocean carbon uptake. Physical processes, particularly in high-latitude regions such as the North Atlantic and the Southern Ocean, through the meridional overturning circulation, drive the formation of deep water masses and transport carbon into the deep ocean. At the same time, biological processes – including phytoplankton photosynthesis and bacterial respiration – regulate how carbon is absorbed and released in surface waters.

Quantifying these contributions remains a major scientific challenge. Models show significant differences, partly due to the use of diverse biogeochemical components, while observational data remain limited and unevenly distributed. “Many of these dynamics have been studied primarily in laboratory settings, while direct ocean observations remain extremely limited,” Bracco explains. “Ocean measurements are very expensive – a research vessel can cost between 25,000 and 100,000 dollars per day.”

CMCC research is actively contributing to addressing these challenges through an integrated and interdisciplinary approach that combines ocean science, modelling, and climate policy. For example, current research activities assess the potential of carbon dioxide removal (CDR) technologies, including marine CDR approaches (mCDR) that aim to enhance the ocean’s capacity to absorb carbon. Future work will focus on developing models for these approaches, particularly ocean alkalinity enhancement.

“Our biogeochemical modelling activities are strategically targeting key processes highlighted in the report to reduce uncertainties and knowledge gaps,” says Momme Butenschön, who coordinates research efforts on Earth System modelling and biogeochemistry at CMCC. “It is essential that progress in this field is developed through strong international collaboration between modelling groups, observational experts, and stakeholders, ensuring that scientific advances effectively support climate policy and decision-making.”

These gaps are not only scientific but also highly relevant for climate policy. While it is well established that the ocean absorbs about 25% of anthropogenic CO₂ emissions, this fraction is expected to decline as ocean temperatures rise and CO₂ becomes less soluble. As a result, a larger share of emissions is likely to remain in the atmosphere, reinforcing the urgency of mitigation efforts.

At the same time, increasing CO₂ uptake is contributing to ocean acidification, with potential impacts on marine ecosystems, particularly in coastal regions. Organisms that rely on calcium carbonate structures, such as shells and skeletons, are especially vulnerable, with potential consequences also for phytoplankton and ocean carbon uptake.

Looking forward, the report proposes a roadmap to address these knowledge gaps, emphasizing the need for enhanced observing systems, improved models, and stronger international collaboration. In this context, CMCC research is well positioned to contribute, bringing together expertise across ocean science, modelling, and policy.

More information:

Read the report: IOC of UNESCO. 2026. Integrated Ocean Carbon Research: a vision primed for implementation. Paris, UNESCO. (IOC Technical Series, 214.) https://doi.org/10.71245/FULK2623