The ocean absorbs around 30 per cent of human-caused carbon dioxide (CO₂) emissions and 90 per cent of excess heat trapped by greenhouse gases. But climate change has already reduced its capacity to absorb carbon by approximately six per cent, a new UN report warns ahead of the COP31 climate conference in November.
The report was a collaboration between the UN’s environment agency, UNEP, and the UN climate secretariat, UNFCCC, which co-organises COP31.
“For a long time the ocean has been doing us an enormous climate service, but that service is under increasing pressure,” Sara Traerup, lead author of the report, told UN News.
Rising temperatures and changes in ocean chemistry, circulation and ecosystems are weakening its ability to absorb and store carbon, leaving more CO₂ in the atmosphere.
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And this process “can definitely accelerate” in the foreseeable future, Ms. Traerup warned.
Bridging our knowledge gap
A major challenge is the lack of reliable ocean monitoring data, particularly in the Southern and Indian Oceans, the Arctic and many coastal regions.
The report therefore calls for stronger “ocean carbon intelligence” – using science, technology, data and local knowledge to better understand and manage ocean carbon systems.
“As of now, we don’t have full information about the ocean, and what we don’t know, we cannot manage and protect,” Ms. Traerup explained.
From sensors to seagrass
UNEP looked at three main types of ocean climate technologies, each offering different opportunities and risks.
The first is ocean monitoring: observation systems, sensors, data systems and modelling. Ms. Traerup called these the most mature technologies and the most immediately needed.
The second is blue carbon ecosystems such as mangroves, seagrasses and salt marshes. They already sequester around 407 million tonnes of CO₂ a year, and restoring them could add significantly more. They also protect coastlines, support biodiversity and sustain livelihoods.
The third is marine carbon dioxide removal, which aims to extract CO₂ from the atmosphere and store it over the long term. While potentially promising, these approaches remain highly uncertain and require further research, monitoring and regulation.
“We shouldn’t treat ocean-based technologies as a shortcut,” Ms. Traerup cautioned, as they must complement, not replace, emissions reductions and ecosystem protection.
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Islands leading the way
Small Island Developing States (SIDS) contribute less than 1 per cent of global emissions, yet are “on the front line of ocean and climate impacts,” Ms. Traerup noted.
The report called for greater access to finance, technology transfer and capacity-building to enable these countries to develop ocean solutions tailored to their needs. Some islands are already showing how this can work.
In 2015, Seychelles, for instance, benefited from a debt-for-nature swap, which involved restructuring part of its foreign debt in exchange for marine conservation commitments. This enabled the country to set up a trust fund to finance marine conservation, climate resilience and the sustainable blue economy.
In the Pacific, Fiji, Papua New Guinea, Solomon Islands and Vanuatu received support to map seagrass meadows and mangrove forests, and measure how much carbon they store. As a result, more than 100 people were trained in blue carbon assessment, giving governments data to feed into their national climate plans.
The report also stressed the importance of integrating local and Indigenous knowledge.
“Communities have been coping with climate change for many, many years,” Ms. Traerup said, pointing to their experience in protecting coastlines through natural habitats and in managing fisheries and coastal resources sustainably.
