The ocean, long one of the planet’s most important defences against global warming, is losing some of its power to soak up carbon dioxide, the United Nations has warned.
A new report, the UN’s 2026 Climate Technology Progress Report, finds that human-induced climate change has already reduced the ocean’s carbon-sink capacity by approximately 6 per cent, compared with a world without human-caused warming. The finding lands just weeks before governments gather for the COP31 climate conference in November.
The ocean currently absorbs around 30 per cent of human-induced carbon dioxide emissions and about 90 per cent of the additional heat generated by climate change. That service has slowed the pace of warming, but the report says it can no longer be taken for granted.
Warming waters, acidification, deoxygenation, shifting circulation patterns, pollution and ecosystem degradation are all disrupting the physical, chemical and biological processes that allow the ocean to take up and store carbon. As the sink weakens, a greater share of carbon dioxide stays in the atmosphere, making climate goals harder and more costly to achieve.
The report’s lead author, Sara Traerup, said the ocean has for a long time provided an enormous climate service, but that service is now under increasing pressure and could weaken further. The UN Environment Programme’s Martin Krause said rapid and sustained cuts in greenhouse gas emissions remain the primary response, with ocean technologies playing only a supporting role.
A central problem, the report argues, is how little is reliably known about the ocean carbon system. Monitoring gaps are especially large in the Southern Ocean, the Indian Ocean, the Arctic and many coastal regions. To close them, it proposes an “Ocean Carbon Intelligence” framework, linking ocean science, monitoring technologies, data infrastructure and analytical tools so that governments and investors can make better-informed decisions.
The report examines three types of ocean climate technology. The most mature, and most urgently needed, is ocean monitoring: observation systems, sensors, data and modelling. The second is blue carbon ecosystems such as mangroves, seagrasses and salt marshes, which already sequester around 407 million tonnes of carbon dioxide a year; restoring them could add significantly more, while also protecting coastlines, supporting biodiversity and sustaining livelihoods. The third, marine carbon dioxide removal, aims to extract carbon dioxide from the atmosphere and store it long-term, but remains highly uncertain and needs further research, monitoring and regulation.
Small island states are on the front line despite contributing less than 1 per cent of global emissions, the report notes, and it calls for greater access to finance, technology transfer and capacity-building so they can develop solutions tailored to their needs. It points to Seychelles, which used a debt-for-nature swap in 2015 to fund marine conservation, and to Fiji, Papua New Guinea, Solomon Islands and Vanuatu, where mapping seagrass meadows and mangrove forests has trained more than 100 people in blue carbon assessment.
The report also stresses the value of local and Indigenous knowledge, noting that coastal communities have long experience of protecting shorelines through natural habitats and managing fisheries sustainably. Ocean-based technologies, it cautions, must complement, not replace, emissions reductions and ecosystem protection.
Sources: UN News, “Ocean’s ability to absorb carbon is weakening as climate change intensifies, UN warns” (https://news.un.org/en/story/2026/10/1168687); UN Environment Programme, “UN report urges investment in Ocean Carbon Intelligence to safeguard the ocean’s climate role” (http://www.unep.org/en/news-and-stories/press-release/un-report-urges-investment-ocean-carbon-intelligence-safeguard).
