Climate change has already reduced the ocean’s capacity to absorb carbon by an estimated 6%, increasing pressure for deeper cuts in greenhouse gas emissions, a United Nations report warned.
The 2026 Climate Technology Progress Report said shifting wind patterns and ocean warming are reducing the ocean’s carbon sink capacity compared with a world without human-induced climate change.
The ocean absorbs about 30% of human-induced carbon dioxide emissions and roughly 90% of the additional heat generated by climate change, helping slow global warming.
But warming, acidification, deoxygenation, pollution and ecosystem degradation are disrupting the physical, chemical and biological processes that allow the ocean to absorb and store carbon.
“A weaker ocean carbon sink leaves more carbon dioxide in the atmosphere and makes climate goals harder and more costly to achieve,” said Martin Krause, director of the Climate Change Division at the UN Environment Programme.
Krause said the ocean has helped slow climate change, but its role as a carbon sink cannot be taken for granted.
The report said rapid and sustained reductions in greenhouse gas emissions remain the primary response to the weakening of the ocean carbon sink.
It warned that ocean-based climate technologies cannot replace deep emissions cuts or broader efforts to protect marine ecosystems. Such technologies can help preserve natural carbon sinks, strengthen climate resilience and improve the evidence used in climate decisions.
The report called for sustained investment in ocean observation, data infrastructure and modelling to close gaps in understanding how the ocean carbon system is changing.
It identified major monitoring gaps in the Southern Ocean, Arctic, Indian Ocean and many coastal regions. Global capacity to observe the ocean carbon cycle has also declined in recent years, the report said.
The report highlighted Ocean Carbon Intelligence, a framework that combines ocean observations, digital infrastructure, analytical models and climate technologies to improve understanding of ocean carbon dynamics and support decision-making.
It said sustained investment in observation infrastructure and marine data systems is needed to support responsible technology development and informed climate action.
The report also examined blue carbon restoration and emerging marine carbon dioxide removal technologies.
Marine carbon removal approaches remain at lower levels of technological readiness and carry significant scientific, environmental, social and governance uncertainties, according to the report. Further assessment would require carefully designed field trials and strong safeguards.
“With pressures on the ocean increasing and the need for effective climate action growing, the priority must be ensuring ocean-based climate solutions are guided by science, equity and transparency,” Krause said.
He said ocean innovation has significant potential but will depend on strong governance, public trust and sustained investment in knowledge, capacity and international cooperation.
The report also warned that Small Island Developing States face some of the world’s most severe ocean-related climate risks despite contributing less than 1% of global greenhouse gas emissions.
Sea-level rise, ocean warming, acidification, extreme events and ecosystem degradation threaten livelihoods, infrastructure, freshwater security, cultural heritage and, in some cases, long-term habitability.
Pacific COP31 Envoy for the Ocean Inia Seruiratu said governments have “both an opportunity and a responsibility to place the ocean where it belongs: at the heart of global climate action.”
“This will require bold leadership, stronger partnerships and sustained investment, while recognizing that science, innovation and Indigenous knowledge together offer our best pathway towards a more resilient future,” he said.
