Climate change is weakening the ocean’s ability to absorb carbon dioxide, according to a United Nations report released on Wednesday that calls for greater investment in ocean monitoring and research.
The Climate Technology Progress Report 2026 was published by the United Nations Environment Programme on October 28.
It examines the physical, chemical and biological processes that allow the ocean to absorb carbon from the atmosphere.
Researchers involved in the report say global warming has already reduced the amount of carbon the ocean can absorb compared with conditions without the same climate-related changes.
Ocean carbon uptake affected by warming
The ocean absorbs approximately 30% of carbon dioxide emissions generated by human activities.
It also absorbs around 90% of the excess heat associated with climate change.
These processes have helped limit the rate at which the atmosphere warms.
However, higher water temperatures, acidification and changes in ocean circulation are affecting the mechanisms responsible for carbon uptake.
Dr. Judith Ziegler, a researcher at the GEOMAR Helmholtz Centre for Ocean Research Kiel and a contributor to the report, said climate change has already reduced ocean carbon absorption by approximately 6% compared with what would otherwise have been possible.
That estimate concerns the effect of climate change on the ocean’s capacity to absorb carbon.
It should not be interpreted as a 6% decline in annual ocean carbon absorption between two consecutive years.
Approximately 30%: Share of human-caused carbon dioxide emissions absorbed by the ocean.
Approximately 90%: Share of excess heat associated with climate change absorbed by the ocean.
Approximately 6%: Estimated reduction in carbon uptake compared with what would otherwise be possible without the same climate-related changes.
Scientists identify gaps in ocean measurements
The report identifies limitations in existing ocean observation systems.
Researchers still face difficulties measuring carbon exchanges across different ocean regions and depths.
Changes in marine ecosystems, ocean circulation and water chemistry can affect how carbon moves between the atmosphere, surface waters and deeper ocean layers.
The processes also vary by location and season.
The report calls for additional monitoring equipment, improved data systems and more accurate models.
It introduces the term Ocean Carbon Intelligence to describe an approach combining scientific observations, technology and analytical tools.
Ocean-based carbon removal requires further research
Governments and private investors have shown growing interest in technologies intended to increase the amount of carbon stored in the ocean.
The report examines approaches involving coastal ecosystems and emerging marine carbon dioxide removal technologies.
These include the restoration of ecosystems capable of storing carbon and methods intended to alter how carbon is absorbed or retained in seawater.
The report warns that scientific uncertainty and environmental risks must be considered before such technologies are deployed at scale.
It also identifies the need for transparent monitoring and appropriate regulation.
The researchers do not present ocean-based carbon removal as a substitute for reducing greenhouse gas emissions.
Coastal countries face additional concerns
The report gives particular attention to coastal states and small island developing countries.
These countries can face substantial consequences from changes in marine ecosystems, ocean temperatures and coastal conditions.
The ability to monitor changes in the ocean also differs considerably between countries.
Research institutions with established observation networks may have access to data that smaller countries cannot collect independently.
The report calls for improved access to scientific information, technology and research funding.
It also identifies international cooperation as necessary for developing a more complete understanding of ocean carbon processes.
Report released ahead of COP31
The Climate Technology Progress Report was prepared by the UNEP Copenhagen Climate Centre in collaboration with the Climate Technology Centre and Network and the Technology Executive Committee of the United Nations Framework Convention on Climate Change.
Its findings will be presented during the COP31 climate conference in Antalya, Türkiye.
The report follows new measurements showing that atmospheric greenhouse gas concentrations continued increasing during 2025.
The latest ocean research examines one of the processes that determines how much additional carbon dioxide remains in the atmosphere.
The researchers say sustained observations will be needed to establish how ocean carbon uptake changes as temperatures continue rising.
