The ocean’s ability to absorb carbon dioxide has weakened by approximately 6 percent due to climate change, raising concerns about accelerating global warming, rising ocean temperatures and the future effectiveness of one of the planet’s largest natural carbon sinks.
A new United Nations report, released ahead of the COP31 climate conference in November 2026, warns that rising temperatures, changing ocean chemistry and disruptions to marine ecosystems are reducing the ocean’s capacity to absorb and store atmospheric carbon.
The findings highlight growing risks for global climate targets, coastal communities, marine biodiversity and countries vulnerable to rising sea levels.
The report, developed by the United Nations Environment Programme (UNEP) and the United Nations Framework Convention on Climate Change (UNFCCC), calls for greater investment in ocean monitoring technologies, blue carbon ecosystems and climate adaptation.
Oceans Absorb 30 Percent of CO2 Emissions and 90 Percent of Excess Heat
The ocean plays a critical role in regulating Earth’s climate by absorbing approximately 30 percent of human-generated carbon dioxide emissions and 90 percent of excess heat trapped by greenhouse gases.
However, climate change is weakening this natural protection system.
According to the UN report, the ocean’s carbon absorption capacity has already declined by approximately 6 percent as warming waters, changes in circulation and marine ecosystem degradation affect carbon storage processes.
A weakening ocean carbon sink means more carbon dioxide could remain in the atmosphere, potentially accelerating global warming and increasing the difficulty of meeting international climate commitments.
Sara Traerup, lead author of the report, warned that the deterioration could accelerate in the coming years.
The findings reinforce the importance of reducing greenhouse gas emissions while strengthening the resilience of marine ecosystems.
Blue Carbon Ecosystems Capture 407 Million Tonnes of CO2 Annually
Mangroves, seagrass meadows and salt marshes are emerging as important natural solutions for reducing atmospheric carbon dioxide.
These coastal ecosystems collectively sequester approximately 407 million tonnes of CO2 annually, according to the UN report.
Protecting and restoring these ecosystems could increase carbon storage while delivering additional environmental and economic benefits.
Mangrove forests help protect coastal communities from storms and erosion. Seagrass meadows support marine biodiversity and fisheries, while salt marshes contribute to coastal protection and long-term carbon storage.
However, coastal development, pollution, habitat destruction and rising sea temperatures threaten these ecosystems.
The report identifies blue carbon restoration as an important opportunity for governments seeking to strengthen climate resilience while protecting marine biodiversity.
Ocean Monitoring Technologies Need Greater Investment
The UN identifies significant gaps in global ocean monitoring capabilities, particularly across the Southern Ocean, Indian Ocean, Arctic and coastal regions.
These gaps limit scientists’ ability to measure changes in ocean carbon absorption and understand how marine ecosystems respond to rising temperatures.
The report calls for stronger investment in ocean carbon intelligence through advanced monitoring systems, sensors, scientific modelling and integrated data platforms.
Ocean observation technologies can help governments track carbon storage, monitor marine ecosystem health and assess climate-related risks.
The report identifies three major technology priorities:
Ocean monitoring systems: Sensors, observation networks, satellite data, modelling and digital platforms to improve understanding of ocean carbon processes.
Blue carbon ecosystem restoration: Technologies and conservation programmes supporting mangroves, seagrasses and salt marshes.
Marine carbon dioxide removal: Emerging approaches designed to remove atmospheric CO2 and store it over extended periods.
Ocean monitoring is currently the most mature of these technology categories.
Marine carbon dioxide removal remains at an earlier stage, with unresolved questions about effectiveness, environmental impacts, measurement and long-term storage.
The UN cautions that emerging ocean carbon removal technologies should complement emissions reductions rather than replace them.
Small Island Nations Face Disproportionate Climate Risks
Small Island Developing States contribute less than 1 percent of global greenhouse gas emissions but face some of the most severe consequences of ocean warming, coastal erosion and rising sea levels.
Countries across the Pacific, Indian Ocean and Caribbean depend heavily on healthy marine ecosystems for tourism, fisheries, food security and economic development.
The report highlights the need for additional climate financing, technology transfer and scientific capacity-building to help these countries protect their marine environments.
Seychelles provides an example of innovative ocean conservation financing.
In 2015, the country implemented a debt-for-nature swap that helped establish financing mechanisms for marine conservation, climate resilience and sustainable blue economy development.
Meanwhile, Fiji, Papua New Guinea, Solomon Islands and Vanuatu have received support to map mangrove forests and seagrass ecosystems and assess their carbon storage potential.
These programmes trained more than 100 people in blue carbon assessment, helping governments incorporate marine carbon data into national climate strategies.
COP31 Climate Talks to Focus on Ocean Protection and Carbon Emissions
The findings add urgency to discussions ahead of COP31, where governments are expected to address climate mitigation, adaptation financing and the protection of natural carbon sinks.
The report highlights the importance of expanding ocean monitoring networks, strengthening marine ecosystem protection and supporting climate technology deployment in vulnerable countries.
It also emphasizes the role of Indigenous communities and local knowledge in managing coastal resources and protecting marine habitats.
The central concern is that continued ocean warming could further weaken natural carbon absorption, leaving more greenhouse gases in the atmosphere and intensifying climate change.
With oceans already absorbing nearly one-third of human-caused carbon dioxide emissions, protecting their carbon storage capacity remains essential to limiting future global temperature increases.
BABURAJAN KIZHAKEDATH
