UN Raises Alarm as Climate Change Weakens Ocean’s Capacity to Absorb Carbon

UN Warns Ocean’s Ability to Absorb Carbon Is Declining as Global Warming Intensifies

The world’s oceans are losing some of their ability to absorb carbon dioxide, raising fresh concerns about the future of the global climate, according to a new United Nations report. Scientists warn that rising sea temperatures, changing ocean currents and increasing acidification are putting growing pressure on one of Earth’s most important natural defences against climate change.

Covering more than 70 per cent of the planet, oceans play a critical role in regulating global temperatures by absorbing carbon dioxide from the atmosphere and storing it in marine ecosystems and deep-sea waters. However, climate change is disrupting the natural processes that allow oceans to perform this essential function.

UN Report Highlights a 6 Per Cent Decline in Ocean Carbon Absorption

A 2026 UN assessment has found that the ocean’s capacity to absorb carbon has declined by approximately 6 per cent due to climate change.

The report states that oceans absorb nearly 30 per cent of human-generated carbon dioxide emissions and take up around 90 per cent of the excess heat trapped by greenhouse gases.

Prepared jointly by the United Nations Environment Programme (UNEP) and the UN Framework Convention on Climate Change (UNFCCC), the assessment comes ahead of the COP31 climate conference scheduled for November.

Sara Traerup, the report’s lead author, cautioned that the ocean’s ability to provide this vital climate service is facing increasing challenges. Changes in temperature, water circulation, marine chemistry and biodiversity are affecting the ocean’s capacity to capture and store carbon.

Scientists fear that continued deterioration could weaken an important natural barrier against rising global temperatures.

Why Warmer Oceans Absorb Less Carbon Dioxide

Ocean temperatures are among the key factors influencing how much carbon dioxide seawater can absorb. Cold water generally holds more dissolved carbon dioxide than warm water. As the oceans heat up, their ability to take in additional carbon can decrease.

Changes in ocean circulation are creating further complications. These currents help transport carbon absorbed near the surface into deeper waters, where it can remain stored for extended periods.

Ocean acidification is another growing threat. As seawater absorbs atmospheric carbon dioxide, its chemical composition changes and acidity increases. This can damage coral reefs and affect shell-forming organisms, including shellfish and other marine species.

Together, warming waters, acidification and declining ecosystem health are threatening the natural mechanisms that help regulate atmospheric carbon levels.

Mangroves and Seagrass Ecosystems Also Under Pressure

The UN assessment draws attention to the importance of blue carbon ecosystems, particularly mangrove forests, seagrass meadows and salt marshes.

These coastal habitats are estimated to capture around 407 million tonnes of carbon dioxide every year. Apart from storing carbon, they provide essential environmental and economic benefits.

They help protect coastal settlements against storms, flooding and erosion, provide breeding grounds for marine species, support fisheries and sustain the livelihoods of millions of people.

However, coastal construction, pollution, rising sea levels and increasing temperatures are putting these ecosystems at risk. Their destruction could result in the loss of valuable carbon storage areas while further damaging marine biodiversity.

UN Recommends Stronger Ocean Research and Conservation

The report calls for greater investment in scientific research, ocean monitoring and climate-related technologies to understand the changing condition of marine ecosystems.

It identifies three important priorities:

1. Strengthening ocean monitoring: Better monitoring systems are needed to track sea temperatures, acidity, carbon absorption and ocean circulation. Significant information gaps remain in regions such as the Southern Ocean, Indian Ocean, Arctic and several coastal areas.

2. Restoring blue carbon habitats: Conservation and restoration of mangroves, seagrass meadows and salt marshes can improve natural carbon storage, protect coastal communities and support marine biodiversity.

3. Advancing marine carbon removal technologies: Scientists are examining new methods to remove carbon dioxide from the atmosphere or oceans and store it for longer periods. However, these technologies require further research, environmental assessments and appropriate regulatory safeguards before wider implementation.

Developing Nations Face Greater Climate Challenges

Small Island Developing States (SIDS) are among the regions most exposed to the consequences of ocean warming and rising sea levels. Although these countries contribute less than 1 per cent of global greenhouse gas emissions, they face serious risks from coastal erosion, flooding and damage to marine ecosystems.

Limited financial resources and technological infrastructure make it difficult for many developing nations to monitor and protect their coastal environments.

The UN has therefore called for increased climate financing, technology transfer and capacity-building support.

Initiatives in Fiji, Papua New Guinea, the Solomon Islands and Vanuatu are helping local communities map mangrove forests and seagrass habitats and evaluate their potential for carbon storage.

The assessment also underlines the importance of incorporating Indigenous knowledge and local community experience into marine conservation strategies.

Ocean Protection Must Go Alongside Emission Cuts

The declining capacity of oceans to absorb carbon could make the fight against global warming considerably more difficult. If less carbon dioxide is stored in marine environments, a greater amount could remain in the atmosphere, adding to the greenhouse effect.

Martin Krause, Director of the Climate Change Division at UNEP, warned that a weakening ocean carbon sink would make climate targets harder and more expensive to achieve.

The report stresses that protecting marine ecosystems and developing ocean-based carbon removal technologies cannot replace direct reductions in greenhouse gas emissions.

Reducing dependence on fossil fuels, expanding clean energy and cutting pollution remain essential to limiting global warming.

With governments preparing for COP31, the UN assessment highlights an urgent message: protecting the oceans is not just about preserving marine life but also about safeguarding one of the planet’s most important natural systems for maintaining climate stability.