The Planet’s Largest Carbon Sink Is Reaching Its Limits
The Planet’s Largest Carbon Sink Is Reaching Its Limits
The Planet’s Largest Carbon Sink Is Reaching Its Limits
The ocean, often referred to as the planet's lungs, generates 50 percent of the oxygen we need and absorbs 30 percent of all carbon dioxide emissions, making it the largest carbon sink. However, increasing greenhouse gas emissions have affected the health of the ocean, causing detrimental changes to life under water and on land, and reducing its ability to absorb carbon dioxide.
According to the United Nations, the ocean is central to reducing global greenhouse gas emissions and stabilizing the Earth’s climate. Ocean habitats such as seagrasses and mangroves can sequester carbon dioxide from the atmosphere at rates up to four times higher than terrestrial forests. Mangroves are some of the most carbon-rich ecosystems on the planet, storing on average 1,000 tonnes of carbon per hectare in their biomass and underlying soils.
A new study published in Nature Climate Change reveals that the global oceans absorbed almost a billion tons, or around ten percent less CO₂, than anticipated based on previous years. This reduction is equivalent to about half of the E.U.’s total CO₂ emissions, or about a fifth of U.S. Emissions. The decline in CO₂ absorption is due to global warming, which reduces the ocean's carbon-absorbing capacity.
Researchers from the Swiss Federal Institute of Technology Zurich (ETH Zurich) investigated the impact of record-breaking temperatures on the ocean's carbon-absorbing capacity. They found that high temperatures, especially in the North Atlantic, reduced CO₂ solubility and weakened the ocean's carbon-absorbing capacity. However, natural mechanisms in the ocean, such as the biological pump, counteracted the CO₂ outgassing promoted by warming, keeping the amount of dissolved carbon low in waters near the surface.
Professor Sabine Fuss, department leader at the Potsdam Institute for Climate Impact Research, notes that the capacity of land and ocean systems to absorb emissions is faltering. "That means we may be underestimating the current emissions gap as well as the pace of future warming." The 10 New Insights in Climate Science 2025 report, authored by more than 70 scientists from 21 countries, reveals that decades of climate change have weakened the capacity of land and ocean systems to absorb emissions.
Dr Katie Smith of the Marine Biological Association (MBA) explains that the ocean has been our greatest ally in buffering the impacts of climate change, but rising temperatures and intensifying marine heatwaves are weakening its ability to store carbon. Marine heatwaves are now occurring more often and lasting longer, destroying kelp forests, bleaching coral reefs, and triggering cascading effects that ripple through entire ecosystems.
The United Nations emphasizes the importance of safeguarding the ocean as our best ally for climate solutions. This includes expanding marine protected areas, which currently cover 8.34 percent of the ocean.
According to Johan Rockström, co-chair of The Earth League, "COP30 must be the COP of implementation; we can no longer afford new promises without delivery." The 10 New Insights in Climate Science provide the best summary of the latest updates in climate research, highlighting the need for immediate action to address the climate crisis.
