The world's oceans set a new heat record in 2025, absorbing about 23 zettajoules of energy in one year, according to a study led by the Institute of Atmospheric Physics (Chinese Academy of Sciences) and published in Advances in Atmospheric Sciences. The research found record warming across the Atlantic, Mediterranean, Indian and Southern oceans — the ninth consecutive year of rising ocean heat. Scientists note that oceans now absorb over 90% of excess trapped energy and warn this trend drives sea level rise, stronger storms and growing stress on marine ecosystems. They call for rapid emissions cuts, a phase-out of fossil fuels and investments in climate resilience.
Oceans 'Under Attack': 2025 Marks Ninth Straight Year Of Record Heat As Seas Absorb 23 Zettajoules
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Researchers warn that the world's oceans reached a new, alarming milestone in 2025: global ocean heat content climbed to its highest level on record, with the seas absorbing roughly 23 zettajoules of additional energy in a single year.
Study and Key Findings
A large international team led by the Institute of Atmospheric Physics at the Chinese Academy of Sciences published the analysis in the journal Advances in Atmospheric Sciences. The study reports record increases across multiple basins — including the Atlantic Ocean, the Mediterranean Sea, the Indian Ocean and the Southern Ocean — and notes that 2025 was the ninth consecutive year of rising ocean heat records.
The authors emphasize that more than 90% of the excess energy trapped by greenhouse gases in Earth's atmosphere is taken up by the oceans, making ocean heat content one of the clearest long-term indicators of planetary warming.
Why Ocean Heat Matters
Because the oceans are Earth’s largest heat reservoir, changes in ocean heat content reflect the strength and persistence of global warming more reliably than short-term surface temperature fluctuations. Ocean warming affects weather, sea levels, and marine ecosystems on regional and global scales.
Consequences For People And Nature
Warming seas drive a range of impacts: higher sea levels that threaten coastlines, increased intensity and frequency of extreme storms such as hurricanes and typhoons, accelerated melting of polar ice, and widespread stress on marine life. Rising temperatures and acidification also undermine coral reefs, reduce oxygen levels in some regions, shift fisheries, and can cascade through food webs.
"We reimagined them not as mighty guardians, but as vulnerable creatures whose armor — their shells and scales — is under attack by ocean warming, acidification, and other environmental changes," wrote Cheng Lijing, one of the paper's authors.
What Scientists Recommend
The paper frames these ocean heat records as a symptom of excessive greenhouse gas emissions. The most direct ways to slow ocean heat buildup are rapid reductions in emissions, phasing out fossil fuels, and scaling clean renewable energy. The authors and climate experts also call for expanded investment in climate-resilient infrastructure, improved coastal defenses, enhanced early-warning and disaster-preparedness systems, and continued global monitoring of ocean heat and related changes.
Takeaway
Tracking ocean heat content gives policymakers and communities a powerful metric of planetary warming and urgency: sustained, large-scale action to cut emissions and invest in resilience is needed now to reduce risks to coastlines, marine ecosystems and human societies.
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