The oceans absorbed a record amount of energy in 2025, according to a scientific study published Friday, a phenomenon conducive to rising sea levels, violent storms and coral dieback.
This is the ninth year in a row that the heat stored by the oceans has reached a record, told AFP Lijing Cheng, professor at the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences (CAS) and lead author of this analysis published in the journal “Advances in Atmospheric Sciences” by more than 50 scientists from around the world.
The total amount of heat stored in the first 2,000 meters of the oceans has thus increased by approximately 23 zettajoules in 2025, an amount of energy equivalent to “12 Hiroshima atomic bombs exploding every second of every day of the year,” underlined Mr. Cheng.
As climate regulators, the oceans absorb around 90% of the excess heat caused by human emissions of greenhouse gases. To calculate the heat absorbed by the oceans, researchers rely on several series of data based in particular on the international program of 4,000 Argo floats, drifting across all the seas around the globe and diving to depths of up to 2,000 meters.
Heavy rains and cyclones
Ocean warming contributes to sea level rise through thermal expansion, strengthens marine heat waves that weaken corals, and worsens extreme weather events such as intense rains or cyclones.
This warming does not occur uniformly: certain areas accumulate heat faster than others. The tropical oceans, the South Atlantic, the Mediterranean, the Northern Indian Ocean and the Southern Ocean are among the regions having absorbed record amounts of heat in 2025.
The 2025 record comes at a time when the average sea surface temperature, more sensitive to short-term variations, has fallen slightly, while remaining the third highest value ever measured. This decline is explained by the appearance of La Niña-type conditions, generally associated with a temporary cooling of the ocean surface.
Reduce gas emissions
In the long term, the rate of ocean warming is accelerating, due to the continued increase in greenhouse gas concentrations. “The greatest uncertainty in the climate system is no longer physics, but the choices that humanity makes,” Karina von Schuckmann, oceanographer at Mercator Ocean International and co-author of the study, told AFP.
“A rapid reduction in emissions can further limit future impacts and help preserve a climate” favorable to societies and ecosystems, she added.
