In 2025, for the ninth consecutive year, Earth’s oceans stored more heat than in any other year since modern records began. The Ocean Heat Content (OHC) reached a new historical record, confirming the upward trend of ocean warming.
The ocean absorbs more than 90% of the excess heat trapped by greenhouse gases, making it the main regulator of the global climate system.
The international study
The results were published in Advances in Atmospheric Sciences by a team of more than 50 scientists from 31 institutions around the world. The analysis combined data from:
- The Institute of Atmospheric Physics of the Chinese Academy of Sciences.
- Copernicus Marine, European Earth observation program.
- NOAA/NCEI, United States environmental monitoring system.
- The oceanic meta-analysis CIGAR-RT, with contributions from Asia, Europe, and America.
All agree that the OHC reached the highest level ever recorded in 2025.
Magnitude of ocean heat increase
The study estimates that ocean heat increased by 23 zettajoules, equivalent to 37 years of global primary energy consumption (oil, coal, and natural gas).
Additionally, about 16% of the world’s ocean surface reached a record OHC, and around 33% was among the three warmest values in their historical records.
Uneven warming
The warming is not uniform:
- More intense in the southern oceans, the North Atlantic, the Mediterranean, and the Indo-Pacific.
- Relative cooling in the equatorial Pacific, western Indian, and tropical Atlantic, associated with the transition to La Niña conditions.
Surface temperatures
The global annual average sea surface temperature in 2025 was the third warmest on record, 0.5 °C above the 1981-2010 reference average.
Although it was slightly lower than those of 2023 and 2024, the change was due to the transition from El Niño to La Niña in the tropical Pacific.
Consequences of ocean warming
The report reminds that the increase in ocean temperature:
- Raises sea levels.
- Intensifies and prolongs heatwaves.
- Favors extreme weather events.
In 2025, warmer surface temperatures caused:
- Floods in Mexico and the Pacific Northwest.
- Droughts in the Middle East.
- Widespread disruptions in Southeast Asia.
- More intense tropical cyclones due to increased evaporation and extreme rainfall.
The greatest uncertainty: human action
The scientific team concludes that, although science continues to advance, the greatest climate uncertainty depends on human decisions.
“Together, we can reduce emissions, better prepare for the changes ahead, and help safeguard a future climate in which humans can thrive,” the authors emphasize.
The record ocean heat in 2025 is an unequivocal sign of the advance of climate change. The oceans, main climate regulators, show that the crisis is not abstract: it is already happening. The response will depend on the global capacity to reduce emissions and adapt societies to a warmer and more extreme future.
