The world’s oceans just keep getting hotter. International analysis published in the journal Advances in Atmospheric Sciences finds that the oceans stored more heat in 2025 than in any year since modern measurements began.
The upper 6,500 feet of ocean absorbed a record-setting 23 zetajoules more energy than in 2024. A zetajoule means the number 1 followed by 21 zeros. It’s a unit only used to describe something enormous like all the energy that gets absorbed by the ocean. This increase in energy corresponds to 37 times more energy than all of humanity consumed in 2023.
The oceans are vast. All that energy only increased average sea surface temperatures by a tiny fraction of a degree, and last year had only the third highest on record, because multiple factors can affect it. Nevertheless, the 2025 Ocean Heat Content reached the highest level on record. Ocean heat content has reached record highs in each of the past nine years.
Ocean warming is not uniform. Some areas are warming faster than others. About 18% of the global ocean area reached a record high heat content, but another 33% ranked among the top three warmest values in history.
The ocean absorbs more than 90% of the excess heat trapped by greenhouse gases in the atmosphere. It is the main heat reservoir of the climate system. Monitoring ocean heat content provides one of the best indicators of long-term climate change. Without urgent action to address the causes of climate change, the oceans will only continue getting hotter.
