The ocean absorbed more heat last year than in any year since modern measurements began around 1960, according to a new analysis published in the journal Advances in Atmospheric Science.
The world’s oceans absorb more than 90% of the excess heat trapped in the Earth’s atmosphere due to greenhouse gas emissions. As heat accumulates in the atmosphere, so does the heat stored in the oceans, making ocean heat a reliable indicator of long-term climate change.
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Scientists measure ocean heat in a variety of ways. One common indicator is the global annual average sea surface temperature, or the average temperature of the upper few meters of ocean water. Global sea surface temperatures in 2025 were about 0.5 °C (0.9 °F) above the 1981-2010 average, making it the third warmest on record.
Another indicator is ocean heat content, which measures the total amount of heat energy stored in the world’s oceans. It is measured in zettajoules. 1 zettajoule is equal to 1,000,000,000,000,000,000,000 joules. To measure the amount of heat in 2025, the study authors evaluated ocean observation data from NOAA’s National Center for Environmental Information, the European Union’s Copernicus Office for Climate Change, and the Chinese Academy of Sciences in the upper 2,000 meters of the ocean, where most of the heat is absorbed.
They found that in 2025, the ocean absorbed a total of an additional 23 zettajoules of heat energy, breaking the ocean heat record for nine consecutive years and the longest continuous ocean heat record ever recorded.
“Last year was a year of tremendous warming,” John Abraham, a mechanical engineer at the University of St. Thomas and co-author of the new study, told Wired.
In one year, 23 zettajoules is equivalent to the energy of 12 Hiroshima bombs exploding in the ocean every second. This is also significantly more than the 16 zettajoules of heat absorbed by the ocean in 2024. The hottest regions of the ocean observed in 2025 were the tropical and southern Atlantic, Mediterranean, northern Indian Ocean, and Southern Ocean.
The results provide “direct evidence that the climate system is out of thermal equilibrium and that heat is accumulating,” the authors wrote.
As ocean temperatures rise, global precipitation increases and more extreme tropical cyclones form. Rising global temperatures may have partially contributed to damage last year, including Hurricane Melissa in Jamaica and Cuba, heavy monsoon rains in Pakistan, and severe flooding in the central Mississippi Valley.
“Ocean warming continues to have profound effects on the Earth system,” the authors write.
This article was originally published on Eos.org. Read the original article.
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