Since 2018, a A group of researchers from around the world has calculated how much heat the world’s oceans absorb each year. In 2025, their measurements broke the record again, making it the eighth year in a row that the world’s oceans have absorbed more heat than in previous years.
The study, published Friday in the journal Advances in Atmospheric Science, found that the world’s oceans could absorb an additional 23 zetajoules in 2025, the most in any year since modern measurements began in the 1960s. This is significantly more than the 16 additional zetajoules absorbed in 2024. The research comes from a team of more than 50 scientists from the United States, Europe and China.
A joule is a common way to measure energy. A single is a relatively small unit of measurement – it is About the coffee To power a small light bulb for a second, or to heat a little water. But a zitijoule is one Sextile JOULES; Numerically, the 23 zillion joules absorbed this year can be written as 23,000,000,000,000,000,000,000,000.
John Abraham, a professor of thermal science at the University of St. Thomas and one of the authors on the paper, says he sometimes has trouble putting these numbers into context. Abraham offers a couple options. His favorite is comparing the energy stored in the ocean to the energy of atomic bombs: the 2025 warming, he says, is as energetic as 12 Hiroshima bombs exploding in the ocean. (Some other calculations he’s done include equating that number to the energy it would take to boil 2 billion Olympic swimming pools, or more than 200 times the electricity consumption of everyone on the planet.)
“Last year was a bonkers, crazy warming year. That’s the technical term,” Ibrahim joked to me. “The scientific term for peer review is ‘bonkers’.”
The world’s oceans are its biggest heat sink, absorbing more than 90 percent of the heat trapped in the atmosphere. Although some of the excess heat warms the surface of the ocean, it also slowly travels down into the deeper parts of the ocean, aided by circulation and currents.
Global temperature calculations — such as those used to determine the hottest years on record — typically only capture measurements taken at sea level. (The study shows that overall sea surface temperatures in 2025 were slightly lower than in 2024, which is on record as Hottest year Since the modern record began. Certain climate phenomena, such as El Niño events, can also increase surface temperatures in some areas, causing the ocean as a whole to absorb slightly less heat in a given year. (This helps explain why there’s such a big jump in excess ocean heat content between 2025, which produced a weak La Niña at the end of the year, and 2024, which marked the end of a strong El Niño year.) While sea surface temperatures have risen since the Industrial Revolution, it’s not a complete picture thanks to our use of fossil fuels.
“If the entire world was just covered by a shallow ocean that was only a couple of feet deep, it would warm more or less at the same rate as Earth,” says Zack Housefather, a research scientist at Berkeley Earth and a coauthor of the study. [than those on land].