Since 2018, a group of researchers from around the globe have crunched the numbers on how a lot warmth the world’s oceans are absorbing annually. In 2025, their measurements broke information as soon as once more, making this the eighth yr in a row that the world’s oceans have absorbed extra warmth than the years earlier than.
The examine, which was printed Friday within the journal Advances in Atmospheric Science, discovered that the world’s oceans absorbed a further 23 zettajoules’ value of warmth in 2025, probably the most in any yr since trendy measurements started within the Nineteen Sixties. That’s considerably greater than the 16 extra zettajoules they absorbed in 2024. The analysis comes from a group of greater than 50 scientists throughout the USA, Europe, and China.
A joule is a typical approach to measure vitality. A single joule is a comparatively small unit of measurement—it’s about sufficient to energy a tiny lightbulb for a second, or barely warmth a gram of water. However a zettajoule is one sextillion joules; numerically, the 23 zettajoules the oceans absorbed this yr may be written out as 23,000,000,000,000,000,000,000.
John Abraham, a professor of thermal science on the College of St. Thomas and one of many authors on the paper, says that he generally has bother placing this quantity into contexts laypeople perceive. Abraham gives up a pair choices. His favourite is evaluating the vitality saved within the ocean to the vitality of atomic bombs: The 2025 warming, he says, is the energetic equal to 12 Hiroshima bombs exploding within the ocean. (Another calculations he’s carried out embody equating this quantity to the vitality it could take to boil 2 billion Olympic swimming swimming pools, or greater than 200 instances {the electrical} use of everybody on the planet.)
“Final yr was a bonkers, loopy warming yr—that is the technical time period,” Abraham joked to me. “The peer-reviewed scientific time period is ‘bonkers’.”
The world’s oceans are its largest warmth sink, absorbing greater than 90 % of the surplus warming that’s trapped within the ambiance. Whereas among the extra warmth warms the ocean’s floor, it additionally slowly travels additional down into deeper elements of the ocean, aided by circulation and currents.
World temperature calculations—like those used to find out the most popular years on document—normally solely seize measurements taken on the ocean’s floor. (The examine finds that total sea floor temperatures in 2025 have been barely decrease than they have been in 2024, which is on document because the hottest yr since trendy information started. Some meteorological phenomena, like El Niño occasions, can even elevate sea floor temperatures in sure areas, which might trigger the general ocean to soak up barely much less warmth in a given yr. This helps to clarify why there was such a giant bounce in added ocean warmth content material between 2025, which developed a weak La Niña on the finish of the yr, and 2024, which got here on the finish of a powerful El Niño yr.) Whereas sea floor temperatures have risen for the reason that industrial revolution, due to our use of fossil fuels, these measurements don’t present a full image of how local weather change is affecting the oceans.
“If the entire world was coated by a shallow ocean that was solely a pair toes deep, it could heat up roughly on the similar pace because the land,” says Zeke Hausfather, a analysis scientist at Berkeley Earth and a coauthor of the examine. “However as a result of a lot of that warmth goes down within the deep ocean, we see typically slower warming of sea floor temperatures [than those on land].”