Since 2018, a group of researchers from around the world has crunched the numbers on how much heat the world’s oceans are absorbing each year. In 2025, their measurements broke records once again, making this the eighth year in a row that the world’s oceans have absorbed more heat than in the years before.

The study, which was published Friday in the journal Advances in Atmospheric Science, found that the world’s oceans absorbed an additional 23 zettajoules’ worth of heat in 2025, the most in any year since modern measurements began in the 1960s. That’s significantly higher than the 16 additional zettajoules they absorbed in 2024. The research comes from a team of more than 50 scientists across the United States, Europe, and China.

A joule is a common way to measure energy. A single joule is a relatively small unit of measurement—it’s about enough to power a tiny lightbulb for a second, or slightly heat a gram of water. But a zettajoule is one sextillion joules; numerically, the 23 zettajoules the oceans absorbed this year can be written out as 23,000,000,000,000,000,000,000.

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