Since 2018, an international team of researchers has been analyzing data on ocean heat absorption annually. By 2025, this absorption reached record-breaking levels for the eighth consecutive year.
Findings published on Friday in the journal Advances in Atmospheric Science reveal that in 2025, the oceans absorbed an additional 23 zettajoules of heat— the highest recorded since measurements began in the 1960s. This figure eclipses the 16 zettajoules absorbed in 2024 according to research conducted by over 50 scientists across the United States, Europe, and China.
A joule is a standard unit of energy measurement. While a single joule powers a small light bulb for a second, a zettajoule equals one sextillion joules. The 23 zettajoules absorbed this year are numerically equivalent to 23,000,000,000,000,000,000,000 joules.
John Abraham, a thermal science professor at the University of St. Thomas and one of the study's authors, explained the magnitude of this number by comparing the energy absorbed by the oceans to atomic bomb explosions: the ocean warming in 2025 equates to the energy of 12 Hiroshima bombs. Alternatively, it matches the energy required to boil 2 billion Olympic pools, or over 200 times global electricity usage.
“Last year was a bonkers, crazy warming year—that’s the technical term,” Abraham humorously remarked, adding that the peer-reviewed scientific term is indeed “bonkers.”
Oceans act as the planet’s largest heat sink, absorbing more than 90% of excess atmospheric warming. As excess heat warms the ocean surface, it gradually penetrates deeper layers, facilitated by ocean circulation and currents.