The world’s oceans absorbed more heat in 2025 than in any year since modern measurements began, says climate scientist Dr Kevin Trenberth.
Heat stored in the upper 2km of the ocean increased by an estimated 23 zettajoules last year, based on research co-authored by Trenberth, an honorary academic at the University of Auckland and affiliate of the US National Center for Atmospheric Research. The increase is equivalent to hundreds of millions of Hiroshima-scale atomic bombs, or around 200 times global electricity consumption in 2023.
“The ocean is the hottest on record,” said Trenberth. “We’re looking at creating a very different planet – do we really want to do that?”
The findings come from a study led by the Chinese Academy of Sciences and published in the journal Advances in Atmospheric Sciences. The research involved an international team of scientists analyzing long-term ocean heat content trends.
Oceans absorb most of the excess heat trapped by greenhouse gases. Rising ocean heat contributes to global sea-level rise through thermal expansion and intensifies extreme weather by adding heat and moisture to the atmosphere.
While global sea-surface temperatures in 2025 were the third highest on record, they were slightly lower than in 2023 and 2024. Researchers attributed this to the transition from El Niño to La Niña in the tropical Pacific. However, the decline was small compared with the sharp increase recorded in 2023.
Warmer ocean surfaces increase evaporation, which can lead to heavier rainfall, stronger tropical cyclones and more frequent extreme weather events.
Trenberth pointed to particularly high sea-surface temperatures in parts of the southwest Pacific: “Sea surface temperatures were exceptionally high near and around New Zealand during December 2025 into January 2026 from La Niña and global warming. There’s a link with our unstable showery recent weather.”
The study also highlights uncertainty around space-based climate observations for monitoring climate change, an apparent reference to US capabilities under the Trump administration.
In related news, China develops deep diffusion model to extend severe convective weather nowcasting to four hours
