In 2025, ocean temperatures were higher than at any point since modern records began, a study published in the Advances in Atmospheric Sciences journal has found.
Ocean heat content increased by 23 zettajoules in 2025, which is comparable to around 37 years’ worth of global primary energy consumption (at 2023 levels), marking a continuation of sustained ocean warming as a result of rising greenhouse gas emissions, the study noted.
The study involved more than 50 scientists from 31 research institutions around the world, drawing on observational data and ocean reanalysis from China, Europe and the United States.
As it noted, while ocean temperatures have risen overall, some areas are warming faster than others – including the the tropical and South Atlantic and North Pacific Oceans, and the Southern Ocean.
Ocean surface
Around 16% of the global ocean’s surface reached a record-high heat content last year, while around one third of ocean areas reported temperates in their top three in recorded history.
As the long-term data indicated, heat stored in the upper 2,000 metres of the ocean has increased steadily since the 1990s, with a slight increase in the rate of warming in recent years.
At the surface, global average sea-surface temperatures (SST) in 2025 were at their third-highest level on record, at around 0.5 °C (approximately 1°F) above the 1981–2010 average baseline. SST was slightly lower in 2025, compared to 2023 and 2024, in part due to the shift from El Niño to La Niña conditions in the tropical Pacific.
Weather patterns
As the study noted, warmer sea surface temperatures influenced weather patterns by increasing evaporation and atmospheric moisture, leading to widespread flooding and disruption throughout much of Southeast Asia, drought in the Middle East, and flooding in Mexico and the Pacific Northwest during 2025.
‘Rising ocean heat drives global sea-level rise via thermal expansion, strengthens and prolongs heatwaves, and intensifies extreme weather by increasing heat and moisture in the atmosphere,’ the study noted. ‘As long as the Earth’s heat continues to increase, ocean heat content will continue to rise and records will continue to fall.’ Read more here.
