World's oceans stored more extra heat in 2025 than ever before

The world's oceans stored more heat in 2025 than in any other year since modern record-keeping began, a new study reveals.

The ocean's heat increase last year amounted to a staggering 23 Zetta Joules of energy – equivalent to 37 years of global energy consumption at the 2023 level. 

The findings, published Friday in the journal Advances in Atmospheric Sciences, stem from a major collaboration involving over 50 scientists from 31 research institutions worldwide. 

By integrating data from across Asia, Europe and the Americas, the scientists concluded that the heat content in the upper 2,000 meters of the ocean reached its highest recorded level in 2025, underscoring a clear and sustained upward trend. This fuels rising sea levels, intensifies storms, hurricanes and typhoons, and exacerbates and prolongs marine heatwaves with devastating impacts on marine ecosystems.

The study highlights that ocean warming is not uniform. In 2025, about 16 percent of the world's ocean area saw record-high heat, while an additional 33 percent ranked among the top three warmest years in their historical records. The fastest warming occurred in regions including the tropical and South Atlantic, the North Pacific, and the Southern Ocean.

While heat stored in the deep ocean set a new record, surface temperatures exhibited a slightly different pattern. The global average sea-surface temperature in 2025 was the third warmest on record, remaining about 0.5 degrees Celsius above the recent baseline and slightly below the peaks observed in 2023 and 2024.

Nevertheless, these elevated surface temperatures have significant real-world impacts, driving increased evaporation and heavier rainfall. They played a key role in intensifying extreme weather events in 2025, such as severe flooding in Southeast Asia and Mexico and drought in the Middle East, the study said.

Scientists emphasize that as long as the planet continues to accumulate heat, ocean heat records will keep being broken.