World's oceans set new heat record in 2025, study finds

A new international study reveals that the world's oceans absorbed more heat in 2025 than in any other year since modern record-keeping began.

Published Friday in the journal Advances in Atmospheric Sciences, the analysis shows that the ocean's heat increase last year amounted to a staggering 23 zettajoules of energy – equivalent to 37 years of global energy consumption at 2023 levels.

The findings stem from a major collaboration involving over 50 scientists from 31 research institutions worldwide. By integrating data from leading international centers and independent research groups 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.

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.

The study warns that continued ocean heating carries profound consequences. It directly contributes to sea-level rise through thermal expansion, exacerbates and prolongs marine heatwaves, and adds more heat and moisture to the atmosphere, which can strengthen storms and other extreme weather phenomena.

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