Global ocean heat hits record high for 9th year in 2025, report says

Despite weak La Nina conditions, global ocean warming continued in 2025 due to increased greenhouse gas concentrations, reflecting long-term heat accumulation in the climate system, a report released on Friday said.

Published in the journal Advances in Atmospheric Sciences, the report showed that the global ocean heat content in the upper 2,000 meters set a record for the ninth consecutive year, increasing by 23 zettajoules compared to 2024. This amount of energy could power an electric car to circle Earth's equator a trillion times.

The ocean's top 2,000 meters, which absorb about 93 percent of the extra heat in Earth's system, serve as a critical indicator of global warming's impact. The report, led by the Institute of Atmospheric Physics of the Chinese Academy of Sciences, involved 55 scientists from 31 research institutes in countries including China, the United States, France, and Italy.

Multiple datasets from China and abroad consistently indicated a trend of ocean warming, with a significant increase in the rate since the 1990s.

The global mean surface temperature in 2025 was slightly lower than in 2024, aligning with the development of La Nina conditions — a climate pattern marked by stronger-than-normal trade winds and cooler sea surface temperatures in the central and eastern equatorial Pacific — starting early 2025.

However, it still remained exceptionally high by historical standards and ranked as the third-warmest year since 1955, the report said.

The web link to the academic paper is as follows: https://doi.org/10.1007/s00376-026-5876-0