World's oceans set record-high heat for ninth straight year

A scientific report found global ocean heat content rose by about 23 zettajoules in 2025, marking the ninth consecutive year of record marine warming; the authors link the trend mainly to rising greenhouse gas emissions.

A report published in Advances in Atmospheric Sciences found that global ocean heat content reached a record high in 2025. Researchers measured temperature changes down to 2,000 meters and estimated the oceans held about 23 zettajoules more heat than at the end of 2024. This marks the ninth straight year of record marine warming, and the authors attribute the trend primarily to rising greenhouse gas emissions. The report notes widespread unusually high ocean temperatures in several regions and links the warming to changes in weather, sea level, and marine ecosystems. Key findings: - Global ocean heat content increased by about 23 zettajoules in 2025, the highest value on record. - 2025 is the ninth consecutive year of record marine warming. - About 14% of the global ocean area reached its warmest state on record, with larger fractions among their top three or top five warmest years. - The researchers identify rising greenhouse gas emissions as the main driver and connect ocean heat gain to stronger storms, sea-level rise, and stress on marine ecosystems. Summary: The report documents persistent, widespread ocean warming with implications for climate systems, sea-level rise, and marine life. The authors say global ocean heat content is expected to continue rising until net-zero greenhouse gas emissions are achieved. They emphasize the need for strengthened ocean monitoring and research into how heat is redistributed to better understand future impacts and trends.