The oceans absorbed approximately 23 zettajoules more heat in 2025 compared to the end of 2024, marking it as the hottest year on record for ocean heat content. This increase is equivalent to around 365 million Hiroshima-sized atomic bombs. The latest findings, published in the journal Advances in Atmospheric Sciences by a team of 55 scientists, indicate that marine warming has reached unprecedented levels for the ninth consecutive year.
Rising greenhouse gas emissions are identified as the primary cause of this trend, contributing to severe weather events and rising sea levels. The report highlights multiple catastrophic occurrences linked to marine warming in 2025, including monsoon rains that resulted in over 1,300 fatalities in Southeast Asia and flash floods in Central Texas that claimed at least 138 lives, including campers.
About 14% of the global ocean area hit record warm temperatures last year, with significant heating observed in the Southern Ocean and parts of the Mediterranean and Indian Oceans. The research underscores the ongoing trend of increasing ocean heat content, which is expected to persist until net-zero emissions are realized.