Global ocean temperatures hit record high for June, surpassing 2023-24 El Niño levels
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Global ocean temperatures reached a record high for June, surpassing levels recorded during the extreme 2023-24 El Niño, with the average sea surface temperature across the world's tropical and temperate oceans now just under 21 degrees Celsius.
Before widespread industrialisation around 1870, the average sea surface temperature was about 19.6 degrees Celsius. Scientists say the increase reflects the vast amount of heat absorbed by the oceans, which have taken in more than 90% of the excess heat trapped by greenhouse gas emissions.
According to the report, the amount of heat added to the oceans in 2025 was equivalent to the energy released by about 12 Hiroshima-sized atomic bombs every second.
Scientists say the warming oceans are likely to intensify cyclones, increase atmospheric humidity, produce heavier rainfall and contribute to more frequent and severe heatwaves over land.
The developing El Niño in the tropical Pacific is expected to strengthen these effects. Sea surface temperatures in parts of the central and eastern Pacific are already about 1.24 degrees Celsius above average, while subsurface temperatures in the eastern Pacific are more than 6 degrees Celsius above normal.
Europe is currently experiencing a severe heatwave, with parts of the Mediterranean Sea up to 6 degrees Celsius warmer than the long-term average and sections of the North Sea about 3 degrees Celsius above average.
Scientists expect 2026 to be among the hottest years on record, with temperatures likely to remain elevated into 2027 as heat stored in the oceans continues to influence the atmosphere.
They also warned that prolonged marine heatwaves pose growing risks to coral reefs, seagrass meadows and other marine ecosystems, while stressing that continued ocean monitoring and climate forecasting are essential for preparing for increasingly severe weather events.