Ocean Temperatures Reach Record High for June

Global average sea surface temperature reached just under 21°C across tropical and temperate oceans in June. The figure surpasses records set during the 2023-24 El Niño years. Before widespread industrialisation in 1870, the same average stood at about 19.6°C. More than 90% of extra heat trapped by greenhouse gases has entered the oceans.

2025 the added heat equalled roughly 12 Hiroshima-scale nuclear bombs per second. Comparable ocean temperatures last occurred around 120,000 years ago, before the most recent ice age. An El Niño is now forming in the tropical Pacific. Sea surface temperatures there are about 1.24°C above average, with subsurface waters more than 6°C above average.

Mediterranean are up to 6°C above the long-term average. Sections of the North Sea are up to 3°C warmer than average. Europe is experiencing a record-breaking heatwave while surrounding seas remain exceptionally warm.

Hotter oceans increase evaporation, humidity, and the intensity of rainfall and tropical cyclones. Marine heatwaves threaten coral reefs, seagrass meadows, and coastal ecosystems. A typical El Niño lasts about one year. Its strongest influence on atmospheric temperatures occurs toward the end of the cycle, making 2027 likely to be hotter than 2026.

Improved forecasts now predict marine heatwaves three to four months ahead in several regions. Authorities have used these forecasts to adjust fishery limits and begin conservation measures. Last year funding for climate data networks was reduced. This year an ocean monitoring network faced proposed cuts before funding was restored.