The world’s oceans recorded their hottest June on record, prompting fresh warnings from scientists about accelerating climate change and intensifying weather extremes.

According to data released by the European Union’s Copernicus Climate Change Service (C3S) and Copernicus Marine Service, the combination of human-driven climate change and the return of the naturally occurring El Niño phenomenon is pushing the planet into a new and potentially dangerous phase.

The average sea surface temperature across the world’s oceans—which cover roughly two-thirds of the Earth—reached 20.98°C in June, surpassing the previous June record of 20.89°C, set in 2024. The data also show that the first half of 2026 ranks as the second warmest on record, behind only the same period in 2024.

Carlo Buontempo, Director of the Copernicus Climate Change Service, said the latest observations could signal the beginning of a new phase that is once again taking the planet into uncharted territory. He added that with ocean temperatures already at unprecedented levels and El Niño strengthening, further climate records are likely to fall in the months ahead.

The most pronounced warming has been recorded in the central and eastern tropical Pacific, where sea surface temperatures reached a record 26.91°C in the first half of the year. Scientists warn that a strengthening El Niño could intensify extreme global weather, while stressing that oceans—absorbing about 90% of excess human-caused heat—are nearing their limits.

Since the beginning of the year, marine heatwaves have affected 82% of the global ocean surface, with half of those areas experiencing conditions classified as strong to extreme.

The Mediterranean has emerged as one of the regions of greatest concern. As a semi-enclosed and highly vulnerable sea, it experienced marine heatwaves across 98% of its surface during the first half of the year. In June, sea surface temperatures climbed to a record 23.34°C. In the northwestern Mediterranean, a recent heatwave pushed temperatures 5.2°C above seasonal averages, driven by the exceptional heat that swept across Europe.

The impacts are already visible, with marine heatwaves causing mass die-offs among vulnerable species such as corals, sea urchins and shellfish, while warmer oceans fuel more powerful storms. Copernicus warns this raises the risk of severe weather, particularly across the Mediterranean.