Global sea surface temperatures have reached an unprecedented level for June, surpassing records previously set during the 2023–24 El Niño years. The Copernicus Climate Change Service reported that waters hit 20.86°C on 21 June, edging past the 20.83°C mark observed in 2023 and 2024, and warned that rising ocean heat threatens weather patterns and marine ecosystems.
The warming is acutely visible in Europe. The Met Office said UK waters are enduring an extreme marine heatwave fuelled by last month's heat dome, with some areas 4–5°C warmer than usual. Parts of the Mediterranean are up to 6°C above the long-term average, while sections of the North Sea sit around 3°C above normal.
Professor Katherine Richardson of the University of Copenhagen described sea temperatures as a key marker of climate change. Professor John Pinnegar warned that such extreme conditions could trigger mass-mortality events for marine species.