European seas have reached exceptionally high temperatures this summer, with climate change responsible for much of the warming, an international team of researchers said in a report.
Sea surface temperatures along almost all European coasts are above the 1990-2020 average, with the western Mediterranean, the Bay of Biscay and the Iberian Peninsula among the worst affected. Temperatures in some areas are more than 6 degrees Celsius above normal.
The World Weather Attribution (WWA) team compared July sea surface temperatures with climate models to assess the impact of global warming. It found climate change had raised average temperatures by about 2 degrees in the Mediterranean, 1.4 degrees around the Bay of Biscay and western Iberian coast and 1.3 degrees around Ireland and Britain’s western coast.
Heatwaves affected 90% of the coasts around the Bay of Biscay and Iberian Peninsula this year and 80% of the western Mediterranean. Without human-caused warming, currently about 1.4 degrees above pre-industrial levels, the researchers estimated the figures would have been around 40% in both regions.
Warmer seas can disrupt marine ecosystems and food chains, potentially reducing populations of marine mammals and seabirds. Fishermen in south-west England have also reported a sharp rise in common octopus sightings since 2025, a species native to warmer waters off North Africa.
Higher sea temperatures can also fuel severe storms, the researchers said, citing the deadly floods in Spain’s Valencia region in autumn 2024.