European waters recorded their hottest summer months since reliable satellite measurements began in 1982, according to a Reuters analysis of sea-surface temperatures. The warming set records from the English Channel to the Mediterranean Sea and is reshaping marine ecosystems, with scientists warning that increasingly severe marine heatwaves threaten fisheries and coastal communities.
European seas averaged 21.6 C (70.9 F) between June and August, the highest in 45 years of available data. An offshore buoy near Mallorca recorded 33.02 degrees Celsius (91.44 degrees Fahrenheit) on August 5, the highest temperature registered in the Spanish port authority's buoy network.
Jean-Pierre Gattuso, a senior research scientist at France's National Centre for Scientific Research, said the pace of the records was striking. 'What is surprising is the speed at which this occurs. Records are broken almost every day in many places.'
Scientists define a marine heatwave as five or more days when water temperatures sit well above an area's historic norm. They say events such as this year's are becoming more frequent, more intense and more widespread as greenhouse-gas emissions raise atmospheric temperatures around the world.
The Bay of Biscay, whose waters have traditionally been cool, illustrates the scale of the change. The sea averaged 21.4 C (70.5 F) between June and August, more than 2.4 degrees (4.4 degrees) above the 1991-2020 average. U.S. National Oceanic and Atmospheric Administration readings reached 23.2 C (74 F) on August 13, the highest temperature of the satellite era in the Bay of Biscay.
During the 1980s, the Bay of Biscay had a handful of marine heatwave days in an average year. By the end of August 2026, it had recorded 186, accounting for more than three out of every four days.
The warmer water is affecting kelp forests along the Asturias coast. Jose Manuel Rico Ordas, who has sampled the rugged coastline since 2010, estimates that roughly 95% of the large, brown seaweed stands have disappeared. Kelp generally requires cold water, typically below 20 C (68 F), to survive.
Kelp forests provide habitat for a range of species associated with fisheries. Rico Ordas said their decline has been accompanied by the disappearance of animals that had lived in those ecosystems. 'We are finding no more lobster, no more crayfish, no more sea urchins and many other species that are associated with the good status of kelp forests.'
The available data show a warming event spanning several European seas, alongside severe local damage to kelp-dependent habitat. The brief does not quantify fishing-industry losses from the 2026 heatwaves, set out recovery prospects for the affected kelp forests or identify policy responses by governments and fisheries authorities. Scientists' warning is that greenhouse-gas-driven warming is making such marine heatwaves more common, more intense and more extensive.
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