Carbon pollution caused by human activity has dramatically increased the scale and intensity of marine heatwaves across European waters during the summer of 2026, according to research from World Weather Attribution. Some parts of Europe experienced sea temperatures as much as 6C above normal, creating potentially serious consequences for marine ecosystems, coastal communities and extreme weather.
Researchers examined four European marine regions and found that the hottest two-week periods recorded this year would have been virtually impossible in three of them without human-caused climate change. In the Celtic region surrounding much of the British Isles, temperatures reached levels that would historically have occurred only about once every 100 years. The analysis estimates that climate change accounted for roughly two-thirds of the excess ocean heat observed.
The effect varied between regions. Human-caused warming increased temperatures by approximately 2C in the Mediterranean, 1.4C around the Bay of Biscay and Iberian Peninsula, and 1.3C around Ireland and the English Channel. Researchers reached these conclusions by comparing observed sea surface temperatures with climate-model simulations representing a world without human-caused global warming.
The geographical expansion of marine heatwaves has been particularly striking. About 90% of the Bay of Biscay and Iberian coast region and 80% of the western Mediterranean have been affected during 2026. Researchers estimate that without human-caused warming, the affected areas would have been roughly half as large. In the eastern Mediterranean, removing the influence of climate change reduced the estimated area affected from 70% to just 9%. In the Celtic region, it fell from 80% to 30%.
Although extreme temperatures on land often attract greater attention, unusually warm seas can have major environmental consequences. Prolonged ocean heat can damage habitat-forming species including corals and macroalgae, disrupting entire marine food webs and contributing to fish and seabird mortality. Coastal economies that depend on fishing and healthy marine ecosystems could therefore face significant economic consequences.
Warm oceans can also influence conditions on land. Because water releases stored heat more slowly than land, unusually warm seas can keep overnight temperatures elevated in coastal areas. Separate research has also linked marine heatwaves with more intense rainfall. Globally, an estimated 5–25% of extreme rainfall events over coastal land occur alongside nearby marine heat events. Extreme downpours associated with particularly strong ocean heat can produce 20–30% more rainfall.
The findings come as Europe experiences one of its hottest summers on record, with extreme heat contributing to deaths, crop damage, drought conditions and wildfires. Europe is already the world’s fastest-warming continent, making its seas increasingly vulnerable to rising temperatures.
Scientists warn that the widespread conditions observed in 2026 should no longer be viewed as isolated anomalies. Instead, the expansion of marine heatwaves demonstrates how climate change is reshaping European seas on a large scale. Continued fossil fuel use could intensify ocean warming further, increasing pressure on marine ecosystems while also amplifying risks for coastal communities, food supplies and weather patterns across Europe.