Carbon pollution has fuelled ‘massive expansion’ of marine heatwaves in Europe, study finds

Hottest periods this year in most sea regions would have been ‘virtually impossible’ in a preindustrial climate

Carbon pollution has fuelled a “massive expansion” of marine heatwaves in Europe this summer, research has found, with some waters recording temperatures 6C higher than normal.

The hottest fortnights of this year would have been “virtually impossible” in a preindustrial climate in three of the four sea regions studied, according to analysis by World Weather Attribution , while in the Celtic region, which covers much of the water around the British Isles, heat hit levels that used to strike just once a century.

Climate breakdown was responsible for about two-thirds of the observed excess heat, the researchers said, having warmed waters by about 2C in the Mediterranean, 1.4C in the Bay of Biscay and Iberian Peninsula, and 1.3C around Ireland and the Channel.

The rapid analysis, which has not yet been submitted for peer review, comes as Europe reels from one of its hottest summers on record. Relentless heatwaves have killed tens of thousands of people and stripped plants of moisture, ruining crops and fuelling large wildfires .

While hot seas receive little attention, they can lead to the death of habitat-forming species such as corals and macroalgae, disrupting ecosystems and leading to large-scale mortality of fish and seabirds. They also raise dangerous overnight temperatures in coastal regions, as oceans cool more slowly than land.

Claire Bergin, a scientist at the Irish climate analysis research units of Maynooth University in Ireland, and co-author of the report said: “While warmer waters for swimming may sound appealing to beachgoers in cooler countries like mine, the impacts on marine life beneath the surface is more serious.

“This has the potential to completely reshape ecosystems that coastal communities rely on for food and income, and drive damaging extreme weather on land too.”

The study, the group’s first to focus on the effect of fossil fuel burning on marine heat , compared observed sea surface temperatures with simulations from climate models to asses the role of global heating.

They found a “massive expansion” of marine heatwaves in 2026 that has so far hit 90% of the Bay of Biscay and Iberian coast region, and 80% of the western Mediterranean. In a hypothetical climate not heated by humanity, scientists said they would expect those figures to be half as big.

Removing the effect of climate breakdown cut the expected marine heatwave area from 70% to 9% in the eastern Mediterranean, and from 80% to 30% in the Celtic region, the analysis showed.

Separate research published in January found that marine heatwaves lead to more intense rainfall on land. Globally, about 5-25% of extreme rainfall over coastal land is accompanied by a nearby marine heatwave, the study found.