The “major part” of the warming of European seas is due to climate change, adding up to 2°C of heat to the Mediterranean this summer and expanding the affected areas, with “serious” consequences in particular for marine life, a scientific study indicates on Wednesday. “From the Atlantic off the coast of Ireland to the Mediterranean, European seas are experiencing an alarming rise in temperatures”, with this summer up to 6°C above normal in certain Mediterranean areas, underlines Thomas Frölicher of the University of Bern, one of the authors.
“Our research clearly shows that this increase is due to climate change, in particular the continued burning of fossil fuels,” he adds. By combining observational data and climate models to compare the current climate to a hypothetical climate without human-caused warming, researchers from the World Weather Attribution (WWA) collective estimated that climate change this summer added about 2°C to temperatures in the Mediterranean, 1.4°C in the Bay of Biscay and Iberian Peninsula region and 1.3°C in the Celtic region (Ireland and western Britain).
In July 2026, the world's oceans reached record heat for the second month in a row, according to the European Copernicus Observatory. A particularly marked phenomenon in Europe, underlines the WWA. During the 14 hottest days of 2026, warming compared to normal reached 3.1°C in the western Mediterranean and 2.6°C in the eastern Mediterranean, compared to 1.5°C in the Bay of Biscay and Iberian Peninsula region and 1.2°C in the Celtic region.
Under the effect of global warming, marine heat waves have also spread to European seas. In 2026, they affect 90% of the Bay of Biscay area and the Iberian coast and 80% of the western Mediterranean, compared to 40% in these two areas if the Earth had not warmed by 1.4°C. In the eastern Mediterranean, it is even more spectacular: almost 70% of the area is currently affected by marine heatwaves, compared to 9% in a colder climate.
Such events would have been “very rare” without global warming, the study points out. “Every additional tonne of carbon we emit pushes European coastal temperatures and ecosystems into uncharted territory,” explains Thomas Frölicher. Warming seas increase air temperature and humidity on the coasts, increasing nighttime temperatures and heat stress.
Marine and terrestrial heat waves “are undoubtedly linked (...) and can reinforce each other. (...) These are two sides of the same coin,” underlined Friederike Otto, professor at Imperial College London during a press briefing. Warming seas can also promote certain extreme weather phenomena, notably heavy precipitation, by increasing evaporation and therefore atmospheric humidity.
If “warmer waters may seem pleasant for swimming in cooler countries, like mine, the consequences for marine life (...) are much more worrying,” notes Claire Bergin, from the University of Maynooth (Ireland). Marine heat can cause massive mortality of corals, sponges and algae, disrupt food chains and reduce populations of seabirds and mammals, with economic consequences for fishing, aquaculture or tourism.
According to John Bruno, a marine ecologist at the University of North Carolina, “minimal warming (...) is enough to push organisms beyond the threshold that kills them”: for corals, 1°C is enough. Certain species, such as jellyfish, can benefit, others migrate further north, “there are winners and losers,” explains the scientist. But “as ocean temperatures continue to rise, we are rapidly approaching the absolute biological limits of adaptation for many species,” emphasizes John Bruno.
On a planet warmed by 2.8°C in 2100, if humanity does not drastically reduce its greenhouse gas emissions, “events like those observed in 2026 would then be another 1.3 to 1.9°C warmer,” underlines the study. Marine heatwaves could occur “every year” in European seas and become “the new normal”, warns Catherine Gregory, of the University of Bern.
