As drought spread and wildfires raged across Europe this summer, the extraordinary heat didn't stop at the shoreline. European waters notched their hottest summer months since satellite sensors began providing reliable data in 1982, according to an analysis of temperatures recorded at the seas’ surface.
Records fell from the English Channel to the Mediterranean Sea, with an offshore buoy near Mallorca recording a temperature of 33.02 degrees Celsius (91.44 degrees Fahrenheit) on August 5, the highest ever registered in the Spanish port authority’s buoy network.
Scientists warn that events like this year’s marine heatwaves are becoming more frequent, more intense and more widespread as greenhouse-gas emissions drive up atmospheric temperatures around the globe. The world’s oceans absorb the majority of the excess heat and retain it longer than the land or atmosphere.
That’s transforming marine ecosystems, with catastrophic consequences for some European fisheries and the people who rely on them, according to a review of the scientific literature and interviews with more than a dozen researchers, fishing industry sources and analysts. Species that have sustained some coastal communities in Spain and southern England for generations are disappearing, as unfamiliar arrivals surge into newly hospitable waters. The cool waters of the Bay of Biscay once gave life to extensive kelp forests. "What is surprising is the speed at which this occurs," Jean-Pierre Gattuso, senior research scientist at France's National Centre for Scientific Research, said of Europe’s warming seas. “Records are broken almost every day in many places.”Taken together, European seas averaged 21.6 C (70.9 F) between June and August, the highest in 45 years of available data.
Few areas strayed further from the norm this summer than the Bay of Biscay, off the Atlantic-facing coast of France and Spain. Stretching from Cape Ortegal in Galicia to the Pointe de Penmarch in southern Brittany, the bay's traditionally cool waters averaged 21.4 C (70.5 F) between June and August, more than 2.4 degrees (4.4 degrees) above the 1991-2020 average. Readings from the U.S. National Oceanic and Atmospheric Administration peaked on August 13 at 23.2 C (74 F), the highest of the satellite era.
Scientists define a marine heatwave as five or more days of water temperatures well above an area’s historic norm. In the 1980s, the Bay of Biscay averaged a handful of heatwave days per year. By the end of August, it had logged 186 this year, more than three out of every four days.
The Bay of Biscay’s cool waters, long prized by Spaniards seeking relief from the heat of the Mediterranean coast, were immortalized in Ernest Hemingway's 1926 novel "The Sun Also Rises." The book’s protagonist recovers after weeks of dissolution on the northern beaches of San Sebastian. "Now if you want to swim in cold water, you have to go to the westernmost portion of Galicia,” in the far northwestern corner of Spain, said Jose Manuel Rico Ordas, a professor of marine ecology at the University of Oviedo in the northern Asturias region. Galicia benefits from strong winds that push warm surface water away from the coast during the summer months, allowing cold, deep-sea water to take its place in a process known as upwelling. Rico Ordas has been spending summers on the bay since he was a child and now studies its transformation.