After sustained hot weather in Europe, sea temperatures around Britain are forecast to reach extreme levels this week, the country’s weather service said, threatening to disrupt and damage sea life.
A marine heat wave, which for days has pushed temperatures well above normal averages, is expected to intensify in the coming days, the Met Office said.
On Wednesday the office said that sea temperatures were sharply above normal, at a level it described as “severe,” one level below its highest category. It said that pockets of the English Channel could reach the highest category, “extreme,” this week.
The marine heat wave is in keeping with rising sea surface temperatures around the world, which have reached record highs for this time of year, according to two European climate and ocean monitoring organizations.
The warming waters are raising concerns among experts. Prolonged periods of marine heat can displace fish populations, damage plants like sea grasses and kelp, and fuel harmful algal blooms.
“They are comparable to forest fires, but for the ocean,” Marie Drévillon, head of operations and ocean monitoring at Mercator Ocean International, a French scientific organization, said of marine heat waves. The marine heat wave, she added, was “really impacting the environment, putting local ecosystems under life-threatening stress, causing mortality and species migration.”
High ocean temperatures can also keep temperatures in the atmosphere warmer, leading to hotter weather on land and increasing the likelihood of powerful storms and extreme weather events.
In Britain, the marine heat wave may push surface temperatures in some areas as far as 9 degrees Fahrenheit (5 degrees Celsius) above average, according to the Met Office, levels it categorizes as “extreme.” Mercator has forecast that the “extreme” level will be reached in some areas on Friday.
Average sea surface temperatures in the region have already reached 66 degrees Fahrenheit (19 degrees Celsius) — temperatures normally recorded in August after months of summer heat. In the first six months of 2026, large areas of the English Channel, Irish Sea and Bay of Biscay have been the warmest on record when compared to the same period over the last 30 years, according to Mercator.
The English Channel has been experiencing marine heat waves for much of 2026, the Met Office said. But water temperatures in the region began to soar after the recent “heat dome” event in June, which broke heat records in Britain and stifled countries across Europe.
More sunny and calm weather is forecast for Britain this week, which could prevent the ocean from releasing excess heat, Ségolène Berthou, an air-sea interaction specialist at the Met Office, said in a statement.
“This means the surface marine heat wave could intensify further, potentially reaching extreme levels in the south,” she said.
The Copernicus Climate Change Service and the Copernicus Marine Service, European organizations that monitor the climate and oceans, said in a joint statement last week that the average global sea surface temperature had reached 69.55 degrees Fahrenheit (20.86 degrees Celsius). The temperature broke records for this time of year that were previously set in 2023 and 2024.
The high temperatures were driven in part by the onset of El Niño, which meteorologists have forecast to be the strongest in decades. Carlo Buontempo, director of Copernicus, said in the statement that he expected more ocean temperature records to fall in the coming months.
