UK — The Met Office reported that UK waters are experiencing an "extreme" marine heatwave, the third and most intense observed in UK seas this year.

Marine temperatures in UK seas have averaged 2C higher than usual, with some areas experiencing temperatures 4-5C warmer than usual. Dr. Ségolène Berthou, an air-sea interaction specialist at the Met Office, said atmospheric conditions from last month's heat dome are driving the marine heatwave. "The ocean didn't have enough time to cool down between the two land heatwaves," Berthou said. She added, "There's no sign of an end to it."

Global sea surface temperatures have surpassed previous records for this time of year, according to the Copernicus Climate Change Service and the Copernicus Marine Service. Previous global records for sea surface temperatures at this time were established in 2023 and 2024. Oceans absorb more than 90% of the excess energy in the Earth system, which is primarily caused by burning fossil fuels.

Prof. John Pinnegar, a principal scientist and lead adviser at the Centre for Environment, Fisheries and Aquaculture Science, said extreme marine heatwave conditions can result in "mass-mortality events" for some marine species. "Prolonged periods of elevated sea water temperatures can also encourage new species to visit UK waters, establish new populations, potentially shaking up UK ecosystems," Pinnegar said. He noted that these conditions can alter the distribution of commercially important fish and shellfish. Record numbers of octopuses were found off the south-west coast of England last year. Temperatures in the UK are also on track to exceed 30C for up to 10 consecutive days.