The Met Office has confirmed that UK waters are being hit with an "extreme" marine heatwave, with sea surface temperatures averaging 2C higher than usual and some areas reaching 4-5C above normal. This comes as global ocean temperatures have surpassed previous records for this time of year, set in 2023 and 2024, according to the Copernicus Climate Change Service and the Copernicus Marine Service.
Heat dome drives rapid warming
The rapid development of elevated temperatures is linked to last month's heat dome, which brought Europe its worst ever heatwave. Scientists said the heatwave would have been impossible without the climate crisis. Dr Ségolène Berthou, an air-sea interaction specialist at the Met Office, explained that atmospheric conditions are driving the marine heatwave. "The ocean didn't have enough time to cool down between the two land heatwaves," she said.
This is the third and most intense marine heatwave the UK has seen this year. Berthou noted that some locations are experiencing "severe" conditions, with water temperatures 4-5C warmer than usual. "There's no sign of an end to it," she added.
Oceans absorb excess energy
Oceans absorb more than 90% of the excess energy in the Earth system, primarily caused by burning fossil fuels. The UN secretary general, António Guterres, urged the world to treat the arrival of El Niño conditions as an "urgent climate warning." He said: "The only effective response is climate action equal to the crisis: ending the addiction to fossil fuels, accelerating the shift to renewables, protecting the most vulnerable, and delivering early warning systems for all."
Risk of mass mortality events
Prof John Pinnegar, principal scientist and lead adviser at the Centre for Environment, Fisheries and Aquaculture Science, warned that extreme marine heatwave conditions can result in "mass-mortality events" for some marine species and alter the distribution of commercially important fish and shellfish. "Prolonged periods of elevated sea water temperatures can also encourage new species to visit UK waters, establish new populations, potentially shaking up UK ecosystems," he said.
Last year, record numbers of octopuses were found off the south-west coast of England, transforming the fishing industry and marine ecosystem. A record 100 tonnes of octopus was sold in one day at Brixham market last month.
