Photo credit: Matt Hardy
The marine heatwave that has gripped UK waters for much of 2026 could reach extreme levels this week, the Met Office has warned. Surface waters around north-west Europe are running at strong to locally severe conditions, reaching temperatures normally seen in August and averaging around 2°C above normal, with some offshore areas along the English and Welsh coasts 4 to 5°C warmer than usual.
Why the heat is persisting
The warmer seas followed last week’s exceptional heat over land, driven by a heat dome that stalled over Europe and trapped heat for days, pushing past the previous June record set in 1976. With another warm spell forecast for the coming week, the sea surface will have little chance to cool, raising the prospect of the marine heatwave tipping into the extreme category, one that has scarcely been recorded in UK seas.
Dr Segolene Berthou, an air-sea interaction specialist at the Met Office, said such conditions would be highly unusual for UK waters, noting that marine heatwaves had developed rapidly after the recent heat dome. The English Channel has been in marine heatwave conditions for much of 2026, leaving that region especially exposed to further warming.
The global picture
The UK conditions sit within a wider ocean warming trend. The EU’s Copernicus Climate Change Service and Copernicus Marine Service confirmed that global sea surface temperatures have passed the previous records for this time of year, set in 2023 and 2024. The new highs were expected following the onset of El Niño, the Pacific warming pattern that is one of several drivers pushing up global temperatures.
Consequences for marine life
John Pinnegar, principal scientist and lead climate change adviser at the Centre for Environment, Fisheries and Aquaculture Science, said prolonged warm spells can shift fish populations, damage seagrass and kelp habitats, and raise the likelihood of harmful algal blooms. He warned such changes can trigger mass-mortality events for some species and alter the distribution of commercially important fish and shellfish.
Pinnegar pointed to a recent bloom of common octopus, which has had serious consequences for crab and lobster fisheries in South West England, as an example of how warming waters can draw new species into UK seas and reshape established ecosystems. Warmer surface temperatures also carry a public safety message: the Met Office cautioned that UK waters remain cold enough below the surface to cause cold-water shock, and urged people to use lifeguarded beaches.