Extreme Marine Heatwaves Threaten UK and Irish Coasts Annually

According to a study published in October 2025, the unprecedented marine heatwave that occurred off the UK and Irish coasts in the summer of 2023 is now estimated to have a 10% chance of happening each year. The heatwave saw temperatures in the shallow seas around the UK, including the North Sea and Celtic Sea, reach 2.9°C above the June average for an extended period of 16 days.

The study, conducted by researchers from the University of Exeter, the Met Office, and the Centre for Environment, Fisheries and Aquaculture Science (Cefas), used climate models to assess the likelihood of such extreme heatwaves. They found that the annual chance of a similar event in the Celtic Sea has risen from 3.8% in 1993 to 13.8% now, while in the central North Sea, the chance has increased from 0.7% to 9.8%.

While the full impact on the marine ecosystem is still being assessed, scientists know the heatwave has significantly disrupted phytoplankton blooms, which are crucial for the entire food chain. Heatwaves can also stress marine species and increase concentrations of bacteria that can harm humans.

"Our findings show that marine heatwaves are a problem now - not just a risk from future climate change," said Dr. Jamie Atkins, who led the study. The researchers warn that these extreme events will become more frequent as steady climate warming continues to impact the oceans.