What is the likelihood of marine heatwaves similar to the 2023 event occurring in the future?

According to the study, there is about a 10% chance of a marine heatwave of the same scale as the 2023 event occurring each year off the UK and Irish coasts.

What are the impacts of these marine heatwaves on the local ecosystems?

The heatwaves have significantly disrupted phytoplankton blooms, which are crucial for the entire marine food chain. They can also stress marine species and increase concentrations of harmful bacteria.

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Extreme Marine Heatwaves Threaten UK and Irish Coasts Annually

Q: How have the chances of such heatwaves changed over time in the Celtic Sea and North Sea?

The study found that the annual chance of a similar heatwave 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%.

7 Oct, 2025

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Summary

10% chance of marine heatwaves like 2023 each year
Temperatures 2.9°C above average for 16 days in 2023
Heatwaves disrupt phytoplankton blooms, harm marine life

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.