Researchers warn the extreme 2023 marine heatwave around the UK and Ireland — once called "unheard of" — could now occur about 10% of years. That event raised sea temperatures nearly 38°F (≈21°C) above average for more than two weeks, disrupting fish, shellfish and kelp ecosystems. Scientists say cutting fossil-fuel emissions, restoring kelp and seagrass, and improving monitoring can help protect coastal communities and marine life.
Once "Unheard Of": 2023 Marine Heatwave Could Become an Annual Threat to UK and Ireland
Researchers warn the extreme 2023 marine heatwave around the UK and Ireland — once called "unheard of" — could now occur about 10% of years. That event raised sea temperatures nearly 38°F (≈21°C) above average for more than two weeks, disrupting fish, shellfish and kelp ecosystems. Scientists say cutting fossil-fuel emissions, restoring kelp and seagrass, and improving monitoring can help protect coastal communities and marine life.
03:43 PM, 11/11/2025Environment
Scientists warn extreme marine heatwaves may become routine around the UK and Ireland
Researchers from the University of Exeter, the Met Office and the Centre for Environment, Fisheries and Aquaculture Science (CEFAS) say the extraordinary marine heatwave that struck in 2023 — once described as "unheard of" — could now occur roughly one year in ten.
The team estimates there is about a 10% chance in any given year of a repeat of the 2023 event, which kept sea temperatures nearly 38°F (≈21°C) above long-term averages for more than two weeks. That episode severely disrupted marine ecosystems and threatened fish, shellfish and kelp forests that underpin coastal food chains.
In some regions the risk has risen sharply since the 1990s: the annual probability climbed from 3.8% to 13.8% in the Celtic Sea, and from 0.7% to 9.8% in the central North Sea.
"Our findings show that marine heatwaves are a problem now — not just a risk from future warming," said lead researcher Dr. Jamie Atkins.
Why this matters
Warmer seas have wide-ranging impacts:
- They disturb the timing of plankton blooms and fish spawning, creating mismatches that can reduce survival of juveniles and disrupt food webs.
- Higher temperatures reduce dissolved oxygen, forcing species to seek cooler waters and increasing the risk of harmful bacteria and algal blooms.
- Marine heatwaves can also amplify heat on land and intensify rainfall by increasing atmospheric moisture.
Professor Ana M. Queirós of the Plymouth Marine Laboratory warned these changes can push wildlife into situations where reproduction and hatching coincide with unsuitable environmental conditions, increasing the risk of population declines or mass die-offs.
What can be done
While the trend is worrying, researchers stress that immediate actions can reduce future impacts. Reducing greenhouse gas emissions and cutting pollution from burning fossil fuels remain the clearest ways to slow ocean warming. At a local level, conservation and restoration measures — such as protecting and restoring kelp forests and seagrass meadows — can help sequester carbon, cool coastal waters and bolster ecosystem resilience.
Scientists are also expanding monitoring tools to detect changes earlier and design targeted interventions. Communities can support these efforts by choosing sustainable seafood, backing habitat restoration projects and advocating for cleaner energy policies.
Key takeaway: Marine heatwaves are not just a future risk — they are already affecting UK and Irish seas. Immediate climate action and local conservation can reduce harm to coastal communities and marine life.