Human-caused climate change was a factor in over 40% of the deaths that occurred during the record-breaking heatwaves in May and June in the UK, a new study from scientists at Imperial College London, the Met Office and the London School of Hygiene & Tropical Medicine has found. More than 2,700 people are estimated to have died in England and Wales during the two periods of extreme heat.

To reach their conclusions, researchers looked at past temperature data and measured the chances of heat-related deaths in approximately 35,000 small areas of England and Wales, and compared these with a projection of what would have happened if the planet had not warmed as a result of human activity.

The first hot spell was in May, when temperatures reached 35.1°C in West London. The second heatwave saw three days of record-breaking temperatures, with 37.7°C recorded at Lingwood, Norfolk, on June 26, and England placed under several red health alerts. There were several hospitals declaring critical incidents, and London Ambulance Service was also having its busiest day on record after a surge in life-threatening calls for ambulances.

The study estimated 550 additional heat-related deaths, with approximately 330, about 60% of these deaths attributed to climate change. In the second wave, from June 18 to 28, scientists made an estimate of nearly 2,200 heat-related excess deaths, with approximately 800, or 40 per cent, of them due to anthropogenic warming. This compares to the estimated 1,504 heat-related deaths in the UK in the summer of 2025.

Dr Clair Barnes, research associate at Imperial College London on extreme weather and climate change, said it was time to recognise that we are now living in a country with dangerously hot summers and to prepare for that climate now, while promptly increasing our global efforts for net-zero emissions to prevent it from getting worse.