The UK's hottest June day on record was made even more oppressive by high humidity, which pushed the "feels like" temperature up to 10°C above the actual air temperature, according to the Met Office.
Record Heat and Humidity Combine
On June 24, temperatures soared to 40.3°C in Coningsby, Lincolnshire, breaking the previous June record of 38.7°C set in 2019. However, the humidity index, which measures the combined effect of heat and moisture, made it feel as hot as 50°C in some areas. The Met Office reported that relative humidity levels remained above 40% even during the peak of the heat, significantly increasing the heat stress on the human body.
Dr. Mark McCarthy, a climate scientist at the Met Office, explained: "Humidity plays a crucial role in how we perceive temperature. When the air is humid, sweat evaporates less efficiently, reducing the body's ability to cool down. This can make a hot day feel unbearable."
Health Risks and Public Response
The combination of record heat and humidity prompted the UK Health Security Agency to issue a Level 4 heat-health alert, the highest possible, for the first time. The alert warned of "illness and death among the fit and healthy" and urged people to stay indoors during the hottest part of the day. Hospitals reported a surge in heat-related admissions, with cases of heat exhaustion and dehydration rising by 30% compared to the previous week.
The extreme conditions also disrupted transport networks, with train services canceled due to track buckling and speed restrictions imposed on several rail lines. Network Rail reported that the heat caused rails to reach temperatures of 55°C, increasing the risk of buckling.
Climate Change Connection
Scientists have linked the extreme heatwave to climate change, noting that human-induced global warming has made such events more likely and intense. Dr. Friederike Otto, a climate researcher at Imperial College London, said: "The UK's record-breaking June heatwave would have been virtually impossible without climate change. The additional humidity, driven by warmer oceans and increased evaporation, is also a fingerprint of a warming world."
According to the Met Office, the UK's average summer temperature has risen by about 1.5°C since the pre-industrial period, and the frequency of heatwaves has increased. The June 2026 heatwave was the third such extreme event in the UK in the past five years, following the 2022 and 2023 summer heatwaves.
Looking Ahead
As the heatwave subsides, the Met Office has warned that similar conditions could become more common in the future. The UK is expected to experience hotter, drier summers, with heatwaves occurring every three to four years by 2050 under current emissions trajectories. Adaptation measures, such as improved building insulation and public cooling centers, are being discussed by local authorities.
