Extreme heat and humidity pose significant health risks, with the recent June heatwave in the UK delivering a stark reminder of how dangerous such conditions can be. The combination of record-breaking temperatures and unusually high humidity reduced the body’s ability to cool itself through sweating, creating what experts describe as oppressive conditions that placed particular strain on the most vulnerable. The Met Office issued Red Extreme Heat Warnings for three consecutive days for the first time in the UK’s weather warning history, underlining the severity of the event.
Health risks of extreme heat
The health implications of heat stress go far beyond discomfort. When high humidity saturates the air, sweat cannot evaporate efficiently, meaning the body struggles to regulate its internal temperature. This can lead to heat exhaustion and, in severe cases, heatstroke – a life-threatening condition. Vulnerable groups are at greatest risk: the elderly, babies, young children, pregnant women, and people with pre-existing health conditions such as heart or respiratory disease. The lack of overnight relief was a defining feature of the 2026 heatwave. “Tropical nights” – when temperatures remain above 20°C – occurred frequently, and on four separate nights temperatures stayed above 22°C somewhere in the UK. In the entire 1976 heatwave, only three such nights were recorded. This sustained warmth prevents the body from recovering overnight, exacerbating heat stress, particularly in urban areas where buildings and concrete retain heat.
The scale of the health impact became visible in emergency response data. In June 2026, the London Ambulance Service responded to its highest ever number of life-threatening emergencies in a single day. The wider toll of extreme heat is revealed by historical figures: during the summer of 2022, an estimated 2,900 heat-related excess deaths occurred in England, the vast majority among people aged 65 and over. Across the UK, heatwaves have been unequivocally linked by scientists to human-induced climate change, and a study of a 2025 heatwave in London estimated that climate change tripled the death toll.
Widespread disruption across sectors
The heatwave brought cascading impacts beyond health. On the railways, Network Rail introduced emergency speed restrictions to prevent tracks from buckling and overhead power lines from sagging in the extreme heat. Major train operators advised passengers to travel only if essential, cutting services and causing significant delays. The Gatwick Express also reduced its services.
Water supply came under severe pressure. In late May, thousands of households in southeast England already faced water supply issues or low pressure due to high demand after a dry spring, with residents queuing for emergency water. During the June heatwave, Thames Water issued warnings in Oxfordshire after a sharp spike in demand – daily household water use surged by around 30 per cent. The wider infrastructure challenge is acute: water companies lose approximately 19 per cent of water demand every day through leaking pipes.
The energy sector also felt the strain. The National Energy System Operator (Neso) issued notices requesting extra electricity generation to meet rising demand from air conditioning and fans. This led to imports of electricity from the continent at significantly higher prices. At the same time, high temperatures reduced the output of some gas and nuclear power plants, and in France, river water temperature restrictions affected the cooling of nuclear reactors. The broader economic cost was also apparent, with studies showing significant losses in work capacity and gross value added during hot weather.
Record-breaking heatwave in context
The June 2026 heatwave was remarkable for its intensity. England recorded its hottest June on record, with a provisional high of 37.7°C at Lingwood, Strumpshaw Hill on 26 June – surpassing the previous June record of 35.6°C set in 1976. A new June minimum temperature record was also set, with 23.2°C at Hastings on the same night. Wales recorded its hottest day of the year so far on 25 June, with 35.9°C at Cardiff Bute Park, breaking the previous June record of 33.7°C from 2000. Wales and the UK as a whole experienced their second-warmest June since records began in 1884. Northern Ireland equalled its June record of 30.8°C at Castlederg on 25 June, matching the 1976 high, and set a new minimum record of 19.1°C at Murlough on 26 June. Only Scotland retained its previous June maximum temperature record.
Regionally, East Anglia recorded the highest mean temperature at 18.3°C, followed by southeast and central south England at 18.1°C – both significantly above their long-term averages. At county level, the City of London had the warmest mean temperature at 19.8°C, with Greater London and Bristol also well above average.
Comparing the 2026 event with the iconic 1976 heatwave reveals key differences. While 2026 delivered higher peak June temperatures and more humid air, the 1976 heatwave was more persistent, lasting several weeks. There were 15 consecutive days above 32°C in 1976, compared with 10 non-consecutive days so far in 2026. But the warmer nights and higher humidity of the recent event made it feel more oppressive and dangerous for health. Critically, the climatic baseline has shifted: 1976 occurred within a cooler period, while today’s heatwaves build on a warming trend driven by climate change. Each of the last four decades has been successively warmer than any preceding decade since 1850. The Met Office has predicted that summer days of 40°C could become average by 2035, and the UK is considered unprepared for the scale of extreme heat already arriving.
