Almost 600 people are expected to die early in the heatwave roasting England and Wales, a rapid analysis has found.
The surge in deaths would not be occurring without human-caused global heating, the scientists said, with temperatures boosted by 2C-4C by the pollution from fossil fuels.
Premature deaths will occur across the two countries but the highest mortality rates are expected in London and the West Midlands. Most of the deaths – 85% – will be people over 65 years old, who are more vulnerable to the extreme heat. People in inner-city homes are also at high risk.
More than 10,000 people died before their time in summer heatwaves between 2020 and 2024, according to the UK Health Security Agency (UKHSA). The government’s preparations to protect people from the escalating impacts of the climate crisis were condemned as “inadequate, piecemeal and disjointed” by official advisers in April.
The 32C heat that will be endured by people in the south-east of England on Saturday will have been made 100 times more likely by the climate crisis, scientists said on Friday.
“Heatwaves are silent killers – people who lose their lives in them typically have pre-existing health conditions and rarely have heat listed as a contributing cause of death,” said Dr Garyfallos Konstantinoudis, at Imperial College London, who is part of the team that estimated the number of deaths.
“This real-time analysis reveals the hidden toll of heatwaves and we want it to help raise the alarm,” he said. “Heatwaves are an under-appreciated threat in the UK and they’re becoming more dangerous with climate change.”
Prof Antonio Gasparrini, at the London School of Hygiene & Tropical Medicine (LSHTM) and also part of the analysis team, said: “Increases of just a degree or two can be the difference between life and death.
“When temperatures push past the limits populations are acclimatised to, excess deaths can increase very rapidly. Every fraction of a degree of warming will cause more hospital admissions and heat deaths, putting more strain on the NHS.”
The analysis used decades of UK data to determine the relationship between temperatures and heat deaths in more than 34,000 areas across England and Wales.
The researchers combined this with high-resolution weather forecasts to estimate that there will be about 570 deaths between Thursday and Sunday, with 129 in London. The number could be an underestimate, they said, as people were less prepared for heatwaves in early summer.
Dr Malcolm Mistry, at LSHTM, said: “Exposure to temperatures in the high 20s or low 30s may not seem dangerous, but they can be fatal, particularly for people aged over 65, infants, pregnant people, and those with pre-existing health conditions.”
The UKHSA sounded the alarm on Thursday with an amber heat-health alert, also warning of “a rise in deaths” and “significant impacts” to health and social care services. The alert is expected to remain in force until 9am on Monday.
Dr Lorna Powell, an NHS urgent care doctor in east London, said: “We are seeing cases of heat-related illnesses rising.
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“Heat exhaustion can quickly trigger more serious illnesses, as dehydration sets in and the cardiovascular system becomes overwhelmed.
“We must stop burning coal, oil and gas if we are to stabilise our climate and prevent scores of preventable health issues, hospital visits and deaths.”
The UKHSA recommends people keep out of the sun between 11am and 3pm on the hottest days, drink plenty of water, and look out for older people. A recent study estimated that 80% of UK homes overheat in the summer.
The hot sun has also led to a warning of high ozone air pollution in London on Saturday, with people with lung problems advised to limit exercise.
The climate crisis drove the annual global temperature in 2024 to a new record and carbon dioxide emissions from coal, oil and gas are still rising. That means heatwaves will get ever more intense and frequent.
A recent report by the UK climate change committee estimated that heat-related deaths could rise to more than 10,000 a year by 2050 if global temperatures rise to 2C above preindustrial levels.
Globally, extreme heat is more deadly than floods, earthquakes and hurricanes combined, taking about 500,000 lives a year, according to a report by the insurer Swiss Re.
“Extreme heat events are more dangerous than natural catastrophes in terms of human lives lost, yet the true cost is only starting to come to light,” said Nina Arquint, a corporate solutions chief executive at Swiss Re.
