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The heatwave that affected England and Wales in June killed about 440 people a day during its three-day peak, scientists have estimated. Across the whole of the June heatwave, plus the one in May, about 2,700 people lost their lives prematurely.
The data starkly illustrates the danger of extreme heat, which is being supercharged by the climate crisis. More than 40% of the people affected would not have died without the 1.4C of human-caused global heating to date, according to the analysis. For comparison, about four people die each day as a result of road traffic collisions and about 35 a day because of alcohol and drug use, according to government statistics.
Extreme temperatures will worsen as continued fossil fuel burning pumps pollution into the atmosphere, making cuts in emissions and measures to protect people from global heating urgent, say experts.
“These are big numbers and we don’t want to see this many people dying,” said Dr Clair Barnes, at Imperial College London, who led the analysis. “We’ve reached the point where the heat is so extreme that we can’t help but acknowledge the impacts it has.”
The June heatwave peak resulted in an unprecedented three successive days of red warnings from the UK Health Security Agency and the Met Office, warning of danger to life for all, though the young, old and those with underlying illnesses are most at risk from high temperatures and humidity.
The UKHSA previously found that more than 10,000 people died in Britain because of summer heatwaves between 2020 and 2024. The Climate Change Committee has warned for more than a decade that the UK’s plans to protect people from rapidly worsening extreme weather are inadequate.
The June heatwave was the widest and most intense ever recorded in Europe and is estimated to have cost more than 20,000 lives. In Germany, where a record high of 41.7C was set, almost 5,500 people are thought to have died, according to preliminary government data. Schools, hospitals and transport have also been seriously affected.
“Hopefully just the sheer size of the numbers is really illustrating to people that this is something we need to be worrying about and preparing for,” said Barnes. “We can stop making it worse by transitioning towards net zero, because that is not a political target, it’s a physics-based target. If we stop adding greenhouse gases, we stop adding warming and we stop making these heatwaves worse.”
Dr Mark McCarthy, at the Met Office and part of the analysis team, said 2026 had been “exceptional for the two early-season heatwaves in May and June – these smashed records”. A high of 35.1C was recorded in west London during the May heatwave and three consecutive days of record-breaking June temperatures ended with a recording of above 37C in East Anglia. Climate change added 3C to 4C, the researchers said.
“We know that human-induced climate change is making heatwaves more frequent and more intense, both globally and here in the UK,” McCarthy said. “Extreme high temperatures in the UK are also warming at a much faster rate than the average temperature.” Next summer may well be even worse due to a major El Niño event.
Denis Fernando, at Friends of the Earth, said: “It’s a national scandal that the UK remains so dangerously unprepared.”
Prof Emma Howard Boyd, at the London School of Economics and the chair of the Heat Risk Commission, said: “Particularly alarming is that these figures, covering just the first half of the summer, are already approaching the reported toll from the record-breaking heat of 2022 … Government cannot afford to treat these figures as an anomaly – they are a warning of the climate we now live in.”
The analysis estimated 550 people died because of heat-related causes during the May heatwave period, 21-29 May 2026. Almost 60% were the result of the extra heat baked in by the climate crisis.
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And about 2,200 heat deaths occurred between 18 and 28 June, a period encompassing the peak 24-26 June period, the study indicated. About 38% were attributed to global heating, the result of the extra heat baked in by the climate crisis.
“The proportion is lower for June,” said Barnes, “primarily because the temperatures were so extreme that even without the extra boost from human-caused warming, the heat-related excess mortality would have been very high.”
The analysis used peer-reviewed methods to analyse weather data and climate models to determine the impact of the climate crisis on the heatwaves. They then used published research that quantifies the link between heat and daily mortality in detail across England and Wales.
This enabled estimates of heat deaths in today’s heated world and how many would have been avoided in a hypothetical cooler world without global heating. The estimated deaths from previous research has aligned closely with official data which takes months to compile from death certificates.
The fatalities counted are “excess deaths” from all causes, ie the additional deaths occurring above the normal level for the time of year, and will include heart attacks and other medical emergencies provoked by the heat. Focusing on heat being recorded as a direct cause of death “would just be the tip of the iceberg”, said Dr Ross Thompson at the UKHSA. “It really underestimates the total burden of heat.”
The UK has kept detailed data of deaths and climate for many years, making it possible to assess heat fatalities. But such analyses are not possible in many countries, including those hardest hit by rising temperatures. Nonetheless, a conservative attempt to estimate global heat deaths by medical experts in 2025 concluded that rising heat kills one person a minute around the world on average.
