During the three-day peak of June’s heatwave, roughly 440 people died every day in England and Wales.

For context: around four people die daily in road traffic collisions. About 35 die daily from alcohol and drug use.

The June heatwave deaths were not a rounding error in the mortality statistics. They were, briefly, the dominant cause of preventable death in the country — and almost nobody noticed while it was happening.

The Numbers

Scientists at Imperial College London estimate that the May and June heatwaves combined killed approximately 2,700 people prematurely.

Breaking that down:

• May 21-29: roughly 550 heat-related deaths, with almost 60% attributable to human-caused warming
• June 18-28: roughly 2,200 deaths, with about 38% attributable to global heating

Across the whole period, more than 40% of those who died would still be alive without the 1.4C of warming humanity has already caused.

Why the June Percentage Is Lower

There is a counterintuitive detail worth explaining.

June saw far more deaths but a lower proportion attributed to climate change. Dr Clair Barnes, who led the analysis, explained why.

“The proportion is lower for June 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.”

In other words: June would have been deadly anyway. Climate change made it deadlier.

An Unprecedented Warning

The June peak triggered something Britain had never seen before — three consecutive days of red warnings from the UK Health Security Agency and the Met Office.

Red means danger to life for everyone, though the young, the elderly and those with underlying conditions face the greatest risk.

Records fell repeatedly. West London hit 35.1C during the May heatwave. Three days of record-breaking June temperatures culminated in readings above 37C in East Anglia.

Researchers calculate that climate change added 3C to 4C to these events.

What “Excess Deaths” Actually Means

The figures count excess deaths — fatalities above the normal seasonal baseline, from all causes.

That includes heart attacks and other medical emergencies triggered by heat, not merely cases where heatstroke appears on a death certificate.

Dr Ross Thompson of the UKHSA explained why this matters.

Counting only deaths where heat is listed as a direct cause “would just be the tip of the iceberg,” he said. “It really underestimates the total burden of heat.”

Heat rarely kills people cleanly. It kills them by pushing a struggling heart, a compromised kidney, or a weakened respiratory system past its limit.

The European Picture

Britain got off lightly by comparison.

June’s heatwave was the widest and most intense ever recorded in Europe, estimated to have cost more than 20,000 lives across the continent.

Germany, where a record 41.7C was set, recorded nearly 5,500 deaths according to preliminary government data.

Schools, hospitals and transport systems were seriously disrupted throughout.

Britain’s Unpreparedness

The criticism from experts was blunt.

The Climate Change Committee has warned for more than a decade that UK plans to protect people from worsening extreme weather are inadequate.

Denis Fernando of Friends of the Earth called it plainly: “It’s a national scandal that the UK remains so dangerously unprepared.”

Professor Emma Howard Boyd, chair of the Heat Risk Commission, offered a warning about scale.

“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,” she said. “Government cannot afford to treat these figures as an anomaly — they are a warning of the climate we now live in.”

The UKHSA has previously found that more than 10,000 people died in Britain from summer heatwaves between 2020 and 2024.

The Physics Argument

Barnes made a point that cuts through the political framing entirely.

“We can stop making it worse by transitioning towards net zero, because that is not a political target, it’s a physics-based target,” she said. “If we stop adding greenhouse gases, we stop adding warming and we stop making these heatwaves worse.”

Dr Mark McCarthy of the Met Office noted something specific about the UK.

“Extreme high temperatures in the UK are also warming at a much faster rate than the average temperature,” he said.

The averages understate the problem. It is the peaks that kill, and the peaks are rising fastest.

Next Year Could Be Worse

A major El Niño event is developing, which typically pushes global temperatures higher.

Next summer, in other words, may exceed this one.

The Global Blind Spot

Britain can produce these figures because it has maintained detailed mortality and climate records for decades.

Most countries cannot — including many of those suffering the worst heat.

A conservative attempt by medical experts in 2025 to estimate the global toll reached a stark conclusion: rising heat now kills one person every minute worldwide, on average.

The Point Barnes Wants Made

“These are big numbers and we don’t want to see this many people dying,” she said. “We’ve reached the point where the heat is so extreme that we can’t help but acknowledge the impacts it has.”

That is the shift. Heat deaths were once invisible — diffuse, unattributed, folded into ordinary mortality.

They are no longer deniable. They are simply, so far, being ignored.