According to the study published in the journal Nature Health, 32,619 of those deaths are attributed to the extra heat caused by burning coal, oil and gas. The figures are roughly 71% higher than the previous deadliest summer, 2022, which killed 29,480 people under the same researchers' methods.

The 17 June to 1 July heatwave alone, when temperatures ran 5.3°C above normal, accounted for roughly a third of the deaths — about 14,500 by the model's count, per Insurance Business.

Lead author Clair Barnes of Imperial College London said some cities saw temperatures 12°C warmer than normal, and that Western and Northern European infrastructure 'is just not designed to cope' with such temperatures.

Western Europe recorded its hottest summer on record, and Europe as a whole is the fastest-warming continent, now about 2.5°C hotter than pre-industrial times.

The most striking finding is the attribution trend: the share of heat deaths blamed on human-caused warming has climbed from about 40–45% in the early 2000s to 65% this summer.

Using the same model, researchers attributed 42% of 2003's heat deaths to climate change and 59% of 2022's, according to Insurance Business.

'In some sense, the absolute numbers... are indeed staggering,' said co-author Malcolm Mistry of LSHTM, 'but perhaps what is even more alarming is the proportion of these deaths that we attribute to anthropogenic climate change.'

People aged 85 and older made up roughly half the death toll — 22,502 of the modelled deaths per Insurance Business — but heat killed younger people too, including more than 800 between 20 and 44.

Italy suffered the largest absolute toll at 13,303 deaths, with France, Spain, Germany and the UK also hit hard; the highest rates per million were in Malta, Italy and Hungary.

Naples was the hardest-hit city, at 815 deaths per million, and the Guardian reports an estimated 4,354 heat deaths across UK cities this summer.

The figures also exclude a deadly May heatwave, and heat deaths are notoriously underreported — death certificates rarely record contributing factors, so families often never learn heat hastened a relative's death.

Researchers checked their model against official data, calculating 2,700 excess deaths for May–June British heatwaves against the UK health statistics agency's 2,800 figure.

Physicians are urging governments to cut fossil fuels while preparing for the heat already locked in.

'We need to prepare for the heat we cannot now avoid, with urgent investments in heat early-warning systems, equitable access to low-carbon cooling, and neighborhood buddy systems,' said Dr. Courtney Howard, president-elect of the Canadian Medical Association.

In Naples, emergency doctor Mario Guarino told the Guardian he saw a 15% rise in ER visits during the hottest weeks, warning that 'the real epidemic these days is loneliness' among elderly people unable to afford air conditioning.