Blistering heat killed more than 47,000 people in Europe last year, scientists have found.

2023 was the hottest year on record, and the second hottest in Europe, as fossil fuels continue to increase greenhouse gas concentrations in the atmosphere. 

A disaster on a vast scale, the heat-related death toll is nonetheless lower than in 2022, when more than 61,000 people died in Europe, according to the same analysis from the Barcelona Institute for Global Health (ISGlobal).

The researchers also found that heat-related mortality would have been 80 per cent higher last year without the introduction of measures to help people adapt in the past couple of decades. 

“Our results show how there have been societal adaptation processes to high temperatures during the present century, which have dramatically reduced the heat-related vulnerability and mortality burden of recent summers, especially among the elderly,” says Elisa Gallo, ISGlobal researcher and lead author of the new study published in the journal Nature Medicine today.

Where in Europe are people most at risk of dying in heatwaves?

In contrast to the persistent heat stress of summer 2022, Europe’s 2023 season was marked by two temperature spikes in mid-July and late-August.

These episodes would have accounted for more than 57 per cent of the overall estimated mortality last year, or more than 27,000 deaths, according to the study.

To arrive at the overall estimation of 47,690 heat-related deaths in 2023, the researchers fitted epidemiological models to weekly death data from Eurostat. These models were made using temperature and mortality records from 823 regions in 35 countries between 2015-2019.

When adjusting for the size of population, the countries with the highest heat-related mortality rates last year were all in southern Europe.

Greece was the most vulnerable country with 393 deaths per million, followed by Bulgaria (229 deaths per million) and Italy (209 deaths per million).

Stefano Olmastroni, a 61-year-old supermarket cleaner, was one of those who lost his life to unbearable heat in the Italian city of Florence last July. His body was 43C after working in an aircon-less greenhouse area.

“There are people who would have died anyway, but those are not counted with this methodology,” Joan Ballester Claramunt, principal investigator of the adaptation group at ISGlobal, previously explained. “We are talking about people for whom the occurrence of these temperatures triggered their death.”

Contrary to what you might think, only a small proportion of heat-related deaths are caused by heat stroke. Heatwaves typically kill people by stopping the body from managing underlying health problems like heart and lung disease, with the heat acting as an additional, fatal stressor. 

When looking at the total number of deaths last year, Italy comes out considerably on top with 12,743 heat-attributable deaths, 8,388 of them women. Spain followed with 8,352 deaths and Germany third with 6,376 heat-related deaths. 

The UK suffered 1,851 deaths last year, placing it seventh on the list of European countries. But as ISGlobal doesn’t have a breakdown of male and female data, Britain doesn’t appear on the bar chart below.

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This gender disparity is evident across the entire dataset. After accounting for the population, the heat-related mortality rate was 55 per cent higher in women than in men across Europe. 

Launching an age and sex-adjusted heat vulnerability map last month, Ballester shared some insights as to why this is the case. Women tend to have lower salaries, for example, and therefore have fewer resources like air conditioning to protect themselves. They are also more frequently widowed and so more likely to live alone and be isolated from help.

Age makes a huge difference too. For people over 80 years of age, the heat-related mortality rate was 768 per cent higher than in people aged between 65 and 79 years.

The study comes with a caution – that the 2023 numbers may underestimate the actual heat related mortality burden. That’s because using weekly death data can dilute the effect of short-term spikes attributed to heat. 

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The researchers estimate that the likely heat-related death toll in 2023 could actually have been closer to 58,000 deaths in the 35 countries studied.

How were 80 per cent of heat deaths prevented?

In order to estimate the number of lives saved through adaptation, the researchers fitted their epidemiological model to the periods 2000-2004, 2005-2009, 2010-2014 and 2015-2019. They then plugged 2023 figures into each of these models to work out the number of deaths that would have occurred in each window if temperatures had been as high as they had last year.

If 2023 temperatures had struck in 2000-2004, they calculated, heat-related mortality would have been higher than 85,000 deaths: 80 per cent higher than in the 2015-2019 period. 

Since 2000, the ‘minimum mortality temperature’ – the optimum temperature with the lowest mortality risk – has been gradually warming on average over the continent, Gallo explains. It has risen from 15°C in 2000-2004 to 17.7°C in 2015-2019.

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“This indicates that we are less vulnerable to heat than we were at the beginning of the century,” she says, “probably as a result of general socio-economic progress, improvements in individual behaviour and public health measures such as the heat prevention plans implemented after the record-breaking summer of 2003.”

However humans can only adapt so far to heat

“We need to take into account that inherent limits in human physiology and societal structure are likely to set a bound to the potential for further adaptation in the future,” warns Ballester. 

There is an “urgent need” for further strategies to save lives, he says, including more precisely monitoring the impacts of climate change on vulnerable changes. But at the end of the day, we need to tackle climate change at root.

In 2023, almost half of the days exceeded the 1.5°C threshold set by the Paris Agreement. “Climate projections indicate that the 1.5°C limit is likely to be exceeded before 2027, leaving us a very small window of opportunity to act,” adds Ballester.

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“[Adaptation] measures must be combined with mitigation efforts by governments and the general population to avoid reaching tipping points and critical thresholds in temperature projections.”