Sometimes, it can be hard to comprehend the enormity of climate change without seeing any immediate effects. That shouldn’t be a problem for much longer: in a grim sign of the planet’s current condition, last year wasn’t only the hottest on record – it also likely caused more heat-related deaths in Europe than any other year bar one.

How was this result calculated?

According to researchers at the Barcelona Institute for Global Health (ISGlobal), approximately 47,690 people in Europe died from heat-related causes in 2023. That’s more than any other year on record other than 2022, when the same team reached an estimate of 61,672 excess deaths from heat.

Now, we should point out right off the bat that this conclusion was probably not found how you’re imagining. Rather than simply counting how many coroners’ records across the peninsula were labeled “cause of death: too hot”, the figure comes from epidemiological models – basically, researchers analyzed temperature and mortality data from 823 regions in 35 European countries between 2015 and 2019, and used that to estimate the death toll in 2023.

As such, while the team put the number of heat-related deaths in Europe last year in the mid-47,000s, they caution that the true number may be as low as 28,853, or as high as 66,525.

More worryingly, however, is the other caveat: that these numbers may be a significant underestimate. While the team used mostly the same methodology as 2022’s report, they hit a snag when it came to sourcing data – rather than standardized daily mortality records, they were forced to rely on weekly updates from Eurostat, the statistical office of the European Union. 

It may not seem like much of a difference, but less regular updates can result in lower estimates of the heat-related mortality burden. The researchers can correct for this, and they did – finding that the heat-related death toll may actually have been more than 10,000 higher than their headline figure.

Who was the worst affected?

Perhaps unsurprisingly, the worst affected countries were those in the south of the continent: Greece topped the list with 393 deaths per million from heat in the year, followed by Bulgaria with 229, Italy with 209, Spain with 175, and Cyprus with 167. 

Many of the worst-hit nations are also those with the highest share of elderly people – a correlation borne out in the study, which found heat-related mortality to be close to eight times higher for people over 80 years of age than in people aged between 65 and 79.

Also worse affected were women, whose mortality rate was found to be 55 percent higher than men’s. Again, this is not totally surprising: women are known to fall prey to heat-related mortality at higher rates than men, even if the reasons why are not totally understood – it’s potentially to do with the fact that women sweat less, and are therefore less able to lose heat; it may be that women have higher core body temperatures on average; it could be a combination of factors, or something as yet unknown.

Obscured by adaptation

Now, perhaps you’re thinking that 47,000, or 58,000, or even 62,000 aren’t such high numbers, all things considered – it is, after all, at most one in every 125 deaths in the region. But there’s a second conclusion drawn in the study which, depending on how you look at it, is either reassuring or even more worrying: in the past two decades of ever-increasing temperatures, we’ve learned to adapt to extreme heat in such a way that it almost halved the number of likely deaths through the year.

“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”, said Elisa Gallo, a researcher at ISGlobal and first author of the study, in a statement. 

“For example, we see that since 2000, the minimum mortality temperature – the optimum temperature with the lowest mortality risk – has been gradually warming on average over the continent, from 15°C in 2000-2004 to 17.7°C in 2015-2019,” she explained. “This indicates that we are less vulnerable to heat than we were at the beginning of the century, probably as a result of general socio-economic progress, improvements in individual behavior and public health measures such as the heat prevention plans implemented after the record-breaking summer of 2003.”

What this means in real terms is that, had the summer of 2023 occurred back in 2003 when we were all still making fun of Al Gore, the death toll would have been much, much higher – like, nearly double. We simply weren’t ready for it. 

Now, extreme heatwaves are so commonplace that we’ve adapted our lives around them.

A warning for the future

So, what’s the major takeaway of this report? Well, it’s hardly a surprise: the planet is warming, and we’re running out of time to mitigate the damage.

“In 2023, almost half of the days exceeded the 1.5°C threshold set by the Paris Agreement and Europe is warming at a rate twice as fast as the global average,” pointed out Joan Ballester Claramunt, Principal Investigator of the European Research Council’s Consolidator Grant EARLY-ADAPT – a project designed to analyze the environmental and socioeconomic causes of trends in public health.

“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,” Claramunt said.

Whether or not you care about the planet, one thing this report makes clear is that we each have a vested interest in slowing and – science willing – maybe even reversing climate change. After all, we can’t adapt forever.

“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,” Claramunt warned. “There is an urgent need to implement strategies aimed at further reducing the mortality burden of the coming warmer summers, together with more comprehensive monitoring of the impacts of climate change on vulnerable populations.” 

“These adaptation measures must be combined with mitigation efforts by governments and the general population,” he advised, “to avoid reaching tipping points and critical thresholds in temperature projections.”

The study is published in the journal Nature Medicine.