The summer of 2023 was the hottest in 2,000 years (though 2024 may end up being even hotter). High temperatures and heat waves occurred around the world, resulting in more than 47,000 heat-related deaths across Europe alone, according to new research. But heat deaths would have been even higher if not for climate adaptation measures.

Those figures come from a new study published in Nature Medicine, from researchers with the Barcelona Institute for Global Health. Researchers didn’t analyze exactly how effective specific heat mitigation measures were at reducing deaths. Instead, says Elisa Gallo, a postdoctoral fellow at the institute and lead author of the study, “we ‘take a picture’ of the societal vulnerabilities in previous historical periods and analyze how the recent temperatures may have affected them.”

Hottest summer on record

Though the summer of 2023 was the warmest on record globally, it was the fifth warmest for Europe specifically. The summer of 2022 was the hottest for Europe, and that year more than 62,000 deaths were attributed to heat, so researchers expected deaths to be lower (they do warn their figure could be an underestimate, because of issues with mortality databases).Still, there’s no denying that summer temperatures have been skyrocketing over the last decade, “and this is leading to tens of thousands heat-related deaths every year,” Gallo says.

Some people—including women and the elderly—are more vulnerable to extreme heat than others. Researchers wanted to see if overall vulnerability to heat was decreasing, so they used epidemiological models to look at four different periods of the past decade (omitting the COVID-19 pandemic): 2000-2004, 2005-2009, 2010-2014 and 2015-2019. Then, they plugged 2023 temperature and mortality data into those different models, to estimate how many heat deaths could have occurred in those periods if they had been as hot as 2023 was.

How people are adapting to heat

Researchers were able to estimate that if the years from 2000 to 2004 had the high temps of 2023, there would have been more than 85,000 heat deaths. That’s 80% higher than the period of 2015 to 2019. (For people 80 and older, deaths from heat would have more than doubled.) They also found that the “minimum mortality temperature,” meaning the temperature with the lowest mortality risk, has been gradually getting warmer over the past decade.

What that all shows, Gallo says, is that there have been “societal adaptation processes” to high temperatures that have actually worked to make people less vulnerable to extreme heat. “Improvements in urban planning, housing conditions, increase of green spaces in the cities are all factors that contribute to adaptation,” she says. “A lot of efforts have been put in recent years also on the improvements of the early warning systems.” The last decade has also seen improvements generally in healthcare, occupational health, building conditions, and so on.

Cities across Europe have taken heat adaptation measures in recent years, from appointing a Chief Heat Officer to naming and categorizing heat waves. Cities have reduced the amount of pavement that covers neighborhoods to lessen the urban heat island effect, and added more greenery and passive cooling technologies. People are also generally becoming more aware of all the ways heat can impact our health.

‘We need to work more and faster on adaptation and mitigation strategies’

Even with these heat adaptation measures, though, the number of heat-related deaths is still too high, Gallo says. “Especially knowing that Europe is warming at twice the rate of the global average, we can’t rest on our laurels because we already had some good results. We need to work more and faster on adaptation and mitigation strategies to avoid reaching temperatures that will have a huge impact on our health,” she says. (Research has already found that climate-related health impacts are not equal and often exacerbate inequalities.)

Adaptation can’t be the only way to deal with heat deaths. There are physiological and societal limits to adaptation that we don’t yet fully understand, Gallo notes, and we still need to focus on mitigation, like by lowering greenhouse gas emissions and investing in renewable energy. “What is certain,” she says, “is that climate change needs to be considered as a health issue.”