Human-Caused Global Warming Spiked the Death Toll of Europe’s Early Summer Heatwave

Researchers found that nearly two thirds of the estimated 2,300 heat deaths resulted from global heating intensified by fossil fuel emissions, but worry that officials undercount heat mortalities.

Human-caused global warming increased the peak temperatures of an early summer heatwave across much of Europe by up to 7 degrees Fahrenheit and tripled the number of expected heat deaths in 12 European cities, an international team of scientists reported Tuesday during an online press conference.

The rapid analysis of heat deaths included Paris, London, Milan, Madrid, Barcelona, Athens, Rome, Lisbon, Budapest, Zagreb, Frankfurt and Sassari in Italy. Of the 2,300 estimated deaths in those cities during the heatwave, 1,500 resulted from the intensification of planetary heating caused mainly by the burning of fossil fuels, the scientists said.

Fredi Otto, a climate scientist with Imperial College London and one of the authors of the new report, said temperatures running 4 to 7 degrees Fahrenheit above average might not seem like a lot to some people, but the analysis is intended to dispel that misconception.

“If you translate that into what it actually means for people, and especially for vulnerable people, it can be the difference between life and death,” she said. “Hopefully that puts into perspective just how serious the problem we have with heat waves is because of climate change.”

The study, covering heat deaths between June 23 and July 2, found that people aged 65 and over made up 88 percent of the deaths linked to climate change, highlighting how those with underlying health conditions are most at risk of premature death in heatwaves.

The 14 researchers from meteorological institutions and universities in the United Kingdom, Switzerland, the Netherlands and Denmark first analysed historical weather data to show this heatwave was 2 to 7 degrees Fahrenheit hotter than it would have been in a world that hadn’t already been warmed by nearly 2 degrees Fahrenheit above the pre-industrial average. 

The team then looked at published research on the relationship between heat and the number of deaths in those cities to estimate a  total of 2,300 heat-related deaths for the 10 days. By comparing the heatwave to a similar event in a hypothetical climate unaltered by human activities, they were able to attribute 1,500 of the heat-related deaths—65 percent—during the recent European heatwave to human-caused warming, Otto said.

The study began the last few days in June when it was already very hot and with more heat in the forecast. Ben Clarke, a co-author and climate researcher at Imperial College London, said the rising temperatures gave a sense of urgency to the work.

“We were absolutely working in real time during the heat,” Clarke said via email. “Some of the work was done in a very hot and un-air conditioned office in London during the elevated temperatures.”

He said there is still a tendency by some media to highlight hot weather with photos and stories about “fun in the sun,” a trend he said is slowly changing but still underscores the need to describe the deadly impacts of heat in near real-time.

“We wanted to know as soon as possible what kinds of effects it was having,” he said.

Co-author Pierrre Masselot, a research fellow at the London School of Hygiene & Tropical Medicine, said more preparations are needed for the public health impacts of extreme heat as global warming increases the frequency of heat waves.

He said some researchers are concerned that official estimates of heat deaths may not be accurate, “not only in the developing part of the world, but also in developed countries, where attributing deaths to heat by local public authorities is, in our opinion, highly underreported,” he said. 

“I think this has got to do with sort of a culture of being a bit conservative by medical practitioners and public health authorities,” Masselot said. “When in doubt, they don’t attribute it directly to heat, because there could be other underlying health causes in the individual. It’s difficult to detect if heat amplified the underlying causes.”

More Days of Extreme Heat To Come

A 2022 study in Nature clearly showed the increasing frequency of European heatwaves, which isn’t surprising on a continent that has warmed twice as fast as the global average since the 1980s, to about 4 degrees Fahrenheit above the pre-industrial average. Another 2022 study found that human-caused warming caused about half the 60,000 heat deaths during that summer’s European heatwaves.

Climate projections anticipate more of the same occurring until humans stop heating the climate. A new analysis by Climate Analytics, a global science and policy institute, projects that heatwave days will double or triple in Berlin, Paris, Madrid and other cities by the end of the century without drastic cuts of global greenhouse gas emissions.

In Berlin and Paris, the annual number of heatwave days could double to 48 and 41 respectively by 2100 with unchecked emissions, but would remain about the same if world leaders meet the long-term target they agreed to in the Paris agreement of limiting the long-term global temperature increase close to 2.7 degrees Fahrenheit above the pre-industrial level. 

And it’s not just Europe that has to worry about heatwaves. A study by University of Pennsylvania climate scientist Michael Mann and other researchers published last month shows how changes to planetary “wave” patterns in the atmosphere over the past 70 years are linked with persistent summer extremes.

“it is important to note that attribution studies, if anything, are actually quite conservative,” Mann said via email. “Our recent article in PNAS demonstrated a three-fold increase in the occurrence of the sort-of stuck, wavy jet stream patterns (planetary wave resonance) that give us such persistent weather extremes in summer, such as stable heat domes and persistent floods, due to human-caused warming.”

He said recent heat domes in Europe and North America were a manifestation of the resonance phenomenon. 

“Climate models such as the ones used in attribution studies fail to adequately account for this effect,” he said. “That implies that, if anything, these attribution studies are underestimating the impact human-caused warming is having on these sorts of weather extremes.”

But he added, attribution studies are still valuable because they show “that the extreme heat we’ve seen so far this summer can only be explained when the warming of the planet from fossil fuel carbon pollution is accounted for.”

There have been numerous peer-reviewed studies showing the “scientific fact” that human-caused warming intensifies heatwaves, said Otto, the attribution researcher, and on some levels, political leaders may be starting to listen.

“I’ve seen some improvement in the political reaction in a wider sense, in that we now do have much better heatwave warnings,” she said. 

Overall, media coverage of extreme heat risks has also improved somewhat, she said. “But especially more right-wing press articles are still illustrated with happy people playing at the beach and children eating ice cream,” she said, which “continues to suggest that heat waves are a time to have fun, and doesn’t get across how dangerous extreme heat can be.” 

Cover photo:  People hold umbrellas to protect themselves from the sun during a heatwave in Paris on June 30. Credit: Ludovic Marin/AFP via Getty Images