‘The results frightened me’: Once-in-a-century heatwaves could now strike every 10 years

ZURICH, Switzerland — It’s late October and many parts of the United States are continuing to see record temperatures for this time of year. Some historically chilly fall locations, like New York, are expecting to reach 80 degrees as we head toward November! Unfortunately, that’s not the worst news, according to scientists. Heatwaves, like the devastating one Europe experienced in 2003 (claiming between 45,000 to 70,000 lives), could become more commonplace in the coming years.

The 2003 disaster, marked by temperatures soaring up to 117.5 degrees Fahrenheit, resulted in forest fires, failed crops, and overwhelmed emergency wards. The heatwave caused $13 billion worth of damage globally. Despite the catastrophic consequences, researchers say the general public remains under-informed about the dangers posed by extreme heat compared to other climate emergencies.

Researchers from the Institute for Environmental Decisions at ETH Zurich collaborated with international epidemiologists to assess the relationship between temperature and mortality. They collected data from 748 cities across 47 countries, identifying the “ideal temperature” for each location, where death rates were the lowest. To illustrate, Bangkok’s ideal temperature sits at 86 degrees Fahrenheit, while Paris is comfortable at 70 degrees Fahrenheit.

“Not all heat is the same,” says study lead author Samuel Lüthi, a climate scientist and doctoral student at ETH Zurich, in a university release. “The same temperature has a completely different impact on heat-​related excess mortality in the populations of Athens and Zurich.”

Factors like local acclimatization, behavioral patterns, urban planning, population demographics, and healthcare systems play a role. Researchers utilized powerful climate models, called SMILEs, to anticipate the future.

“We ran the same model up to 84 times, with slightly different weather conditions each round,” explains Lüthi. “That gave us a multitude of possible weather systems that are likely to occur if there is a certain amount of CO2 in the atmosphere.”

Researchers then incorporated this data with an epidemiological model to predict heat-related deaths and found the frequency of deadly heatwaves, like the one in 2003, has risen substantially. Such extreme events, previously expected once in a century, could now happen every 10 to 20 years.

With global temperatures increasing, such extremes might become even more frequent. In regions like America’s Gulf and Atlantic Coasts, Latin America’s Pacific Coast, the Middle East, Southeast Asia, and the Mediterranean, a significant heatwave could account for up to 10 percent of a country’s annual deaths. Paris’ 2003 heatwave, for instance, led to the premature deaths of approximately 2,700 individuals.

“According to our calculations, up to 15 percent of deaths in Paris could be heat-​related in future,” says Lüthi.

Southern Europe faces a dual challenge: temperatures rising twice as rapidly as the global average and an aging population.

“The results frightened me,” says Lüthi. “While I was working on the study, I always tried to look behind the figures and see the real lives of people who are affected by the changes. It’s worrying.”

Predictions don’t factor in potential population growth, increasing urban migration, and an aging global population. Also, there’s insufficient data for regions like Africa and India, both severely impacted by climate change and poverty.

Lüthi stresses the need for immediate action, particularly the swift transition away from fossil fuels. Though risks are already high with a 1.5-degree temperature rise, they escalate dramatically at two degrees.

“We should now prepare and manage the unavoidable, while avoiding the unmanageable at all costs,” recommends Lüthi.

The study is published in the journal Nature Communications.

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