Global warming raises heat risk for major cycling race

(CN) — For decades, the Tour de France has unfolded under the July sun, fortunately without crossing into the highest heat-risk category during race stages. But researchers say that as climate change drives more frequent and intense heatwaves across Europe, that luck may not hold.

Climate data, linked to more than 50 editions of the race between 1974 and 2023, show a steady rise in heat stress risk, with recent years coming closest to breaching high-risk limits.

The study, published Tuesday in Scientific Reports, shows that rising temperatures have steadily increased heat stress risk during the race over the past five decades. While the Tour has so far avoided the highest danger levels, researchers say it has done so narrowly in recent years, sometimes by just days or fractions of a degree.

Led by the French National Research Institute for Sustainable Development, in collaboration with partners including the London School of Hygiene & Tropical Medicine and the Barcelona Institute for Global Health, researchers assessed heat stress risk at locations and dates where the race has been held.

They used the Wet Bulb Globe Temperature, or WBGT, a heat index that combines air temperature, humidity, solar radiation and wind to estimate heat-related health risk.

Under the Union Cycliste Internationale’s protocol, a WBGT above 28 degrees Celsius, or 82.4 degrees Fahrenheit, is considered high risk.

“In our analysis, we observe that the city of Paris, for example, has crossed the high-risk threshold for heat on five occasions in July, four of them since 2014,” said Ivana Cvijanovic, a researcher at the institute and the study’s first author, in a press release. “Other cities have experienced many days of extreme heat in July, but thankfully not on the date of a Tour de France stage.”

Still, the margin appears to be shrinking.

“In a way, we can say that it is an extremely fortunate race, but with record-breaking heatwaves becoming more frequent, it is only a matter of time before the Tour encounters extreme heat stress day that will test existing safety protocols,” Cvijanovic said.

Researchers found that episodes of dangerous heat levels have been most common around Toulouse, Pau and Bordeaux in southwestern France, and near Nîmes and Perpignan in the southeast. They also identified Paris and Lyon as emerging hotspots, increasingly crossing the high-risk threshold.

“Extra caution should be exercised when planning stages in these regions,” said Desislava Petrova, a researcher at ISGlobal, in the press release.

By contrast, classic mountain stages such as the Col du Tourmalet and Alpe d’Huez have historically remained within low to moderate risk ranges. No extreme heat episodes were recorded at those high-altitude sites during the period studied.

The timing of stages also matters.

Researchers say morning hours tend to present the lowest risk, while elevated heat stress can persist well into the afternoon. That finding points to possible adjustments in start times, routes and safety measures to protect cyclists, race staff and spectators.

According to researchers, the Tour is just one example of a broader issue. As global temperatures rise, elite sporting events scheduled during summer months may face mounting health risks.

Heat can impair performance and, in severe cases, endanger athletes’ lives.

International sports federations, including cycling’s governing body and organizations such as FIFA, have adopted heat safety protocols that trigger measures like additional hydration or cooling breaks. However, there is no universal standard across sports, and each federation sets its own risk thresholds.

“Science still has many unanswered questions about how the human body responds to heat, and even more so in the case of elite athletes, who face sustained physical exertion while also having physical conditioning and training levels well above those of the general population,” said James Begg, a researcher at Galson Sciences, in the press release. “To investigate sport-specific vulnerabilities, we would need access to anonymised physiological data that would allow us to go beyond heat indices alone.”