Tour de France on heat alert as scientists warn race edging towards safety threshold

For half a century, the Tour de France has narrowly avoided the most dangerous extreme heat scenarios. But that margin is shrinking. A new international study warns that rising temperatures across Europe are steadily pushing cycling’s biggest race towards its safety limits.

The research, published in Scientific Reports, was led by the Institut de Recherche pour le Développement (IRD) as part of the European TipESM project, in collaboration with the London School of Hygiene & Tropical Medicine (LSHTM) and Barcelona’s ISGlobal. Scientists examined meteorological data from 50 editions of the Tour between 1974 and 2023 to assess the level of heat stress riders have faced.

Their conclusion is stark: the risk has increased consistently, with the past decade accounting for the highest number of extreme heat episodes recorded during the race. Although the Tour has so far avoided exceeding the maximum health risk threshold, in several cases it has done so by only a matter of days, and even fractions of a degree.

“In a way, we can say it is an extremely lucky race, but with heatwaves breaking records more and more frequently, it is only a matter of time before the Tour encounters a day of extreme heat stress that tests existing safety protocols,” said Ivana Cvijanovic, IRD researcher and lead author of the study.

She highlighted how some host cities have repeatedly come close to dangerous levels. “Paris, for example, has crossed the high heat risk threshold five times in July, four of them since 2014. Other cities have experienced many extreme heat days in July, but fortunately not during a Tour stage.”

The analysis identifies several vulnerable regions. In south-west France, areas near Toulouse (29.7°C in 2020), Pau (28.8°C in 2019) and Bordeaux (30.1°C in 2019) recorded concerning figures. In the south-east, locations around Nimes (30°C in 2020) and Perpignan also stood out. Further north, Paris (28.8°C in 2019) and Lyon are increasingly nearing the high-risk threshold, emerging as new hotspots.

By contrast, high mountain stages have historically remained within lower or moderate heat risk ranges. Iconic climbs such as the Col du Tourmalet and Alpe d’Huez have generally offered more benign conditions. However, researchers stress that even these stages are not immune to the broader warming trend.

To measure heat impact, the team used the WBGT (Wet Bulb Globe Temperature) index, which combines temperature, humidity, solar radiation and wind. They compared results with the UCI protocol, which classifies values above 28°C WBGT as high risk. The study found that mornings remain the safest time of day, while elevated heat stress can extend well into the afternoon.

Beyond cycling, the researchers say their findings should act as a warning for summer sport across Europe. Extreme heat affects not only performance but also poses a serious health risk. If current climate trends continue, organisers may need to reconsider race calendars, stage timings and medical protocols to adapt to increasingly demanding conditions.