By Stephen Beech
The Tour de France may need to be rescheduled due to global warming, warns a new study.
Soaring temperatures as a result of climate change raise the danger of potentially deadly heat stroke for riders in the annual summer cycle race, say scientists.
An analysis of 50 years of climate data shows that the iconic Tour has so far avoided the most extreme conditions, although the risk is steadily increasing.
Climate scientists say the progressive rise in temperatures poses a growing threat to the staging of summer sporting events in Europe and, more specifically, to the Tour de France, due to the increasing risk of heat stress for athletes.
The new study, published in the journal Scientific Reports, analyzed climate data associated with more than 50 editions of the French race.
The research was led by scientists at the French National Research Institute for Sustainable Development (IRD) in Marseille.
Researchers from the London School of Hygiene and Tropical Medicine (LSHTM) and the Barcelona Institute for Global Health (ISGlobal) in Spain were also part of the team.
The aim of the study was to assess under which heat stress risk levels the Tour de France has taken place at different locations and dates between 1974 and 2023.
Many heat safety protocols used by international sports federations are based on a heat index known as the Wet Bulb Globe Temperature (WBGT).
Ith combines several meteorological variables – including air temperature, relative humidity, solar radiation and wind – to estimate heat-related health risk.
To conduct the study, the research team retrieved historical meteorological records for 12 locations frequently visited by the Tour de France, as well as for all July dates corresponding to the different editions of the race.
Using the data, the team calculated WBGT values and analyzed the occasions on which the high-risk category in the UCI protocol (above 28 °C WBGT) was reached.
The results show that, at the times and places where the race is held, heat stress risk has increased steadily over the years – with the most recent decade accumulating the highest number of extreme heat episodes.
But, despite this trend, the Tour has so far managed to avoid conditions of maximum health risk, in some cases by only a matter of days or tenths of a degree.
Study first author Dr, Ivana Cvijanovic, of the IRD, said: “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.
“Other cities have experienced many days of extreme heat in July, but thankfully not on the date of a Tour de France stage.
“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.”
The research team found that episodes of dangerous heat levels have been most common around Toulouse, Pau and Bordeaux in south-western France, and around Nîmes and Perpignan in the south-east.
They also warn that locations such as Paris and Lyon are increasingly crossing the “high-risk” heat threshold, becoming new heat stress hotspots.
Dr. Desislava Petrova, of ISGlobal, said: “Extra caution should be exercised when planning stages in these regions.”
By contrast, classic mountain stage locations – such as the Col du Tourmalet and Alpe d’Huez – have historically remained within low to moderate heat stress risk thresholds, with no recorded episodes of extreme heat risk to date.
The analysis showed that morning hours remain the safest part of the day, while high heat stress levels can persist until late in the afternoon.
Researchers say the patterns highlight the need to adapt schedules, routes and safety protocols in order to reduce risks for both cyclists and event staff and spectators.
The research team used the Tour de France to illustrate the broader challenge that rising temperatures driven by climate change pose to the organization of summer sporting events, particularly in elite sport.
They say heat not only affects athletic performance but can also pose a serious risk to athletes’ health.
The Union Cycliste Internationale (UCI), like FIFA and other international sports federations, has implemented safety protocols that assess heat risk and trigger protective measures, such as hydration or cooling breaks in football.
But each federation defines its own risk thresholds, and no universal standard currently exists across sports.
Dr James Begg, of UK-based Galson Sciences, added: “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.
“To investigate sport-specific vulnerabilities, we would need access to anonymized physiological data that would allow us to go beyond heat indices alone.”
