Global Warming Threatens the Tour de France (and Other Summer Sporting Events)

A study published in Scientific Reports suggests that it is only a matter of time before the French race faces situations of extreme heat stress risk for cyclists, staff and spectators.

[This article has been written by Desislava Petrova, Pau Rubio, Ivana Cvijanovic and James Begg.]

It is highly likely that in the coming years the Tour de France will run into a wall. And we are not referring to the slopes of Alpe d’Huez. In a study we have recently published in Scientific Reports, we show how extreme heat is closing in on the race to the point where its current format and timing are becoming questionable, due to the high risk of heat stress this would pose for cyclists, teams and the general public.

We describe the Tour de France as an extraordinarily fortunate race because, despite the growing number of extreme heat episodes, it has managed to avoid the most adverse conditions

But let us start at the beginning. In this study, we set out to assess how the risk associated with extreme heat has changed over the decades in the world’s most famous cycling race. To do so, we selected 12 locations that are typical of the Tour, such as Bordeaux, Lyon and, of course, Paris, as well as the Col du Tourmalet and Alpe d’Huez. We then gathered meteorological data for the month of July between 1974 and 2023. Using all these data, we calculated hourly heat stress risk for each date and location.

The results allow us to draw three main conclusions:

• Heat stress risk has increased steadily over the years.
• The most recent decade concentrates the highest number of extreme-risk episodes.
• The Tour de France has been very lucky — but it is only a matter of time before it hits the wall.

Let us develop this third point.

Why has the Tour de France been lucky?

We describe the Tour de France as an extraordinarily fortunate race because, despite the growing number of extreme heat episodes, it has managed to avoid the most adverse conditions. The route and the race dates are planned months in advance, while reliable weather forecasts are available maximum 14 days beforehand.

Between 2014 and 2023, the city of Paris experienced maximum heat risk conditions on up to four occasions during the month of July, but never on the date of a Tour stage. A similar pattern is observed in other cities analysed in the study, where extreme risk has been avoided. However, given the trends in the data, it would be naïve to assume that this good fortune will continue for another five decades.

Which regions face the highest risk?

What we observe in the data is that risk is not evenly distributed across locations. In cities in southwestern France, such as Toulouse, Pau and Bordeaux, and in the southeast, such as Nîmes and Perpignan, heat stress risk is higher. Others, including Paris and Lyon, are emerging as new heat stress hotspots, crossing the high-risk heat threshold with increasing frequency.

At the other end of the spectrum, mountain locations such as the Tourmalet or Alpe d’Huez have historically remained within low to moderate risk thresholds.

What do we consider extreme heat and extreme risk?

Heat stress risk is not determined by air temperature alone. Other meteorological variables —such as relative humidity, solar radiation and wind— play a crucial role in determining how dangerous heat can be for human health. The Union Cycliste Internationale (UCI) already has a safety protocol based on an index that incorporates all these variables, known as the Wet Bulb Globe Temperature (WBGT). In our study, after calculating WBGT values, we analysed the occasions on which the highest risk category defined in the UCI protocol was reached.

The issue is that temperatures have not yet peaked, and they threaten not only the Tour, but also the Olympic Games and the Football World Cup. It is time to sit down, conduct sport-specific research and make bold decisions

What measures do we recommend?

If the Tour de France is to remain the great sporting spectacle that it is while also being held under safe conditions for the health of all those involved, certain decisions will need to be made. Just as some regions are more prone than others to heat episodes, the times of day at which stage finishes are scheduled also tend to coincide with higher risk, while early morning hours are safer. Event organisers will need to adapt schedules, routes and safety protocols.

Will we see a Tour de France that is no longer raced in summer?

What about the Olympic Games or the Football World Cup?

Although this study focuses on the Tour de France, its conclusions apply to any other sporting event held in summer in Europe or in other regions facing high heat stress risk. Many sports federations already have their own protocols in place —FIFA, for example, introduced hydration breaks in football. The issue is that temperatures have not yet peaked, and they threaten not only the Tour, but also the Olympic Games and the Football World Cup. It is time to sit down, conduct sport-specific research and make bold decisions.

Reference

Cvijanovic I, Begg JD, Mistry MN, Petrova D, Brimicombe C, Sultan B. The future of European outdoor summer sports through the lens of 50 years of the Tour de France. Scientific Reports. 2026 (in press).

More information

Global warming and heat stress risk close in on the Tour de France