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The future of European outdoor summer sports through the lens of 50 years of the tour de France - Scientific Reports In this study, we consider how excessive heat, due to changing climate conditions, could affect the safety of summer sport competitions in Europe. We use the example of the world’s largest bicycle race, the Tour de France, to assess the changes in heat stress over the past five decades and discuss extreme heat protocols, data gaps and safe ways forward. We show that although July heat stress values have been increasing throughout France, the actual Tour de France race dates have so far been fortunate to avoid the days featuring the highest heat. For example, although July hourly heat stress values for Paris and its surroundings have crossed the high-risk threshold (Wet Bulb Globe Temperature (WBGT) > 28 °C) on five occasions over the last 50 years, four of which have occurred since 2014, this has so far not happened on the date of the Tour de France stage through Paris. Between 1974 and 2023, the hottest Parisian stage finish was in July 2002, with the hourly WBGT maximum of 26.8 °C staying just below the high-risk mark. With record-breaking heatwaves becoming more frequent, it seems only a question of time as to when the race will encounter the extreme heat stress days that will test the existing heat safety protocols. Considering the historical heat stress values, we find that the episodes of dangerous heat levels exceeding 28 °C WBGT, have been most common around Toulouse, Pau and Bordeaux in France’s southwest, and around Nîmes and Perpignan in the southeast. However, locations like Paris and Lyon are starting to cross the 28 °C WBGT threshold more frequently, becoming new heat stress hotspots. Our hourly July analysis for France, shows that morning hours are the safest part of the day and that high heat stress can persist late into the afternoon hours. Mountain locations largely remain safe. https://go.nature.com/4cotaVz