A Guardian analysis has found that nearly one in five matches at this year's World Cup were played in heat and humidity levels that the football players' union Fifpro has warned should trigger delays or postponements, highlighting mounting concerns about the safety of major sporting events as the climate crisis intensifies. Experts say the tournament has become a stress test for heat mitigation, raising questions about whether football can continue to be played safely in extreme conditions for both players and spectators.

The analysis of all 104 matches found around 20 games were played in conditions with a wet bulb globe temperature at or above 28C, the threshold beyond which Fifpro says fixtures should be delayed or postponed, while a further 23 matches took place in cities experiencing similar heat but in air-conditioned stadiums. The findings coincide with a record-breaking heatwave affecting the United States, with over 125 million Americans under heat alerts and wildfire smoke degrading air quality ahead of Sunday's final, which is expected to be played in slightly cooler, lower-humidity conditions. Fifa did not respond to a request for comment, though it has previously said it stationed meteorologists at venues to help manage extreme weather.