When the 2026 World Cup kicks off across the United States, Canada and Mexico on 11 June, the football world will be watching Kylian Mbappe’s acceleration, Vinicius Junior’s footwork and Erling Haaland’s predatory instincts.
But there is another variable at play, one that no training camp or tactical setup can fully neutralise: the heat. And history has a very clear verdict on what extreme heat does to a football tournament.
Fourteen of the 16 World Cup host cities are likely to exceed the 28-degree Celsius wet bulb globe temperature threshold considered dangerous by sports scientists and several football governing bodies, according to research published in 2025.
The global players’ union FIFPRO has classified six cities, Atlanta, Dallas, Houston, Kansas City, Miami and Monterrey, as extremely high risk for heat stress injury.
Temperatures in several American venues regularly push past 35 degrees in June and July, with humidity levels that transform a 90-minute match into something approaching an endurance event.
The 2025 FIFA Club World Cup, played across many of the same venues in high summer, offered the sharpest recent preview. Borussia Dortmund manager Niko Kovac said after a match in Cincinnati he was “sweating like I’ve just come out of a sauna.”
Chelsea midfielder Enzo Fernandez described conditions as “very dangerous,” adding that “everything becomes very slow.”
Juventus manager Igor Tudor revealed that ten players asked to be substituted during a match against Real Madrid in Miami, where temperatures reached 30 degrees with 70 per cent humidity.
Seven of the eleven Club World Cup venues were judged high risk by FIFPRO, and union officials subsequently warned that the World Cup will present an even greater challenge.
History supports that concern. Of the World Cups played in genuinely hot conditions, South American nations have won the overwhelming majority.
In 1970, Brazil swept to the title in Mexico, playing seven matches in temperatures that regularly exceeded 35 degrees at noon, the kickoff time chosen to suit European broadcast schedules. Their fluid, high-tempo football never visibly degraded.
Italy, their opponents in the final, had already been drained by a semi-final against West Germany so gruelling it became known as the Game of the Century. Brazil won 4-1. In 1986, also in Mexico, European sides progressively wilted as the tournament progressed.
In 1994, played across Dallas, Orlando and Los Angeles in fierce summer heat, the average goals-per-game figure was the lowest in tournament history to that point, a statistic sports scientists have since linked to the physical toll of sustained heat. Brazil won again, managing the conditions better at every stage.
The contrast with cooler conditions is instructive. France won in 1998 on home soil in mild summer temperatures. Germany won in South Africa in 2010 during the southern hemisphere winter. European sides win when the climate cooperates. The historical record is unambiguous.
FIFA has responded to pressure with some scheduling adjustments, moving games in the hottest cities away from peak afternoon heat and building in three-minute cooling breaks midway through each half. These are useful but partial measures.
The current FIFA threshold for mandatory stronger intervention remains a WBGT of 32 degrees, a figure scientists consider dangerously high.
An open letter from medical experts has urged FIFA to double cooling break duration to six minutes, lower the intervention threshold and introduce clearer protocols for delaying or postponing matches in extreme conditions.
FIFPRO has called for 20-minute half-time intervals instead of 15 and cooling breaks every 15 minutes rather than once per half. “We are anticipating that this problem is going to be even more crucial for the coming years,” FIFPRO medical director Vincent Gouttebarge said.
The union’s general secretary Alex Phillips acknowledged FIFA had been responsive during the Club World Cup but warned that structural solutions were still needed. “At some point the practical things probably won’t be enough,” FIFPRO strategy director Alexander Bielefeld added.
The risk extends beyond the players. In the hottest cities, indoor air-conditioned stadiums protect those on the pitch, but tens of thousands of spectators will spend hours travelling, queueing and celebrating in dangerous outdoor heat. Many fans are older, less physically fit, dehydrated from alcohol consumption or arriving from cooler climates with no acclimatisation.
England’s pressing system depletes faster in Miami than it does at Wembley in October.
Argentina, acclimatised through South American qualifiers, and African nations whose players develop in high-temperature environments, carry a thermal advantage that pre-tournament rankings rarely account for. The cumulative effect across seven matches over a month is something no cooling break fully addresses.
There is also the wildcard of extreme weather events. The 2021 western North America heatwave shattered records by more than four degrees in some locations.
A similar event during the tournament could push lower-risk cities such as Seattle, Toronto and Vancouver into dangerous territory while prolonging extreme evening heat in Miami and Philadelphia. Six Club World Cup matches were also stopped due to electric storms, with one delay approaching two hours in Charlotte.
The 2026 World Cup may ultimately become a defining test for how global sport adapts in a warming world. Scheduling matches outside the hottest hours is a sensible start. But as temperatures continue to rise, timing alone may no longer be enough.
History keeps returning the same verdict: when football is played in serious heat, the physically clever outlast the merely gifted, and acclimatisation proves worth more than any tactical briefing. The grass will be very warm indeed.
