France and Paraguay are due to play an afternoon World Cup knockout match in Philadelphia with extreme heat expected to create risks for players, officials and tens of thousands of fans in an open-air stadium.
A heat wave across the eastern and central U.S. is expected to continue through the end of the week, with the Weather Service projecting peak heat indexes of 100 F to 115 F (37.78 C to 46.11 C). High overnight temperatures are expected to offer little relief, and records could be broken.
French players already dealt with heavy heat earlier this week in New Jersey, using field sprinklers to cool off during a match against Sweden as temperatures reached 90 F (32.22 C).
Concern over heat at World Cup matches in the U.S., Canada and Mexico has grown for months. Some scientists have criticized FIFA’s heat safety guidelines as inadequate, even for players who have trained for hot conditions.
The world has warmed about 1.26 F (0.7 C) in the three decades since the U.S. last hosted the World Cup, according to Berkeley Earth. World Weather Attribution scientists said the humid heat affecting parts of the U.S. and Canada would have been virtually impossible without climate change.
Heat rules face renewed scrutiny
FIFA uses mandatory three-minute hydration breaks midway through each half to protect players and referees from extreme heat illness. Critics have argued that the breaks can disrupt the flow of the match, while some scientists say they are too short for meaningful cooling and rehydration in severe conditions.
FIFA has said outdoor matches in peak heat hours have been limited, with warmer windows prioritized for covered stadiums. Its guidelines allow a match to be postponed if the wet bulb globe temperature reaches 89.60 F (32 C).
Douglas Casa, CEO of the University of Connecticut Korey Stringer Institute, said that threshold is already extreme by military training standards in America. FIFPRO and the American College of Sports Medicine have called for matches to be delayed at 82.40 F (28 C).
Players face performance and health risks
Bharat Venkat, director of the Heat Lab at the University of California, Los Angeles, said exertion in hot, humid weather makes heat illness or death more likely because the body is taking in heat from the environment while also generating it through exercise.
Intense activity in those conditions can lead to fatigue, impaired performance, headache, irritability, nausea, dizziness, cramping and dehydration. Exertional heat stroke requires immediate medical attention and is the third leading cause of death in athletes.
Ryan Calsbeek, a professor of biological sciences at Dartmouth College, said when wet bulb globe temperature rises above about 95 F (35 C), the body’s cooling mechanisms begin to break down. He also said heat-induced confusion could affect player decisions and potentially influence a match.
Guilherme Passos, a sport scientist with the Brazilian Football Federation, has helped Brazil prepare for U.S. heat through acclimation work, including saunas and hot baths during competition. He said players can lose training quality if exposed directly to the hottest part of the day.
Passos said that during the 2014 World Cup in Brazil, players covered less distance, reduced high-speed running and relied more on technical and tactical precision. Calsbeek noted that soccer demands endurance, explosive speed and quick decisions, all of which can be affected by temperature.
Fans also face danger in Philadelphia heat
The risk extends beyond the field. Many World Cup spectators drink alcohol while watching matches, and dehydration can become more dangerous in extreme heat.
Cities and stadiums have increased access to shade, cooling areas and water, with medical personnel stationed at FIFA Fan Festivals and around stadiums. Calsbeek said fans may be dehydrated, excited and reluctant to leave a match, making spectators vulnerable in extreme temperatures.
The 2022 World Cup in Qatar was moved from summer to winter because of extreme heat concerns. One of the hottest World Cup matches was played in 1994 in Orlando, Florida, when temperatures reached 110 F (43.33 C).