Eastern U.S. Heat Wave Raises Safety Concerns for World Cup Players and Fans as Philadelphia Match Faces Triple-Digit Heat

Heat builds over the eastern U.S. during World Cup knockout rounds

A dangerous heat wave is spreading across the eastern and central United States, bringing a serious test for World Cup players, fans and organizers during the July Fourth weekend.

Saturday’s afternoon knockout round match between France and Paraguay in Philadelphia, PA, could become the hottest game of this World Cup tournament. The match will be played in an open-air stadium, with athletes on the field and tens of thousands of spectators exposed to humid, oppressive heat.

The air will be heavy.

According to the National Weather Service, the heat wave is expected to continue across the eastern and central U.S. through the end of the week. Peak heat indexes, which combine air temperature and humidity, are forecast between 100°F and 115°F, or 37.78°C to 46.11°C.

High night temperatures will bring little relief, and records could be broken.

Philadelphia match could be the hottest of the tournament

Temperatures are forecast to exceed 100°F, or 37.78°C, during Saturday’s match in Philadelphia, PA.

That level of heat creates concern not only for spectators in the stands, but also for players who must sprint, recover, think quickly and sustain repeated physical effort through the match.

Earlier this week, French players cooled off under field sprinklers during their match against Sweden in New Jersey, after temperatures reached 90°F, or 32.22°C.

The image was clear: players standing under water on the pitch, trying to lower body temperature before returning to competition.

Heat risk has been building for months

Concerns about extreme heat during World Cup games in the U.S., Canada and Mexico have been growing for months. Some scientists have said FIFA’s heat safety guidelines are “inadequate" and “impossible to justify," even for players who are acclimatized to heat.

For spectators, extreme heat may also change the character of the game. The pace can slow. The intensity can drop. Players may conserve energy rather than press constantly in dangerous conditions.

The issue is not new. The 2022 World Cup in Qatar was moved from summer to winter because of the threat from extreme heat. Last year, temperatures also soared during the Club World Cup.

The global soccer players’ union has warned that extreme heat is likely to become a bigger problem at this World Cup and the next ones.

One of the hottest World Cup games was in 1994

One of the hottest World Cup matches on record was played in 1994 in Orlando, FL, when temperatures reached 110°F, or 43.33°C.

Three decades later, the world is warmer. The climate monitoring group Berkeley Earth says the planet has warmed roughly 1.26°F, or 0.7°C, in the last 30 years since the United States last hosted the World Cup.

Global temperature increases intensify heat waves and make severe weather more common.

Scientists with World Weather Attribution said the humid heat engulfing the country, as well as parts of Canada, would have been “virtually impossible" without climate change.

World Cup Heat Risk: Eastern U.S. Heat Wave Threatens Players and Fans on July Fourth Weekend

Heat is a leading killer of athletes

Heat affects athletes from two directions: from the surrounding environment and from the body’s own heat production during exercise. When humidity is high, cooling becomes harder because sweat evaporates less efficiently.

Bharat Venkat, director of the Heat Lab at the University of California, Los Angeles, explained why exertion in extreme heat raises the risk.

Bharat Venkat: “So when you’re exerting yourself on a particularly hot day, the likelihood of experiencing heat related illness or even death is much higher."

Intense exercise in very hot conditions can lead to extreme fatigue, impaired performance, headache, irritability, nausea, dizziness, cramping and dehydration. These are symptoms of exertional heat illness.

Exertional heat stroke requires immediate medical attention and is the third leading cause of death in athletes.

When the body can no longer cool quickly

Ryan Calsbeek, professor of biological sciences at Dartmouth College, said danger rises sharply when wet bulb globe temperature reaches about 95°F, or 35°C.

Wet bulb globe temperature includes temperature, humidity, cloud cover and wind.

Ryan Calsbeek: When the wet bulb globe temperature rises above about 95°F, people lose their ability to cool off quickly, and “the physiological mechanisms just break down."

Heat can affect more than endurance. Calsbeek said heat-induced confusion could influence player decisions and even help determine the outcome of a match.

Ryan Calsbeek: “Soccer players are a really unique mix of athletic attributes. They have to have extreme endurance and explosive speed. And then on top of that, they have to make really critical decisions. All of those different facets of the sport will be affected by the temperature."

FIFA heat rules face scrutiny

FIFA uses mandatory three-minute hydration breaks midway through each half to protect players and referees from extreme heat illness.

Those breaks have drawn criticism from several directions. Some say they interrupt the rhythm of the game and give coaches a chance to change momentum. Some scientists say the breaks should be longer when heat is extreme, allowing players enough time to cool and rehydrate.

FIFA says outdoor matches during peak heat hours have been limited, and matches expected in warmer windows are prioritized for covered stadiums.

Under FIFA guidelines, a match could be postponed if the wet bulb globe temperature reaches 89.60°F, or 32°C.

Douglas Casa, CEO of the University of Connecticut’s Korey Stringer Institute, said that threshold is extremely high.

Douglas Casa: “So extreme that in the military, at our basic training facilities in America, if it reaches 32, it’s black flag and all training has to be canceled and stopped."

The players’ union FIFPRO and the American College of Sports Medicine have called for matches to be delayed at 82.40°F, or 28°C, for safety.

Teams train for heat stress

Teams are also preparing for extreme heat through acclimation.

Guilherme Passos, a sport scientist at the Brazilian Football Federation, monitors and prepares Brazil’s national team for extreme heat. He has helped players adapt to U.S. heat during the competition.

Guilherme Passos: “If you expose them straight to the hottest time of the day you can lose a bit of training quality."

Brazil uses saunas and hot baths as part of heat training during competition.

When Brazil hosted the World Cup in 2014, Passos said players covered less distance and reduced high-speed running. They increased technical and tactical precision instead.

That kind of adjustment can change the feel of a match. Fewer long sprints. More measured movement. More careful use of energy.

Fans face serious heat risks too

Players are not the only ones at risk. Many fans will be drinking alcohol and watching World Cup matches in extreme heat. That combination can increase dehydration risk.

Cities and stadiums have increased access to shade, cooling areas and water. Medical personnel are stationed in FIFA Fan Festivals and around stadiums.

Calsbeek warned that spectators may also be affected by the heat.

Ryan Calsbeek: “People are going to be dehydrated, super excited, and not wanting to leave the match."

Ryan Calsbeek: “We’re likely to see, in those extreme temperatures, spectators pay the price as well."