For Norway’s national men’s soccer team, Saturday’s World Cup quarter-final against England will be a first in more ways than one. As the Scandinavian side prepares for the biggest match of its history, it will also face conditions almost unimaginable back home: the punishing combination of South Florida heat, humidity, and blazing sunshine that scientists warn can push the human body to its limits.

South Florida’s mix of strong sun, hot-air temperature, and high humidity—boosted by a plume of dusty air from the Sahara desert sweeping across the Atlantic through the state—will put the northern European players under a level of heat stress rarely experienced in their native countries.

Scientists quantify this heat stress by calculating the WetBulb Globe Temperature. On top of air temperature, the index takes into account humidity, which limits evaporation of sweat from the skin; wind, which can act as a coolant; and solar intensity, as sunshine directly raises individuals’ skin and core temperatures.

Saturday’s match is forecast to be played at an extremely high WBGT of around 88 degrees Fahrenheit (31 degrees Celsius). The American College of Sports Medicine recommends that athletic activities cease when this measure exceeds 82 degrees Fahrenheit because at this level, humans struggle to cool down and body temperature starts to increase rapidly. FIFA itself stipulates that if the WGBT exceeds 90 degrees Fahrenheit, players and referees need to take breaks after 30 and 75 minutes of play to cool themselves down with ice-water-soaked towels.

While both teams will have been training to adapt to the environment, the conditions could make for a more sluggish match, according to Matt Maley, a researcher in environmental ergonomics and physiology at Loughborough University in the UK. He told WIRED: “At Miami this weekend, we may actually see players reduce the amount of sprints or the distance they cover.” That would be a far cry from the fast-paced Premier Lea...