NEW YORK: Climate change linked to fossil fuel use set the stage for extraordinary heat and humidity that has cast at least one World Cup game into a potential danger zone, according to the World Weather Attribution group of climate scientists.

Saturday's (Jul 4) game between Paraguay and France is set to kick off at 5pm ET in Philadelphia with temperatures that exceed FIFPRO's recommendations for safe play, as a heat dome settles over large swaths of the US and parts of Canada.

The US National Weather Service warned this week that the heat dome - a high-pressure system which traps hot air beneath it - could see heat indices hit 40.5°C to 46°C in parts of the Midwest and East Coast, with many World Cup host sites affected.

The conditions threaten to strain power grids and impact outdoor celebrations for the United States' 250th anniversary in a busy Fourth of July holiday weekend. 

"When a historic Fourth of July celebration is disrupted, and World Cup matches are played in conditions that are unsafe for players and fans, it shouldn't take another scientific study to wake people up," Friederike Otto, Professor of Climate Science at the Centre for Environmental Policy, Imperial College London, said in a statement.

“Climate change is here, it’s already impacting the things we enjoy in our everyday lives, and it will continue to get worse the longer we drag out the inevitable transition to net-zero emissions."

Soaring temperatures and sweltering humidity have become a key talking point of the tournament a year after the world players' union FIFPRO sounded the alarm over dangerous heat at the Club World Cup, which was played in the US

FIFPRO praised FIFA in December for making an effort to "align the competition schedule planning and venue selection with the concerns around player health" at the World Cup, but said there were still some games that had risk attached.

"The lesson for everyone in the industry is that with a warming planet, heat conditions will play a bigger part in tournament and league scheduling decisions in the future," FIFPRO said.

Football's world governing body, however, has no rule that would automatically trigger the postponement of a match because of extreme heat. FIFA was not immediately available to comment.