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The extreme heat and humidity gripping large parts of the United States during the FIFA Club World Cup and ahead of Independence Day celebrations would have been “virtually impossible” without human-caused climate change, according to a new study released on Friday.
The research, conducted by the World Weather Attribution (WWA) group, found that the dangerous heat affecting much of the central and eastern United States, as well as southern Canada, has been significantly intensified by global warming.
“On America’s 250th birthday, our study gives a clear reality check,” said Theodore Keeping, an extreme weather and wildfire researcher at Imperial College London and co-author of the report.
“The climate the country has today is fundamentally different from the one it had when the Founding Fathers signed the Declaration of Independence,” he said.
Researchers said the ongoing heatwave is being driven by a powerful “heat dome”, a high-pressure system that traps hot, moisture-laden air over a wide region. While such weather systems occur naturally, climate change has made them far hotter and more dangerous.
Daytime temperatures have exceeded 100 degrees Fahrenheit (38 degrees Celsius) across many areas, with high humidity making conditions even more oppressive.
The study assessed heat stress using the Wet Bulb Globe Temperature (WBGT), an index that combines temperature, humidity, wind and solar radiation to measure how dangerous heat is for the human body. Forecast WBGT levels are expected to reach record highs across much of the affected region.
Using climate models, WWA compared today’s climate, shaped by human-caused greenhouse gas emissions, with a hypothetical world unaffected by climate change. Global temperatures have already risen about 1.4 degrees Celsius (2.5 degrees Fahrenheit) since the pre-industrial era.
The researchers concluded that without climate change, the forecast WBGT levels would have been so rare as to be virtually impossible, occurring at most once every 5,000 years.
Even under current climate conditions, they estimated the event is exceptionally unusual, with a return period of around once every 200 years, although they noted considerable uncertainty because of its unprecedented intensity.
To determine whether natural climate variability played a role, the team examined the influence of developing El Niño conditions in the Pacific Ocean. They found that El Niño would have had only a minor cooling effect over northeastern North America, ruling it out as the primary cause of the extreme heat.
The findings come as the United States hosts FIFA Club World Cup matches, including the July 4 fixture between France and Paraguay in Philadelphia. Forecast WBGT levels at kick-off are expected to exceed 82 degrees Fahrenheit, a threshold at which FIFPRO, the global football players’ union, has urged organisers to delay matches because of the health risks to players, officials and spectators.
The study adds to growing scientific evidence that climate change is increasing the frequency and severity of extreme heat events, raising concerns over the safety of outdoor sporting events and public gatherings during increasingly hot summers.