A severe heatwave sweeping much of the United States this week has been deemed "virtually impossible" without the influence of the climate crisis, according to researchers. The high temperatures and humidity pose risks to Independence Day festivities and World Cup soccer matches scheduled for the weekend.

Theodore Keeping, an extreme weather and wildfire researcher at Imperial College London, stated, "The climate the country has today is fundamentally different to the one it had when the founding fathers signed the Declaration of Independence."

The analysis, conducted by World Weather Attribution, an international consortium of climate scientists, attributes the heatwave to a high-pressure system known as a heat dome affecting large parts of the central and eastern US and southern Canada. Although such heatwaves are rare—occurring about once every 200 years—even this frequency is due to climate change caused primarily by fossil fuel emissions. Without the planet-warming emissions that have increased global temperatures by 1.4°C (2.5°F), events like this would be expected only once in many thousands of years.

Washington DC is expected to experience soaring temperatures as thousands gather to mark the 250th anniversary of the United States. Meanwhile, World Cup matches face challenges: France’s game against Paraguay in Philadelphia is forecasted to encounter heat levels that a global players’ union has indicated should prompt delays or postponements. Similarly, a Miami match between Cape Verde and Argentina the day before is expected to be played under potentially hazardous heat and humidity conditions.

Friederike Otto, professor of climate science at the Centre for Environmental Policy at Imperial College London, emphasized the urgency of the situation: "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. 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."

This heatwave serves as a stark reminder of the immediate need to reduce greenhouse gas emissions globally to mitigate further climate impacts.

Sources