Scientists say 4th of July heatwave was “virtually impossible” without fossil fuels

Listen to the audio version of this article (generated by AI).

This year’s Fourth of July celebrations were marked by extremes, as communities across the country commemorated America’s 250th independence day with fireworks, parades, and lookalike contests. The holiday weekend was also marked by record-setting temperatures and event cancellations due to extreme heat.

Cities along the nation’s northeast corridor such as Washington, D.C., Philadelphia, and New York saw temperatures upwards of 100 degrees. 

Washington experienced its hottest Fourth of July on record, with temperatures reaching 102 degrees. Philadelphia saw three consecutive days above 101 degrees for the first time on record, and Atlantic City, New Jersey tied its all-time hottest temperature of 106 degrees over the weekend.

In New Jersey, officials said at least 29 people died from heat-related illnesses. The Fourth of July heatwave comes after weeks of record-breaking heat in Europe, which caused over 2,000 excess deaths in France alone.

Now, a group of scientists say such temperatures would have been unheard of in a pre-industrial world, before the advent of fossil fuels.

“On America’s 250th birthday, our study gives a clear reality check,” Theodore Keeping, study co-author and extreme weather researcher at Imperial College London, said in a press release. 

“The climate the country has today is fundamentally different to the one it had when the Founding Fathers signed the Declaration of Independence,” Keeping added.

“The climate the country has today is fundamentally different to the one it had when the Founding Fathers signed the Declaration of Independence.” — Theodore Keeping, Imperial College London

A study released by World Weather Attribution analyzed a 5-day window around the Fourth of July weekend. Researchers used historical records dating back to 1950, real-time data, and weather forecasts.

The authors determined that in a preindustrial world, “temperatures as high as those forecast in early July 2026 would have been so extreme as to be virtually impossible,” the report stated.

In attribution studies such as this one, researchers compare models consistent with present observations versus those that simulate an earth without human activities — in other words, “Planet B,” said Baylor Fox-Kemper, professor of earth, environmental, and planetary Sciences at Brown University.

“It’s more and more clear from the data that we couldn’t be seeing these extreme temperatures that we’re seeing today unless we had this change in background with climate change,” said David Keellings, professor of geography at the University of Florida.

Urban heat island affect

In big cities, extreme heat tends to be particularly dangerous due to the urban heat island effect. It’s a phenomenon where buildings and roads trap heat and reduce nighttime cooling. 

“The city’s always going to be hotter because of all those man-made materials, the steel, the asphalt, the glass, the buildings — everything radiates heat,” explained Keellings, whose research focuses on climate extremes.

According to the Intergovernmental Panel on Climate Change, the urban heat island effect is only bound to get worse in coming years.

It’s a fact that doesn’t surprise Keellings. The urban heat island effect compounded with climate change increases the probability of extreme temperatures. “When you put all of that together, it just means that cities in the US are going to be hotter and hotter and hotter,” he said.

The study also noted that historically redlined neighborhoods — communities that were systematically denied mortgages and insurance due to racial discrimination — are particularly vulnerable to extreme heat events. The authors cited findings which showed that redlined communities, which tend to be low income, can experience temperatures up to 7°C hotter than non-redlined neighborhoods.

“If you look at big cities in the US, there is a huge amount of inequality, both in terms of wealth, but also just in terms of the geography of where people live,” said Keellings. “It does make a big difference to how many people are dying and who’s dying,” he said.

Keellings is skeptical about whether this report and others like it will have an impact on policy. “Science is not really driving policy in terms of climate change,” he said. Still, he’s hopeful of its impact on public perception around extreme weather events. 

Fox-Kemper from Brown agrees, viewing weather attribution studies as a valuable communication tool for the public.

“From a public perception we notice big events, we notice huge snowstorms, we notice summer heat waves, we notice flooding events,” he said. “Connecting those pieces together to the extent that we can with the accurate scientific justification is an important part of communicating what it means when the statistics change.”

Featured Image: Fujiphilm For Unsplash+