As the United States celebrates its 250th anniversary, its climate has changed profoundly

July is still the hottest month in the United States, but today’s Julys are significantly warmer than they were when Benjamin Franklin, Thomas Jefferson, and the other Founding Fathers declared the United States an independent nation. THE brutal heat wave Smothering the eastern half of the country as it celebrates its 250th anniversary is a stark reminder of how profoundly the climate has changed since the American Revolution.

During this period, the United States has warmed about 3 degrees Fahrenheit, faster than the global average increase of 2.5 degrees Fahrenheit. This warming is due to greenhouse gases accumulating in the Earth’s atmosphere from the burning of fossil fuels that began on a large scale with another revolution, the industrial revolution. In the mid-18th century, concentrations of carbon dioxide in the atmosphere were around 280 parts per million. This year, they exceeded 430 ppm. And historically the The United States has become the largest emitter of greenhouse gases in the world.

Global warming is creating noticeable changes in the weather we experience each day, although it varies from place to place: some regions of the United States are warming faster than others; some become wetter; others become drier. Winter snows have decreased while downpours have increased, and the hurricanes hitting our coasts are getting stronger and causing greater flooding.

On supporting science journalism

If you enjoy this article, please consider supporting our award-winning journalism by subscribe. By purchasing a subscription, you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

But while it’s summer, let’s look at how the heat – with one of the most obvious links to global warming – has changed. Summer has of course always been the hot season, and heat waves have always occurred. But based on temperature records dating back to the late 1800s, one thing is clear: Summer temperatures are higher overall across the country, and heat waves are lasting longer, more intense, and occurring more frequently than in the past. The 50 largest U.S. cities are experiencing twice as many heat waves as in the 1980s. Take Philadelphia, where the Declaration of Independence was signed and the Constitution ratified: the average July temperature there has increased by 4.4 degrees F since 1970. And children growing up there today experience four more heat waves each summer than their grandparents.

In the 1770s, there was about the same probability of setting heat or cold records, but today heat records are twice as likely. The heatwave sending temperatures into the triple digits for this July 4th weekend is a prime example of an event where climate change has loaded the dice. Such heat and humidity would have been “virtually impossible” when the United States was founded, according to scientists with the World Weather Attribution research group.

“On America’s 250th birthday, our study provides a clear reality check,” Theodore Keeping, a WWA team member and researcher in extreme weather and wildfires at Imperial College London, said in a statement about his analysis of the heat wave.

Because heat is the deadliest weather phenomenonauthorities have warned those celebrating the holiday to take precautions: avoid being outside during the hottest hours of the day, stay in air conditioning as much as possible and stay hydrated and aware of signs of heat illness.

Climatologists and environmental advocates say the event highlights the urgent need to rein in emissions.

“Climate change is here,” said Friederike Otto, a researcher at WWA and also from ICL, in the press release. “It’s already impacting the things we enjoy in our daily lives, and it will continue to get worse as we delay the inevitable transition to net zero emissions.”