The signing of the Declaration of Independence in Philadelphia on July 4th, 1776 (by John Trumbull, American, 1756 – 1843), 1819. The painting shows the five-man drafting committee presenting the Declaration of Independence to the United States Congress, and is located in the Capitol rotunda. Oil on canvas. (Photo by GraphicaArtis/Getty Images)
Philadelphia, Pennsylvania is likely to experience one of the warmest 4th of July celebrations in the era of official records. A massive heat dome has gripped much of the eastern United States this week. While July 4th represents the near peak of the current heatwave, there are a few days left of dangerous heat. As our country celebrates the Semiquincentennial, which is the 250th anniversary of the United States Declaration of Independence, I thought it would be fun and instructive to compare weather conditions on that date in 1776 and today. And by the way, I am able to do this thanks to Thomas Jefferson.
On the eve of July 4th, organizers canceled Philadelphia’s Salute to Independence Semiquincentennial Parade because of temperatures in excess of 100 degrees Fahrenheit. The previous day Philadelphia tied a maximum temperature record with a reading of 103 degrees Fahrenheit. The Great American State Fair in Washington D.C. was temporarily disrupted by extreme heat on Friday, and the district’s July 4th Independence Day parade was also canceled.
Expected temperatures from Washington D.C, to Boston, Massachusetts on the afternoon of July 4, 2026.
The National Weather Service has issued an extreme heat warning for the Philadelphia area until 8 pm on July 4. “Dangerously hot conditions with maximum heat index values between 105 and 110 degrees expected,” wrote the NWS. “Heat related illnesses increase significantly during extreme heat and high humidity events,” they continued. While we are all susceptible to adverse effects from heat, which kills more Americans annually than any other weather event according to NWS, some groups are particularly vulnerable. These include elderly, the poor, children under 5, and communities of color.
Weather-related heat fatalties in the U.S.
While the triple digit readings in the daytime garner headlines, elevated temperatures at night are also very dangerous. “Very warm low temperatures in the mid 70s to low 80s at night will not offer any relief from the heat,” cautioned the NWS Philadelphia. They also warned that, “Multiple days of near record breaking temperatures will exacerbate the impacts from the heat and humidity.” There is also a 30% chance of afternoon thunderstorms in the late afternoon. That rainfall could certainly provide some temporary relief.
What was the weather like on this date 250 years ago? In 1776, we did not have the National Weather Service. That didn’t come along until 1870. However, there is information about the weather on that date available thanks to Thomas Jefferson. It is well known that Jefferson kept meticulous weather records over several decades. “On July 4, 1776, Thomas Jefferson awoke to a cool Philadelphia summer morning: it was 20°C (68°F) at 6 am,” according to the American Museum of Natural History website. By 1 pm, temperatures were in the mid-seventies, according to a post by the organization Climate Reality.
I gave you a glimpse of “weather” on two dates in history. It is irresponsible to draw conclusions from two data points, but I don’t have too. Using proxies for past weather and more recent observations, studies confirm that climate is warming. I encourage you to read the most recent U.S. National Climate Assessment report housed at Climate.us. “Since 1970, July has warmed in 94% of 243 U.S. cities analyzed — by 2.6°F on average,” according to a report by Climate Central. In most places, July is the hottest month of the year.
July temperature trends in Philadelphia.
Since 1970, temperatures have steadily increased. The graphic above shows that there is year-to-year variability due to things like El Niño and La Niña, but the overall trend clearly establishes a warming trend. By the way, El Niño years, which we are currently within, tend to be warmer.
At this point, I will pause and reaffirm that scientists like me understand that climate has changed naturally throughout history. I promise you we know about icehouse periods, hothouse periods, Younger Dryas, the 1930’s Dust Bowl and so forth. Since the Industrial Revolution, a human steroid is sitting on top of the naturally-varying climate. It is a flawed narrative to assume it is either natural “or” anthropogenic change. Like most things in life, “and” is more appropriate.
Graphic showing global carbon dioxide emissions (blue) and global temperature change anomalies.
This article was originally published on Forbes.com
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