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Philly’s summer temps have risen 3 degrees since 1970 — and nights have gotten even warmer

The average summer temperature in Philadelphia has risen 3 degrees since 1970, and summer nights have gotten ever warmer than that in a city where some neighborhoods feel the heat more than others.

Friends stay cool in the heat June 7, 2021, playing dominoes in their 'clubhouse' at Jefferson Street & Germantown Avenue in the Old Kensington neighborhood.
Friends stay cool in the heat June 7, 2021, playing dominoes in their 'clubhouse' at Jefferson Street & Germantown Avenue in the Old Kensington neighborhood.Read moreTOM GRALISH / Staff Photographer

The Hunting Park Neighborhood Advisory Committee surveyed residents last year about how they cope with heat and asked how many had air-conditioning.

Out of 563 who answered that question, only 100 had air-conditioning, said Charles Lanier, the nonprofit’s executive director.

“We all know climate change is real and environmental justice is real,” said Lanier, whose group is seeking donations to buy air conditioners and fans. “So we are looking at how can we help people to stay cool, with most of them staying indoors without proper cooling or ventilation.”

That mission has become especially important as Philadelphia declared its first heat emergency of the season Monday. It is in effect until 11:59 p.m. Wednesday as heat indexes are expected to reach triple digits.

An analysis of 51 years of weather data shows summers are getting hotter in Philadelphia. The average temperature for the city in the summer of 1970 was 75.09 degrees, while last year’s summer average was 78.39.

Overall, the average summer temperature in Philadelphia has gotten 3 degrees warmer.

Perhaps worse, average summer nights have warmed by 3.8 degrees. The rising heat especially affects economically stressed neighborhoods populated mostly by Black and Latino residents, like Hunting Park, where there are more heat-absorbing hard surfaces and fewer tree-lined streets to offer residents shade. The result is known as the heat island effect.

Summers now average five more days of temperatures of 95 or above compared with 1970. And half of the top 10 hottest average summers occurred in the last decade.

The new data were provided by Climate Central, a group of scientists and journalists who study climate change. To derive their findings, researchers downloaded daily temperature data from the Applied Climate Information System and calculated an average temperature for June, July, and August each year. They then looked at trends for 246 weather stations around the nation.

The researchers found that Philadelphia followed the experience of much of the country — rising average summer temperatures, warmer summer nights, and an increase in the number of extremely hot days.

Their scientists say that heat-trapping greenhouse gases are causing the temperature rise and that most states will continue to see increases and more record-breaking heat events like that of the Western U.S., where the Olympic track trials had to be delayed four hours this week until temperatures dropped enough at night.

The national data showed:

  1. 95% of locations saw an increase in average summer temperature, with half of those increasing by 2 degrees or more.

  2. Nine out of the top 10 fastest-warming summer locations were in the Western U.S. and Texas, with Reno, Nev., up 10.6 degrees, Las Vegas up 5.6 degrees, and El Paso, Texas, up 5.5 degrees.

  3. Summer night temperatures increased by 2 degrees or more in 61% of locations.

  4. And 38% of locations reported, on average, at least one additional week of extremely hot temperatures annually, with the largest change in Miami with 79 additional days above 90 degrees.

Hotter summer days means more air pollution, as heat helps transform harmful pollutants close to ground level into ozone, which can worsen asthma and other lung diseases. Extreme heat is particularly hard on seniors, younger children, and people without air-conditioning. Warmer nights also interrupt sleep.

» READ MORE: Philly's air pollution soars in summer

“The impact of nighttime temperatures is a big concern to us,” said Saleem Chapman, Philadelphia’s chief resilience officer. “All the research points out that the most adverse effects happen in the nighttime hours because people’s bodies can’t cool down.”

Philadelphia saw four heat deaths each of the last two years, according to the city’s Department of Public Health.

Chapman, who has a background in biomedical engineering, said the city is researching ways to make the region more adaptable to climate change through a partnership with the Academy of Natural Sciences at Drexel University, the Delaware Valley Regional Planning Commission, and the Consortium for Climate Risks in the Urban Northeast.

He also noted the city’s plan to grow its tree canopy in neighborhoods that are lacking it. Trees can help cool an area by 20 degrees. In fact, there is a wide temperature disparity in Philadelphia, with some neighborhoods much cooler in summers than others.

» READ MORE: Climate change makes some Philadelphia neighborhoods extra steamy

Hard surfaces such as asphalt can bake up to 140 degrees in high heat. Chapman said hard surfaces continue to release energy at night, keeping the immediate surrounding area warm. Black roofs only add to that, although the city adopted an ordinance requiring some roofs to be white.

Lanier, the director of the Hunting Park neighborhood group, said the nonprofit has set up a GoFundMe page to take donations for air conditioners and fans.

“We found that it can be 22 degrees hotter here in Hunting Park than other neighborhoods,” Lanier said.

The organization is training heat ambassadors, starting Wednesday, to reach out to residents and identify their needs, including air conditioners and fans. The group will also provide cooling kits with sunscreen, electrolyte tablets, and other items, as well as showing residents where to find local cooling centers.

“It’s a community that needs all kinds of support and services, particularly our seniors,” Lanier said.

The Hunting Park pool, which has structural issues, is one of 22 of the city’s outdoor pools that will remain closed this summer.

In the Hunting Park group’s survey, 80% of residents identified “high heat” as a concern, Lanier said, noting that most people also said they stay home when it gets too hot.

And that, he said, is another reason why access to air-conditioning is so important.