PHILADELPHIA - As a girl growing up here, Natalie McHugh used to play on the vast expanses of asphalt and concrete that coated the city's schoolyards.
She didn't question as a student why there weren't more trees or think twice about the blacktop during her decades as an educator at Southwark Elementary School in South Philadelphia. Then, one day, as McHugh monitored recess with the school's principal, her boss said something that made her see all that asphalt differently: "He said, 'This is not good, Nat.' And I was like, 'What do you mean?'" she said.
Since then, Southwark's schoolyard has been transformed, one of more than a dozen in Philadelphia where the Trust for Public Land, a nonprofit that helps create public parks, has done things such as plant trees, build rain gardens, and install play equipment and an outdoor classroom. Activists and parents have long worked, school by school, to turn asphalt playgrounds into islands of greenery. But as climate change sends temperatures soaring, the movement to replace heat-absorbing pavement around schools has gained urgency. School districts, cities and states are increasingly taking up the cause, spurred by research showing that asphalt play areas - many of which were installed decades ago - magnify the health risks of extreme heat.
The Trust for Public Land, which has helped renovate more than 300 school playgrounds in 23 states and on tribal lands, describes the need as massive. According to the group, public schools cover about 2 million acres of land, much of which has been cleared of trees.
Within cities, temperatures are typically hottest in dense, low-income neighborhoods with little tree cover, where roads, buildings and parking lots soak up the sun's rays - known as the urban heat island effect. Schools in these areas tend to be even hotter, said Kelly Turner, a heat expert at UCLA, because they have less shade and more asphalt.
"Schools are basically shade deserts," said Turner, who has studied public schools in Los Angeles and is working to quantify how much shade is enough to keep children safe.
"Often what we see at outdoor play spaces, where asphalt was thought to be the safest surface in the 1980s, is a little heat island within the larger heat island," said Jennifer Vanos, an associate professor at the School of Sustainability at Arizona State University.
This is not unique to urban school districts, Vanos added. "It's going to be a problem everywhere because of the ways in which schools have been just paved over."
Hotter play spaces are increasing the risk of contact burns and heat illness among children. Researchers at UCLA have documented surface temperatures of 145 degrees Fahrenheit on schoolyard asphalt. They have found that rubber and artificial turf, many districts' go-to alternatives to pavement, can get even hotter.
This summer, California's governor and legislature agreed to place a $10 billion school bond before voters in November. If approved, a portion of it may be used to plant trees and reduce the amount of pavement around public schools. In Los Angeles, the school district has committed $500 million to greening projects, and the board has approved a $9 billion school facilities bond, its largest ever, of which about $1.25 billion could go toward planting trees, creating shade structures and removing asphalt.
There are other changes the state can enact without voter approval. California is spending millions to plant trees in school playgrounds throughout the state, partnering with Green Schoolyards America, a nonprofit that helped the San Francisco and Oakland school districts start play-space renovation programs. The organization's CEO, Sharon Danks, said early efforts are underway to replicate this work in Nevada and New Mexico.
"When you plant trees, you also get benefits for children's well-being, for their learning, for play, for community access," Danks said. "But this work is primarily about heat and mitigating the impacts of climate change."
Today, the Los Angeles Unified School District has a goal of converting at least 30% of every schoolyard to green space, a yearslong project that it expects to cost $3 billion. By its own estimate, about 475 schools do not meet that standard and, of them, more than 200 elementary schools have less than 10% green space. This analysis does not include school parking lots or truck delivery areas - paved surfaces that are likely to remain that way and raise the temperature around schools.
About 100 schools have greening projects in design or under construction, officials said. In the meantime, the district has begun providing schools with outdoor misters and shade tents.
In an example of just how hot areas around schools can get, surface temperatures rose above 160 degrees at a Los Angeles public elementary schoolyard on a Monday afternoon in May 2021, according to data gathered by the NASA Jet Propulsion Laboratory. An L.A. Unified spokesperson said the district is planning to green Sunny Brae Elementary School's playground and expects to solicit construction proposals in early 2025.
Turner has found schools in Los Angeles that, under the glare of high noon, are less than 1% shaded.
"When we have quantified the amount of shade in schools versus the communities that surround them, in virtually every single one, the school has less shade," she said.
"If they knew what they were doing, they wouldn't have done what they did 30 or 40 years ago," said Christos Chrysiliou, L.A. Unified's chief eco-sustainability officer, referring to the district's past enthusiasm for asphalt. "It was under different logic, different thinking, but the impacts have become bigger."
The difficulty of fixing the problem was on display at Webster Elementary in Philadelphia's Kensington neighborhood. A sea of asphalt greeted students arriving to school, interrupted only by some wooden benches, a flagpole flanked by metal bollards and a stretch of concrete where trucks deposit deliveries of heating oil into underground tanks. There were no trees, no slides, no swings. It was as inviting a play space as the school parking lot.
Ripping up all that asphalt is expensive, advocates said, and city schools typically have more of it to begin with. This can make greening a schoolyard like Webster's significantly more costly than renovating a suburban school's playground, yet large urban districts often have less money to spend.
Webster, after years of waiting, is now on the list of schools to be renovated by the Trust for Public Land. The nonprofit will work with a class of third-graders and landscape architects for the next year to design a new schoolyard. Projects like this can take two to three years to complete, at a cost ranging from $400,000 to as much as $2.5 million, said Danielle Denk, who directs the organization's schoolyard transformation work. In Philadelphia, most of the money for these projects comes from the water department, which is trying to make the city more capable of absorbing storm runoff.
Persuading states to pay for these projects long-term takes "a demonstration of this work in many different places, so that people can begin to understand what could be there if they advocated for it," Denk said.
Funding disparities between school districts are another obstacle, advocates said. Because poorer districts can't afford large maintenance crews, advocates said that officials are sometimes less enthused about replacing pavement with cooler materials such as wood chips and decomposed granite, preferring artificial turf and rubber. These materials can be cheaper to maintain, but brutally hot.
Some districts have refused shade structures, citing liability and maintenance fears, proponents said. Others fear planting trees because kids might run into them. Many of the debates, Turner said, are driven by a lack of funding as school districts and advocates struggle to create the most cooling for the least money.
"Everybody knows how to design a cool space: You put in more greenery, a ton of shade, you have lots of cross-ventilation. The problem is funding," she said. "Are voters prepared to really pony up the money to make our schools safe for children in 20 or 30 years?"