This Is Your Kid’s Brain on Extreme Heat

It’s too hot for school, as stifling classrooms cause some teachers to switch to remote learning—or cancel lessons altogether. And the heat will only get worse.

THE HEAT TAKES a slow and brutal toll on the teens in Sarah Mueller’s high school chemistry class in Pittsburgh, Pennsylvania. By 7:30 in the morning, the classroom can hit 84 degrees Fahrenheit. Mueller tries to keep students’ spirits up by joking with them. (“People pay a lot of money for saunas, and you’re getting it for free!”) She estimates that over the years she has spent at least $1,000 of her own money on fans. It’s still not enough. By the end of the day, her students are sweating, exhausted, and unable to focus. “Trying to make someone who’s practically melted learn about different types of matter is just against the Geneva Convention,” says Mueller.

Blistering heat and humidity pummeled schools across the United States last week, just as young people were returning for the new school year. As temperatures soared to the 90s during the first week of September, students in Detroit, Michigan, and Newark, New Jersey, were dismissed early; in Mueller’s district, schools without air-conditioning pivoted to remote learning for two days, in a move that recalled Covid-19 emergency remote learning. Schools are getting hotter—and it’s getting increasingly impossible to teach and learn in them.

Heat affects the brain in a few key ways. First of all, overheating is just distracting. If a kid is miserably sweating out a heat wave, they’re not focusing properly on the test in front of them. On hot days, Mueller says her students struggle to keep their heads up off their desks, much less focus on a lesson about lab safety.

And physiologically, young people are extra vulnerable to heat stress because their bodies are still developing. To keep from overheating, the body sweats, of course. But it also diverts some blood from the organs toward the skin, releasing heat into the surrounding air. (That’s why skin flushes when it’s hot out.) This can lead to a deficiency in oxygen in certain tissues, which in turn leads to cognitive impairment. This can happen to overheating teachers, too, potentially reducing the quality of their instruction on hot days.

“When we don't have as much blood—with a lot of hemoglobin and oxygen—going into the brain, we can't focus, we can’t think, and we can't learn as efficiently as we should,” says Tarik Benmarhnia, an environmental epidemiologist at UC San Diego. “Concentration is just not a priority, obviously, because the body is working very, very hard to try to cool down the temperature—that's a priority.”

Children with asthma are particularly at risk, because high temperatures lead to the formation of ozone, which irritates the airways. At its least harmful, this discomfort further distracts asthmatic students. But extreme heat can also send them to the hospital if an asthma attack escalates. That’s not only dangerous, it also disrupts their schooling.

Heat waves raise the risk of mental health issues like mood and anxiety disorders, and are well known to increase aggression. Mueller, the teacher in Pittsburgh, observes that fights tend to happen more frequently on her campus when it’s warmer. Just last week, she says, two broke out on the same day.

Lengthy heat waves are especially damaging because they prevent students from resting at night and coming back to school refreshed. For kids without AC at home, it’s already hot when they wake up. Then many of them walk to school in the heat, or ride a less-than-comfortable bus. They may return home to a hot house and struggle to sleep. “They can't sleep very well, so they're super tired when they go to school, and this is just exacerbating all of these patterns,” says Benmarhnia. “Kids, especially teenagers, need a lot of sleep—and good sleep—for incorporating the learning, but also just to be ready for the next day.”

Scientists are beginning to quantify just how significantly heat is affecting schoolchildren in this way. In one 2020 paper, researchers gathered data on students who’d taken the PSAT multiple times, most commonly in October of their sophomore year, then again a year later. They also got daily temperature data from thousands of weather stations dotted across the US showing what the weather was like in those years. They surveyed some of those students, asking, for instance, how often it was too hot to learn in their classrooms. They were able to show how high temperatures—and lack of air-conditioning—in the run-up to the PSATs affected scores. In schools with no AC, for each increase of 1 degree Fahrenheit, students’ PSAT scores the second year were 1 percent lower than a typical year’s gain between PSAT takes.

“It turns out when a student experiences a particularly hot year, they score lower on that exam than you would expect given their other test scores,” says Boston University education economist Joshua Goodman, who coauthored the paper. “And so we took that as evidence that it's not just heat on the day of the exam that matters, it's heat having a longer-term impact. Having spent the year learning in an unusually hot classroom has that cumulative effect on the day of the exam, even if the day of the exam itself is perfectly temperate.”

COURTESY OF SARAH MUELLER

A 2021 follow-up study conducted in 58 countries found that this trend is internationally true: Students schooled in warmer years do worse on exams than students from those same countries schooled in cooler years.

In the US, there are both geographical and demographic disparities that affect who ends up struggling in a hot classroom. A 90-degree day in Phoenix, for example, is a different beast than a 90-degree day in Boston. Phoenix is built on air-conditioning, whereas northern climates have until recently managed with less AC penetration. The human body also adapts to heat over time, to a certain extent: Phoenix residents might be physiologically better equipped to deal with 90-degree temperatures than Bostonians.

“Areas of the country that appear to be less adapted—that have cooler climates—on average there appears to be a higher marginal effect,” says University of Pennsylvania environmental economist R. Jisung Park, coauthor of both the 2020 and 2021 papers. “So the same hot day appears to do more damage in terms of learning.”

Goodman and Park’s 2020 paper finds that the learning of Black and Hispanic students is three times as inhibited by excessive heat as that of white students—most likely because schools in their neighborhoods lack AC. The researchers further estimate that somewhere between 3 and 7 percent of the PSAT score gap between white students and their Black and Hispanic schoolmates could be explained by temperature. “Even within a major metropolitan area, we find evidence consistent with there being a correlation between higher-minority schools having less adequate air-conditioning,” says Park. “That is certainly the case in many urban contexts, where low-income folks tend to live in places that are more susceptible to urban heat islands.”

COURTESY OF SARAH MUELLER

Park is referring to the increasingly severe phenomenon of urban areas getting way, way hotter than surrounding rural ones. Concrete and buildings soak up the sun’s energy by day and slowly release it at night, and cities lack vegetation that can “sweat” to cool the landscape. “Unfortunately, the case is that we see lower-income communities—which tend to be those that have a larger preponderance of impervious surfaces, buildings, and asphalt, and a lower cover of trees and other vegetation—those do tend to be the hotter ones,” says Edith de Guzman, who studies urban heat at the UCLA Luskin Center for Innovation. Schools are themselves little urban heat islands, with lots of densely packed buildings surrounded by impermeable surfaces like basketball or tennis courts, parking lots, and courtyards.

There’s an obvious fix: more school air-conditioning. That will come at a cost, for sure, and US schools are already catastrophically underfunded. But in their 2020 paper, Goodman and Park frame it as an investment, estimating that when the climate warms by 5 degrees Fahrenheit during a school year, equipping a school with AC would avoid $1,060 in future earnings loss per student, thanks to their improved academic performance. “You better air-condition schools, you plant more trees,” says Goodman. “This one has a fairly clear policy solution. Not necessarily cheap, but clear at least.”

Revamping American schools to prepare them for hotter temperatures will be an immense undertaking. An estimated 41 percent of school districts require upgrades to their heating, ventilation, and air-conditioning systems, according to a 2019 survey from the US Government Accountability Office. This represents about 36,000 schools.

There’s federal Covid relief funding available to help fix schools, and an analysis from the nonprofit FutureEd found that half of school districts in the US plan to spend it on HVAC upgrades. But it’s unclear how much will be put toward air-conditioning. In older buildings, installing AC could mean overhauling a decades-old electrical system, a costly, years-long undertaking that may require public votes for approval.

And even when schools secure the resources to install air-conditioning, the pandemic’s lingering supply chain issues can cause significant slowdowns. In Highland Park, Illinois, superintendent Michael Lubenfeld says that recent major renovations to two middle schools took over four years from approval to completion. As part of the renovation, the district overhauled a 1950s heat-only HVAC system to install air filtration and air-conditioning. The HVAC and cooling renovation costs alone for one middle school were estimated at $6.7 million. “We need help,” he says. “We almost need a Marshall Plan for school infrastructure from the federal government.”

Air-conditioning is also just one item on a long list of much needed (and increasingly urgent) upgrades to schools as temperatures climb. Franca Muller Paz, a Spanish teacher at Baltimore City College High School, says her students can’t drink from school water fountains because of high levels of lead. Instead, schools provide water coolers. “Students are really thirsty. They feel groggy from the heat,” she says. “You’re not going to retain what you’re learning when your body is feeling like that.” Last week, Baltimore City Public Schools instructed teachers in 20 schools without air-conditioning, including Muller Paz’s campus, to switch to remote learning due to extreme heat, per the district’s inclement weather protocol.

Representatives from the Baltimore City and Pittsburgh school districts did not immediately respond to requests for comment. But in May, Cyndi Smith, Baltimore City Public Schools’ director of facilities design and construction, told WBAL-TV that the district has plans and funding to update 13 schools that do not have air-conditioning, although in some cases that’s part of a major renovation. Last week, superintendent of Pittsburgh Public Schools Wayne Walters told Pittsburgh’s Action News 4 that because schools in his district are more than 80 years old on average, adding air-conditioning often requires also doing asbestos abatement, which is costly.

Bouts of extreme weather call into question whether schools are prepared for a worsening climate crisis. In June, schools across the US East Coast were closed due to dangerous levels of smoke from Canada’s wildfires. Protecting schools, advocates say, means combating the climate crisis at large. “Climate change and extreme weather is a threat multiplier around educational equity,” says Jonathan Klein, cofounder and CEO of UndauntedK12, a nonprofit that maintains a map of school closures due to extreme weather. He points to California’s Senate Bill 394 that would task a commission with coming up with a plan to fund and design “climate-resilient” schools.

Even in schools equipped with air-conditioning, teachers worry about high temperatures outdoors. Air-conditioning is the norm in Las Vegas, Nevada, where desert temperatures can soar into the triple digits. But first grade teacher Shivani Bhakta says that it’s hard to get her kids to focus after recess, when her classroom becomes “like a revolving door” of students asking for water and going to the bathroom. “If it gets any hotter, I’d be questioning the whole recess situation,” she says.

For now, schools without AC are resorting to short-term fixes that cause kids to lose valuable learning time—often in ways that exacerbate inequalities. In some schools, teachers must take time to move their students out of the classroom and into cooler areas. These are often common areas, like libraries, that are shared with other classes and aren’t always equipped with classroom supplies. Other schools resort to early dismissals, which are a challenge for working parents who struggle to find child care. Virtual learning on hot days is a band-aid; even though schools are now largely equipped with laptops for students, emergency remote learning has been associated with larger academic losses. Wealthier students can make up for lost learning time with tutoring, and in the event of school closures, they may have reliable access at home to air-conditioning and a comfortable learning environment. But low-income kids may continue to fall behind.

Muller Paz, the Spanish teacher in Baltimore, worries about how the worsening heat will affect her students’ futures. Many of them hope to be the first in their families to attend college. “It makes me angry because I want to see our students succeed, and it feels so unfair that they have to learn in these conditions, whereas their peers in other, wealthier schools are able to comfortably learn and not have to deal with these issues. It absolutely impacts my students’ focus,” she says. “Our kids deserve so much better.”

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