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.