Human bodies react swiftly when they overheat.
Blood rushes to the skin, trying to find cool air. Sweat seeps out of the skin and evaporates, dissipating body heat. But these processes have a cost: they reduce blood circulation, which means our most important organ, the brain, gets less blood.
“And with reduced brain blood flow, we have reduced brain function,” said Tony Wolf, a researcher at Penn State University who studies how the body reacts to heat.
In short, heat can lower our cognition.
But it doesn’t take a PhD to know this. Just ask middle school students.
Researchers have long known about heat’s profound impact on the human body – and found a pretty effective way to combat it: air conditioning.
But nearly a century later a huge portion of American classrooms are still sweltering hot and don’t have air conditioning. And new research is showing that the ramifications are devastating: the more hot school days there are, the less students learn – and the effect is noticeably worse for students of color.
“It’s another form of the same message: ‘We’re not investing in you,’” said Shelley Goulder, who teaches in rooms without air conditioning in the Oakland public school district.
Researchers have found that our cognition really starts to suffer at about 80F (27C). So first we need to find out how many school days exceed 80F in your district.
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“It’s not that we don’t understand atmospheric effects or don’t have technology to cool a room,” Park said. “So why is it that plurality of US classrooms don’t appear to have working air conditioning?”
Starting in the 1930s, the US government started to back home loans for Americans to help them build up wealth – but the US refused to back loans for Black people, or even white people who wanted to live near Black people. This is called redlining. This policy created segregated Black neighborhoods that cities often failed to invest in.
That’s largely why American cities are still highly segregated today. And that underlying segregation plays out in schools because US students are usually assigned schools based on where they live.
In the four maps of major cities below, we can see that within the same school district there are school zones with high percentages of Black and Hispanic families, while just miles away there are school zones with predominantly white families.
In many historically redlined neighborhoods, cities built elements that trap and radiate heat, like highways and parking lots. Meanwhile in more affluent white neighborhoods, they installed heat-soaking elements, like parks and trees.
When Portland State University researcher Vivek Shandas measured the temperature in historically redlined areas compared with the rest of the city, he found that redlined areas were 5F hotter than their non-redlined counterparts across the US.
This ultimately means Black and Hispanic children are living and going to school in hotter neighborhoods, which could largely explain why hot days hurt them more.
“If they’re never really able to cool down to a normal body temperature, then that’s an issue,” said Wolf, the heat researcher. “We know that constant heat stress, where you don’t really get a break from this, is a really large stressor. That compounds itself from day to day.”
The racial disparity is apparent in many districts.
At Brooklyn Collaborative, a public school in New York City that is predominantly students of color, teachers spend hot days trying to help their students cope without air conditioning.
“Summer is a mad dash for fans. People label their fans so they don’t get stolen,” said Tracy Wu, who teaches middle schoolers there. “I’ve also in years past looked up how to make a DIY air conditioner with a styrofoam cooler and ice.”
Park and his colleagues found that this racial disparity in air conditioning is true across the country, after controlling for how hot a region is.
During one memorably hot week in California’s Oakland public school district, middle school teacher Shelley Goulder remembers the odor of hormonal adolescent kids building up throughout the day.
Normally one small relief would have been to crack a window, just a bit.
But that week, the nearby California wildfires made the air unsafe to breathe. “There was no way to ventilate safely,” Goulder said. So the windows stayed closed.
“They say our education is so important – yeah, our education is important. They give us hope, but at the end of the day it’s not there,” said Emely Rodriguez-Alvarado, a student who was in that class.
Another student, Hazel Zarate Fernandez, mentioned a nearby school district – one she knows has air conditioning: “It doesn’t surprise me because I think I’m maybe used to it. I understand how everything works and how everything in the world is unfair.”