Heat Wave Study Shows How Extra-Hot Summers Can Make People Dumber

Your brain really is feeling the heat.


Over 200 years ago, colonial Bostonians were concerned about freezing to death on a foreign continent when they built some of the city’s famous brick buildings. But now, those thick colonial walls aren’t just making modern life too sweaty but actually making 21st-century college students dumber, suggests research published Tuesday in PLOS Medicine. The implications of this, lead researcher Jose Guillermo Cedeño-Laurent, Ph.D. tells Inverse, have wide-reaching implications for how our buildings and bodies adapt to an ever-warming world.

We have all been warned about outdoor effects of climate change. For instance, places from Los Angeles to Quebec are currently experiencing heat waves that underline its dramatic effects. In the new study, Cedeño-Laurent, a research fellow at Harvard University’s T.H. Chan school of Public Health, shows that those effects, measured among students suffering through a historic Boston heat wave in the summer of 2016, can include measurable declines in cognitive ability.

He’s been thinking about how climate change follows us indoors since 2013. “We noticed that looking at the temperature profiles of indoor spaces,” he tells Inverse. “Despite the outdoor temperatures going down, the structures retained a lot of the heat. The indoor temperatures stayed very hot even after a couple of days.”

The Boston 2016 heat wave in which temperatures rose to 97 degrees during the day 

Time and Date 

Working off his previous research, Cedeño-Laurent’s new study reveals that high indoor temperatures can have very real physiological impacts that in turn affect cognitive ability. He and his team conducted the study on 44 undergraduate students, 22 of whom lived in un-air-conditioned Boston buildings built between 1930 and 1950 in a brick-based Georgian architectural style.

As they monitored these undergrads for 12 days during the heat wave, the team tracked a variety of physiological factors, including caffeine intake, hours of sleep, hydration, and heart rate. They even tracked the indoor temperature of each undergrad’s bedroom by installing thermostats. Then, each morning, each student received a text from the researchers prompting them to do ten math problems and correctly identify colors on their smartphones. The students living in non-air-conditioned, Neo-Georgian style buildings, like those lining Harvard’s campus, performed between 4 percent and 13 percent worse on these cognitive tests.

Cedeño-Laurent suggests that this decline is actually due to a series of physiological effects that are increased by spending extended time in hot, un-air-conditioned spaces. “In terms of direct physiology, we see a sustained increase in the heart rate of students in the non-air conditioned spaces,” he says. “More in-depth analysis is needed, but there is a chance of some dehydration and disruption of sleep patterns.”

An example of colonial-era buildings designed to trap heat inside. 


Anyone who has slept in a stuffy, hot room during the summer will be able to relate to his findings. For each 1 °C increase in indoor temperature, the students lost an average of 2.74 minutes of sleep, which can lead to decreased performance the next day, as previous studies have shown.

This said, turning up the air conditioners isn’t necessarily the best option. While AC might provide a good short-term strategy for preventing heat-induced declines in intelligence, the real problem is that some of New England structures built in the 1700s were designed to be especially suffocating because the region was in the grips of a “little ice age,” as previous climate research suggests. This is why some buildings in Boston, like the ones in this study, had “thick masonry walls” and few windows. They were designed to trap heat inside.

“Historically, our buildings provide shelter from cold temperature,” Cedeño-Laurent adds. “Basically, they’re being subjected to an unprecedented rise in temperature, and they’re being pushed to the limits of their performance.”

The Delaware River rarely freezes over today, but this famous painting of George Washington crossing the Delaware shows a river choked with ice. During the revolutionary war, the world was in the midst of a "little ice age" which informed how buildings were designed. 


To make matters worse, says Cedeño-Laurent, air conditioning actually exacerbates the problem. Air conditioning provides a dangerous positive feedback loop by expending energy and using coolants that are responsible for “some of the most potent greenhouse gases that humans know,” he says.

Cedeño-Laurent argues that architects and scientists need to fundamentally rethink building design to prevent issues like heat-related heart rate spikes during the era of anthropogenic climate change. For now, as we continue packing 21st-century people into buildings designed for a 17th-century climate, we’ll have to be prepared to deal with the consequences as our brains start to feel the effects.

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