Researchers say global warming might affect how well we sleep at night

It’s no surprise that a change in our planet’s climate would affect our coastlines, our weather patterns and our food supply. But here’s something you may not have considered before: Global warming might also affect how well we sleep at night.

In a paper published Friday in Science Advances, researchers show that when local temperatures get unusually high people don’t sleep as well as they usually do. And if climate trends continue, we can expect to have more frequent heat waves that also last longer.

“There are going to be lots and lots of impacts of climate change and this is just another factor in a mosaic of negative factors,” said Nick Obradovich, a postdoctoral fellow at the Harvard Kennedy School and a research scientist at the Massachusetts Institute of Technology media lab, who led the work.

If you’ve ever weathered a particularly sweaty summer in a stuffy apartment with no air conditioning, then you know how hard it can be to fall asleep when the temperature is sky high.

It turns out that we actually need to cool down a bit before we go to sleep. Previous research has shown that just before bedtime our core temperature dips, signaling that it’s time for some shut-eye.

Our bodies have a few mechanisms for shedding the excess heat; the blood vessels in our skin dilate, which helps heat escape through the skin, and our hands and feet get warmer, which helps move heat away from the core.

However, lab studies have shown that the body has trouble shedding its core heat when the room temperature is uncomfortably warm. These studies have also found that elevated core temperature is associated with trouble falling and staying asleep.

Obradovich, who studies the social effect of climate change, was curious if he could find evidence that heat waves and other temperature anomalies had any influence on people in the real world. The idea came to him when he was struggling to sleep in his own just-barely air-conditioned apartment in the midst of a particularly hot stretch in the fall of 2015.

“We had an old window unit that could barely cool the living room, and certainly couldn’t send cool air back to the bedroom,” he said. “At night I was tossing and turning, no sheets. And it wasn’t just me. The next day I noticed that my friends and colleagues were all lethargic and grumpy.”

Obradovich wondered if he could get more quantitative evidence that would show that people don’t sleep as well when the temperature starts to climb. To find out, he turned to a survey of 765,000 U.S. residents that asked respondents to say how many of the past 30 days they felt they did not get enough rest or sleep and compared their answers with weather data at the city level.

The results were telling: the higher the temperature was compared to average, the greater the number of nights that people report not being able to sleep well.

“If the entire United States experienced a warming of 1 degree Celsius, that would be associated with 9 million nights of insufficient sleep per month,” Obradovich said.