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 MIT 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 impact of climate change, was curious if he could find evidence that heat waves and other temperature anomalies had any effect 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.
Further analysis revealed that hot nights don't affect all of us the same way. He found that people who earn $50,000 or less a year are three times more likely to report a poor night's sleep on an unusually warm night than those who make more than $50,000. That result could be because poorer people don't have air conditioners or don't have the money to run them.
In addition, he found that people over 65 are twice as likely to have trouble sleeping on a hot night than their younger neighbors. This might be due to a previously reported result that older people have more difficulty regulating their body temperature than younger folks.
Finally, Obradovich looked at the predicted effects of climate change on temperature in the future and found that, on average, by 2050 rising temperatures will cause six additional nights of insufficient sleep per 100 individuals, and by 2099 it will cause an excess of about 14 nights of tossing and turning per 100 individuals.
Maybe you don't think that's such a big deal. So a bunch of people won't be able to sleep so well in the future — who cares? Well, keep in mind that insufficient sleep is associated with a whole host of issues including raising the risk of heart disease, diabetes and obesity, as well as a reduction in memory, attention and processing abilities. It also puts people in bad moods and has been linked with the onset of depression.
And if all that isn't bad enough, Obradovich warns that the effects of climate change on sleep might easily be worse in parts of the planet where most people can't afford to take measures to keep themselves cool.
"When I started the study, it wasn't clear to me that we would even observe an effect in the U.S. because we do have air conditioning here," he said. "The fact that we do observe an effect makes me think that if we had data from India or Brazil, we would observe a much larger effect."
MORE IN SCIENCE