Millions of Americans will wake up cranky because climate change made it too hot to sleep, new research has found.

“As the global temperature rises, there will be greater levels of sleep difficulty, particularly in places where people do not have or can not afford air conditioning,” Sara Mednick, a University of California psychologist and co-author of the study, tells Inverse. “When we are trying to fall asleep, decreasing body temperature is one of the strongest signals to our brain to bring on sleep onset. This decrease in temperature is regulated in part by the ambient temperature. Thus, when the ambient temperature is too high, the body cannot cool itself and therefore can’t fall asleep, and if it wakes up at night the body will have a hard time getting back to sleep.”

The research, published Friday in Science Advances, quantified just how much global warming will disturb sleep in the United States. The researchers took survey data from 765,000 respondents over 10 years and correlated self-reported restless sleep with night time temperature data, and indeed found that abnormally warm nights correlated with grumpy mornings. That was the case in particular for poorer people and the elderly.

Areas of the western and northern United States -- where nighttime temperatures are projected to increase most -- may experience the largest future changes in sleep.
Some U.S. regions will feel the night-time heat more than others.

By accounting for expected future warming, the researchers predicted that by 2050 there will be six additional restless nights each month per 100 people because of the heat. By 2099 that figure will jump to 16. That’s millions of Americans waking up tired when they otherwise would have slept well. Of course that’s on average — in reality, winter months will have much less, and summer months much more. “Ultimately, it’s hard to predict with any high degree of certainty exactly what human behaviors will look like in 2099, but we see from recent data that our sleep is disrupted by unusually warm summer nights, and there’s every reason to believe that absent additional adaptation, this trend could continue into future decades,” lead author Nick Obradovich tells Inverse by email. Obradovich completed this research as a Ph.D. candidate at University of California San Diego; he is currently a postdoctoral fellow at Harvard’s Kennedy School of Government and a research scientist at the MIT Media Lab.

Access to an air conditioner in your bedroom probably mitigates a large part of this effect, but perhaps not all, Obradovich explains. It could be that daytime exposure to heat affects a good night’s sleep, too. There’s certainly lots of evidence that the dog days of summer increase levels of stress and violence.

People may adjust to a new normal as temperatures climb, but it’s hard to say how quickly they will adapt, says Obradovich. But it’s a good lesson for all, that in addition to making sure your bedroom is nice and dark, you should do what you can to keep the temperature a little bit cooler than other rooms or outside, so your body gets the message that it’s time to shut down.

Abstract:

Human sleep is highly regulated by temperature. Might climate change — through increases in nighttime heat — disrupt sleep in the future? We conduct the inaugural investigation of the relationship between climatic anomalies, reports of insufficient sleep, and projected climate change. Using data from 765,000 U.S. survey respondents from 2002 to 2011, coupled with night time temperature data, we show that increases in nighttime temperatures amplify self-reported nights of insufficient sleep. We observe the largest effects during the summer and among both lower-income and elderly respondents. We combine our historical estimates with climate model projections and detail the potential sleep impacts of future climatic changes. Our study represents the largest ever investigation of the relationship between sleep and ambient temperature and provides the first evidence that climate change may disrupt human sleep.

Photos via N. Obradovich, Callee MacAulay / Wikimedia