Doyle Rice

USA TODAY

Climate change is even getting in the way of a decent night's sleep. Hotter nighttime temperatures are disrupting sleep patterns, a new study finds, with more sleep lost in the summer and among elderly and lower-income Americans.

It's the largest real-world study yet to link lack of sleep and unusually warm nighttime temperatures, and the first to look at what that means in the future if global warming remains unchecked.

"In recent years, we found that unusually warm nights are associated with increased reports of nights of insufficient sleep," said study lead author Nick Obradovich, who conducted much of the research as a doctoral student at the University of California San Diego.

In October 2015, an unusual heat wave hit San Diego, where not everyone has air conditioning. Obradovich and his colleague Robyn Migliorini noticed "friends and colleagues in grad school weren't sleeping well at night — sheets off, tossing and turning in the heat — and as a result people were lethargic and somewhat grumpy," he said. "It was pretty unpleasant."

Spurred on by that experience, Obradovich found no one had studied sleep disruptions as a potential impact of climate change.

Researchers collected sleep data from 765,000 U.S. residents and compared the nights they reported trouble sleeping to temperature data from the National Oceanic and Atmospheric Administration. They found that unusually warm temperatures led to three nights of poor sleep per 100 people per month.

Lower-income people suffered more sleep loss because they face tighter budgets than high-income individuals. "Running the air conditioning all night can be costly," Obradovich said.

The study found that if global warming isn't slowed by the end of the century, scorching temperatures could cost Americans several hundred million nights of lost sleep each year.

"Human sleep is affected by nighttime temperatures, and in order to sleep well during the summer when temperatures are warmer than normal, we may need to adapt using more air conditioning, added fans at night and other technologies to counteract altered future temperatures," said Obradovich, now at Harvard University’s Kennedy School of Government.

And it might be more than an American phenomenon: “We don’t have sleep data from around the world, but assuming the pattern is similar, one can imagine that in places that are warmer or poorer or both, what we’d find could be even worse,” he added.

University of Miami scientist Laurence Kalkstein, an expert on the impacts of heat waves on human health who was not involved in the study, complimented the research.

"Increased nighttime temperatures can lead to other health problems, including increased emergency room visits and even increased heat-related deaths … the authors acknowledge that other negative health-related factors can be affected by higher overnight temperatures,” he said.

Kalkstein said a good topic for future research would be whether people adapt to the more frequent warmer nights, noting “humans do have a great ability to acclimatize.”

The study was published in Science Advances, a peer-reviewed journal published by the American Association for the Advancement of Science.