If global emissions are allowed to continue at a high level, the paper found, then additional nights of sleeplessness can be expected beyond what people normally experience. By 2050, for every 100 Americans, an extra six nights of sleeplessness can be expected every month, the researchers calculated. By 2099, that would more than double, to 14 additional nights of tossing and turning each month for every 100 people, in their estimation.
Researchers have long known that being too hot or too cold at night can disturb anyone’s sleep, but nobody had thought to ask how that might affect people in a world grown hotter because of climate change.
Dr. Obradovich is a political scientist who researches both the politics of climate change and its likely human impacts, holding appointments at Harvard and the Massachusetts Institute of Technology. He started the research while completing a doctoral degree at the University of California, San Diego.
He got the idea for the study while enduring a 2015 heat wave in an apartment in San Diego with no air-conditioner in the bedroom.
”I wasn’t sleeping,” he recalled. “My friends weren’t sleeping. My colleagues weren’t sleeping. The levels of grumpiness were higher than normal.”
To calculate the effect of warmer temperatures in the future, he turned to data collected by the Centers for Disease Control and Prevention, which asks people in a survey to recall their sleep patterns in the previous month. Sure enough, he found a correlation between higher temperatures in particular cities and disturbed sleep as reported by their residents. To make forecasts, he drew on computer estimates of how hot particular places will get if greenhouse emissions continue at a high level.
Dr. Obradovich acknowledged that a survey about sleep over the previous month was subject to the vagaries of memory. More definitive research would involve putting lots of people in a sleep laboratory and manipulating the temperature to see what happened. “Those ideal data don’t exist and would be prohibitively expensive to collect,” he said.
A bigger weakness in the study, perhaps, is that it is impossible to know what human society will look like 100 years from now. How many people will be without air-conditioning in that world?
Jerome M. Siegel, head of a sleep laboratory at the University of California, Los Angeles, who was not involved in the study, said the assumptions and data limitations gave him pause.
“It’s sort of a nice exercise — yes, this is something that might affect people,” Dr. Siegel said. “But this would be way down on my list of things to worry about with climate change, even though I’m a sleep researcher.”