Warmer Nights Caused by Climate Change Take a Toll on Sleep

A massive data crunch reveals how much sleep people across the planet could lose by the end of the century.

Two men sleep in a roadside bed during the heatwave in Kolkata, India on April 25, 2022. Maximum temperature was 38 degrees Celsius and minimum temperature in Kolkata was 28 degree Celsius according to an Indian Meteorological Department of Kolkata. Credit: Indranil Aditya/NurPhoto via Getty Images
Two men sleep in a roadside bed during the heatwave in Kolkata, India on April 25, 2022. Maximum temperature was 38 degrees Celsius (100.4 degrees Fahrenheit) in Kolkata and minimum temperature was 28 degree Celsius (82.4 degrees Fahrenheit) according to an Indian Meteorological Department in Kolkata. Credit: Indranil Aditya/NurPhoto via Getty Images

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Trouble sleeping?

Climate change may be to blame and, according to researchers, it’s only going to get worse.

A study released last week by a team of climatologists found that by the end of this century, sleeplessness related to global warming will be so pervasive that our descendants will likely lose roughly two and a half days of sleep per year compared to the levels that typical adults enjoy today.

The findings, published in a peer-reviewed study in the journal One Earth, used data from more than 10 billion sleep-duration measurements from tracking wristbands across 68 different countries and combined that with local weather and climate data.

“We found that warmer than average nights harmed human sleep globally and unequally so people sleep less and the probability of having a short night of sleep steeply increases as the temperatures warm outside,” said Kelton Minor, a doctoral student at the University of Copenhagen Center for Social Data Science and the lead author of the study.

“And I think importantly, we found that this hidden human cost of heat is not distributed equally in the population,” Minor said, noting that he and his colleagues found that sleep loss per degree of warming occurs approximately twice as much among the elderly as compared to younger or middle aged adults. That rate was approximately three times higher for lower income versus high income countries.

Minor said that nighttime temperatures are warming faster than daytime temperatures for two reasons: anthropogenic – or human-induced – climate change and urbanization.

“On top of the global warming that we are experiencing, which is warming in most land-based regions faster at night than during the day, we also have more people moving into urban environments where the urban fabric itself—the asphalt, the lack of greenery—releases heat at night when people are sleeping,” he said. “So it creates this urban heat island effect, which amplifies nighttime temperatures.”

Donald Edmondson, a social psychologist and the director of the Center for Behavioral Cardiovascular Health at Columbia University Irving Medical Center, said the study was one of the first to measure the effects of climate change on sleep patterns.

That is significant, Edmondson said, because of what research has found about the links between length of sleep and the risk of adverse health events.

He said that one analysis has shown that when people sleep for fewer than 6 hours, they are as much as 50 percent more likely to have a cardiovascular event.

“In the long term, as short sleep nights accumulate, the risk continues to increase,” Edmondson said.

Minor said that researchers were unable to determine why those lower-income countries were at greater risk for sleep loss.

“We don’t know exactly why,” Minor said. “It could be access to air conditioning, it may be access to other technologies. Unfortunately, we did not randomize or measure those outcomes. But what we do know is that there is a large disparity in the size of the effect by country income level. And, you know, that’s sort of ground for future research as well to try to understand what is driving that vulnerability.”

Christian Braneon, a climate scientist who is co-director at Columbia University’s Environmental Justice and Climate Just Cities Network, urged urban planners, public policy experts and others to keep the most vulnerable in mind as they work to mitigate the effects of climate change.

“In the context of low income countries, what you see previously in the literature is people say, ‘These folks are maybe in areas of high crime, so they can’t just leave their window open.’ And so that’s a concern,” Braneon said.

“We often don’t talk about climate change impacts on quality of life,” he said. “Folks won’t necessarily die during every extreme weather event or every heat wave, but their quality of life is being compromised. And this could exacerbate chronic illnesses, and ultimately lead to shorter life lifespans and and other other challenges for people.”

Minor and his team found that by 2099, people could lose anywhere from 50 to 58 hours of sleep annually—the equivalent of two and a half days when combined or 11 nights of short sleep per person per year.

“And that number is going to increase,” Minor said. “But how much it increases will depend on the actions we take today to lower the future burden of nighttime temperature on human slumber. And we don’t know at this point in time which trajectory we will take within the Earth’s climate system. 

“We are in control of our destiny,” he said. “We have to act as a society if we want to make a dent.”