Quirks & Quarks

Hot nights are disrupting our sleep — and climate change is making it worse, study finds

A new study analyzing the sleep data for thousands of people worldwide has found that we’re getting less sleep as nighttime temperatures increase, and it’s only going to get worse with climate change.

People are losing 45 hours of sleep per year, says study that tracked data of 47K people worldwide

A new study analyzing the sleep data of over 47,000 people worldwide has found that we're getting less sleep as nighttime temperatures increase, and it's only going to get worse with climate change. (Maridav/Shutterstock)

A new study analyzing the sleep data for thousands of people worldwide has found that we're getting less sleep as nighttime temperatures increase — and it's only going to get worse with climate change.

The study looked at over 7.4 million daily sleep records from people living in 68 countries, using data from increasingly popular fitness and activity health tracking devices to look at changes in sleep patterns with increasing nighttime heat.

After correlating them with local weather and climate data, it found that on hotter-than-average nights, people slept less — no matter what type of climate they live in.

"We know that in most populated regions, nighttime temperatures are outpacing the daytime rise in temperatures," said Kelton Minor, lead author of the study and a PhD candidate at the University of Copenhagen Center for Social Data Science.

The research was published this week in the journal One Earth.

Most fitness and health tracking apps or devices require users to agree allow the manufacturers to collect and share their data to access their services. Many of these services have options to choose which types of data are recorded, though some critics say they still collect more information than many users are aware.

50 hours of lost sleep per year by 2099

The study found that right now people are already losing an estimated 45 hours of sleep per year due to hotter nighttime temperatures. Since climate change tends to cause nighttime temperatures to rise faster than daytime temperatures, people worldwide are projected to lose an increasing amount of sleep every year.

"By 2099, under a moderate emissions scenario in which we actually successfully are able to stabilize emissions globally, we projected that people will be losing about 50 hours of sleep per person per year," said Minor.

However, the work suggests some people are likely to be more affected than others. The study found that people over the age of 60 are two times more impacted by the degree of warming compared to young or middle-aged adults.

Women were also found to be more sensitive to hotter nighttime temperatures than men. Lower-income countries were affected three times more than higher-income countries.

Kelton Minor is a PhD candidate at the University of Copenhagen Center for Social Data Science. (Submitted by Kelton Minor)

"The warmest parts of the world that in many cases are the least responsible for climate change are disproportionately losing more sleep," said Minor.

"Surprisingly, we found that people already living in warmer climates lose more sleep per degree of warming globally than those living in colder climates, suggesting limited adaptation."

Cooler nights had the opposite effect, increasing sleep duration, suggesting that humans are better at buffering against the effects of cold.

Sleep loss hidden cost of climate change

Hotter-than-average temperatures have many negative health effects and have been linked to higher mortality rates. But Minor says sleep loss was, until now at least, a hidden human cost of these deadly heat waves.

The study estimated that on nights that exceed 25 C, approximately 4,600 people out of 100,000 get fewer than seven hours of sleep.

The sun sets behind power lines in Los Angeles on Sept. 3, 2020, during a heat wave. (Frederic J. Brown/AFP/Getty Images)

"So, you can imagine if you're in a city of 1 million, we would estimate that one night of greater than 25 C temperature would exact about 46,000 additional nights of short sleep in that population," said Minor.

"With increased nighttime temperatures, sleep erosion impacts the entire population, which can have serious consequences."

Lack of sleep linked to health issues

Minor suggested that air conditioning is a good tool to combat sleep loss due to heat, but only if it is accessible to lower-income populations as well. He noted that air conditioners actually contribute to heating the air outside by releasing their waste heat into the surrounding environment. 

A few extra hours of lost sleep every year might seem like a small issue compared to deadly impacts of heat waves or climate-related food shortages , but scientific studies have shown that a lack of sleep disrupts the brain's ability to form new memories, causes more negative thinking, reduces cognitive function and can even be linked to Type 2 diabetes and reduced immune function. 

"Getting a good night's sleep is possibly the single most important thing you can do every day," David Dinges, associate director of the Center for Sleep and Circadian Neurobiology at the University of Pennsylvania, told CBC in 2020.

Produced and written by Maya Lach-Aidelbaum.


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