The rising temperatures driven by the climate crisis are cutting down sleeping hours of people across the world, according to findings of the largest study to date. 

Due to climate change, temperatures during the night are increasing and even at a faster pace than daytime, making sleeping a difficult task.

According to the study, the average citizen - around the world - is already losing 44 hours of sleep a year, which constitutes 11 nights with less than 7 hours of sleep: a standard.

Loss of sleep will exacerbate with time as global warming is on the rise, affecting some groups more than others, based on gender and socioeconomic status. The sleep loss, per degree of warming, is around a quarter higher in women compared to men, twice as high for those over 65 years old, and three times higher for those living in low-income nations.

The methodology of the study required 47,000 people to wear wristbands that track sleep. The research was conducted over 7 million nights across 68 countries.

Rising temperatures damage health and increase the risk of heart attacks, suicides, mental health crises, accidents, and injuries, in addition to reducing the ability to work. 

“For most of us, sleep is a very familiar part of our daily routine; we spend nearly a third of our lives asleep,” said Kelton Minor, at the University of Copenhagen, Denmark, who is a leading author in the research. “But growing numbers of people in many countries around the world do not sleep enough.”

“In this study, we provide the first planetary-scale evidence that warmer than average temperatures erode human sleep,” he said. “It might actually be the tip of the iceberg because it’s very likely our estimates are conservative.”

A night in which temperatures rise above 25 °C for a million people would lead to 46,000 extra people suffering from fewer sleeping hours.

“And if you look at the heatwave that’s transpiring right now in India and Pakistan, we’re talking about billions of individuals exposed to conditions expected to result in considerable sleep loss,” Minor said.

The study was published in One Earth, and it includes an analysis of sleep and weather data collected between 2015 to 2017. 

Women, due to having higher levels of subcutaneous fat, have slower cooling rates than men.

In addition, older people are known to sleep less and have less body temperature regulation, making it increasingly difficult to fall asleep. 

Furthermore, people living in poorer nations are less privileged, and therefore have less access to cooling facilities and services, such as air conditioning, fans, and window shutters, which also affects their sleep. However, the representation of lower-income people was not as high as higher-income study participants. 

“Lower-income people are underrepresented in the data and we’re very transparent about that,” said Minor. People living in hot areas such as Africa and the Middle East were not well represented in the study population.

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The impact of global warming on sleep was seen across all destinations in the study, regardless of the countries' natural climates.

“Worryingly, we also found evidence that people already living in warmer climates experienced greater sleep erosion per degree of temperature rise,” said Minor. “We had expected those individuals to be better adapted.” Furthermore, people did not catch up on missed sleep at later times, according to the data.