The climate crisis could significantly “erode” the amount of sleep people get each year by the end of the century, warns a new study.
While a significant chunk of research on climate change assesses overall macro effects like economic and societal health outcomes from extreme weather events, scientists have now said the ongoing crisis may also have a strong influence on fundamental human activities like sleep.
About 50-58 hours of sleep per person could be eroded every year by 2099 because of changing ambient temperatures and suboptimal temperatures due to the global climate crisis, said the new study published last week in the journal One Earth by scientists including those from the University of Copenhagen in Denmark.
They said the climate crisis could lead to a host of behavioral, psychological and physiological outcomes essential to human wellbeing.
Scientists said the temperature effect on sleep loss could be substantially larger for residents from lower-income countries as well as in older adults and females.
“Our results indicate that sleep – an essential restorative process integral for human health and productivity – may be degraded by warmer temperatures,” Kelton Minor, first author of the study and PhD candidate from the University of Copenhagen, said in a statement.
“In order to make informed climate policy decisions moving forward, we need to better account for the full spectrum of plausible future climate impacts extending from today’s societal greenhouse gas emissions choices,” he said.
While previous studies have clearly shown hot days increase deaths and hospitalisations and worsen human performance, researchers said biological and behavioral mechanisms underlying these impacts have not been well understood.
Studies have also found the subjective quality of sleep to decrease during periods of hot weather.
How temperature fluctuations impact changes in objective sleep outcomes in people living in a variety of global climates, however, remains unclear.
“In this study, we provide the first planetary-scale evidence that warmer-than-average temperatures erode human sleep. We show that this erosion occurs primarily by delaying when people fall asleep and by advancing when they wake up during hot weather,” Mr Minor said.
In the research, scientists analysed anonymised global sleep data collected from accelerometer-based sleep-tracking wristbands.
The analysis included 7 million nightly sleep records from more than 47,000 adults across 68 countries spanning all continents except for Antarctica, researchers said.
On very warm nights – greater than 30C (86F) – scientists said sleep declines an average of just over 14 minutes, with the likelihood of getting less than seven hours of sleep increasing as temperatures rise.
“Our bodies are highly adapted to maintain a stable core body temperature, something that our lives depend on,” Mr Minor explained.
“Yet every night they do something remarkable without most of us consciously knowing – they shed heat from our core into the surrounding environment by dilating our blood vessels and increasing blood flow to our hands and feet,” he added.
For our bodies to transfer heat, researchers said the surrounding environment needs to be cooler.
Previous controlled studies in sleep labs have also shown both humans and animals sleep worse when the room temperature is too hot or too cold.
Under normal living routines, people appear far better at adapting to colder outside temperatures than hotter conditions.
“Across seasons, demographics, and different climate contexts, warmer outside temperatures consistently erode sleep, with the amount of sleep loss progressively increasing as temperatures become hotter,” Mr Minor observed.
He said people in developing countries seem to be more affected by these changes.
While the greater prevalence of air conditioning in developed countries could play a role, researchers could not definitively identify the reason because they did not have data on air conditioning access among subjects.
The study also warned that the impact of warming temperatures on sleep loss is unequal globally.
They called for further research to consider more vulnerable populations, particularly those residing in the world’s hottest – and historically poorest – regions.
“Without further adaptation, and should greenhouse gas concentrations not be stabilised until the end of the century, each person could be subjected to an average of 2 weeks of temperature-attributed short sleep each year,” scientists concluded in the study.