Losing sleep over climate change: warmer nights are already disrupting our sleep cycles

While we’re familiar with the environmental and economic impacts of climate change, there are some unexpected indirect effects that could dramatically influence our fundamental daily human activities – including sleep. Yes, precious sleep.

Sleep is vital in maintaining our mental and physical health. Each night when we lay our heads the pillow, our cerebrospinal fluid (CSF) enters the brain and clears out metabolic waste. Now, in a study published in One Earth, the investigators have found that increasing ambient temperatures brought on my global warming are negatively impacting human sleep worldwide.

The team analysed seven million nightly sleeps of more than 47,000 adults across 68 countries. This anonymised global sleep data had been collected from accelerometer-based sleep-tracking wristbands, which tracked quality and quantity of sleep.

On very warm nights (greater than 30°C/86°F), sleep declined on average by almost 15 minutes. Sleepers also struggled to get seven hours or more of sleep on these warmer nights. At this rate, by year 2099, we might lose 50-58 hours of sleep per year, equivalent to almost two weeks, with older adults and females being impacted the most.

“Our bodies are highly adapted to maintain a stable core body temperature, something that our lives depend on,” says lead author Kelton Minor (@keltonminor) of the University of Copenhagen. “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.”

This drop in core body temperature that slows our metabolism in order to go to sleep is triggered by the hormone melatonin. For our bodies to shed heat, the surrounding environment also needs to be cooler than we are. This research also found that people appeared to be better at adapting to colder temperatures outside than hotter.

“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,” says Minor.

Socioeconomic status also seems to matter, with those in developing countries more strongly affected by temperature change, possibly due to lack of access to insulation and air conditioning. This highlights that the most vulnerable populations live in some of the world’s hottest regions, are they’re also historically some of the poorest.

To help save our sleep (along with our planet), the team hope to collaborate with global climate scientists, sleep researchers and tech companies to extend their scope of global sleep and behaviour research to more people and contexts.

“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,” says Minor.