More severe and frequent droughts, storms and other extreme weather events are ways scientists expect climate change to endanger human health, but global temperatures can also impact our wellbeing in more insidious ways. Scientists are beginning to explore this idea with regard to human sleep, based on the premise that rising ambient temperatures are impacting the quality of our rest. And a new study indicates they may already be costing us dozens of hours of shuteye per year.
The restlessness that comes with a night spent tossing and turning in the stifling heat is one many might be familiar with, just as they might know the feelings of fatigue that can follow the next day. While occasional disruptions to our sleep might be part of the deal when enjoying a tropical holiday or a spurt of warm summer weather, long-lasting and regular impacts on our sleep quality can have significant impacts on our health, as studies continue to show.
Just in the last few years, we have seen research link poor sleep habits to a higher risk of heart disease, dementia, obesity, cancer and a shorter lifespan. Meanwhile, global temperatures continue to rise, last year sitting around 1.11 °C (1.99 °F) above pre-industrial levels, with the last seven years the warmest on record. So is climate change making it harder to get a good night's sleep, and in doing so impacting human health?
Observational studies and survey data have previously suggested that may be the case, finding links between increases in nighttime temperature and self-reported nights of poor sleep. In search of more concrete evidence, the authors of this new study have tapped into global sleep data collected through accelerometer-based tracking wristbands worn by more than 47,000 adults across 68 countries, covering every continent except Antarctica.
"In this study, we provide the first planetary-scale evidence that warmer-than-average temperatures erode human sleep," said first author Kelton Minor from the University of Copenhagen. "We show that this erosion occurs primarily by delaying when people fall asleep and by advancing when they wake up during hot weather."
Minor and his co-authors arrived at these conclusions after their analysis of the data, which included seven million nightly sleep records, finding that on very warm nights with temperatures in excess of 30 °C (86 °F), sleep declined by an average of just over 14 minutes. Averaged across the entire globe, the authors calculate that people are each losing 44 hours of sleep per year due to suboptimal night-time temperatures, which also cause them to experience around 11 nights of insufficient sleep.
"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," Minor said.
With carbon dioxide continuing to build up in the atmosphere and global temperatures continuing to rise, the scientists expect this trend to continue, and may erode up to 58 hours of sleep per person per year by the end of the century. Those in lower income countries and elderly people were the most affected, while sleep loss was also marginally higher for women than men.
The scientists point out that developing countries may be feeling these effects more due to a lower prevalence of air conditioning, though this is not something they could control for as they didn't have access to data on air conditioning for the study participants. Whether this is the case or not, the findings are consistent with other forecasts regarding climate change disproportionately affecting the world's poor, who are expected to find adaptation much more difficult as the world grows warmer.
Because of this imbalance and the findings that sleep loss due to climate change will be felt unevenly across the globe, the scientists say further research should focus on vulnerable populations living in the world's warmer and often poorer regions. They hope to work with sleep researchers and climate scientists to broaden the scope of their studies, and also look at the effects on incarcerated populations with limited access to air conditioning.
The research was published in the journal One Earth.
Source: Cell Press via ScienceDaily