Climate change has been linked to sleepless nights. A 2020 survey found that anxiety about climate change and the state of the planet is causing people to lose sleep, but now the actual effects of a warming planet may impact rest too. According to a new study by a team of scientists around the world, published in the journal One Earth, increases in global temperature are affecting how long people sleep, and the problem is likely to get worse even if there is radical action on curbing carbon emissions. Kelton Minor of the University of Copenhagen and lead author of the study, said: “Our results indicate that sleep – an essential restorative process integral for human health and productivity – may be degraded by warmer temperatures. 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.”
There have been previous studies into the impact of above-average night temperatures on sleep, but these have faced a number of limits – they’ve been confined to single countries, they’ve been lab studies, or they’ve had to take into account the notoriously unreliable self-reporting of sleep. In order to gain a more accurate real-world picture, the team took data from sleep-tracking wristbands used by 48,000 people in 68 countries between 2015 and 2017. There were 7 million data points taken from every continent but Antarctica. They then paired the sleep data with local weather data and found that unusually hot nights are causing people to fall asleep later, rise earlier, and generally sleep less. Susan Clayton at the College of Wooster, Ohio, says the study’s methodology is sound and includes a “very thorough” examination of other explanations: “The implications are clear: higher temperatures associated with climate change are already reducing the amount of sleep people get and are projected to do so even more. Since we know that lack of sleep can negatively impact mood, behaviour, health and cognitive functioning, this is concerning.”
The evidence already suggests that people are losing an average of 44 hours of sleep each year after measuring the level of sleep loss on hot nights in relation to a baseline of how much an individual sleeps normally. They also controlled for alternative possible explanations for sleep erosion, such as the weather and the season, before making the determination. Thus, the researchers estimate that people will lose 58 hours of sleep a year by 2100 if emissions go unchecked and the warming factor remains consistent. Even in a lower-emissions future, the figure still rises to 50 hours.
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.
–Kelton Minor of the University of Copenhagen and lead author of the study
According to the research, some groups are hit by the lack of sleep worse than others. Above-average heat at night had a larger impact on those in lower-income countries, women, and elderly people. For those aged 65 and older, the effect on sleep of a 1°C increase in the minimum overnight temperature was at least twice that of younger age groups. The researchers found that people were failing to change their behaviour to cope (such as by taking a nap) and that they failed to adapt across a season. They also noted that the type of person who chooses to wear a sleep tracker may have access to other technologies that can curb the effect of hot nights on their sleep, and so the estimates of climate change’s impact on sleep are likely to be skewed on the low side.
The implications are clear: higher temperatures associated with climate change are already reducing the amount of sleep people get and are projected to do so even more. Since we know that lack of sleep can negatively impact mood, behaviour, health and cognitive functioning, this is concerning.
–Susan Clayton at the College of Wooster, Ohio
The researchers suggested that there is a need for future research on the impact of rising temperatures on sleep, and they say it should focus on how sleep loss is unequal globally. They noted a particular need to consider the world’s most vulnerable populations – those who reside in the hottest environments and who are already being hit hardest by rising temperatures.