A global study has found that climate change is depriving people around the world of sleep, and the problem is likely to get worse even if significant cuts to global carbon emissions are achieved.
Published by the journal One Earth, the study by the University of Copenhagen used sleep-tracking wristbands to record the sleeping patterns of 48,000 people in 68 countries from 2015 to 2017.
The data collected was then paired with local weather data to reveal that unusually hot nights cause people to fall asleep later and wake up earlier. On average, people are losing 44 hours of sleep a year, set to rise to 58 hours by 2100 if emissions remain at the current levels. That would drop to 50 hours in a lower-emissions future.
Previous research has shown there is a close relationship between sleep and mental as well as physical health. Short sleep can affect productivity, a person’s immune system, raise the risk of hypertension, as well as of depression, anger and suicidal behaviour. It also affects memory and plays a role in the onset and progression of neurodegenerative diseases.
Vulnerable groups most affected
According to the study, people in lower-income countries, women and the elderly were more likely to be affected by sleep loss linked to above-average nighttime temperatures. Those aged 65 and older were twice as affected by a 1°C increase in the minimum overnight temperature than younger groups.
The researchers were unable to establish a definitive link between the use of air-conditioning in higher-income countries, which they considered a form of adaptation, and people’s ability to cope with higher nighttime temperatures, but it is likely that lack of access to air conditioning, fans and other cooling methods may be the reason. Their use also tends to drive up carbon emissions.
The research did find, however, that people generally failed to adapt. For instance, they did not tend to take naps to make up for the lack of sleep, and were more likely to sleep on a warm night at the end of the summer than at the beginning of it.
As people’s bodies have to cool down every night before they fall asleep, women’s bodies cool slower as they tend to have higher levels of subcutaneous fat which retains heat. Older people may be more affected due to having poorer body temperature regulation.
“Our bodies are highly adapted to maintain a stable core body temperature, something that our lives depend on,” says Kelton Minor of the University of Copenhagen, one of the authors of the report.
“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, explaining that in order for bodies to transfer heat, the surrounding environment needs to be cooler than we are.
“In order to make informed climate policy decisions moving forward, we need to better account for the full spectrum of plausible future climate impacts,” Minor says.