Climate change is driving sleep loss as nights get warmer

Climate change is increasingly disrupting people’s sleep.

High nighttime temperatures led to 5 per cent more hours of sleep lost worldwide over the past five years compared to the period between 1986 and 2005, according to the latest edition of the Lancet’s study of climate and health. It marks the first time the prestigious medical journal has examined this metric. Sleep loss peaked in 2023, the hottest year on record, when there was a 6 per cent rise.

The eighth annual Lancet Countdown on health and climate change report, authored by 122 global experts, found that high temperatures, drought and heavy rainfall are increasingly impacting people’s health. In 2023, a record 512 billion potential hours of labor were lost globally due to high temperatures. Heat-related deaths in people over the age of 65 reached the highest levels on record, 167 per cent higher in the 1990s.

“This isn't just about extreme weather events”, said Jeremy Farrar, chief scientist at the World Health Organisation. “This is about every week, every month of the year, and the impact on all of our health.”

In many places, nighttime temperatures are rising faster than daytime temperatures. As well as impacting sleep, overheating at night reduces the body’s ability to cool down and recover from the heat of the day, exacerbating heat wave deaths, especially among people with pre-existing heart and respiratory problems.

The study used historic sleep-tracking and temperature data to estimate the effects on sleep from high nighttime temperatures across different years. The biggest increases in lost sleep were in the Middle East and sub-Saharan Africa.

Even in more temperate climates, overheating at night can be exacerbated by poor building design that leaves indoor temperatures warmer than outdoor temperatures. Buildings can be better ventilated or shaded to reduce how much they heat up during the day and how much they retain that heat. Power demand from air conditioning use is expected to triple by 2050.

A lack of sleep negatively affects attention span and quality of life and can also have knock-on effects for other health conditions. Kevin Lomas, a professor of building simulation at Loughborough University who studies the relationship between heat and sleep, has found in the UK that bedroom temperatures higher than about 27C (80.6F) is the threshold at which people struggle to cool themselves down.

“Once you start tinkering with how much sleep people get, then the consequences aren't just relatively trivial things,” said Lomas, who wasn’t involved in the Lancet study. “They can be long term.”