Warmer nights caused by climate change will affect Montrealers' sleep, study suggests

Montrealers having trouble sleeping at night when it's warmer than usual are not alone.

According to a study published in the environment-focused scientific journal One Earth, warmer temperatures have a direct effect on the average person's ability to fall and stay asleep.

"People slept less and the probability of having a shorter night of sleep grew as the temperatures became warmer," said Kelton Minor, the study's principal author and a PhD student at the University of Copenhagen's Center for Social Data Science.

The study followed 47,000 people in 68 countries using special bracelets, and combined their sleep data with each participant's local weather and climate data.

The study comes as climate data shows that — even with conservative estimates about greenhouse gas emissions — the number of nights each year where the temperature will not dip below 20 C is expected to more than quadruple over the next 60 years in some parts of Canada.

Montreal, for example, has historically averaged about eight of these nights each year, according to the Climate Atlas of Canada. But over the next 30 years that number could rise to anywhere between 19 and 22 nights with such temperatures, then between 28 and 45 in the following three decades.

The project also predicts that heat waves in Montreal, defined as consecutive days when the temperature rises above 30 C, will climb from lasting an average of three days in 2005, to lasting as long as eight days by 2080.

A clear correlation

Minor's study also suggests that the ideal sleep temperature for the average human could be around or below 5 C, so sleep could be seriously affected in summer months for those without air conditioning, and electricity bills will likely rise for those who do.

The average person currently loses an estimated 40 hours of sleep each year due to excessive nocturnal temperatures, the study says, with the elderly, women and people who live in poorer countries disproportionately affected.

The number of hours of lost sleep is predicted to increase to between 50 and 58 hours, depending on society's ability to adapt and mitigate the changes.

"If we conceive of new technologies that help cool down nocturnal temperatures and protect sleep, it's possible that the impact is reduced," said Minor. "On the other hand, if the global population continues to age, the average person could be more vulnerable to the effect of rising temperatures."

"Everything that disturbs our balance will disturb our sleep," said Roger Godbout, a professor at the Université de Montréal and director of the sleep clinic at the Rivière-des-Prairies Hospital.

Elevated temperatures are no exception, Godbout added, as they have a direct effect on people's ability to fall asleep and how often they wake up.

Studies have shown that some animals are able to adapt to sleeping in colder temperatures within a matter of weeks, but there's no evidence that they, or humans, can adapt to sleeping in warmer temperatures, he said.