The heat of the night is when you can really feel climate change in Calgary

Researchers say it's one of the more tangible effects of climate change: Like the Arctic is warmer faster than the Equator, the nights in Calgary are heating up more than the days.

It doesn't get as cold overnight as it used to, Environment Canada data shows

A moonrise over Calgary is seen in this file photo from Sept. 23, 2010. Overnight temperatures in the city have been noticeably higher in the past decade, according to Environment Canada weather data. (© Alan Dyer/

Calgary is in the midst of a heat wave, so it's probably hard to imagine that around this time in 1992, the city was dealing with a persistent overnight frost.

Gardeners, in particular, may remember that summer with frustration; temperatures dropped below zero for three consecutive nights in August.

More recently, though, things have been changing. The overnight lows have been noticeably warmer.

Researchers say it's one of the more tangible effects of climate change. Like the Arctic is warming faster than the Equator, the nights are heating up more than the days.

Minimum daily temperatures in Calgary have been trending upward for more than a century, according to historical data maintained by Environment Canada.

Through Aug. 17, there have been 42 days this year where the overnight low has stayed above 10 C.

During the same period from 1901 to 1910, there were just 11 days per year, on average, that saw such warm nights.

By the 1960s, that was up to an average of 23 days.

In the 2000s, it was up to 30 days.

And the past decade has been the warmest on record, in these terms, with an average of 43 days.

"This is a trend we're seeing all around the world, but most dramatically in places where we usually get, on average, cooler overnight lows — like most of Alberta," said CBC senior meteorologist Johanna Wagstaffe.

"The boundary layer — or that lower level of the atmosphere that warms up and cools down — is much thinner overnight, so it's warming much faster than our afternoon temperatures."

'One of the most noticeable trends'

Wagstaffe said the trend toward warmer temperatures, especially overnight, is "alarming" and likely to continue, even accelerate.

"It is directly linked to human-caused climate change," she said.

"This, unfortunately, is a trend that is likely to get worse."

James Byrne believes so, too. He's a geography professor at the University of Lethbridge who has been studying climate change for more than 30 years.

"Without a doubt, we're seeing strong trends," Byrne said.

"One of the most noticeable trends is in the cool temperatures, the daytime low temperatures."

Nighttimes "just aren't cooling off" like they used to, Byrne said, and that can come with a range of consequences.

Fortunately, for Calgary, the direct consequences for human health aren't as dire as in other parts of the world.

At least, not yet.

'2020 is different from 1990'

As a high-altitude city with a relatively dry climate, Calgary's nights are still cooler and more comfortable than many other places in Canada and around the world.

Dr. Joe Vipond, an emergency-room physician at the Rockyview General Hospital, says overnight temperatures here are not typically in the dangerous range, even with the recent increases.

"The temperatures need to be quite a bit higher than 20 degrees at night to have an impressive impact," he said.

"But things are evolving. We have to recognize that 2020 is different from 1990 when it comes to these events."

Looking at that same historical data from Environment Canada, we can see how Calgary is getting closer to nighttime temperatures that might be of more concern.

So far in 2020, we've had five nights where the temperatures stayed above 15 C in Calgary.

In the past, the city would go for years without seeing such warm nighttime temperatures by this point in August. From 1899 to 1909, it only happened once.

But we've seen at least one such night every year since 2006, and as many as seven in 2012.

That trend concerns Vipond.

Heat and health

As an ER doctor, he's seen the effects heat can have on human health. Even with Calgary's cooler nights, prolonged daytime and evening heat can still cause problems — especially for older people, who tend to be more vulnerable.

A lot of seniors living on low or fixed incomes don't have access to air conditioning, Vipond said, and those who are isolated may not recognize symptoms or receive care for heat-related illness.

"And also their physiology is different," he said of older adults. "So they have a harder time regulating their temperature when the temperature goes up.

He noted that a couple of years ago, in Quebec, high temperatures were linked to dozens of deaths.

"The reason why we know that about Quebec is Quebec specifically records the information about heat-related deaths," Vipond said. "And the rest of the provinces do not."

During the current heat wave, he advised checking in on loved ones who are isolated or vulnerable to make sure they're doing OK.

If you don't have air conditioning, he also recommended taking advantage of Calgary's still-relatively cool nighttime temperatures by opening windows and running fans once the exterior temperature drops below the temperature indoors.

People living in a lot of other places don't have that luxury, and Byrne noted it's likely to become increasingly rare.

'The future is frightening'

The effects of climate change are already "moving along at a very rapid pace," Byrne said, and so far have been at the "upper end" of many expectations.

At current rates, within 40 to 60 years, large swaths of the planet could see temperatures so high as to render them uninhabitable "for months at a time" each year, he said.

This could lead to mass numbers of climate refugees, he said, creating global migration challenges that dwarf those the world is currently experiencing.

"The future is frightening," he said.

"The positive thing is: we can truly fix this," Byrne added. "We can truly mitigate and adapt."

Vipond had a similar outlook.

"We need to recognize that this is not getting better; it will only get worse," he said.

"And however bad it gets is dependent on the policies that we make on mitigating greenhouse gases."


Robson Fletcher

Data Journalist

Robson Fletcher's work for CBC Calgary focuses on data, analysis and investigative journalism. He joined CBC in 2015 after spending the previous decade working as a reporter and editor at newspapers in Alberta, British Columbia and Manitoba.


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