For Nunavummiut, a temperature of minus 30 degrees Celsius could be considered a nice January day.
But for people living 2,300 kilometers south, in the Greater Toronto area, that kind of chill warrants an extreme cold weather warning from Environment and Climate Change Canada.
So how exactly is “extreme cold” determined, and why is the threshold for declaring it different across the country?
In Nunavut, the threshold to issue an extreme cold warning is the highest in the country, according to Environment and Climate Change Canada meteorologist Sara Hoffman.
Baffin Island has an extreme cold threshold of minus 50 C or a windchill index of minus 50 C. In Iqaluit, that temperature means local elementary schools close for the day, as happened one afternoon last week.
But for the rest of Nunavut, that threshold is slightly higher at minus 55 C. That temperature must also persist for at least two hours for a warning to be issued.
For example, a temperature of minus 50 C in Iqaluit warrants an extreme cold warning, while the same temperature in Baker Lake does not.
No extreme cold warning for Baker even tho it’s gonna be windchill -50 tn and -52 tmrw. pic.twitter.com/8h27iuwVg2
— Shane Niego (@ShaneConrad13) January 22, 2020
So why the five-degree difference?
Hoffman says Environment Canada takes into account a number of factors, including how frequently a region experiences cold temperatures and what effect those temperatures have on people who live there.
“Usually we have consultation with territorial and provincial health authorities to help come up with that number,” she says.
Regions like southern Ontario, which have an extreme cold threshold of minus 30 C for at least two hours, experience that kind of cold less frequently than places like Baffin Island.
In fact, southern Ontario has one of the lowest extreme cold thresholds in the country.
“Sometimes health authorities will even look at emergency room visits or how that temperature will impact the body physiologically with their own threshold,” says Hoffman.
“In the south we have a higher population density and also a more robust reporting structure for those types of things. So we can look at that type of data to help in that analysis and create that type of threshold.”
In the North, the focus is more on the climate, rather than things like visits to the hospital, as that can be more difficult to measure, Hoffman says.
“There has to be special consideration for the North, given there’s a bit less of a robust network that way. There is special consideration given to that when we set those extreme cold warning thresholds. And that’s why the thresholds are always set in partnership with provincial and territorial health authorities.”
Climate change is causing the Arctic to warm at a faster rate than the rest of the country. But how does a changing climate factor into the extreme cold threshold?
“As for extreme cold thresholds changing due to climate change, climate change has not changed extreme cold thresholds up until now. It is possible that in the future it could. However, we expect more extreme swings in temperature and weather as our climate changes, which would mean a change in the alerting criteria would not be warranted,” Hoffman says.
Although Nunavut is consistently cold, it doesn’t crack the top five for the number of consecutive days where an extreme cold warning was in effect in 2018-19.
The top five coldest places in Canada for the most consecutive days according to Environment and Climate Change Canada (with the extreme cold thresholds in brackets) are:
1. Tadoule Lake, Manitoba — 44 days (-45)
2. Fond-du-Lac-Stony Rapids, Saskatchewan — 41 days (-45)
3. Tie with 40 days: Brochet, Manitoba and Wollaston-Collins Bay, Saskatchewan (-45)
4. Fort Chipewyan-Wood Buffalo National Park, Alberta — 39 days (-40)