Freezing nights are disappearing across Canada as the climate warms
The number of subfreezing nights across vast swaths of Canada has declined over the past couple of decades
The vast majority of Canada’s major cities experience fewer freezing nights now than they did just a few decades ago.
Warming temperatures are a hallmark of climate change around the world. Extreme summertime heat waves grab most of the headlines, but rising overnight low temperatures are a major driver of the world’s warming.
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Warming nights during the cool season
Meteorologists use 30-year periods to calculate climate normals. The current set of weather data used to determine average temperatures and precipitation runs from 1991 through 2020.
According to the 1991-2020 climate normals, Vancouver averages about 40 days per year with a low temperature at or below the freezing mark. Calgary typically sees around 193 days per year at or below freezing. Toronto registers about 130 freezing nights per year.
How much has that changed over the years? Let’s take a look at the 1971-2000 set of climate normals and see how it compares to 1991-2020.
Between the two sets of data, Vancouver has lost about six freezing nights, while Calgary has lost around three days with temperatures that dipped to or below 0°C.
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Toronto has seen a nearly 16-day reduction in the number of days with freezing temperatures, the largest change between data sets among Canada’s major cities.
Despite the vast majority of Canada experiencing a general trend of warming nights, portions of the Prairies such as Edmonton, Regina, and Brandon have actually seen an increase in the number of subfreezing nights per year.
Rising nighttime temperatures isn’t a trend confined to Canada.
An analysis by U.S.-based Climate Central found that 210 American cities have seen a decline in the number of freezing nights since 1970, while average wintertime temperatures have warmed by several degrees throughout the country.
Plants are feeling the changing climate, as well
Warming nights throughout the year have contributed to a change in growing areas across the country.
Natural Resources Canada recently updated the map of plant hardiness zones, which helps residents decide which types of plants to grow based on the region’s climate.
The maps take into account factors such as the number of frost-free days, annual rainfall patterns, and mean snow depth.
Much of southern Canada advanced one or two plant hardiness zones between 1961-1990 and 1991-2020. Vancouver moved from 8a to 9a, while Winnipeg moved from 2b to 3b—a reflection of our changing climate.
Header image created using graphics and imagery from Canva.
