Climate Shift Index AlertJanuary 16, 2024

Analysis: Climate change drove Canada’s warm December

January 16, 2024

El Nino isn’t acting alone this winter. Climate Central analysis shows that human-caused climate change made the exceptionally warm conditions across Canada during December 2023 much more likely.

Six provinces and one territory had their warmest December since 1970.

 CSI Heat Retro Alert: December 2023 Canada (EN)

Event: what unusual temperatures occurred?

December 2023 was unusually warm across much of North America, especially in Canada. Much of the country, especially the central provinces, had monthly temperatures more than 5°C above the long-term (1991-2020) average. The three most unusually warm provinces were Manitoba (8.6°C above normal), Saskatchewan (8.0°C), and Alberta (7.1°C), but every province and territory was above normal (Nova Scotia had the smallest anomaly: 2.4°C). 

Six provinces and one territory (Alberta, British Columbia, Manitoba, New Brunswick, Ontario, Saskatchewan, and Nunavut) each had their warmest December since 1970. December 2023 ranked in the top 3 warmest since 1970 for every province and territory except Nova Scotia (fourth warmest) and Yukon (eighth warmest).

Attribution analysis: how did climate change influence these temperatures?

The Climate Shift Index system allows us to quantify how climate change influences the temperature on any given day. For this analysis, we counted the number of days at each location that had a Climate Shift Index (CSI) value of 2 or higher. A CSI value of 2 means that climate change made that day’s temperature at least twice as likely.

Most of Canada had more than five days with a detectable climate fingerprint. The number of days at or above CSI 2 was especially high in the Northwest Territories (territory-wide average of 13.9 days), Nunavut (13.8 days), Ontario (11.2 days), British Columbia (11.2 days), Manitoba (9.9 days), and Quebec (9.3 days). 

Tip: Use the Climate Shift Index global map to see past CSI levels in any specific city and region, on any day.

El Niño is certainly an important driver of weather conditions across the planet this winter, and Canada typically has milder winters when El Niño is active. The CSI system considers the influence of human-caused warming (i.e. the long-term trend) and accounts for year-to-year changes like those caused by swings between El Niño and La Niña. On its own, El Niño is not sufficient to produce record temperatures like those observed in December. Instead, temperature records are being shattered because El Niño is acting on top of global warming caused by burning fossil fuels.

ProvinceTemperature Anomaly (°C)2023 Rank (since 1970)Average CSI 2+ daysAverage CSI 3+ days
British Columbia4.8111.27.3
New Brunswick4.014.11.4
Newfoundland and Labrador4.232.90.1
Northwest Territories6.5213.93.8
Nova Scotia2.443.40.7
Prince Edward Island2.937.83.2

What impacts were experienced?

In the Northwest Territories, ice roads — which connect remote communities in winter — delayed opening in December for multiple weeks, creating higher costs for consumers and companies as supplies needed to be flown in. Similar delays to ice roads opening occurred in northern Saskatchewan. 

Warmer weather in December also created challenges for economies that rely on cold-weather sports. In British Columbia, some ski hill operators delayed opening, or temporarily shut down waiting for fresh snow. Warmer weather delayed ski hills from opening in Ontario. And in Ottawa, the historic Rideau Canal skateway has still not yet opened — a delay that has only occurred twice in the canal’s 53-year history. 

Warmer temperatures thinned the ice on Canadian waterways, creating deceptively treacherous conditions that endangered the lives of people across the country. These risks are more likely to fall disproportionately on children and Indigenous peoples.

What do experts say?

Dr. Andrew Pershing, VP of Science at Climate Central, said: 

“While El Niño is important, climate change caused by burning gas, coal, and oil is the primary reason Canada experienced record warm temperatures this December.“

To request an interview, please contact Dr. Pershing at

About the Climate Shift Index

The Climate Shift Index (CSI) uses peer-reviewed methodology to estimate how human-caused-climate change has increased the likelihood of a particular daily temperature. It can be run using historical or forecast temperatures. For this analysis, temperatures come from ERA5.

Using computer models, we compared the likelihood that these temperatures would occur in a world without carbon emissions released by humans, versus in today's world with decades of carbon emissions building up in the atmosphere. This is an established scientific method to determine how much climate change has or has not affected individual extreme weather events.

Positive CSI levels 1 to 5 indicate conditions that are increasingly likely in today’s climate. Level 1 indicates that climate change is detectable in that day’s temperature. Level 2 means that climate change made exceptionally warm temperatures in a given location at least twice as likely. Level 5 is the maximum and indicates temperatures at least 5 times more likely because of climate change. CSI level 5 events would be very difficult to encounter in a world without climate change—not impossible, but extremely unlikely.

The CSI can also be applied to temperatures that are unusually cool. For instance, a CSI level -2 means that the temperature in question is two times less likely due to human-caused climate change.