Results: Extreme weather event attribution
Important notice
See the latest results for extreme event attribution as of July 17, 2025, for extreme heat. Read the latest news release for details.
Heat waves, heavy rainfall, and wildfires are all types of extreme weather events linked to human-caused climate change.
Extreme weather event attribution is the science of calculating how much human-caused climate change influences extreme weather events.
We examine the extreme heat and extreme cold events in 17 regions across Canada.
Latest results
Extreme heat: latest attribution analysis and results
During the warm season, we share detailed analysis about the most intense heat waves in Canada. The results show how human-caused climate change influenced the likelihood of heat waves.
Each analysis shows:
- the dates of each analysis period
- the peak daily high temperature averaged over the region during the heat wave
- degrees above normal daily high temperature
- a statement of likelihood: the event was xxx likely because of human influence on the climate.
June 2025
Yukon
- Dates: June 20-23, 2025
- Peak daily high temperature during the heat wave: 22.0 °C
- Degrees above normal daily high temperature: 6.5 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
May 2025
Alberta
- Dates: May 28-31, 2025
- Peak daily high temperature during the heat wave: 28.8 °C
- Degrees above normal daily high temperature: 11.3°C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
September 2024
Eastern Ontario
- Dates: September 11 to September 21, 2024
- Peak daily high temperature during the heat wave: 25.9 °C
- Degrees above normal daily high temperature: 7.9 °C
- Statement of likelihood: The event was more likely because of human influence on the climate.
Fort Smith
- Dates: September 6 to September 8, 2024
- Peak daily high temperature during the heat wave: 19.0 °C
- Degrees above normal daily high temperature: 7.3 °C
- Statement of likelihood: The event was more likely because of human influence on the climate.
Northern Qikiqtaaluk
- Dates: September 10 to September 14, 2024
- Peak daily high temperature during the heat wave: 0.4 °C
- Degrees above normal daily high temperature: 5.8 °C
- Statement of likelihood: The event was more likely because of human influence on the climate.
Northern Quebec
- Dates: September 14 to October 3, 2024
- Peak daily high temperature during the heat wave: 20.6 °C
- Degrees above normal daily high temperature: 10.6 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Saskatchewan
- Dates: September 7 to September 10, 2024
- Peak daily high temperature during the heat wave: 28.5 °C
- Degrees above normal daily high temperature: 11.2 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Southern British Columbia
- Dates: September 4 to September 8, 2024
- Peak daily high temperature during the heat wave: 24.8 °C
- Degrees above normal daily high temperature: 8.8 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Southern Qikiqtaaluk
- Dates: September 20 to October 16, 2024
- Peak daily high temperature during the heat wave: 8.8 °C
- Degrees above normal daily high temperature: 10.2 °C
- Statement of likelihood: The event was far more likely because of human influence on the climate.
Southern Quebec
- Dates: September 15 to September 20, 2024
- Peak daily high temperature during the heat wave: 23.6 °C
- Degrees above normal daily high temperature: 8.9 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Western Ontario
- Dates: September 13 to September 21, 2024
- Peak daily high temperature during the heat wave: 24.9 °C
- Degrees above normal daily high temperature: 10.1 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
August 2024
Atlantic Canada
- Dates: August 24 to August 27, 2024
- Peak daily high temperature during the heat wave: 23.9 °C
- Degrees above normal daily high temperature: 6.7 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Eastern Ontario
- Dates: July 31 to August 2, 2024
- Peak daily high temperature during the heat wave: 29.2 °C
- Degrees above normal daily high temperature: 5.8 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Fort Smith
- Dates: August 8 to August 13, 2024
- Peak daily high temperature during the heat wave: 26.9 °C
- Degrees above normal daily high temperature: 9.2 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Inuvik
- Dates: August 6 to August 10, 2024
- Peak daily high temperature during the heat wave: 26.5 °C
- Degrees above normal daily high temperature: 13.0 °C
- Statement of likelihood: The event was far more likely because of human influence on the climate.
Kitikmeot
- Dates: August 7 to August 12, 2024
- Peak daily high temperature during the heat wave: 25.0 °C
- Degrees above normal daily high temperature: 12.4 °C
- Statement of likelihood: The event was far more likely because of human influence on the climate.
Kivalliq
- Dates: August 8 to August 14, 2024
- Peak daily high temperature during the heat wave: 27.1 °C
- Degrees above normal daily high temperature: 12.2 °C
- Statement of likelihood: The event was far more likely because of human influence on the climate.
Manitoba
- Dates: July 30 to August 1, 2024
- Peak daily high temperature during the heat wave: 28.3 °C
- Degrees above normal daily high temperature: 6.4 °C
- Statement of likelihood: The event was more likely because of human influence on the climate.
Northern British Columbia
- Dates: August 7 to August 11, 2024
- Peak daily high temperature during the heat wave: 23.6 °C
- Degrees above normal daily high temperature: 7.0 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Northern Quebec
- Dates: August 13 to August 16, 2024
- Peak daily high temperature during the heat wave: 23.6 °C
- Degrees above normal daily high temperature: 7.8 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Southern Quebec
- Dates: July 27 to August 3, 2024
- Peak daily high temperature during the heat wave: 28.3 °C
- Degrees above normal daily high temperature: 7.6 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Yukon
- Dates: August 5 to August 9, 2024
- Peak daily high temperature during the heat wave: 24.1 °C
- Degrees above normal daily high temperature: 8.9 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
July 2024
Atlantic Canada:
- Dates: July 28 to July 31, 2024
- Peak daily high temperature during the heat wave: 26.1 °C
- Degrees above normal daily high temperature: 6.7 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Alberta:
- Dates: July 7 to 11, 2024
- Peak daily high temperature during the heat wave: 31.5 °C
- Degrees above normal daily high temperature: 9.8 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Fort Smith:
- Dates: July 15 to July 20, 2024
- Peak daily high temperature during the heat wave: 28.4 °C
- Degrees above normal daily high temperature: 9.2 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Northern British Columbia:
- Dates: July 17 to 22, 2024
- Peak daily high temperature during the heat wave: 24.2 °C
- Degrees above normal daily high temperature: 7.2 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Northern Quebec:
- Dates: July 28 to 30, 2024
- Peak daily high temperature during the heat wave: 24.2 °C
- Degrees above normal daily high temperature: 7.0 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Southern British Columbia:
- Dates: July 14 to 22, 2024
- Peak daily high temperature during the heat wave: 29.2 °C
- Degrees above normal daily high temperature: 9.2 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Saskatchewan:
- Dates: July 17 to 22, 2024
- Peak daily high temperature during the heat wave: 30.9 °C
- Degrees above normal daily high temperature: 8.0 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Western Ontario:
- Dates: July 26 to July 28, 2024
- Peak daily high temperature during the heat wave: 27.9 °C
- Degrees above normal daily high temperature*: 6.1 °C
- Statement of likelihood: The event was more likely because of human influence on the climate.
Yukon:
- Dates: July 21 to July 26, 2024
- Peak daily high temperature during the heat wave: 23.0 °C
- Degrees above normal daily high temperature: 6.5 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
June 2024
Atlantic Canada
- Dates: June 18 to 20, 2024
- Peak daily high temperature during the heat wave: 26.1 °C
- Degrees above normal daily high temperature: 10.6 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Eastern Ontario
- Dates: June 17 to 19, 2024
- Peak daily high temperature during the heat wave: 29.0 °C
- Degrees above normal daily high temperature: 7.4 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Fort Smith
- Dates: June 29 to July 1, 2024
- Peak daily high temperature during the heat wave: 24.9 °C
- Degrees above normal daily high temperature: 6.7 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Inuvik
- Dates: June 28 to 30, 2024
- Peak daily high temperature during the heat wave: 22.0 °C
- Degrees above normal daily high temperature: 7.2 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Kivalliq
- Dates: June 30 to July 2, 2024
- Peak daily high temperature during the heat wave: 22.1 °C
- Degrees above normal daily high temperature: 7.5 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Northern Quebec
- Dates: June 18 to 19, 2024
- Peak daily high temperature during the heat wave: 21.5 °C
- Degrees above normal daily high temperature: 7.2 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Southern Quebec
- Dates: June 18 to 20, 2024
- Peak daily high temperature during the heat wave: 29.5 °C
- Degrees above normal daily high temperature: 10.7 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Yukon
- Dates: June 26 to 30, 2024
- Peak daily high temperature during the heat wave: 21.4 °C
- Degrees above normal daily high temperature: 5.3 °C
- Statement of likelihood: The event was much more likely because of human influence on the climate.
Data from 2024 to 2025
In 2024, we used an earlier version of the system for our analysis. As new system capabilities, data and research becomes available, climate scientists can adjust and improve the system. As a result, the data from 2024 are not directly comparable to data from 2025.
Extreme cold: Latest extreme cold attribution analysis results
During the cold season, we share detailed analysis about the coldest extreme temperatures in Canada. The results show how much human-caused climate change influenced the coldest extreme temperatures.
Each analysis shows:
- the dates of each analysis period
- the coldest daily temperature averaged over the region during the extreme cold event
- degrees below normal daily low temperature
- a statement of likelihood: The event was xxx likely because of human influence on the climate.
February 2025
Saskatchewan
- Dates: February 12 – 19, 2025
- Coldest daily temperature: -34.5 °C
- Difference from the normal daily low temperature: -17.2 °C
- Statement of likelihood: The event was much less likely because of human influence on the climate.
January 2025
Western Ontario
- Dates: January 20 – 21, 2025
- Coldest daily temperature: -34.0 °C
- Difference from the normal daily low temperature: -12.0 °C
- Statement of likelihood: The event was much less likely because of human influence on the climate.
Understanding results
Understanding attribution results
We use three different ways to share the results from extreme weather attribution analysis:
- a statement of likelihood
- probability/risk-range percentage
- graphs and visuals
Statement of likelihood
We use seven set statements to describe the likelihood that an extreme weather event was influenced by climate change from human activities.
On one end of the scale, the event was:
- far less likely because of human influence on the climate
- much less likely because of human influence on the climate
- less likely because of human influence on the climate
In the middle:
- no evidence of an attributable change in likelihood
On the other end of the scale, the event was:
- more likely because of human influence on the climate
- much more likely because of human influence on the climate
- far more likely because of human influence on the climate
Events that are more, much more, or far more likely, happen more often today than they did in the pre-industrial era (1850-1900). Events that are less, much less, or far less likely are becoming more rare.
Figure 1 Statement of likelihood
Long description
On one end of the scale, the extreme weather event was:
- far less likely because of human influence on the climate
- much less likely because of human influence on the climate
- less likely because of human influence on the climate
In the middle:
- no evidence of an attributable change in likelihood for this event
On the other end of the scale, the extreme weather event was:
- more likely because of human influence on the climate
- much more likely because of human influence on the climate
- far more likely because of human influence on the climate
Probability/risk range
The probability/risk range scales show how human activity impacts the likelihood of an extreme weather event occurring.
On one end of the scale, the event was:
- far less likely: at least 10X less likely to have happened
- much less likely: at least 2X to 10X less likely to have happened
- less likely: at least 1X to 2X less likely to have happened due to human influence on the climate
In the middle, the weather event has:
- no evidence: no change due to human influence on the climate identified
On the other end of the scale, the event was:
- more likely: at least 1X to 2X more likely to have happened
- much more likely: at least 2X to 10X more likely to have happened
- far more likely: at least 10X more likely to have happened due to human influence on the climate
Figure 2 Probability risk / range
Long description
On one end of the scale, if the event was:
- far less likely: at least 10X less likely to have happened
- much less likely: at least 2X to 10X less likely to have happened
- less likely: at least 1X to 2X less likely to have happened due to human influence on the climate
In the middle, if there was:
- no evidence: no change due to human influence on the climate identified
On the other end of the scale, if the event was:
- more likely: at least 1X to 2X more likely to have happened
- much more likely: at least 2X to 10X more likely to have happened
- far more likely: at least 10X more likely to have happened due to human influence on the climate
Graphs and visuals
We use a variety of graphs to show extreme weather attribution, such as probability distribution graphs.
Probability distribution graphs can help show how much more or less likely an extreme weather event was because of human influence on the climate. The image below shows how temperature extremes change with climate change.
Figure 3 Probability distribution graph*
Long description
Climate scientists use the rapid extreme weather event attribution system to compare past and present climates. The image shows how temperature extremes change with climate change.
The image has six different parts:
Left curve (blue): The left curve shows the likelihood of temperatures in a past climate. It begins on the left. It rises to a peak to the right and then falls and ends in a tail
This is based on levels of atmospheric gases that existed before the Industrial Revolution.
Right curve (red): The right curve shows how likely today’s temperatures are. It begins to the right of the blue curve and rises to a peak. It falls and ends in a tail to the right of the blue curve
This is based on current, observed levels of greenhouse gases and other results of human activity.
Scale: Below the red and blue curves, a scale ranges from extreme cold on the far left, average temperatures in the middle, and extreme heat on the right. The left of the scale is for cooler temperatures and the right side of the scale is for hotter temperatures.
Vertical line: The vertical black line shows an observed extreme event. Where the black line is put on the scale shows how strong the event was.
Shaded area (left curve, dotted): The dotted area shows the chance of a heat wave at least as strong as that observed in the past climate.
Shaded area (right curve, diagonal lines): The lined area shows how much more likely a heat wave, at least as strong as that observed, is in our current climate.
Comparing the curves
Comparing the left curve (blue) and the right curve (red) shows that the current climate is warmer than the past climate.
The shaded area for the red curve is larger than the shaded area for the blue curve. This shows that heat waves are more likely to occur in today’s climate than the past.
The first curve (blue) shows the likelihood of temperatures in the past. The second curve (red) shows the likelihood of temperatures today. The dots and lines shade the end of the curves to show the chances of an extreme heat event occurring.
When we compare the two curves, we see the climate of today, the red curve, has shifted to the right. This shift shows that we have more chances of extreme heat. The total shaded area for the red curve is larger than the shaded area for the blue curve. This shows that heat waves are more likely to occur in today’s climate than the past.
*Illustrative. Not an actual probability distribution graph.
The rapid system
The Rapid Extreme Weather Event Attribution system
The Rapid Extreme Weather Event Attribution system analyzes extreme weather events quickly. This system shows how human-caused climate change changes the likelihood of extreme weather events happening.
A pilot system for extreme weather event attribution
The Rapid Extreme Weather Event Attribution system is new for Canada and is still developing. In 2024, it was used to determine the link between human-caused climate change and recent extreme heat events. In 2025, climate scientists began piloting a new function to analyze cold weather events. They will add extreme precipitation later in the year.
How it works: comparing two different climates
The Rapid Extreme Weather Event Attribution system uses climate models to compare two different climates:
- the climate of the 1800s, based on levels of atmospheric gases that existed before the Industrial Revolution
- the climate of today, based on observed levels of greenhouse gases and other results of human activity
Several days after a heat wave or cold event, scientists can compare the number of extreme heat or extreme cold events in the two different climates. Then, they calculate the ratio of the two to find how much human activity has changed the chances of such a heat wave or cold event happening.Footnote 1
Normal daily temperature
We determine the normal daily temperature from an average of the historical temperatures (1991-2020) of the month around the event.
Importance of the Extreme Event Attribution analysis system
When we can understand the causes and calculate the likelihood of extreme events such as heat waves, wildfires, extreme cold, drought, and floods, we can:
- better plan for, respond to, and rebuild from weather emergencies
- support informed decision making to protect health, safety, and property
- encourage further environmental studies
- support climate change adaptation efforts
Regions across Canada for extreme event attribution analysis
Climate scientists analyze the temperatures in 17 regions covering all of Canada.
Figure 4 Regions for Extreme Event Attribution analysis
- Yukon
- Inuvik, Northwest Territories
- Fort Smith, Northwest Territories
- Kitikmeot, Nunavut
- Kivalliq, Nunavut
- Northern Qikiqtaaluk, Nunavut
- Southern Qikiqtaaluk, Nunavut
- Northern British Columbia
- Southern British Columbia
- Alberta
- Saskatchewan
- Manitoba
- Western Ontario
- Eastern Ontario
- Northern Quebec
- Southern Quebec
- Atlantic Canada
Learn more
Learn more about extreme weather events
An extreme weather event is when we get unusual or unseasonal extremes compared to historical data. Extreme weather events include:
- heat waves, which can drive wildfires and drought
- extreme cold events
- extreme rainfall, which can cause flooding
Human-caused climate change
Human activities, mainly greenhouse gas emissions, are causing the global climate to change. This leads to changes including:
- more extreme heat
- less extreme cold
- shorter snow and ice-cover seasons
- thinning glaciers
- thawing permafrostFootnote 2
Our warming environment affects the strength, number, and risks of extreme weather events.
Some events, like heat waves, are happening more frequently as a result of our warming environment. Other events, like extreme cold, are happening less frequently as a result of the warming environment and will be more rare in the future.
Research on past extreme weather event attribution
As part of our mandate, we conduct and share the results of extensive climate science research in Canada and internationally.
Our research helps decision-makers, leaders, and professionals to make science-based, informed decisions.
Canada’s National Adaptation Strategy is the long-term vision to reduce the damaging effects and risks of climate-related disasters. Our goal is to help prepare our communities for the effects of climate change and give them information that helps protect their health, well-being, and livelihoods.
Climate change in Canada
Canada is warming faster than the global average
Canada’s large land area, location on the planet, and declining snow and ice coverage cause the country to warm about twice as fast as the global average. Canada’s Arctic region is warming even faster.
Learn more:
Related resources
Climate research
Extreme weather events
- Prepare for weather events
- Wildfire smoke, air quality and your health: Overview - Canada.ca
- Air Quality Health Index - Canada.ca
- Prepare for floods (getprepared.gc.ca)
- Canadian Drought Outlook - agriculture.canada.ca
- Severe weather - Canada.ca
- Seasonal weather hazards - Canada.ca
Adapting to climate change
- Canada’s National Adaptation Strategy: Building Resilient Communities and a Strong Economy
- Causes of climate change - Canada.ca
News releases
- July 16, 2025 - Climate scientists calculate role human-caused climate change plays in shifting weather extremes
- October 25, 2024 - Climate change sets and breaks heat records across Canada this summer
- September 25, 2024 - Climate change fuels August heat waves across Canada
- August 12, 2024 - Science shows climate change made summer heat waves much more likely
- July 9, 2024 – Canada releases first results from rapid extreme weather event attribution system
June 11, 2024 – Environment and Climate Change Canada presents summer seasonal outlook and outlines new heat wave attribution system
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