Latest attribution analysis and results

Throughout the year, we share detailed analysis of the most intense extreme heat, cold, and precipitation events in Canada. The results show how human-caused climate change influenced the likelihood these events.

To obtain analysis data, please visit the extreme weather event attribution data catalogue.

Attribution results: extreme heat events

Each extreme heat attribution analysis includes:

• 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 current likelihood: in a future climate with a global warming of 2.0°C the event would be xxx likely compared to the pre-industrial climate.

Attribution results: extreme cold events

Each extreme cold attribution analysis includes:

• 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 current likelihood: the event was xxx likely because of human influence on the climate, in today's climate compared to the pre-industrial climate
• a statement of future likelihood: in a future climate with a global warming of 2.0°C the event would be xxx likely compared to the pre-industrial climate.

Attribution results: extreme precipitation

Each extreme precipitation analysis includes:

• the date of each event
• the total accumulated precipitation averaged over the region during the event
• the percentage of normal monthly precipitation that accumulated during the event
• a statement of current likelihood: the event was xxx likely because of human influence on the climate, in today's climate compared to the pre-industrial climate
• a statement of future likelihood: in a future climate with a global warming of 2.5 °C the event would be xxx likely compared to the pre-industrial climate.

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

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

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*

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 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. Climate scientists began piloting new functions to analyze extreme cold weather and precipitation events in 2025.

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, extreme cold, or extreme precipitation event, scientists can compare the number of those extreme 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 an 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.

Normal monthly precipitation

We determine normal monthly precipitation using historical data. It is an average of total precipitation accumulations for the month of the event (over 1991-2020).

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

For heat and cold extremes, climate scientists analyze the temperatures in 17 large regions covering all of Canada. For extreme precipitation events, these 17 regions are further subdivided into 89 smaller sections.

Figure 4 Regions for extreme temperature event attribution analysis

Figure 5 Regions sub-divided for extreme precipitation event analysis

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 permafrost^{Footnote 2}

Carbon dioxide (CO₂) and other emissions from human activities 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 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.

Related resources

Climate research

• Climate change science, research, and data
• Canadian Climate Normals

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

• December 11, 2025 - Environment and Climate Change Canada presents winter seasonal outlook and expansion of the Rapid Extreme Weather Event Attribution system
• September 17, 2025 - Recent Canadian heat waves made much more likely by human caused climate change
• 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