Environment and Climate Change Canada says human-caused climate change made a late-August heat wave in Alberta far more likely.
In a Sept. 17 news release, the department said its Rapid Extreme Weather Event Attribution system analyzed 10 of the hottest heat waves across Canada in July and August 2025. Nine were found to be at least two to 10 times more likely to occur because of climate change.
The Alberta event ran from Aug. 25 to Aug. 31, with a peak daily high temperature of 28.8 °C and an anomaly of 9.3 °C above normal.
The release said other regions affected included Fort Smith, N.W.T., which saw 25.5 C, 11.6 C above normal, from Aug. 24 to 31; southern British Columbia, where highs reached 27.1 C, 10.3 C above normal, between Aug. 23 and Sept. 7; and northern British Columbia, where temperatures peaked at 23.5 C, 9.6 C above normal, from Aug. 23 to Sept. 9.
According to the department, southern Quebec recorded 29.3 °C, 9.1 °C above normal, from Aug. 7 to 13, while northern Quebec reached 23.8 °C, 7.0 °C above normal, from Aug. 6 to 9. Fort Smith, N.W.T., also experienced a separate heat wave from July 30 to Aug. 1, with 25.2 °C, 6.0 °C above normal. Atlantic Canada saw 25.6 C, 7.1 C above normal, from July 10 to 15, and northern Quebec reached 24.2 C, 7.5 C above normal, from July 10 to 13.
The department noted that the Atlantic Canada heat wave from Aug. 7 to 14 reached a peak of 28.4 °C, 9.6 °C above normal, and was at least 10 times more likely to occur because of climate change.
The release explained that the attribution system compares today’s climate to a pre-industrial one to show how carbon dioxide and other human emissions increase the chances of some extreme events while reducing others. It said the heat waves observed in July and August would have been rare in a pre-industrial climate.
Environment and Climate Change Canada said scientists began analyzing the connection between climate change and extreme cold events in winter 2025. It added that work will begin later this year on extreme precipitation, noting that, as with heat waves, human influence increases the likelihood of heavy rainfall.
The department stated that prolonged heat waves and longer fire seasons are major contributors to more frequent and intense wildfires. It said the 2023 season burned almost 15 million hectares of forest and cost Canadians tens of billions of dollars, while 2025 is already the second-worst on record for area burned.
According to the release, wildfire season in Canada generally runs from May to September. The 2023, 2024 and 2025 seasons are all among the top 10 on record for area burned.
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