Here’s how much humans influenced 2025’s summer heat waves

This summer, human-caused climate change has already made two heat waves in Canada much more likely to have occurred, which, in turn, increases the risk of wildfires, says new research by Environment and Climate Change Canada. 

This summer, climate scientists are analyzing heat waves across Canada to determine how CO2 and other emissions from human activities impact extreme heat, using a process called ‘extreme weather event attribution.’ 

According to their findings, human influence on the climate made the following heat waves at least two to 10 times more likely to occur: 

• Yukon (June 20 to 23): Peak daily high temperature was 22°C, which is 6.5°C above the normal daily high for that period

• Alberta (May 28 to 31): Peak daily high temperature was 28.8°C, which is 11.3°C above the normal daily high for that period.

“Rising global temperatures are creating longer dry seasons and hotter conditions, which in turn increase the risk of wildfires,” Julie Dabrusin, Minister of Environment and Climate Change, said in a statement. 

“With this important work, our scientists are proving that the changing climate plays a significant role in severe weather,” she said. “This knowledge helps us so we can work together to protect our environment, our communities and our future.” 

Extreme weather event attribution analyzes how current weather events are connected to human-caused climate change by comparing today’s climate to the pre-industrial era (1850 to 1900). 

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Summer so far 

Canada is experiencing hotter-than-normal temperatures this summer, and extreme heat is known to fuel drought and wildfire events.  

Southern Ontario entered its third heat wave of the summer earlier in July. And on June 23, Toronto recorded its hottest temperature (36°C) since July 13, 2016, according to the Weather Network. 

The 2025 wildfire season is already one of the worst on record for Canada, and there’s a high risk more fires will break out in August, The Canadian Press reports. More than 55,000 square kilometres of land has burned so far this year — that’s double the 10-year average of area burned by mid-July. 

“During this demanding and challenging wildfire season, it’s clear that more extreme natural disasters and severe weather events are becoming increasingly common,” Eleanor Olszewski, Minister of Emergency Management and Community Resilience and Minister responsible for Prairies Economic Development Canada, said in a statement. “Before the mid-1990s, Canada had seen just three disasters that caused over $500 million in damages — now, we’re seeing disasters of that scale almost every year.” 

Still, 2023 remains the country’s record wildfire season — when over 6,000 fires burned more than 150,000 square km of land. 

But climate change is causing extreme hot temperatures at a greater frequency than in the past, increasing the severity of heat waves and contributing to the risk of drought and wildfires, ECCC says.  

Its climate scientists analyzed the 37 most extreme heat events during the summer of 2024. In all cases, they found the heat waves were likely because of climate change. 

Certainly, temperatures will continue getting hotter — and that means more frequent and intense wildfires. A report from the World Meteorological Organization confirms 2024 was the hottest year on record and the first year to be more than 1.5 degrees Celsius above the preindustrial era.  

The last ten years have all been in the top ten hottest years globally, WMO says. 

Alyssa DiSabatino

Alyssa Di Sabatino has been a reporter for Canadian Underwriter since 2021, covering industry trends, market developments, and emerging risks.