Fossil fuel-driven climate change made the extreme fire weather conditions behind this summer’s ferocious wildfires in Ontario and the Northwest Territories roughly twice as likely to occur, concludes new research from Imperial College London’s World Weather Attribution (WWA) initiative. 

The 2026 wildfire season got off to a slow start, but “has quickly intensified to dangerous levels through July” thanks to “multiple occurrences of hot, dry weather since the end of June combined with significant lightning activity,” write the authors of the just-released report.

Based only on observational data, the extreme fire weather events seen in today’s climate are now “expected to occur once every two to six years in the Northwest Territories, and every six to 15 years in Ontario,” WWA said in a release.

In a world without climate change, such extreme fire weather would occur “less than once in 40 years,” the report authors found.

“The science is in: these fires have been made twice as likely by global heating. They are tearing through homes, communities, businesses, and the forests that economies depend on,” UN climate secretary Simon Stiell said in a release. “The science backs up what people on the front lines already know: humanity’s addiction to burning massive amounts of coal, oil, and gas is heating our planet, turning more of Canada’s vast forests into tinderboxes, and spreading dangerous smoke far beyond the flames.”

Stiell added: “The world must move much faster away from polluting fossil fuels and towards clean energy, while protecting communities already living with the worst impacts, including the Indigenous communities on the front lines of these fires.”

Determined by the complex interplay between high air temperatures, low relative humidity, strong and/or gusty winds, and dry vegetation, “fire weather” is a term used to describe the atmospheric conditions that help wildfires ignite and grow.

When climate models are factored in, the extreme fire weather conditions that drove, and are driving, the fires in Ontario and the NWT have been made “about two or more times more likely” than what would exist in a world without fossil fuel-driven climate change.

Used in combination with observational data to allow researchers to determine a “clear” climate attribution signal, climate models produce a “conservative” estimate, report co-author Prof. Friederike Otto, professor of climate science at the Centre for Environmental Policy, Imperial College London emphasized at a media briefing.

“The doubling might sound very little, but the impacts of that are really, really strongly non-linear, so a small change makes a huge difference for an ecosystem, and a community,” Otto added.

The 130th report produced by the World Weather Attribution initiative, now a decade into its work, aims “to provide scientific evidence on the question of the role of human-induced climate change in the immediate aftermath of extreme weather occurring, or as in this case, while the event is still unfolding,” Otto explained.

As of Aug. 3, 3.8 million hectares have burned across Canada this season, well above the annual 30-year average of 2.7 million hectares from 1994-2023.

The report identifies “the exceptionally rapid rate at which burned area accumulated over a very short period of time” as a “particularly remarkable” characteristic of this year’s wildfire season.

To quantify the role of climate change in exacerbating “rapid blow-ups” of wildfire activity, as seen especially in northwestern Ontario this summer, researchers used seven-day accumulations of most extreme “fire weather,” as captured in a measurement known as the Daily Severity Rating (DSR).

To evaluate the long-term conditions that result in widespread fire, such as that experienced in the Northwest Territories this summer, researchers used 30-day accumulations of the DSR.

Using both observational data and climate models, they then compared conditions conducive to “rapid blow-ups” and those that contribute to expansive fire behaviour to what would have been expected in a world without fossil fuel emissions. 

The new assessment includes detailed comment on the impacts of that conjunction.

“Since the wildfires were primarily in remote and ecologically dense areas, First Nation communities were disproportionately affected,” the authors write.

Recalling that 13 communities in Ontario alone have been under evacuation orders this summer—the majority of them small, remote First Nations—the report cited the evacuations as a compound trauma, beginning in several cases with a disorganized official rescue response that left some communities to manage their own evacuations.

Near total loss of property, combined with interrupted access to hunting grounds and traplines, layered atop a colonial history of prior displacement into residential schools and other forms of forced assimilation, are all conditions the report cites as making wildfire evacuations “an even more intense social and psychological stressor for Indigenous populations.”

The report also expressed concern for the well-being of firefighters, many of whom are seeing increased physical and mental stress as fires become larger and more difficult to fight. Four Canadian firefighters, all of them involved in aerial operations, have died on the job so far this summer, note the report authors. 

Those risking their lives and well-being on the front lines of the firefight “are also at increased risk for post-traumatic stress, anxiety, depression, and suicidal ideation.”

And then there are the broader public health impacts—from wildfire smoke, in particular. Air quality ratings “are considered hazardous over a rating of 300” for PM 2.5 particulate matter. In some parts of North America this summer, wildfire smoke drove that number above 1,000.

At least “5,400 acute deaths and 64,300 chronic deaths in North America and Europe were attributable to PM2.5 exposure to the 2023 Canadian wildfires,” the authors wrote, citing a 2025 study.

The overlap between heat waves and wildfires in many parts of Canada and the United States this summer is “becoming increasingly more common, with the highest co-exposure burden falling on rural communities with lower adaptive capacity,” the report added. “Those who cannot afford or do not have access to air conditioning are highly vulnerable, often forced to choose between exposure to dangerous temperatures or hazardous air quality.”

Otto told the press briefing that while direct comment by policy-makers on WWA’s climate attribution findings have tended to be fairly rare, this year has been notable for “a very, very loud silence.”

“All of Europe is on fire, and in Canada as well, and we see very, very, very little response at all from, especially, the highest policy-makers,” she said.

Asked to comment on Canadian Prime Minister Mark Carney’s commitment to use public dollars to fund a new export pipeline while funneling billions into carbon and capture technologies, report co-author Theodore Keeping, research associate in extreme weather and climate change at Imperial College’s Centre for Environmental Policy, did not hesitate.

“The message that I would want to send to Mark Carney, very simply, is that if you export fossil fuels, the impacts of the burning of those fossil fuels come home.”