What’s to blame for Canada’s wildfires?
We can expect future smoky days. And — surprise — it makes no sense to fight every blaze
Canadian wildfires in northern Ontario sent thick plumes of smoke thousands of kilometers to the east and south, blanketing many U.S. cities in hazardous haze. Here, a NASA visualization tracks the smoke from July 14 through July 20. Darker smoke colors indicate increasing smoke intensity, corresponding to worse air quality. Bright red regions indicate active fires.
NASA Scientific Visualization Studio
Canada is on fire. Over 190 wildfires raging in Ontario in July have so far burned more than 735,000 hectares of boreal, or subarctic, forest. And the thick smoke from those blazes smothered the U.S. Midwest and East Coast for days with thick plumes of hazardous haze.
A similar scenario happened in 2023, when smoke from a devastating, record-breaking fire year in Canada also turned some U.S. city skylines orange. Projections of future climate change suggest there will probably be many more such events.
What’s behind the rise in extreme fires in North America? Here are three sometimes counterintuitive facts about boreal fires that might help pierce through the haze.
Lightning sparks the biggest fires
The recipe for an extreme wildfire consists of three ingredients: an ignition source; dry vegetation that’s primed to burn; and hot, windy weather.
Fires in Canada’s boreal forests are primarily ignited by lightning or by human activities: the careless toss of a cigarette butt, a stray ember from a bonfire or a spark from a railway. In terms of the simple number of fires they start each year, lightning and humans are roughly on a par.
But when it comes to total area burned, it’s not even close. Lightning is by far the primary ignition source, responsible for an estimated 92 percent of area burned — often in Canada’s remotest regions, where fires tend to be monitored rather than fought.
“The boreal forest is evolved to burn; that’s how it replaces itself,” says Chelene Hanes, a wildland fire scientist with the Canadian Forest Service who is based in Sault Ste. Marie in Ontario. “It’s ecologically responsible to let fires do what they do,” as long as they’re not threatening to impact communities, she says.
Canada is so vast and sparsely inhabited that fighting fires in its uninhabited wilderness is also not a good use of resources. Effective fire suppression typically requires quick response for maximum effectiveness, perhaps within the first 30 minutes after ignition. That’s far less possible for remote fires than for those in populated areas.
Public messaging about fire management probably contributed to a decline in human-caused fires by 2018. But recent data suggest that human-caused fires are again on the rise. That may not be because people have become more careless, Hanes says. Instead, as global climate change increasingly makes the landscape drier and hotter, even smaller sparks could lead to massive blazes.
The worst fires add fuel to the fire
Extreme wildfires — those that burn more than 200,000 hectares of land — now dominate Canada’s annual fire statistics. These behemoths are relatively few in number, comprising just 3 percent of the annual fires. But they are responsible for 97 percent of the land burned.
“Extreme fire weather really drives the fire world in Canada. And, I would argue, the [United] States as well,” says Mike Flannigan, a wildland fire scientist at Thompson Rivers University in Kamloops, British Columbia.
“Extreme” in fire lingo refers specifically to huge burn areas — but such huge fires can also be extremely intense, burning so hot that they generate their own weather. The heat rising from these fires high into the atmosphere is increasingly likely to form pyrocumulus clouds, fire thunderstorms that in turn can spawn more lightning and spark new fires.
“We’re seeing more and more of these suckers,” Flannigan says. “They have always been around, but the sheer numbers of them are increasing.” The 2023 Canadian wildfire season, for example, had the most fire-generated thunderstorms on record, at over 140; the previous record was set in 2021, with 100.
Fire suppression is also dramatically more challenging with these intense fires. Generally, fire containment strategies include direct aerial attacks, such as dropping water, fire retardant chemicals or foams from airplanes. Indirect attacks are next in line: burnout operations that burn land in front of where the fire is spreading with the wind, trying to rob it of fuel.
But “when you get a really intense fire, the tools in the fire manager’s toolbox start to decline quickly,” Hanes says. “At a certain point, fire becomes a flood or a hurricane — when it’s generating its own weather, that is no longer something we can fight.”
Aerial attacks may buy a bit of time by slowing the blazes, but the soil may still smolder for weeks. “If you don’t get the hot spots, a week later you get a big wind event, and it’s off to the races we go,” Flannigan says. Ground crews armed with infrared cameras are needed to find those hot spots and put them out.
Canada’s fire managers are also battling another kind of wildfire: misinformation on social media suggesting the country’s out-of-control fires are the result of poor management practices. Some claims suggest reining the fires in should be a relatively simple matter of removing older, fuel-rich trees or forest floor debris.
But that kind of routine management would not be possible or desirable across Canada’s vast hinterlands, which span some 300 million hectares. Moreover, the logic is flawed, researchers say: Those regions have never been managed, so it doesn’t make sense that a lack of management there would be responsible for the recent uptick in extreme fires.
The real underlying problem, scientists say, is that the boreal forests are increasingly conducive to severe fires, thanks to climate change.
How wildfire smoke impacts health
As wildfires consume forests and grasslands, they spew fine particulates into the air, inhalable bits of biomass about 30 times smaller than the width of a human hair.
The tiny particles can lodge in the lungs or make their way to the bloodstream — and as a result are linked to lung damage, increased risk of heart attack and shortened life expectancy. Years of repeated exposure to wildfire smoke can also increase chances of premature death, researchers say.
What’s more, gases in smoke, including formaldehyde, benzene and ozone, can also negatively affect respiratory health.
Combine these smoky dangers with high temperatures — a scenario that will probably increase as the planet continues to warm — and mortality risk gets even higher, says Sarah Henderson, the scientific director of environmental health services at the British Columbia Centre for Disease Control in Vancouver.
The impact of smoke and heat together is greater than the sum of their individual effects, Henderson says. So when summer smoke looms, “move to a good indoor environment with cleaner, cooler air, if you can.”
Yes, climate change is making it worse
Forecasts suggest that 2026, while still projected to be a big fire year, won’t dethrone 2023 as the record-holder.
“2023 was bonkers; it was off the charts,” says Flannigan. That year, a record 15 million hectares — an area roughly the size of the state of Illinois — of land was on fire in Canada, beginning in early May. That dwarfed the previous record, a mere 6.9 million hectares.
As shocking as 2023 was, it’s part of a longer-term worrisome trend. A climate attribution study that analyzed the unusually severe fire season in eastern Canada determined that climate change more than doubled the likelihood of extreme fire conditions existing in the region.
Canada is warming at roughly twice the global rate, with longer, hotter summers and earlier snowmelt. A warmer atmosphere much more quickly sucks moisture out of dead fuel in the forest floor or from soils. Shifts in the Northern Hemisphere jet stream are reducing precipitation as well. And warmer winters are expanding the ranges of pine bark beetles that kill trees. All of this means more fuel available to burn.
“Big fires are getting bigger, covering a larger area and burning for longer,” Hanes says. Drier landscapes also mean fewer wetland areas that once served as fire breaks, and bigger fires can pass over Canada’s many lakes without being extinguished significantly.
In a 2025 analysis, Hanes, Flannigan and others examined trends in the country’s fires since detailed recordkeeping began in the 1950s. From 1959 to 2024, the study found, very large fires — those that burn more than 20,000 hectares — are getting larger and are accounting for a greater proportion of the area burned.
The six most active fire years in Canada on record all occurred in the last decade, and more land area burned from 2017 to 2025 than in the entire rest of the record.
And 2023, 2024 and 2025 were all big fire years, the first time on record that there were three in a row, Flannigan says. So “2026 was a litmus test: Will we see another active fire season in Canada? Then we can probably expect one every year, because of our changing climate.”
