Canada is on fire. More than 190 wildfires that raged across Ontario in July have so far burned more than 735,000 hectares of boreal or subarctic forest. And the thick smoke from those fires choked the Midwest and East Coast of the United States for days with thick plumes of dangerous haze.
A similar scenario played out in 2023, when smoke from a year of devastating and unprecedented fires in Canada also turned the skylines of some American cities orange. Projections of future climate change suggest that there are likely to 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 could help cut through the haze.
Lightning starts the biggest fires
The recipe for an extreme wildfire consists of three ingredients: an ignition source; dry vegetation ready to burn; and hot, windy weather.
Fires in Canada’s boreal forests are primarily started by lightning or human activities: the careless throwing of a cigarette butt, a stray ember from a bonfire, or a spark from a railway. In terms of sheer number of fires they start each year, lightning and humans are pretty much on equal footing.
But when it comes to total area burned, it’s not even close. Lightning is by far the main source of ignition, responsible for about 92 percent of the area burned — often in the most remote parts of Canada, where fires tend to be monitored rather than fought.
“The boreal forest evolved to burn; that’s how it replaces itself,” says Chelene Hanes, a forest fire specialist with the Canadian Forest Service, based in Sault Ste. Marie in Ontario. “It’s environmentally responsible to let fires do what they do,” as long as they don’t threaten to impact communities, she says.
Canada is so large and so sparsely populated that fighting fires in its uninhabited wilderness is not a good use of resources either. Effective fire suppression generally requires a rapid response for maximum effectiveness, perhaps within 30 minutes of ignition. This is much less possible for remote fires than for those in populated areas.
Public messages on fire management probably contributed to a decline caused by 2018. But recent data suggests that human-caused fires are on the rise again. It may not be because people have become more careless, Hanes says. Instead, as global climate change makes the landscape increasingly drier and hotter, even smaller sparks could cause massive fires.
The worst fires fuel the fire
Extreme wildfires – those that burn more than 200,000 hectares of land – now dominate Canada’s annual fire statistics. These giants are relatively few in number and represent only 3% of annual fires. But they are responsible for 97 percent of the burned land.
“Extreme fire weather is really driving the world of fires in Canada. And, I would say, the [United] So does the United States,” says Mike Flannigan, a wildfire scientist at Thompson Rivers University in Kamloops, British Columbia.
“Extreme” in fire lingo specifically refers to huge areas of burning – but such fires can also be extremely intense, burning so hot that they generate their own weather. Heat rising from these fires into the atmosphere is increasingly likely to form pyrocumulus clouds, firestorms that in turn can spawn more lightning and start new fires.
“We’re seeing more and more of these suckers,” Flannigan says. “They have always existed, but their numbers are increasing.” Canada’s 2023 wildfire season, for example, saw the highest number of fire-generated storms on record, more than 140; the previous record was set in 2021, with 100.
Fire suppression is also much more difficult with these intense fires. Typically, fire suppression strategies include direct aerial attacks, such as water drops, flame retardant chemicals or airplane foam. Then come indirect attacks: burning operations that scorch the land in front of where the fire is spreading with the wind, trying to deprive it of fuel.
But “when you’re faced with a very intense fire, the tools available to the fire manager start to decline quickly,” says Hanes. “At a certain point, the fire turns into a flood or a hurricane. When it generates its own weather, it’s no longer something we can fight.”
Air attacks can buy some time by slowing the fires, but the ground can 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’re in,” Flannigan says. Ground teams armed with infrared cameras are needed to find these hot spots and extinguish them.
Fire managers in Canada are also battling another type of wildfire: misinformation on social media suggesting the country’s out-of-control fires are the result of poor management practices. Some claims suggest that controlling fires should be a relatively simple matter of removing older, fuel-rich trees or debris from the forest floor.
But this type of routine management would be neither possible nor desirable in Canada’s vast hinterland, which covers some 300 million hectares. What’s more, the logic is flawed, the researchers say: These regions have never been managed, so it doesn’t make sense that a lack of management in these regions is responsible for the recent surge in extreme fires.
The real underlying problem, scientists say, is that boreal forests are increasingly prone to severe fires, due to climate change.
How wildfire smoke affects health
When wildfires ravage forests and grasslands, they release fine, inhalable biomass particles into the air about 30 times smaller than the width of a human hair.
The tiny particles can lodge in the lungs or make their way into the bloodstream – and are therefore linked to lung damage, increased risk of heart attack and increased risk of heart attack. shortened life expectancy. Years of repeated exposure Smoke from wildfires may also increase the risk of premature death, researchers say.
Moreover, gases found in smoke, including formaldehyde, benzene and ozonecan also negatively affect respiratory health.
Combine these smoky dangers with high temperatures – a scenario that will likely worsen as the planet continues to warm – and the risk of mortality becomes even highersays Sarah Henderson, scientific director of environmental health services at the British Columbia Center for Disease Control in Vancouver.
The impact of smoke and heat is greater than the sum of their individual effects, Henderson says. So when summer smoke looms, “move to a good indoor environment with cleaner, fresher air, if you can.”
Yes, climate change is making the situation worse
Forecasts suggest that 2026, while still considered a large fire year, will not dethrone 2023 as the record holder.
“2023 has been crazy; it was out of this world,” Flannigan says. 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. This eclipsed the previous record, just 6.9 million hectares.
As shocking as 2023 is, it is part of a worrying longer-term trend. A climate attribution study analyzing the unusually intense fire season in eastern Canada has determined that climate change has more than doubled the likelihood extreme fire conditions existing in the area.
Canada is warming at a rate about twice as fast as the planet, with longer, warmer summers and earlier snowmelt. A warmer atmosphere draws moisture from dead fuel into the forest floor or soils much more quickly. Changes in the Northern Hemisphere jet stream also reduce precipitation. And warmer winters expand the range of tree-killing pine bark beetles. All this means more fuel available to burn.
“Large fires are getting bigger, covering a larger area and burning longer,” says Hanes. Drier landscapes also mean fewer wetlands that once served as firebreaks, and larger fires can spread over many of Canada’s lakes without being significantly extinguished.
In a 2025 analysis, Hanes, Flannigan and others examined fire trends across the country since detailed record keeping began in the 1950s. From 1959 to 2024, the study found, very large fires, meaning those that burn more than 20,000 acres, are more common. are growing and represent a greater proportion of the area burned.
Canada’s six most active wildfire years on record all occurred in the last decade, with more land burned between 2017 and 2025 than in any other time in history.
And 2023, 2024 and 2025 were all fire years, the first time there have been three in a row, Flannigan says. Thus, “2026 was a decisive test: will we see another active fire season in Canada? Then we can probably expect to have one every year, due to n of climate change.
