Canada’s wildfires result from a combination of lightning, human activity, climate change, and decades of fire suppression that have left forests loaded with fuel. Fire is a natural part of Canadian forests, but recent conditions have pushed wildfire seasons far beyond historical norms. The 2023 season burned roughly 15 million hectares, shattering previous records and sending smoke across North America and Europe.
Lightning and Human Activity Split Ignitions Evenly
About half of Canada’s wildfires are started by lightning, and the other half by people. But those numbers are misleading if you stop there. Lightning-caused fires account for roughly 90% of the total area burned. The reason: lightning often strikes in remote, hard-to-reach areas where fires can grow unchecked for days or weeks before suppression crews arrive. Human-caused fires tend to start closer to roads, towns, and infrastructure, where they’re detected and fought much sooner.
Human ignitions include everything from campfires and discarded cigarettes to power lines and equipment sparks. These fires are more frequent near populated areas but generally stay smaller. Lightning fires, by contrast, can ignite multiple spots across vast stretches of boreal forest during a single storm, sometimes in places with no road access at all.
Climate Change Is Drying Out the Forest
Rising temperatures are making Canadian forests more flammable through a straightforward physical mechanism. As air warms, it can hold more moisture before reaching saturation. When the air’s capacity for moisture rises faster than actual moisture in the atmosphere increases, the gap between the two widens. Scientists call this gap vapor pressure deficit, and it’s one of the most important drivers of wildfire risk because it determines how aggressively the atmosphere pulls water out of vegetation and soil.
The key detail: this relationship is exponential, not linear. For every degree of warming, the air’s moisture-holding capacity jumps about 7%. But actual atmospheric moisture doesn’t keep pace in many regions, because there simply isn’t enough evaporation from land and water to fill that growing gap. The result is air that dries out forests, deadfall, and undergrowth faster and more intensely than it did a few decades ago. Hotter summers don’t just raise the temperature. They fundamentally change how quickly fuel becomes ready to burn.
This drying effect compounds with longer warm seasons. Snow melts earlier in spring, and fall rains arrive later, stretching the window during which forests are vulnerable to ignition. What used to be a fire season concentrated in June and July now regularly extends from May through September.
Decades of Fire Suppression Built Up Fuel
For much of the 20th century, Canada’s fire management strategy was simple: put fires out as quickly as possible. That approach protected communities in the short term but created a long-term problem. Forests that would naturally burn every few decades instead aged undisturbed, accumulating layers of dead wood, brush, leaves, and dense undergrowth. Research published in Nature Communications found that aggressive suppression around communities in boreal Canada promoted the retention of older forest stands compared to what a natural fire cycle would produce.
This is sometimes called the “fire paradox.” Extinguishing wildfires before they grow large increases the age of the forest and the amount of continuous flammable vegetation, unintentionally amplifying fire hazard around the very communities suppression was meant to protect. The effect has been well documented in fire-prone ecosystems across the United States, and evidence now shows it’s happening in parts of Canada too. Without follow-up measures like fuel treatments or controlled burns, successful suppression inevitably leads to conditions ripe for larger, more intense fires when ignition finally occurs.
Fire Is Part of How Boreal Forests Work
Canada’s boreal forest, a vast belt of spruce, pine, tamarack, aspen, and birch stretching across the country, evolved with fire. Many species depend on it. Pine and spruce cones in the boreal are often serotinous, meaning they’re sealed with resin that only melts in intense heat. Fire literally opens these cones, releasing seeds onto freshly cleared, nutrient-rich soil where they can germinate without competition from older trees.
Fire also controls pests and disease. It kills pathogens, insects, and the organisms that carry them, acting as a periodic reset for forest health. The natural cycle of burning and regrowth thins out accumulated fuels like deadwood and brush, creating a mosaic of forest patches at different ages. That patchwork historically acted as a natural firebreak, limiting how far any single fire could spread. When suppression prevents this cycle, the mosaic disappears, replaced by uniform stretches of old, dense, highly flammable forest.
Zombie Fires Smolder Through Winter
One of the more unusual features of Canadian wildfires is “overwintering” or “zombie” fires. These occur when a fire burns down into peatlands or deep organic soils and continues smoldering underground through the entire winter, insulated by snow. When spring arrives and the snow melts, these fires re-emerge at the surface, sometimes igniting new blazes before the official fire season has even begun.
Research has found that both peat and woody biomass can sustain this underground smoldering. Climate warming is increasing the prevalence of zombie fires, which is particularly concerning because deep burning of organic soils releases carbon that took centuries to accumulate. Peatlands are enormous carbon stores, and when they burn from below, the climate impact extends well beyond the immediate fire.
The 2023 Season Broke Every Record
The 2023 wildfire season illustrated what happens when all these factors converge. Roughly 15 million hectares burned, an area larger than Greece. More than 200 communities were evacuated, some of them twice, under chaotic and logistically difficult conditions. Firefighting resources across the country were stretched beyond anything previously experienced.
The health impacts extended far beyond the fire zones. Smoke from the 2023 fires exposed an estimated 354 million people across North America and Europe to hazardous fine particulate matter. In Canada, annual average exposure to these tiny particles (small enough to penetrate deep into the lungs and enter the bloodstream) increased by nearly 4 micrograms per cubic meter. In the United States, the increase from Canadian fire smoke was four times larger than the contribution from fires originating within the U.S. itself.
A study published in Nature estimated that this smoke exposure was linked to approximately 5,400 acute deaths in North America and 64,300 chronic deaths across North America and Europe. The chronic figure reflects long-term cardiovascular and respiratory damage from sustained exposure to polluted air, not just the immediate effects of breathing smoke during the worst days. Europe, thousands of kilometers from the fires, saw measurable increases in air pollution due to long-range smoke transport across the Atlantic.
Indigenous Fire Stewardship Offers a Different Approach
Long before European colonization, Indigenous peoples across Canada used fire deliberately to manage landscapes. Cultural burning, as it’s known, involves small, slow, cool fires designed to reduce undergrowth, promote biodiversity, and manage resources like berry patches and grazing areas. These are sometimes described as “fires we can walk beside,” a phrase that captures how different they are from the large-scale prescribed burns used by government agencies.
Cultural burning is Indigenous-led and guided by Indigenous knowledge systems that determine when and how to burn. It differs from agency-driven prescribed fire in both its objectives and its methods. Where prescribed fire typically focuses on hazard reduction or ecological goals using Western science frameworks, cultural burning is rooted in community and cultural practice passed down through generations.
Parks Canada established an Indigenous Fire Circle in April 2023 to support the return of these practices. In concrete terms, this has meant addressing barriers like training, resources, and regulatory hurdles that have prevented cultural burning for decades. At Waterton Lakes National Park, Parks Canada staff joined Kainai Nation fire practitioners to return fire to the land both within and beyond park boundaries, marking the first time the agency supported a First Nation in burning outside a site it directly administers. These efforts are still small in scale relative to Canada’s vast forests, but they represent a shift toward integrating fire as a management tool rather than treating all fire as a threat to be eliminated.