[Note: In Part 1 of this post, I discussed how average burn areas have been growing across North America over the last 50 years, and how global warming is a key driver in this trend. I also discussed how many regions in North America used to burn as much as present back in the late 19th Century and before. I left off discussing how the boreal forest fire regime appears to be changing quickly]
The experts I spoke to noted how many of the historical fires in the boreal likely were crown fires – not just surface fires – since boreal tree species require crown burning for regeneration. Despite this, Flannigan noted how boreal fires are indeed becoming more intense in our present era (and the data backs this up). One main line of evidence for this includes the proliferation of pyrocumulonimbus (pyroCb) events – a situation in which a wildfire is so intense that it literally creates its own thunderstorm cloud. Back in the 1980s, Flannigan told me, these types of PyroCB events were exceptional. Today, he said, they are “becoming commonplace” (with Canada’s 2023 wildfire season producing 142 PyroCb events that year alone!).
Thus, Flannigan was skeptical about there being the types of ‘Coast-to-Coast-to-Coast’ wildfire seasons like we saw in 2023 (or this year, 2025) in the pre-20th Century era, since the boreal simply wouldn’t have survived this long if that kind of fire year was common. He also noted that dendrochronological reconstructions (the kind often used to infer historical burn rates) have greater uncertainty in time and space as compared to our modern record. Flannigan noted how, for instance, in the Northwest Territories, Indigenous oral histories suggest that the kind of fires experienced in 2023 in that region were unprecedented, pointing to a territorial review in which an Elder from Salt River First Nation was quoted as follows: “(It was) an experience that we do not have in our oral traditions - it was like nothing we have ever experienced or imagined.” This is powerful evidence given that Dene people have had a continuous presence in the area for several thousand years.
“(It was) an experience that we do not have in our oral traditions - it was like nothing we have ever experienced or imagined.” - Elder from Salt River First Nation, about the 2023 wildfires.
The emerging picture suggests that many parts of North America likely experienced wildfire burn rates before the 20th Century that are akin to the recent past – particularly in the U.S. – but a) with some regional variation and several exceptions; and b) likely not at the level seen in 2023 (in Canada) or 2020 (in the US); and c) not of the save severity.
Canada’s 2023 (and now 2025) wildfire season(s) likely represent examples of burn rates exceeding those seen historically. It is telling, for instance, that the figure below in a paper by Raphaël Chavardès et al. from 2022 shows contemporary burn rates in Wood Buffalo much lower than prior historical peaks, while new research by this same group specifically found Wood Buffalo burn rates in the decade leading up to 2023 to be higher than the historical range (as noted above).
Why did it burn more?
The outstanding question is why? Why did many areas of North American burn more in the past relative to today? From a climatic point of view this is especially confusing. The 16th through 19th Centuries generally coincide with a period of time known as the ‘Little Ice Age’ – when average temperatures (especially in the Northern Hemisphere) were relatively colder than present.
There are a few hypotheses: Danneyrolles et al. emphasize that despite the relatively lower average temperatures back then, there were also “periods of particularly high climatic dryness during fire seasons” in North America at that time, which could have triggered high burn areas. Another factor – significant in some areas of North America – was more intensive fire use by Indigenous people in the pre-Colonial era (though this was not as well documented in the Canadian boreal as it was in the U.S., for instance). Whitman suggested that there is some dendrochronological evidence in various regions of Canada where fire scars suggest low-intensity, spring surface fires, given the species of trees that appear to have survived such fires, which potentially implies human-managed fire. Flannigan emphasized how the use of fire by Indigenous people in the land now called Canada was commonplace – with many dozens of distinct known uses for fire (from cultural reasons to landscape management to support with food production and hunting). Yet another reason could be fire-induced changes in the forest tree species mix – with less flammable tree species moving into the area as the boreal forest continues to migrate North.
Another way of asking this question, however, is not why it burned more back then, but why did burn rates decline in the 20th Century across North America? And, it seems a crucial part of the answer involves the era of suppression and fire exclusion that came into full force during this time, which may also have coincided with a relatively wetter period in North America, resulting in lower burn rates compared to both before and after the 20th Century.
Fundamentally, the mix of human management and land use practices, alongside anthropogenic and natural changes to North America’s climate, have created this see saw effect, where burn rates appear to have been elevated, then declined, and now are surging again. Which begs a final question… what’s coming down the pike?
What does the future hold in store?
I asked each of the experts I spoke with what they expected in the future, given current rates of increase in wildfire burn area and severity.
Victor Danneyrolles said he expects the high rate of variability from one year to the next to continue, while at the same time average burn area to continue to trend upwards. This is what the Canadian government expects across the boreal as well, as shown in the figure below. Even in the low emissions/low warming scenario, the annual area burned by large fires is expected to continue growing through to mid-Century at the very least.
Ellen Whitman also expressed a similar vision of the future, noting she expects "some very challenging fire years" ahead (in Canada). For his part, Sean Parks – focusing largely on the US context – also saw a future with more fire, in general: “As the climate continues to warm, we're going to see more and more fires not get filtered out by fire suppression,” meaning that climate change will increasingly overwhelm fire suppression capabilities, leading to more large, uncontrollable fires.
Mike Flannigan put it in more dire terms. Thinking of Canada’s record 2023 wildfire season in the context of two additional very large fire seasons in 2024 and 2025, he noted that (modern) Canada is largely in “uncharted territory”. We will likely see more extreme fires, he said: More PyroCB events; a pronounced increase in fires in Eastern Canada (which may be new to many Canadians who grew up in a time when large wildfires seemed to be more of a ‘Western’ and ‘Northern’ Canadian thing); and likely some continued losses of the boreal forest to grasslands. Despite evidence of more extensive burn rates in the past, Flannigan thinks what we’re seeing in this day and age is in fact different: “I do believe we are entering uncharted territory with no historical analogue.”
“I do believe we are entering uncharted territory with no historical analogue.” - Mike Flannigan
Thx Ryan. It was a long and winding road -- I appreciate your commitment to the complex truth. for those who may not have read to the end, I fear they may have left with the belief that fire was worse in the past in north america... but I don't think that's where you landed.
Perhaps that's a polite way of saying you (may have) buried the lead: going forward, more fire, more severe fire, that more often exceeds suppression ability -- we're in uncharted territory. There was also much fire in the past.
:)
Very thoroughgoing coverage. I find myself in agreement with Mike Flannigan.especially in regards to eastern Canada.