Wildfires and climate change: seeking the facts through the haze

by Stan Hirst

Living under smoky skies every day is an uncommon experience for Vancouverites. The TV spectacle of thousands of people having to evacuate their homes and ranches in the interior of British Columbia as threatening forest fires advance is not so unfamiliar. Just one year ago we watched over 88,000 people leaving their homes in Fort McMurray as wildfires swept through nearly 600,000 hectares in northern Alberta. This year nearly 500,000 hectares have burned within B.C., 75% of those in the Cariboo region and another 25% around Kamloops.

It was probably inevitable that the conversation would switch easily to global climate change and its connection to the wildfire blight. For many people and most Suzuki Elders the link between wildfires and climate change is taken as a given. The linkage is now commonly quoted in the press, in current literature and in conversations. The same theme of wildfires becoming ever more frequent as the world warms appears often in the media for western Canada, the western U.S.A., Australia, Portugal and parts of Africa, South America and Asia.

Yet the sceptics remain unmoved and say so through social media. “Fires have always been a feature of forests and rangelands in North America” they say. They point to history books abounding with descriptions of massive fires, some deliberately set, but many linked to natural causes, especially lightning.

It’s not uncommon to find fire scars in centuries-old trees such as sequoias and western junipers across western North America. Studies of lake sediments have found wood charcoal layers which can be dated back for thousands of years. Early researchers attributed these historic fires to lightning strikes, but studies in the past few decades indicate that they may also have resulted from deliberate burning by aboriginals to keep forests free of undergrowth and small trees.

The specific question is not whether wildfires are a natural feature of North American forests or not, but whether global climate change is prompting an increase in wildfires. By being overly simplistic about the two parts of the equation (climate change and fire) we could obscure the underlying linkages between the two and possibly mistake the causalities.

I find it helpful to break the subject matter into simpler relationships (dissecting the argument always helps in winning arguments anyway).

First, the question of a changing climate. This is the easy part; the answers are unequivocally yes. Temperature trends summarized by Environment Canada for the period 1948 through 2012 show statistically highly significant rises across most of Canada. Mean increases range from 0.5 to 3oC, with the highest numbers occurring in the arctic and subarctic regions. Mean ambient temperatures in the Pacific region of B.C. rose 0.7 oC over the same period and 1.2oC in the mountainous areas of southern B.C.

There are also statistically significant changes in geophysical and ecological parameters which are driven by ambient temperatures:

  • longer growing seasons, more heat waves and fewer cold spells, thawing permafrost;
  • earlier river ice break-up;
  • increase in precipitation over large parts of Canada;
  • more snowfall in the northwest Arctic;
  • earlier spring runoff and the earlier budding of trees.

Indigenous people of the Arctic are no longer able to predict the weather as accurately as their forefathers did (cited by the Society for Ecological Restoration).

Have wildfires increased significantly in B.C. over the same period? This brings us to the realization that fires can be measured by more than one parameter, i.e. the frequency with which they occur, the area which is burned over, the costs of fire damage, suppression and management, etc. Any, all or none could be linked to climate change.

Three measures of wildfire activity in B.C. are available from the B.C. government website. These are all shown below for the twelve most recent years.


The broad conclusions from these data are that while the annual frequency of wildfires across B.C. has dropped by roughly one-half over little more than a decade, the areal extent of wildfires for the same period has increased six-fold and the associated costs of dealing with the fires has increased twelve-fold.

These results are very similar to those reported in the western U.S. for recent years. University researchers and federal and state forest agencies in California have linked the occurrence of more widespread, bigger, longer-lasting wildfires to higher ambient temperatures and less or later snowfall. They have also indicted past practices of aggressively preventing fires as having had the perverse effect of creating much more fuel within forests themselves to feed future wildfires. The average California wildfire in the 2000s was double the size and burned twice as long as the average fire in the 1990s. Escalating fire-associated costs have also been linked to higher levels of damage as more homes are built on picturesque hillsides and mountains and other areas prone to wildfire.

A recently published study from the University of Idaho has neatly linked wildfires in western forests to human-caused (anthropogenic) climate change. The research group has quantitatively examined the statistical relationship between the essential requirements for wildfires (fuel availability, fuel aridity, etc.) to climate variables such as ambient temperature and vapour pressure which are changed by human activities such as increased greenhouse gas emissions.

The university research group concluded that for the period 2000–2015 climate change contributed to 75% more forested area across the western U.S. experiencing high fire-season fuel aridity. It also added an average of nine additional days per year of very high fire potential. Anthropogenic climate changes were calculated to have accounted for ∼55% of observed increases in forest fire fuel aridity from 1979 to 2015 across western US forests.

Hopefully this all adds a little more fuel to the fire in a quest to hasten meaningful climate action in B.C. and the rest of the reasonable world.





  1. Thanks, Stan. Very well done. I would like to add another way of seeing climate change in B.C. As land temperatures increase faster than the world average, El Ninos become more extreme, and jet stream stalls become more frequent, leading to longer lasting high (or low) pressure systems over B.C., we can expect bigger floods as well as deeper droughts. Given Vancouver’s proximity to the ocean on the west side of the Coastal Mountains, I expect floods will be worse here. Likewise, dry air in the B.C. interior and higher temperatures should mean more fire. I see this as part of eco-systems moving north. The arid interiors of Washington, Oregon, and the divide between the western slopes of the California Sierra Nevada Mountains, and the eastern slopes (think Reno, Las Vegas, etc.) are previews for B.C.’s interior during the coming decades and centuries. Therefore, the rangeland climate should become semi-desert, then desert: no trees, except at cooler higher western slopes. That means forestry practices and infrastructure engineering must consider much more dynamic changes in climate compared to the relative stability of the past 10,000 years.

      1. If that were so, the percentage of wildfires caused by human activity would decrease, no? The bar chart at the end of the article shows that isn’t so. Are there fewer lightening strikes? Has the data collection changed?
        I don’t understand why the area burned has increased but the number of fires has decreased. That is, why the average fire should be much larger.

        1. From Globe & Mail 10 July 2017 (https://www.theglobeandmail.com/news/british-columbia/almost-half-of-fires-burning-across-bc-caused-by-humans-province/article35652545/) –
          “Regardless of the cause of the fires, Lori Daniels, an associate professor of forest ecology at UBC, said successes in fighting fires has actually made the risk worse. Dr. Daniels said firefighting efforts over the past 60 to 100 years have allowed for denser forests with a lot of dead material on the ground. Now, when the province has hot, dry weather and lightning strikes or there is a human ignition, the fires are much more severe and fast-moving.

          “The irony is we tried to protect our forests from fire and we created a situation where they’re much more susceptible and the fires are more damaging,” she said.

  2. What really concerns me is how many of those fires were “man caused” i.e. cigarettes, campfires etc. Not enough is being done about it. The fines are very small and people are very careless. One problem is there are no ashtrays in cars now, so people just throw their cigarettes out the window.
    A few days ago Global TV showed a little boy (looked about 8 years old) with a stand with plastic bottles, some water in each and written on them “Put your cigarette butts in here”. I only saw It once and phoned Global TV and asked them to display it again, which they did not. Not enough is being done about it. I am going to write every political leader from the Prime Minister down to the Mayor of Vancouver and suggest they all get together to try and put a stop to this carnage.
    I realize it is almost impossible to catch someone throwing a cigarette out a car window. Maybe the Police have to stop every car to see that they have something to put their cigarettes in. My son-in-law used to smoke and kept a can in his car for his butts. Fines should be in the thousands of dollars not a couple of hundreds. Please write your concerns to the “powers that be”. They have to figure out a way to at least control man-caused fires. I realize we cannot control the lightning strikes. But surely there is a way to control “man caused” fires.

  3. From the 2017 report of the Fourth National Climate Assessment (NCA4) of the U.S. Global Change Research Program:
    Recent decades have seen increased forest fire activity in the western United States and Alaska. For the western United States, one study has estimated that human-caused climate change was responsible for nearly half of the total forest acreage burned by wildfires over 1984 to 2015, while another study found an increased risk of fire in California due to human-caused climate change. For Alaska, one study found that human-caused climate change had increased the risk of severe fire seasons like 2015 by 34%–60%. None of the studies demonstrates that a long-term increase in forest fire activity is highly unusual in comparison to natural variability. The degree of forestry management, which is greater in the western United States than in Alaska, is a confounding factor that complicates attribution of changes to anthropogenic climate change. There is medium confidence for a human-caused climate change contribution to increased forest fire activity in Alaska in recent decades, but low confidence for a detectable human climate change contribution in the western United States based on existing studies.

  4. I think forest fires and smoky air are something people can relate to about climate change. Ocean acidification and melting sea ice are not so much in your face.

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