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.