Human-caused climate change is beginning to have a significant impact on wildfire behaviour in western North America. Scientists have predicted that fire seasons are likely to grow longer, summer storms will produce more lightning and fire will occur more often in places where it has rarely occurred over the past several thousand years.
Each of these predictions has come true. And unfortunately, more fire leads to more carbon emissions and increased global warming.
This summer, we’ve witnessed fires in places where it has infrequently occurred in the past, and due to those fires, we are likely to experience some dramatic ecological and economic consequences at both local and global scales.
The first example involves large, high-severity fires in B.C.’s coastal forests. Two large fires, one in the upper Elaho Valley and one in the upper Pemberton Valley, have burned a combined 18,000 hectares (as of the writing of this article). What makes them of note ecologically is how they burned.
The Coast Mountain snowpack was a mere fraction of normal for 2015; in fact, by late March the snowpack depth was two per cent of normal (with the weather pattern causing the paucity of moisture attributed to climate change). The lack of snowpack and spring rain contributed to extremely dry forest fuels (downed logs, duff, etc.).
The fires that were ignited in June have burned deep into and through organic soil and down to bedrock in places. The soil that is left on the site has changed its structure and chemistry, and will now repel moisture instead of letting it soak in.
When the fall and winter rains hit these steep, burned slopes, they are likely to cause local and regional downstream erosion, flooding and infrastructure damage. This condition, and the consequence of it, can last for a decade after the fire.
The second example involves the large fires occurring in northerly latitudes in Alaska, Yukon, Northwest Territories, Alberta, British Columbia and Saskatchewan. Over the past decade, the incidence of fire and the area burned in the boreal and tundra regions has increased at an alarming rate. More than 3.4 million hectares burned in the Northwest Territories last year, and this year 1.9 million hectares have burned in Alaska and 1.7 million hectares in northern Saskatchewan.
The dramatic increase in mean annual temperatures across the Arctic and sub-Arctic, which is a consequence of climate change, is the culprit. Vast areas of the region are tinder dry by late spring, and fires, once they break out, are nearly impossible to extinguish due to size and remoteness.
These fires will result in significant global-scale ecological and economic impacts. Emissions of greenhouse gases during the combustion phase of these fires are significant, and are followed by even more emissions for several years after the fire has gone out.
Much of the northern boreal and tundra ecosystems are growing on top of large deposits of peat, which is a vast storehouse of carbon. Under non-burned conditions, the peat is encased in permafrost where very little decomposition and subsequent release of greenhouse gases takes place.
However, once the site is burned, the permafrost recedes, the peat begins to warm up, decomposition increases and greenhouse-gas emissions, especially methane — which is a far more potent greenhouse gas than carbon dioxide — increase rapidly.
Our inability to control human-caused emissions of greenhouse gases has greatly contributed to these changes in fire behaviour in western North America. Unfortunately, some of these changes are self-reinforcing, meaning fire emissions lead to more warming, which leads to more fire emissions, which leads to more warming.
Getting out of this loop will not be easy and will not be painless. And in an ironic illustration of just how far we need to go, the government of Alberta has recently imported firefighters from across the globe to protect fossil-fuel-industry infrastructure from wildfires.
Robert W. Gray is a fire ecologist based in Chilliwack.
