In 2016, a territory as large as Prince Edward Island went up in smoke in the region of Fort McMurray, Alberta. In 2019, there are tens of thousands of fires in the Amazon; the international community jumped up. In 2020, the flames ignite the south-east of Australia where three years of drought are linked. Also in 2020, California is experiencing fires of an unprecedented scale in its modern history; these fires claim 33 human lives. And this year, Canada’s boreal forest is igniting from coast to coast even before the summer solstice.
Have forest fires increased in recent years? Complex question, complex answer. The causes of wildfires — which affect forests, but also grasslands, shrublands, peatlands, etc. – are many. Both humans and climate play a role. Deforestation, changes in agricultural methods and climate change sometimes have opposing influences.
All in all, scientists’ analyzes show that the Earth has been burning less since the beginning of the 21st century.e century. This counter-intuitive observation, which clashes with the impressions left by the catastrophic fires of recent years, was stated in 2017 in Sciencethen reiterated in 2022 in a major review of the literature published in Reviews of Geophysics. According to this second exercise, co-signed by the renowned Franco-Quebec climatologist Corinne Le Quéré, the area burned in the world decreased by 27% between 2001 and 2019.
Several variables
One region of the world weighs very heavily in this downward trend: african savannahs. Over the past 20 years, northern sub-Saharan Africa has seen an almost 40% reduction in the area burned annually, even as fire-prone weather has become more common. This decrease is explained by the fact that, since the beginning of the century, industrial agriculture has gained a lot of ground in Africa, at the expense of traditional techniques involving the burning of grasslands and savannahs.
Mediterranean Europe has also experienced a decline in forest fires since 2000, when more accurate satellite data are available. In general, this trend is explained by the increased efforts devoted to fire suppression. Some extreme fires have nevertheless occurred on the Old Continent during major droughts. Think of the fires in Greece in the summer of 2018, which occurred during a heat wave that would have been “impossible” in the pre-industrial climate, according to a study.
“Forest fires are events that occur under extreme conditions. We are used to thinking in terms of averages, but averages often misrepresent the entire fire regime. There is a lot of variability,” notes Sylvie Gauthier, researcher emeritus at Natural Resources Canada and forest fire specialist.
In the Amazon, fire is commonly used to clear deforested land for planting crops. As a result, the areas burned annually go hand in hand with deforestation. After peaking around the turn of the millennium, deforestation (and the fires it entails) retreated, before rebounding in 2019 and 2020. Droughts in the Amazon in 2005, 2010 and 2015 also led to important incendiary seasons.
The propensity to fires increases very markedly in the forests of western United States. Recent analyzes show a fivefold increase in the area burned annually since the 1970s. In this region of the world, scientists observe an excellent agreement, season by season, between fires and dry and hot weather. According to a study, climate change has doubled the area burned there since 1984. The total size of the fires is now similar to what was observed at the beginning of the 20th century.e century, before efforts were made to put out wild fires.
In Siberia, the trend of recent decades is ambiguous. There seems to be an increase, but the extent of the fires varies a lot from year to year in the boreal forest. In recent years, significant fires suggest that the flames are now able to attack Arctic territories whose vegetation was previously not dry enough to burn.
Relatively few studies focus on south east australia, but one of them reports a jump in the number of megafires (more than a million hectares) since the year 2000 compared to the last century. The 2019-2020 summer bushfires came just after the hottest year on record for the country. A study estimates that climate change has increased the risk of such an event by 30%.
A longer fire season
And in Canada? The area burned annually has increased “significantly” — it has more than doubled — since 1959. The trend is stronger in the northern Prairies, but also points to an increase in northwestern Quebec. In addition, large fires (200 hectares and more) have grown, on average. And the fire season starts a week earlier in the spring, and ends a week later in the fall. In Canada, the size of the fires corresponds mainly, from one season to the next, with the weather conditions, which are increasingly favorable to fires.
Obviously, humans have changed their habits in the Canadian boreal forest over the past sixty years. Air tankers became more numerous; forestry has developed. However, these phenomena typically go against fires, explains Victor Danneyrolles, professor of forest ecology at the University of Quebec at Chicoutimi. “The more cuts there are, the more leafy species we will see growing back, and the less flammable the landscapes will be,” he says. “The effect of climate change on the observed trend [au Canada] is perhaps mitigated by these human factors,” he says.
According to the last cycle of reports of the Intergovernmental Panel on Climate Change (IPCC), the runaway fires in certain regions of the world are attributable to climate change. Locally, however, the IPCC notes, other factors — such as deforestation, peatland drainage, agricultural expansion and El Niño — may exert a greater influence. On a planetary scale, the group of experts anticipates a 35% increase in burnt areas in a world that is 2°C warmer.