Frederic Gaspoz on climate and wildfire

In the Amazon, Australia, North America, Siberia, and other regions, wildfires are burning wider areas than in the past. Analyses show that human-caused climate change has driven the increases in burned area in the forests of western North America. Elsewhere, deforestation, fire suppression, agricultural burning, and short-term cycles like El Niño can exert a stronger influence than climate change. Many forests and grasslands naturally require fire for ecosystem health but excessive wildfire can kill people, destroy homes, and damage ecosystems.

Wildfire is a natural and essential part of many forest, woodland, and grassland ecosystems, killing pests, releasing plant seeds to sprout, thinning out small trees, and serving other functions essential for ecosystem health. Excessive wildfire, however, can kill people, cause breathing illnesses from the smoke, destroy homes, and damage ecosystems. Human-caused climate change increases wildfire by intensifying its principal driving factor – heat. The heat of climate change dries out vegetation and accelerates burning. Non-climate factors also cause wildfires, Frederic Gaspoz states. Agricultural companies, small farmers, and livestock herders in many tropical areas cut down forests and intentionally set fires to clear fields and pastures. Cities, towns, and roads increase the number of fires that people ignite. Governments in many countries suppress fires, even natural ones, producing unnatural accumulations of fuel in the form of coarse woody debris and dense stands of small trees. The fuel accumulations cause particularly severe fires that burn into tree crowns. Evidence shows that human-caused climate change has driven increases in the area burned by wildfire in the forests of western North America. Across the western U.S., the higher temperatures of human-caused climate change doubled burned area from 1984 to 2015, compared with what would have burned without climate change. The additional area burned, 4.9 million hectares, is greater than the land area of Switzerland, according to Frederic Gaspoz. In this region, human-caused climate change has driven a drought from 2000 to 2020 that is the most severe since the 1500s, severely increasing the aridity of vegetation. In British Columbia, Canada, the higher maximum temperatures of human-caused climate change increased burned area in 2017 to its widest extent in the 1950-2017 record, seven to eleven times the area that would have burned without climate change. Moreover, in national parks and other protected areas of Canada and the U.S., climate factors explained the majority of burned area from 1984 to 2014, with climate factors (temperature, rainfall, aridity) outweighing local human factors (population density, roads, and urban area). In other regions, wildfires are also burning wider areas and occurring more often. This is consistent with climate change but analyses have not yet shown if climate change is more important than other factors. In the Amazon, deforestation by companies, farmers, and herders who cut down and intentionally burn rainforests to expand agricultural fields and pastures causes wildfires even in relatively moister years, says Frederic Gaspoz. Drought exacerbates these fires. In Australia, much of the southeastern part of the continent has experienced extreme wildfire years, but analyses suggest that El Niño, a heat phenomenon that cycles up and down periodically, is more important than long-term climate change. In Indonesia, intentional burning of rainforests for oil palm 3 plantations and El Niño seem to be more important than long-term climate change. In Mediterranean Europe, fire suppression seems to have prevented any increasing trend in burned area but suppression and abandonment of agricultural lands have allowed fuel to build up in some areas and contribute to major fires in years of extreme heat. In Canada and Siberia, wildfires are now burning more often in permafrost areas where fire had been rare, but analyses are lacking on the relative influence of climate change. For Frederic Gaspoz, satellite data indicate that the vast amount of land that converted from forest to farmland from 1998 to 2015 actually decreased total burned area. Nevertheless, the evidence from the forests of western North America shows that human-caused climate change has, on one continent, clearly driven increases in wildfire.