Editing IPCC:AR6/WGII/Chapter-2 (section)

===== 2.4.4.2.1 Detection and attribution of observed changes in wildfire =====

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Wildfire is a natural and essential component of many forest and other terrestrial ecosystems. Excessive wildfire, however, can kill people, cause respiratory disease, destroy houses, emit carbon dioxide and damage ecosystem integrity (see Sections 2.4.4.2 and 2.4.4.4). Anthropogenic climate change increases wildfire by exacerbating its three principal driving factors: heat, fuel and ignition ( [[#Moritz--2012|Moritz et al., 2012]] ; [[#Jolly--2015|Jolly et al., 2015]] ). Non-climatic factors also contribute to wildfires—in tropical areas, fires are set intentionally to clear forest for agricultural fields and livestock pastures ( [[#Bowman--2020|Bowman et al., 2020]] ). Urban areas and roads create ignition hazards. Governments in many temperate-zone countries implement policies to suppress fires, even natural ones, producing unnatural accumulations of fuel in the form of coarse woody debris and high densities of small trees ( [[#Ruffault--2015|Ruffault and Mouillot, 2015]] ; [[#Hessburg--2016|Hessburg et al., 2016]] ; [[#Andela--2017|Andela et al., 2017]] ; [[#Balch--2017|Balch et al., 2017]] ; [[#Lasslop--2017|Lasslop and Kloster, 2017]] ; [[#Aragao--2018|Aragao et al., 2018]] ; [[#Kelley--2019|Kelley et al., 2019]] ). Globally, 4.2 million km 2 of land per year burned on average from 2002 to 2016 ( [[#Giglio--2018|Giglio et al., 2018]] ), with the highest fire frequencies in the Amazon rainforest, deciduous forests and savannas in Africa and deciduous forests in northern Australia ( [[#Earl--2018|Earl and Simmonds, 2018]] ; [[#Andela--2019|Andela et al., 2019]] ).

Since the AR5 and the IPCC Special Report on Land, published research has detected increases in the area burned by wildfire, analysed relative contributions of climate and non-climate factors and attributed burned area increases above natural (recent historical) levels to anthropogenic climate change in one part of the world, western North America ( ''robust evidence'' , ''high agreement)'' ( [[#Abatzoglou--2016|Abatzoglou and Williams, 2016]] ; [[#Partain--2016|Partain et al., 2016]] ; [[#Kirchmeier-Young--2019|Kirchmeier-Young et al., 2019]] ; [[#Mansuy--2019|Mansuy et al., 2019]] ; [[#Bowman--2020|Bowman et al., 2020]] ). Across the western USA, increases in vegetation aridity due to higher temperatures from anthropogenic climate change doubled burned area from 1984 to 2015 over what would have burned due to non-climate factors including unnatural fuel accumulation from fire suppression, with the burned area attributed to climate change accounting for 49% (32–76%, 95% confidence interval) of cumulative burned area ( [[#Abatzoglou--2016|Abatzoglou and Williams, 2016]] ). Anthropogenic climate change doubled the severity of a southwest North American drought from 2000 to 2020 that has reduced soil moisture to its lowest levels since the 1500s ( [[#Williams--2020|Williams et al., 2020]] ), driving half of the increase in burned area ( [[#Abatzoglou--2016|Abatzoglou and Williams, 2016]] ; [[#Holden--2018|Holden et al., 2018]] ; [[#Williams--2019|Williams et al., 2019]] ). In British Columbia, Canada, the increased maximum temperatures due to anthropogenic climate change increased burned area in 2017 to its highest extent in the 1950–2017 record, seven to eleven times the area that would have burned without climate change ( [[#Kirchmeier-Young--2019|Kirchmeier-Young et al., 2019]] ). In Alaska, USA, the high maximum temperatures and extremely low relative humidity due to anthropogenic climate change accounted for 33–60% of the probability of wildfire in 2015, when the area burned was the second highest in the 1940–2015 record ( [[#Partain--2016|Partain et al., 2016]] ). In protected areas of Canada and the USA, climate factors (temperature, precipitation, relative humidity and evapotranspiration) accounted for 60% of burned area from local human and natural ignitions from 1984 to 2014, outweighing local human factors (population density, roads and built area) ( [[#Mansuy--2019|Mansuy et al., 2019]] ).

In summary, field evidence shows that anthropogenic climate change has increased the area burned by wildfire above natural levels across western North America in the period 1984–2017, at GMST increases of 0.6°C–0.9°C, increasing burned area up to 11 times in one extreme year and doubling it (over natural levels) in a 32-year period ( ''high confidence'' ).

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