Résumé
We are experiencing fast changes in the timing, frequency, seasonality, size, intensity and severity of wildfires worldwide 1-3 when compared to historical ranges, i.e. altered fire regimes. Climate change modifies the fire weather 3 promoting extreme fire behaviour 4 and, in many regions, it has increased vegetation flammability 1,3 , the frequency and intensity of wildfires 5 (Table 1). Overall, fire seasons lengthened by about 20% between 1979 and 2013 1 . Model projections suggest that burned area will increase by 9-14% by 2030 and 20-33% by 2050 even under the lowest emissions scenario 6 . Changing climate can increase the areas where fire occurs (i.e. fire-prone areas), impacting biodiversity, disrupting ecosystem functioning and endangering health, cultures and livelihoods, all of which amplify the vulnerability of ecosystems and human populations 7 . Extreme fire behaviour, characterised by fast and erratic spread, abnormally high intensity, and broad fire fronts, overwhelm civil protection and fire-fighting capacities 8 . These new conditions pose unprecedented challenges to the economy, society 9,10 and fire governance by reducing the time window for planned fire-use 11 and increasing firefighting costs 12 (Table 1).
Wildfires impact the climate system by emitting large quantities of greenhouse gases into the atmosphere: they currently account for 37.8% of the total emissions from natural sources and 16.9% of total natural and anthropogenic emissions 13 . Altered fire regimes are exacerbating wildfireassociated emissions. Forest fire carbon emissions have increased by 60% overall since 2001, driven largely by increased emissions from extratropical forests 14 . For example, wildfires in boreal forests released a record of 0.48 GtC in 2021, twice the average of the 2001-2018 period 15 . Fires in Canada emitted 1.3 Pg CO 2 (0.39GtC) in 2023 16 , double the total CO 2 equivalent emissions for this country in 2021 (estimated to be 0.67 Pg CO 2 (0.2 GtC) 17 ).