Attribution of observed pan-Arctic extreme fire events to anthropogenic forcings

Abstract Over the past two decades, the pan-Arctic has experienced rapid climatic change, accompanied by an unprecedented rise in extreme wildfire activity. However, a systematic and regionally comprehensive assessment of the recent extreme fire events in the pan-Arctic and the role played by human emissions is still pending. In this study, we apply a probability-based extreme event attribution framework to evaluate the role of anthropogenic forcings in enabling the extreme pan-Arctic wildfire seasons of 2019, 2020, and 2021. Using large ensemble simulations with the Community Earth System Model version 2, capable of isolating anthropogenic climate forcings, alongside remote sensing burned area products and ERA5 reanalysis, we assess both magnitude (burned area) and extreme fire risk (Canadian Forest Fire Weather Index, FWI). Our results demonstrate that anthropogenic forcings were a necessary condition for the occurrence of these extreme events: the fraction of attributable risk (FAR) exceeded 0.75 for burned area and reached virtual certainty (FAR <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>&gt;</mml:mo> </mml:mrow> </mml:math> 0.99) for FWI in 2020 and 2021. However, the probability of sufficient causation remained low, highlighting that anthropogenic forcings alone are not enough to guarantee such extreme wildfire events. Risk ratios (RRs) indicate that recent extremes have become over 200 times more likely compared to a climate without anthropogenic influence (RR = 235 [5%–95% CI: 98–489], in 2021). By decomposing FWI, we show that temperature and humidity dominate the recent increase in fire weather risk, supported by a substantial elevation in vapor pressure deficit over the pan-Arctic region.