Attribution of Observed Pan-Arctic Extreme Wildfire Events to Anthropogenic Forcings and Their Implications for Future Compound Carbon Extremes

Over the past two decades, the pan-Arctic region has experienced rapid climatic change, accompanied by an unprecedented rise in extreme wildfire activity. Yet, a systematic and regionally comprehensive attribution of these events, and their broader ecosystem impacts, remains limited. Here, we apply a probabilistic extreme event attribution (EEA) framework to quantify the role of anthropogenic forcings in enabling the extreme pan-Arctic wildfire seasons of 2019–2021, and assess their compound implications for Arctic carbon-cycle dynamics.

Using large ensemble simulations with the Community Earth System Model version 2 (CESM2), alongside remote sensing burned area products and ERA5 reanalysis, we evaluate both event magnitude (burned area) and extreme fire risk (Canadian Forest Fire Weather Index, FWI). Anthropogenic forcings emerge as a necessary condition for these extremes, with the fraction of attributable risk (FAR) exceeding 0.75 for burned area and reaching FAR>0.99 for FWI in 2020 and 2021. However, low probabilities of sufficient causation indicate that anthropogenic forcing alone is insufficient, highlighting the importance of interacting drivers. Risk ratios (RRs) show that such events have become over 200 times more likely compared to a pre-industrial climate (RR = 235 [5–95% CI: 98–489] in 2021). By decomposing FWI into its individual meteorological components, we are able to attribute this increase primarily to anthropogenically driven temperature and humidity changes, linked to enhanced vapour pressure deficit in the pan-Arctic.

Furthermore, we place these wildfire extremes within the context of compound climate  extreme events and their impacts on land–atmosphere carbon exchange. Using a multivariate framework, we assess how fires co-occurring with other extreme events modulate extremes in gross primary productivity, ecosystem respiration, and Arctic net carbon balance.