Increasing Large Wildfires over the Western United States Linked to Diminishing Sea Ice in the Arctic

The compound nature of large wildfires affected by multiple natural and anthropogenic factors in combination with complex interactions involved in hydroclimate-related physical processes make it difficult to directly connect wildfire changes over fire-prone regions like the western United States (U.S.) with anthropogenic climate change. Here we show that increasing large wildfires during autumn over the western U.S. are fueled by more fire-favorable weather associated with rapid declines in Arctic sea ice during preceding months on both interdecadal and interannual time scales. Our analysis (based on observations, climate model sensitivity experiments, and a multi-model ensemble of climate simulations) demonstrates and explains the Arctic-driven teleconnection through circulation changes with the poleward-shifted North Pacific jet stream and enhanced fire-favorable surface weather conditions. The climate model sensitivity results suggest more pervasive fires in the western U.S. with the probability of extreme burning years increasing by more than 3-fold under diminished sea-ice cover conditions when compared to the years featuring expanded sea-ice cover conditions. The amplitude of the Arctic-driven fire weather change is of similar magnitude to other leading modes of climate variability such as the El Niño-Southern Oscillation (ENSO) that also influence fire weather in the western U.S.