Fingerprint of anthropogenic climate change detected in long-term western North American fire weather trends

The anthropogenic fingerprint has been detectable in observed global climate change for decades, yet it is still difficult to detect at the regional scale beyond temperature due to the presence of large internal variability and modeling and observational uncertainties. Here we demonstrate regional optimal fingerprinting of long-term fire weather trends in western North America, leveraging large ensembles of high resolution, atmosphere-only climate models to adequately sample internal variability. Considering the full spatiotemporal response to thermodynamic and dynamic climate change, we find that anthropogenic forcings have contributed 81–188% of the region’s observed increasing linear trend in fire weather over the last 50+ years. The natural fingerprint, which contains inter-annual and decadal variability, is also robustly detected. We detect the anthropogenic fingerprint in relevant meteorological variables – temperature, precipitation, and relative humidity – and link model differences in fire weather response to differences in simulated precipitation and relative humidity responses. Anthropogenic climate change has been the dominant driver of increasing fire weather trends in western North America over the past 50 years, contributing 81–188% of the observed linear trends, according to regional optimal fingerprinting applied to large ensembles of high-resolution climate models.