Atmospheric variability contributes to increasing wildfire weather but not as much as global warming.

Devastating wildfires have occurred around the world in recent years. While fire has always been part of the landscape, the trend toward increasingly widespread and severe wildfires is a key sentinel of the rapidly intensifying risks caused by global warming and climate change. Using atmospheric observations and climate model simulations, Zhuang et al. (1) quantify the relative contributions of natural climate variability and anthropogenic climate forcing to the increasing area burned in the western United States. They find that atmospheric variability can explain at most approximately one-third of the historical trend in atmospheric aridity that is conducive to wildfire. By contrast, global warming has contributed at least two-thirds of the rising trend in atmospheric aridity. Understanding the causes of increasing wildfire risk is a critical scientific and societal challenge. First and foremost, the rapidly increasing size and intensity of wildfires is having severe impacts. In California, the eight largest wildfires in recorded history have occurred in the past 5 y, and 9 of the 17 largest have occurred in the past 2 y (including the two largest and six of the top seven). Recent fires have had widespread impacts on people and ecosystems. Just in California alone these impacts include dozens of lives lost and tens of thousands of homes destroyed, leading to extended displacement of individuals, families, and communities. In addition, the massive plumes of smoke that have blanketed much of the western United States have impacted millions of people and have accounted for up to half of fine particulate matter pollution in some areas of the region (2). Recent fires have also exceeded the intensity to which fire-adapted vegetation is accustomed, posing risks to ecosystems and individual species such as California’s giant sequoias (e.g., ref. 3). While California’s fires have received much public attention, similar challenges are playing … [↵][1]1To whom correspondence may be addressed. Email: diffenbaugh{at}stanford.edu. [1]: #xref-corresp-1-1