Wildfires across western United States have increased in number and size over the past three decades. This trend may continue in response to climate warming. A study conducted by a research term from The Pennsylvania State University projected that wildfire emissions in western American may increase by 19-101% (median: 56%) by the end of this century, compared to the baseline values in 1990s, with the largest emission increases concentrated in northern California.
During these days, public attention has been drawn to the massive Thomas Fire in Ventura and Santa Barbara counties, California, which have scorched 242,500 acres so far according to Cal Fire. It is now considered the 4th largest wildfire in California history. Currently, only 30% of the wildfire were contained.
Further information indicates that a series of 20 wildfires have ignited across Southern California in early December 2017. Six of the wildfires, including the massive Thomas Fire, became major fires resulting in widespread evacuations and property losses. According to media news reported by Los Angeles Times and CNN, these fires have charred over 260,000 acres and forced over 212,000 people to evacuate, with more than 1,000 structures destroyed. The worsening situations led to that U.S. President Donald Trump declared a state of emergency for the state of California on December 8, 2017.
Furthermore, around 250 wildfires flamed across Northern California in October 2017, with over 245,000 acres charred, 8,900 structures destroyed, and 44 people killed. According to media reports, 5 of the 20 most destructive wildfires in the state’s history burned between October and December 2017, making the 2017 California wildfire season “the most destructive one on record”.
Increased wildfire activities across the western United States during recent decades have contributed to widespread forest mortality, carbon emissions, degraded air quality, and substantial fire suppression expenditures. These fire activities have likely been enabled by a number of factors, including natural climate variability, human settlement, population growth, development patterns, and human-caused climate change. Although observed climate warming and drying have significantly increased fire-season fuel aridity, fostering a more favorable fire environment across forests, a recent study cooperated by two researchers from University of Idaho and Columbia University demonstrated that anthropogenic climate change accounted for ∼55% of observed increases in fuel aridity from 1979 to 2015 across western US forests. The study further estimated that human-caused climate change contributed to an additional 4.2 million ha of forest fire area in western US during 1984–2015. These results suggest that anthropogenic (man-caused) climate change has emerged as a major driver of increased wildfire activities and will continue to chronically enhance the potential for western US forest fire activities.
Increased emissions from wildfires may have detrimental impacts on global warming, air quality and, combined with a growing population, result in increased population exposure to unhealthy air pollutants. How to reduce the risk of wildfire, increase the capability of wildfire containment, and mitigate the negative impact of wildfires remains an imperative challenge for local government, policy makers, relevant professionals, and general publics.
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