As parts of the western United States choke on smoke from wildfires scorching more than 660,000 hectares, renewed attention is falling on the role that people have played in starting some of these blazes. An Oregon fire that has consumed 13,000 hectares, for instance, is thought to have been started by teens tossing firecrackers.
Jennifer Balch, a wildfire ecologist at the University of Colorado in Boulder, has examined just how big a role people are playing in starting wildfires in the United States. Nationwide, humans are responsible for starting 84% of wildfires, according to a paper co-authored by Balch, published this past March in the Proceedings of the National Academy of Sciences. In California, the eastern United States, and the coastal Northwest, people are behind more than 90% of wildfires. And, by starting so many fires, humans are essentially lengthening the fire season, into times of the year when natural causes—such as lightning—don’t play a major role.
ScienceInsider spoke with Balch about those numbers, and their implications. This interview has been edited for brevity and clarity.