These findings do not discount the ongoing role of climate change, but instead suggest we should be most concerned about where it overlaps with human impact. Climate change is making our fields, forests and grasslands drier and hotter for longer periods, creating a greater window of opportunity for human-related ignitions to start wildfires.

Jennifer Balch, study lead author and Director of CU Boulder's Earth Lab

• Analyzes two decades' worth of US government agency wildfire records spanning 1992-2012
• Finds that human-ignited wildfires accounted for 84 percent of all wildfires, tripling the length of the average fire season and accounting for nearly half of the total acreage burned