People have triggered five out of six wildfires in the US over the last two decades, tripling the length of the wildfire season and making it start earlier in the East and last longer in the West, a new study finds. Even as climate change worsens the nation's fire season—making it longer and easier to burn more acres—researchers said human activities play an even bigger role. While fire experts have long blamed people more than lightning, the new work details the extent of human-caused ignitions and how they interact with global warming to make matters worse, the AP reports. Scientists analyzing fire data from 1992 to 2012 found that 84% of all US wildfires—but only 44% of the total acres burned—were started by people, either by accident or on purpose. And human-caused blazes have more than tripled the length of the wildfire season from 46 days to 154 days, according to a study in Monday's journal Proceedings of the National Academy of Sciences.
"People are moving more and more into natural wild areas and essentially providing ignition for wildfires," said lead author Jennifer Balch, a fire ecologist at the University of Colorado. Of the more than 1 million human-started fires since 1992, about 29% began by trash burning, another 21% were arson, and 11% were from misuse of equipment, Balch said. Last year's Soberanes fire in California was sparked by an illegal campfire and burned for nearly three months. The blaze surpassed $200 million in firefighting costs, the most expensive in US history. One out of every five wildfires occurs on the Fourth of July from fireworks, Balch said. As for the worst-hit area, the Southeast is a hot spot for human-triggered wildfires. Kentucky, West Virginia, Tennessee had fire seasons that lasted more than 200 days and 99% of the wildfires in those states are caused by people. (Read more wildfires stories.)