Over 80 Percent of All Wildfires in the Past 20 Years Were Caused by Humans, Study Shows

A new study revealed that humans are responsible for starting 84 percent of all wildfires in the continental United States from 1992 to 2012.

The study, published in the journal Proceedings of the National Academy of Sciences, showed that humans have "a remarkable influence" on modern wildfire regimes. Out of the 1.5 million fires that required firefighting in two decades, human-started fires accounted for 44 percent of the burned area.

"We saw significant increases in the numbers of large, human-started fires over time, especially in the spring," said co-lead author Bethany Bradley, from the University of Massachusetts, in a press release. "I think that's interesting, and scary, because it suggests that as spring seasons get warmer and earlier due to climate change, human ignitions are putting us at increasing risk of some of the largest, most damaging wildfires."

For the study, the researchers analyzed federal, state and local wildfire records in public and private lands using the publicly available U.S. Forest Service's Fire Program Analysis-Fire-Occurrence Database. The researchers included in their studies all wildfires caused by arson, smoking, railroads, fireworks, children, campfires and burning debris from 1992 to 2012. However, prescribed burns or agricultural fires were not included in the study.

The researchers found that wildfires started by humans account for 84 percent of all wildfires, while the remaining percentage were caused by lightning. Additionally, human-started fires have tripled the length of fire season.

The area affected by wildfires caused by human ignitions have also expanded the "fire niche", a measure of ignition sources, fuel mass and dryness. This means that locations and environmental conditions with historically low lightning strike density are still at risk of burning due to human ignition.

Because humans are one of the major contributors to wildfires, the researchers noted that humans could also be a major factor in reducing the number of costly and damaging wildfires. The researchers recommend that humans should focus on living more sustainably with fire by shifting the human contribution to ignitions to more controlled, well-managed burns.