Rocky Mountain forests burning more than any point in past 2,000 years

Following 2020's extreme fire season, high-elevation forests in the central Rocky Mountains now are burning more than at any point in the past 2,000 years, according to a study published in Proceedings of the National Academy of Sciences.

U.S. National Science Foundation-funded researchers at the University of Montana and the University of Wyoming analyzed a unique network of fire-history records to understand how 21st-century fire activity compares to wildfires in the past. The findings highlight that burning in recent decades in high-elevation forests of northern Colorado and southern Wyoming is unprecedented over the past several millennia.

As fire paleoecologists -- scientists who study historical ecosystems -- the team uses charcoal found in lake sediments to piece together the fire history of forests across the Rocky Mountains. The idea, said lead author Philip Higuera of the University of Montana, is that understanding the past is key to understanding changes seen today and how forests may change in the future.

When 2020's massive fire season hit, its ferocity startled Higuera and his co-authors. Last year, wildfires in Colorado burned through October, unusually late in the year. By November, the 2020 wildfires alone were responsible for 72% of the total area burned in the study region's high-elevation forests since 1984, and Colorado had seen three of its largest fires on record.

The authors found that since 2000, wildfires are burning nearly twice as much area on average compared to the last 2,000 years. Whereas a high-elevation forest historically burned once every 230 years on average, in the 21st century that has now shrunk to around 120 years. That is more fire activity than occurred during the "Medieval Climate Anomaly," a period around 1,200 years ago when temperatures spiked higher than they were during the 20th century.

While human activity and past fire suppression are important contributing factors to wildfires across the West, the work highlights increasingly warm, dry conditions as an overarching cause of increased burning in these high-elevation forests.