- A team led by researchers from the University of Wyoming reconstructed the 2,000-year wildfire history of the Rocky Mountains in northern Colorado by examining charcoal accumulation in the sediments of 12 lakes.
- The only time the Rocky Mountains experienced an increase in size and frequency of forest fires was during a period known as a Medieval Climate Anomaly, when temperatures rose as much as they have today.
- Researchers conclude that even modest regional warming trends can cause exceptionally large areas to burn.
Some of the largest wildfires in US history have occurred in recent years, and 2015 has so far been no exception to the trend. A staggering 5 million acres of Alaska has already been destroyed this year. Oregon and Washington have both had about a million acres burn, while California has already seen 600,000 acres go up in flames.
Climate scientists have consistently predicted that rising global temperatures will exacerbate wildfires, making them more frequent and larger, but there are still many questions about just how much of an impact climate change will make.
But according to a study led by researchers from the University of Wyoming, the history of wildfires in northern Colorado’s Rocky Mountains over the past two millennia indicates that large fires will continue to increase as a result of a warming climate. Their results have been published in the Proceedings of the National Academy of Sciences, shedding new light on how climate change might increase the risk of large wildfires in the American West.
The researchers reconstructed the 2,000-year wildfire history of a 100,000-hectare (247,000-acre) region in northern Colorado by examining charcoal accumulation in the sediments of 12 lakes in and around the Mount Zirkel Wilderness, a mountainous area of subalpine forest. They found that wildfires burned large tracts of land in the area when average temperatures spiked approximately 0.5 degrees Celsius (0.9 degrees Fahrenheit) some 1,200 to 1,100 years ago, during a period known as a Medieval Climate Anomaly (MCA).
The researchers write in the report that the MCA was the only time in the past 2,000 years, aside from the past few decades, when there was a substantial increase in the size and frequency of wildfires in the Rockies. They estimate that as much as 83 percent of their study area burned at the beginning of the MCA — a 250 percent increase over the total area that burned in all of the 20th century, according to the report.
“When we look back in time, we only see evidence of large areas burning one time in the last 2,000 years,” John Calder, a Ph.D. candidate with the University of Wyoming’s Department of Geology and Geophysics and the lead author of the paper, said in a statement. “This suggests that large wildfires of the magnitude we have recently seen used to be very infrequent.”
Average temperatures in the Rocky Mountain region have risen about 0.7 degrees Celsius (1.25 degrees Fahrenheit) since 2000, an amount of regional warming comparable to what was experienced during the MCA, Calder and his co-authors note in the report. And sure enough, just as temperatures have again been rising in recent decades, there has been an increase in the frequency of large wildfires in the American West since the mid-1980s, they write.
“Over the entire record, temperature positively correlated with the median percentage of sites burned… suggesting an influence of low-frequency temperature trends on the extent of past fires,” the researchers write in the report.
Calder and team say their results suggest a link between our warming climate and the bigger wildfires that are occurring more frequently in the American West, and that if the present warming trend continues, as it is projected to do, the fires of recent years could be a mere prelude to more extensive and devastating blazes to come.
“What our research shows is that even modest regional warming trends, like we are currently experiencing, can cause exceptionally large areas in the Rockies to be burned by wildfires,” Calder said.