From Climate Central (Bobby Magill):
Catastrophic wildfires in the Western U.S. are often discussed in superlatives these days, with blazes burning land more violently and more frequently in recent years than at any point on record. Those changes are considered partly driven by global warming, and a new University of Wyoming study shows that even the smallest increase in average temperature — 0.5°C (0.9°F) — could bring a dramatic increase in wildfire activity at higher elevations.
The study also suggests that global warming may be ushering in an era of high-elevation wildfires unlike any seen in more than 1,000 years…
The new study, published Monday in the Proceedings of the National Academy of Sciences, provides more evidence that even a small amount of warming has a huge effect on wildfire.
University of Wyoming researchers studied charcoal samples representing 2,000 years of wildfire that were taken from lake beds in a subalpine forest — above 8,000 feet — in northern Colorado’s Mount Zirkel Wilderness near Steamboat Springs. With them, they were able to measure the increased wildfire frequency during a period of global warming similar to today.
That period, called the Medieval Climate Anomaly, or MCA, was about 1,100 to 1,200 years ago, when average temperatures in Northern Colorado were 0.5°C warmer than they were the preceding century, but moisture levels were not dramatically different.
Before the warm period, about 50 percent of the sites the researchers studied burned per century, increasing to 83 percent during the warm period and declining to 33 percent afterward. Most sites burned roughly at a rate of every 360 years prior to the warm period, increasing to every 120 years during the warm period — a 260 percent increase. Fire frequency declined before temperatures cooled, however, and the researchers think that happened because there was little forest left to burn.
The study is the first to discover how much land across an entire mountain range burned over a period of 2,000 years and shows that large wildfires similar to those burning today only occurred when temperatures increased like they have in recent years, the study’s lead author, University of Wyoming Ph.D. candidate John Calder, said.
“When we look into the past for evidence of these large wildfires we only see them one time when temperatures rose about 1°F,” he said. “Our study then adds more evidence that the recent increase in large wildfires is related to climate change because the only time we see these types of large wildfires in the last 2,000 years is when we had a similar amount of warming.”
The study only applies to dense high elevation forests, not those that have burned at lower elevations elsewhere in Colorado.