This is Part Two of an article that first appeared on BigPivots.com on July 9, 2021.
Fires are natural. Even big fires are natural, as charcoal collected from the mud of lakes and the scars of trees demonstrate. What we see now is not natural.
It begins with rising temperatures. The Colorado River Basin — including Aspen and Vail and the location of the East Troublesome Fire — have warmed 2 degrees Fahrenheit since 2000 as compared to the 20th century average. This, according to a report by Western Water Assessment, is likely warmer than at any time in the past 2,000 years.
A 2009 paper by Connie Woodhouse, of the Laboratory of Tree-Ring Research at the University of Arizona in Tucson, and others, compared the 21st century warming with a notably warm period of 1,000 years ago. During that period from 900 to 1300 AD, the Northern Hemisphere was warmer than all but the most recent decades. Drought was a companion. The worst 10-year period was 1146 to 1155. That, perhaps not incidentally, was about the time the ancestral Pueblo — as the Anasazi are now more commonly called — began emigrating from the Four Corners area.
Mike Metcalf, an archaeologist based in Eagle, takes the long view. His work has examined human habitation of Colorado and other Western states since the glaciers rapidly retreated 13,500 years ago. “Somebody who has studied climate tends to be skeptical of simplistic explanations,” he says. “There are so many things, so many variables that control climate.”
But the warming and consequent aridification of the last few decades defy conventional explanations. “The amount of drought in the West is off the charts,” says Metcalf.
A study published in 2020 in the journal Science concluded that climate change has made drought conditions 46% worse between 2000 and 2018.
Drought, as conventionally understood, no longer serves a useful purpose in describing what is being measured. Instead, some are using the word “aridification.” The effect can be seen in the reduced runoffs of the Colorado River into Lake Powell. The river flowed 543,000 acre-feet this year, compared to the May average of 2.34 million acre-feet since Glen Canyon Dam was completed in 1966. In 2020, the winter snowpack was actually pretty good, but the runoff was subpar. This year, with drying soils sopping up more amounts of moisture, the fast-falling levels in the giant reservoirs in Utah, Arizona and Nevada have become a national story. As Metcalf points out, the trends just keep accelerating.
Now comes new evidence that high-elevation forests in Colorado since 2000 have burned at a rate greater than at any time in the past 2,000 years. To draw this conclusion, the University of Montana’s Philip Higuera, a fire ecologist, and two colleagues waded into the work of paleoecologists who had plumbed the depths of 20 lakes to document the fire history.
Twelve of the lakes were in the Park Range near Steamboat Springs. Others lakes were on the southeast side of Rocky Mountain National Park, near Estes Park.
Comparing the fire record of recent years with that 2,000-year history, Higuera and his co-authors, the University of Wyoming’s Bryan Shuman and University of Montana doctoral candidate Kyra Wolf, came up with a startling conclusion: The frequency of fire in high-elevation forest has shrunk from once every 230 years on average in the last two millennia to about 120 years during the current century.
Warm, dry conditions provide the overarching cause of increased burning in high-elevation forests.
“It isn’t unexpected to have more fire as temperatures rise,” said Wolf, the co-author. “Our records show that fire tracked past variations in climate just as it does today. What’s striking is that temperatures and correspondingly fire are now exceeding the range that these forests have coped with for thousands of years — largely as a result of human-caused climate change.”
This wasn’t necessarily unexpected, although the timing may be. For decades, scientists have predicted that climate warming will increase wildfire activity in high-elevation forests beyond the historical range of experience, said Higuera — who spoke in March at a session sponsored by Carbondale’s Wilderness Workshop.
“It’s sobering to see that it’s clearly happening, and early in the 21st century — not in 2050, not in 2075, but in 2020,” he said.
Very limited tool box
We don’t know exactly how hot it will get. That’s partly because we don’t know whether the atmospheric pollution can be bent down. The rate of accumulating carbon dioxide, the most common greenhouse gas, has not abated in the 21st century even as the science around the risk has solidified.
We’re polluting the sky as if there were no tomorrow. The observatory located at an elevation of 11,135 feet at Hawaii’s Mauna Loa has documented the pollution of carbon dioxide. CO2 levels in 1958 stood at 320 parts per million, a relatively modest increase from pre-industrial times. In 2013 the levels surpassed 400 ppm. This year it hit 420.
Staying in this fast lane, what temperatures will that produce in Aspen, Vail and other ski towns in Colorado? A study expected to be issued later in July will paint a more definitive picture of that future heating in headwater communities.
A 2016 study along the northern Front Range by the Rocky Mountain Climate Organization delivers a glimpse of that hotter future. Fourteen days with temperatures greater than 80 degrees were recorded during the late 20th century at a site in the foothills west of Boulder comparable in elevation to Aspen and Vail. This is projected to more than double in the next decade or two. By the time today’s toddlers reach retirement age, there will be 100 days.
“We will be hotter and we will be drier,” says Stephen Saunders, a former undersecretary in the Department of the Interior who was the lead author of that study. “If you have increased temperature and the same amount of precipitation, you will indeed be drier.”
That observation was demonstrated last week in a PowerPoint presentation by Russ Schumacher, the Colorado state climatologist. The first slide shows standardized precipitation index for Colorado since 1900. There are periods of wet and periods of dry — including during the 21st century. But the standardized evaporation-transpiration chart — transpiration is what a plant “exhales” in response to heat — tells a very different story during the 21st century. There are no peaks in the 21st century; only valleys of drought. The warming atmosphere is absorbing moisture from the ground and from vegetation.
Measurements conducted by federal agencies at the Garfield County Airport in Rifle, on Hardscrabble Mountain near Eagle and in Summit County bear this out. One measure of the dryness, called the thousand-hour test, showed the moisture content in wood on Hardscrabble dropping from 12% on June 1 to just 8% at mid-month. “From a wildfire behavior standpoint, you don’t necessarily like to see 8%,” said Ryan Hughes, a fuels specialist for the U.S. Forest Service. Five days later after that measurement, the Sylvan Lake Fire broke out south of Eagle.
Tom Veblen, now a professor emeritus of forest ecology at the University of Colorado Boulder, has studied wildfires in Colorado from almost every angle: tree rings, lake deposits, journals of explorers and 19th century newspaper accounts. We know 1847 was a fiery year, and so was 1851.
Also 1879, the year that Vail’s Back Bowls became mostly treeless, the result supposedly of “spite” fires set by Ute Indians, although the evidence is lacking, he says. It was a dry year, the only time fires in high-elevation forests spread, and fires and prospectors were everywhere — including, at that point, in the hamlet that soon became Aspen.
What annoys Veblen most is the phrase “healthy forests.” The metaphor, contained in the title of a 2004 federal law and also a 2021 Colorado law, powerfully draws on an analogy to human health. It also misleads in the context of high-elevation forests, says Veblen, and it was misused, he says, to characterize the East Troublesome Fire.
Areas covered by East Troublesome included large swaths of trees killed by bark beetles during an epidemic of the last 25 years. If bark beetles always have been in a fandango with forests, they came on particularly strong with rising temperatures and drought in the 21st century. The argument has been made that those trees killed by beetles need to be removed, to abate fire danger. Scientific studies in the last decade don’t leave that idea standing. One of them, by Hart and colleagues in 2015, found that prior beetle kill is not causing an increase in the extent or severity of fires of Western states.
“The fuels are the needles,” explains Veblen. “Once needles turn (red) and fall to the ground, to the forest floor, we actually have a decline in the ability of fires to spread through the crowns, through the canopy of the forest,” he says.
“What we are seeing is an increase in fire, yes, and an increase in bark beetle activity, both of which are driven by climate change, both driven by warmer conditions.
“Within the research community and also within the fire management community over the last 5 to 10 years there has been a greater realization how all of those changes are being driven by climate change,” he says. “But there is still a tendency to hold onto some of the old narrative.”
Thinning of forests, he says, has little value except in areas adjacent to communities and structures. “The people in the fire mitigation business are very motivated to use the tools they have, but those tools are very, very limited.”
Allen Best publishes the e-journal Big Pivots, which chronicles the energy transition in Colorado and beyond.