The Warming Meadows experiment near Crested Butte began in 1991 and soon the wildflowers started fading. The more challenging question was happening underground—and what are the implications for planetary warming?
by Allen Best
An experiment called Warming Meadows ended a year ago. For 29 years, day and night during every season, shoulder-high electric infrared radiators directed heat downward to warm the top 6 inches of soil on half the 10 plots staked out between two stands of evergreens. This is on a ridge overlooking the East River, five miles from the Crested Butte ski area.
Unique at its launch in January 1991, the experiment at the Rocky Mountain Biological Laboratory was the world’s first attempt to foretell the effects of global warming on the natural environment by the mid-21st century. It accomplished that. Anybody who treasures the shimmer and glow of mid-summer’s pageantry of wildflowers in Colorado’s high country should be alarmed.
The experiment assumed increased temperatures of 2 degrees Celsius (3.6 degrees Fahrenheit). Those temperatures will almost certainly occur by the middle of this century given the continuing accumulation of greenhouse gases in the atmosphere. The planet altogether has already warmed 1.2 degrees C since the start of the industrial era, in some places—including higher elevations, and those inland and at higher latitudes—more; and other places less. Given a doubling of emissions, according to a study published in the Reviews of Geophysics, we can expect temperature increases of between 2.6 and 4.1 degrees C (4.1 to 8.1 degrees F).
Summer’s broad smile will dull with these rising temperatures as the broad-leafed forbs that produce the rainbow of wildflowers give way to more muted sagebrush. This is a story that Warming Meadows from its location at 9,400 feet in elevation has told quickly, vividly.
rom the beginning, John Harte, the scientist who conceived of Warming Meadows in the waning days of the administration of Ronald Reagan understood there was a deeper story, the interplay of atmosphere and soil.
Soil holds 4 or 5 times as much carbon as both the atmosphere and living vegetation. The first comparison is especially important, he explains. “It tells us that small (by percent) changes in soil carbon can result in big changes in atmospheric carbon dioxide. For example, a 25% loss of soil carbon results in a doubling of atmospheric carbon dioxide.”
Changes in vegetation carbon are not as likely to result in atmospheric changes as are possible changes in soil carbon. “We should look to the soil for potentially very large effects.”
The question, in other words, is whether the warming climate causes more carbon to be transferred from the soil to the atmosphere in coming decades as sagebrush replaces the forbs? If so, that could in turn accelerate warming.
Understanding this feedback is crucial to creating global climate models that can help predict what will happen in mountains, not just in Colorado, but across the planet.
The laboratory itself is at a one-time silver mining camp called Gothic.
Never robust with mineral wealth, Gothic was decaying back into the wilderness in 1919 when visited by a biology professor from a nearby college then called Colorado State Normal School. It’s now called Western Colorado University.
Enchanted by the diversity of ecosystems, the professor, Dr. John Johnson, returned with students. In 1928, what is now called the Rocky Mountain Biological Laboratory was established. Professors and students from across the continent have been returning ever since to conduct studies from the old mining shacks now supplemented over the decades by other, still modest offices and dormitories. They call the Rocky Mountain Biological Laboratory by its acronym, RMBL. It’s pronounced like the sound of distant thunder: rumble.
At any one time, about 200 experiments are underway at RMBL. One study launched in 1962 was of the yellow-bellied marmot, and it has been followed by 225 since then. At the start of the 21st century, researchers noted that the marmots were emerging from hibernation 38 days earlier than they had about a quarter-century before. None of the studies, though, have gained the same attention as Warming Meadows.
The greenhouse effect
Harte, a physicist turned ecologist from the University of California, Berkeley, wrote his first paper about global warming in 1970. By the 1980s, he had begun pondering the future effects of greenhouse-gas emissions and land-use changes.
“Predicting future climate entails more than just knowing about the physics of heat and light, air and water,” Harte wrote in “Ecosystem Consequences of Soil Warming,” a 2019 book with chapters by multiple authors.
“Ecosystems are a big player as well,” he wrote.
In his chapter, Harte describes the importance of what goes on underground and also feedback effects.
“Vegetation influences the physical stage on which climate plays out, and microorganisms regulate the gases that control energy flow in the atmosphere. And vegetation and microorganisms are controlled not only by climate, but by each other as well.
In this truly complex system, as ecosystems are altered by climate, the climate is in turn altered. These feedback effects can only be understood and reliably incorporated into climate models if we first understand how ecosystems respond to climate change.”
This “need to unravel this complexity, to characterize climate-ecosystem feedbacks” motivated Harte in 1988 to start assembling Warming Meadows. At Gothic he chose land tilting southward on a ridge maybe a football field away from the road to Crested Butte. Being on the ridge was important to prevent delayed runoff of snowmelt. In this small area he laid out 10 plots. Half were to be heated, and half not.
How to heat the plots? Harte hit upon the mechanism while at dinner in an outdoor restaurant in San Francisco. There he noticed the overhead heat lamps that repelled the chill fog of evening. Searching through farm equipment catalogs, he settled on a product from Pennsylvania designed to warm piglets and chickens during winter.
Harte decided to heat the ground a steady 2 degrees Celsius, with no variation for seasons, hoping to mimic “the relatively constant infrared flux from the great big heater in the sky, otherwise known as incremental greenhouse gases.” The heat dried the surface soil 15% to 20%, moisture being an important part of this investigation of global-warming effects.
All 10 plots had a mixture of woody shrub, or sagebrush, and forbs, the latter being broad-leafed herbaceous plants. Think of sunflowers, primrose, and mountain bluebells. All plots had four times as many forbs as sagebrush covering the ground when the experiment began.
The ratios were nearly upside down by year 27 of Warming Meadows: Shrub production had become three times greater than that of forbs.
The plots thicken
Warming Meadows also documented another effect of warming temperatures. Replacement of leafy green plants to woody shrubs causes a shift in the albedo. Snow reflects light more, while a black rock absorbs the sun’s energy. Woody shrubs absorb more energy than the wildflowers, the equivalent of a 10-watt light bulb per square meter averaged over night and day during the growing season. That’s double the incremental energy absorbed as a result of the increased atmospheric carbon dioxide.
Effects of increased heat were not uniform across the plants, however. Shallow-rooted plants in the heated plots showed greatly reduced growth and symptoms of moisture stress. Deep-rooted plants showed only a weak response to the heat. This, Harte wrote in the book, suggests “changes in community composition as the planet warms.”
It gets more complex. The increased heat from the lamps accelerated the runoff of snow, lengthened the growing season and, in some cases, emboldened pathogens and herbivores. This effect was not universal, though. Some pests actually did better in cooler or later-melting plots, not so well with the incremental heat.
Even by 2014, Harte had concluded that Warming Meadows provided “a realistic preview of real global warming.”
Crucial, he went on to say, was the nature of the experiment: heated plots paired with unheated plots. Without the artificial stimulation, it would have been impossible to say exactly what caused the changes in the subalpine meadows above Gothic. Many other things are at work, including acid deposition from distant coal-fired power plants, more intrusion from cross-country skiers, plus dust blown from deserts of the Southwest. Also, there could be natural cycles in the dominance patterns of vegetation. The duality of the plots, heated and unheated, made clear the effect of temperature increases during coming decades.
Meanwhile, in Washington
Harte was and remains friends with Tim Wirth. They both were, and still are, part-time residents of Crested Butte. Harte says his friendship with Wirth was only incidental as he worked out the design for Warming Meadows in 1988 even as Wirth was busy in Washington D.C. trying to draw national attention to the threat of global warming.
In his role as a U.S. senator from Colorado, Wirth helped with the staging of testimony in June 1988 by James Hansen from NASA’s Goddard Institute for Space Studies. With sweat dripping from his brow, Hansen said there was a “high degree of confidence that greenhouse gas emissions and global warming were incontrovertibly related.”
“It is already happening now,” he said.
Hansen’s testimony was the No. 2 story in the New York Times the next day. The lead story was that a new law had failed to stem the flow of immigrants from Mexico.
People in Colorado mountain towns that summer took note of Hansen’s testimony, because it was a hot summer, by mountain standards. Yet the threat of global warming, like Washington D.C., still seemed distant.
The threat of warming is less distant now, if overshadowed for much of this year by concerns that a stray cough from an unmasked stranger could send you to the hospital—that is, until the wildfires arrived with their suggestion that this will become the new normal.
But for places like Crested Butte, there’s good reason to wonder whether tourism, like the mining that preceded it, will in time wane. Since the 1990s, its summer tourism has bustled with greater liveliness than its ski economy. It self-promotes, not without good cause, as the wildflower capitol of Colorado. One of its signature pre-covid events was a wildflower festival.
Can sagebrush ecosystems be celebrated as readily? Today, as you drive the 29 miles downvalley along the East River to Gunnison, dropping 500 feet in elevation, the montane ecosystem gives away to high desert. The annual precipitation decreases by more than half. Where Crested Butte is surrounded by wildflowers, Gunnison is in a sea of sagebrush. That is likely Crested Butte’s future.
The subterranean dance
But as much as Harte hoped to predict above-ground impacts, he was just as attentive to what was happening underground.
“Climate change can alter the quantities of carbon sequestered in plants and soil, resulting in feedbacks that either enhance or retard the anthropogenic buildup of atmosphere carbon dioxide,” Harte explains in Ecosystem Consequences of Soil Warming.
“Such feedbacks are especially likely in montane and high-latitude ecosystems where soils are carbon rich, vegetation is sensitive to climate variables, such as snowmelt date and length of growing season, and climate change is expected to be large due to snow albedo feedback.”
From 1991 forward, he was trying to discern the implications for atmospheric carbon in this dance with the subterranean. For 28 consecutive years, twice each summer, he took 4 soil carbon measurements in each of the 5 heated and each of the 5 control plots, resulting in a unique and accurate record of changes in soil carbon.
The measurements were to depths of 10 cm and occasionally to 25 cm. Those areas nearest the surface have the most carbon, he points out.
“We found a 25% loss of soil carbon going to the atmosphere as CO2, which, on a large spatial scale, would translate to a huge incremental warming,” he says.
Harte hoped for a still-longer run at Gothic with Warming Meadows. Continued warming until 2050 could, he pointed out, predict climate effects in that ecosystem to the end of the century. But the costs, if not staggering, at about $15,000 a year, including $6,000 for electricity (produced mostly at coal-burning power plants), persuaded funders it was time to move on.
“It led the way for a type of research that is now very common,” says Ian Billick, director of RMBL who first arrived in Gothic as an undergraduate student in 1988. The experiment cannot perfectly foretell the effects of warming on other regions, says Billick, but the intense study can “provide insights, even if not perfectly, that help us think about the entire world.”
By way of example, he points to work on human diseases that often start with fruit flies or mice. “Not because they are perfect models for humans, but because they are way easier and cheaper to start with. We can’t study everything about everywhere, so places like Gothic serve as starting points that serve as a model for understanding all of the Earth’s ecosystems,” he says.
Seeking mountain patterns
Six years ago, a new effort was launched in the hopes of finding patterns in mountainous places across the world, to better detect general trends in the effects of warming on species loss, on diversity, and ecosystem function. It’s called WaRM, which stands for Warming and (species) Removal in Mountains (some acronyms come easier than others).
Among the 11 cold-weather sites in the WaRM network around the globe is Kluane Lake, in the Yukon Territory. The chief investigator at that site, Jennie R. McLaren, who teaches at the University of Texas at El Paso, observes on her website that woody shrubs are replacing grasses in both tundra ecosystems and in the Chihuahua Desert where she lives.
In July 2019, after the power was cut off to the warmed meadows, a small backhoe trundled up the trail to excavate narrow pits 1.5 meters deep. Several dozen scientists then gathered for a month to collect samples of 30 to 40 plant species and 30,000 or so microorganisms.
“Essentially we had to destroy the [Warming Meadows plots], but it’s really important because half the carbon is stored below 20 cm,” explained Stephanie Kivlin when I talked with her a month later.
“Putting this all together will be really interesting, but this will take time,” said Kivlin, who teaches at the University of Tennessee, Knoxville.
The core question motivating these pits was whether the soil carbon at this greater depth responded differently than that closer to the surface. Sensors had all along kept track of heat and soil moisture relatively close to the surface.
A secondary and related question is whether rising temperatures above ground alter interaction among the species living underground.
Better climate models
Researchers hope this second phase of Warming Meadows, the underground work, may yield a high-profile paper, perhaps in Science, the prestigious journal. The goal, says Kivlin, is to “understand how ecosystems are going to respond to warming. That includes plants above ground, plants below ground, and all the carbon and nutrients and microorganisms, including the carbon that plants are picking up from the atmosphere and putting into their roots. We want to understand how the entire ecosystem responds.”
Classen taught middle school for three years while working weekends in a soil laboratory before returning as a student to earn a Ph.D. “It was such a neat mashup of ecology and chemistry,” she says. Unlike the layperson, she understands something about “all these crazy microorganisms” that are part of the web of life. Now directing the Aiken Forest Science Laboratory at the University of Vermont, she wonders about things about which most of us have absolutely no notion. For example, how will those tens of thousands of microorganisms in the soil react to warming temperatures? Another one is whether the microorganisms absorb the atmospheric carbon through the roots of plants? Or will they emit more carbon themselves? “I spend all my time thinking about this,” says Classen.
This post-Warming Meadows study, she says, will almost certainly be used to build better climate-change models. Billick, the RMBL director, agrees. “This will be the first good estimate of deep soil carbon response to warming,” he says.
So, as you take your next hike out into the backcountry, consider that what lies underfoot may be just as interesting and important as what you see above ground. As for those wildflowers, try to imagine sagebrush as being just as beautiful. Not the easiest thing to do, but try.
This is from Big Pivots, an e-magazine focused on climate change, energy and water in Colorado. For a free e-mail subscription, go to BigPivots.com
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