Aspen is running out of snow.

The ski season is a month shorter than it was 50 years ago. It will be nearly two weeks shorter still by 2030, and it will continue to shrink in subsequent decades. In the spring, wet slab avalanches – in which an entire slope slides slowly down a mountain, devouring the trees, rocks, and ski lifts in its path – will become increasingly common. The slope most prone to avalanches lies directly above Spar Gulch, an intermediate ski trail that is one of Aspen Mountain's main thoroughfares, and one of the only routes off the mountain. The beginner slopes will become pockmarked with rocks and turf, requiring snow machines to make up the difference. By 2100, should current conditions persist, there will no longer be any snow at the base of Aspen Mountain.

But Aspenites may not worry very much about skiing then. They will have larger concerns. As the mountain's snowpack shrinks, the waterways will languish. Streams will flow higher in midwinter, from January to March, but they will run dangerously low in June and July, threatening the survival of the riparian ecosystem – its brown and cutthroat trout, chorus frogs, aquatic snails, and backswimmers; the common muskrats, American beavers, and moose that drink from it; the olive-sided flycatchers, Brewer's sparrows, and bald eagles that roost on its banks; and the wetlands and forests it nourishes. Eighty percent of Colorado's wildlife needs access to a riparian habitat in order to survive, but today these habitats make up only 1 percent of the state's land. Aspenites also need access to waterways in order to survive – two frail mountain creeks, Castle and Maroon, provide the city with its water. During early spring and autumn, the creeks will flood more often, while during summer, when water demand from crops and residents is at its highest, they will be more likely to run dry. A 2006 report by the Aspen Global Change Institute concluded that the Roaring Fork River, the repository of all of the mountains' streams, "could be dried up in most years."

With less snowmelt, fighting the forest fires will be more difficult. During the first half of this century, fires are expected to burn as much as three times larger than in the previous half. In the second half of the century, the fires will be smaller but more frequent; they will occur, on average, every other year. But that is not taking into account the damage done by increased outbreaks of insect infestation. As fewer winter nights drop below freezing, the populations of gypsy moths and various types of bark-eating beetles will thrive. The Aspen study concluded that "the risk of unprecedented insect outbreaks could be one of the most dramatic effects of climate change on Aspen's forests." So far the Roaring Fork Valley has been spared the fires that have victimized so much of the West, but in recent years, a ravenous population of pine beetles has been busily preparing the lodgepole pines that surround Aspen for future conflagrations.

Many of the trees aren't waiting around for that eventuality, however. Species that thrive in cold temperatures and high altitudes, like firs and spruces, have begun migrating up the mountains, fleeing the increasingly inhospitable valley. "One might expect a slow creep of the tree line and vegetation upward," says Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research's Climate Analysis Section. The dominant vegetation type will shift from taiga-tundra to boreal conifer forest. Aspen is even losing its aspens.

Yet many of Aspen's current homeowners don't seem to have noticed. This might be because the typical Aspen homeowner lives there only a couple of months a year. A majority of the homes are second homes, or third or fourth or fifth homes, but, like the automated house in Ray Bradbury's "There Will Come Soft Rains," they are programmed to run in perpetuity. The heat runs in the winter, lest the pipes freeze, and the air-conditioning in the summer, lest the oil paintings drip. The wine coolers and refrigerators never sleep. Aspen's homes – which belong to owners like the Koch brothers, Walmart's Walton family, the cofounder of Amway, and a fleet of oil magnates – have solved problems that most Americans don't even realize they have. To avoid the unsavory sensation of stepping from a hot shower onto tepid marble, the bathroom floors are heated; so are towel racks. Driveways and roofs are undergirded by snowmelt systems. The heating tape that zigzags around most Aspen roofs, sometimes kept electrified throughout the summer, can alone cost more than $1,000 in annual utility bills – particularly since the homes these roofs cover are among the largest in the world. To deter burglars, homeowners keep their exterior and interior lights on year-round, simulating occupancy. There were 25 burglaries in Aspen in 2012, though police were summoned by home alarm systems 1,263 times.

This profligacy doesn't take into account the ubiquitous SUVs, which in Aspen never went out of fashion; the cost of shipping meat and other supplies over the mountains; or the Gulfstreams and Bombardiers lining the runway of Aspen/Pitkin County Airport. In 2012, the airport welcomed 11,000 private planes. Aspen's population is only 6,680. But it has been living much larger.

This makes it all the more surprising that Aspen has taken it upon itself to save the world from catastrophic ecological collapse.

"I get annihilated," says Auden Schendler, an executive at the Aspen Skiing Company, when I ask whether he appreciates the irony. "People call me a hypocrite. They say, 'Shut up; you're from Aspen.' But who ought to lead, if not Aspen? Bangladesh?"

Schendler stands at the foot of a coal-powered gondola that, even though it is the middle of the summer, is running circuits up Aspen Mountain. He has been employed 14 years at Skico, as it is known locally, but Schendler doesn't think of himself as a "company guy." He prefers "dirtbag." Although he was raised in Weehawken, New Jersey – or perhaps because he was raised in Weehawken – he has been a devoted "outdoors guy" since his uncle took him on a brutal, three-day hiking trip through Montana's Bob Marshall Wilderness at the age of 14, when he fell in love with the West – its wild beauty and its doctrine of virtuous toil. Today Schendler's appearance strikes a compromise between his nature and his nurture. As a concession to Skico, he is freshly shaved, with a crisp haircut and a pressed oxford shirt. But the shirt is tucked baggily into his jeans, and the sandals and black Oakleys belong to the kind of person who sneaks away from work in order to take a 25-mile bicycle ride in the mountains – which he does whenever the opportunity presents itself, with his boss's encouragement. Like most Aspenites, Schendler is exuberantly, ostentatiously healthful; he's tall and hale, with a strong jaw, strong hands, and a strong brow. The man is 43 but looks 10 years younger and has the energy of a man 20 years younger. He is the skier or biker or marathoner who races past you with a smile and a friendly wave, going twice your speed.

At Skico, Schendler is vice president of sustainability, an odd title for a job unlike any other in corporate America. He was originally hired to reduce the company's environmental footprint. This was a considerable responsibility, since Skico is the largest employer in not only Aspen but the entire Roaring Fork Valley – the broad, green plain that runs 40 miles southeast from Glenwood Springs to Aspen, circumscribed, like arches on a crown, by seven 14,000-foot peaks. Skico operates all four local ski mountains, 17 restaurants, and two luxury hotels, including the Little Nell. On Schendler's first day of work, he told the Little Nell's manager that he was going to replace all the lights in the hotel with compact fluorescent bulbs. The new bulbs would last 10 times longer, save money, and cut energy use by 75 percent. It seemed an obvious baby step. The hotel manager flatly refused. "When you go to Las Vegas and stay in a Motel 6," he told Schendler, "it has compact fluorescent bulbs. This isn't a Motel 6."

Schendler, defeated, realized he would have to take a more cunning approach. Largely he has succeeded. More than a decade later, Skico's emissions have fallen by approximately 4 percent, despite the fact that its revenue has grown by 41 percent. The company now operates its own solar array, a hydroelectric plant, and, since November 2012, a methane-capturing plant – a $5.5 million investment that alone generates enough energy to offset Skico's total usage. Two years ago, the Little Nell even switched out its incandescent lightbulbs. Schendler wrote about his successes, and his many failures, in Getting Green Done, a complimentary copy of which appears in every room of Skico's Limelight Hotel. The hotel does not keep records of how many guests take the book home with them.

Schendler now has a new objective: "To make sure that Aspen Skiing Company stays in business forever." That is another way of saying that his job is to stop global warming. Schendler is perhaps the only corporate executive in the United States whose success can be measured not in profit but in snowfall. His tone, accordingly, has shifted. "Auden's ready to pick a fight any minute," says Chris Davenport, a world-champion mountain skier who sits with Schendler on the board of Protect Our Winters, an advocacy group for the winter sports community that seeks to influence national environmental policy. "He's a beacon of hope for our industry. He broke the ice, took risks, and made it easier for other people."

"Climate change is so big," says Schendler. "How do we begin to solve it? The ski industry offers a metaphor. And we've had a disproportionate role in the conversation."

He visits congressmen in D.C., gives lectures at the Googleplex and the Yale School of Management, and publishes essays in 'The Atlantic' and 'Grist' with titles like "Selma, Montgomery, and Climate Change" and "The Wall Street Journal's Willful Climate Lies." He reserves his greatest scorn for "green­washing," the cosmetic, ostentatious gestures toward "sustainability" that corporations make – plastic-bag bans, for instance, or the sign in hotel bathrooms offering not to launder soiled bath towels – while declining to lobby for major reforms. The bluntness of Schendler's arguments has damaged his relationships with colleagues, including his mentor, the scientist and environmental activist Amory Lovins. Before joining Skico, Schendler worked for three years at Lovins' Rocky Mountain Institute, which promotes the doctrine of "natural capitalism." In Getting Green Done, Schendler called Lovins "one of the most important – and accurate – thinkers on the subject of how we solve the climate problem." Lovins is the face of "corporate sustainability" – the belief that companies, and, by extension, the world, will inevitably convert to renewable sources of energy and conservation practices because as technology advances, that will become profitable. This argument may hold true for lightbulbs, but, as Schendler wrote in a recent essay, it fails to "deal with the problem at anywhere near sufficient scale." That essay was titled "Corporate Sustainability Is Not Sustainable." Lovins no longer returns Schendler's calls.

"We need to create a civil rights–style revolution in climate," says Schendler. Aspen, he believes, can be this revolution's Selma. "Aspen can tell a story. We have the money and access to the most influential people in the world – which is another way of saying the wealthiest people in the world. We can model solutions, and they can be difficult solutions. Then the press will come from all over, and we'll tell them how we did it."

Not all ski companies consider it wise business practice to discuss the consequences of a heating planet. In December 2012, Protect Our Winters and the Natural Resources Defense Council funded a study to determine how much money warmer, shorter winters were costing the ski resort industry. The answer: $1.07 billion, in the past decade alone. Vail's CEO, Rob Katz, responded with an editorial in the 'Denver Post.' "It's hard to understand how the weather changes the way it does," he wrote. "You can count me out of the group that says we need to address climate change to save skiing."

"They think we shouldn't talk about this too much," Schendler tells me. "But it's not a negative message. We're going to save this industry." He pauses. "We have an opportunity to use Aspen as a weapon on climate policy. As a baseball bat."

Schendler is not the only one who speaks this way.

"We have a tradition of great humanism here," says Chelsea Congdon Brundige, an activist for local waterways. "Aspen is a laboratory where you can look for solutions."

"Aspen can be a model for other communities," says David Hornbacher, who manages the city's power grid. "Local actions, with a global result. That's what we do."

"Aspen views itself as a pioneer," says Mirte Mallory, an effervescent 33-year-old Aspen native who, a week after New York City began its bike-share program, launched Aspen's WE-cycle. "Living here is a privilege. It's our responsibility to be stewards."

"Our goal is to be a factory of Auden Schendlers," says Chris Lane, CEO of the Aspen Center for Environmental Studies (ACES). Lane has organized an "environmental civil engagement campaign" designed to foment Schendler's "civil rights–style revolution" in climate policy. In the past year, ACES instructors, through its various programs, reached more than 100,000 people, almost half of whom were children. "My philosophy is that there's a bunch of Rush Limbaughs out there," says Lane. "There could be a kid in there who one day might become an adult who thinks global warming is crazy. But we're changing his mind."

"We have the liberty and the time to think about the big picture," says Mick Ireland, who completed his third and final term as Aspen's mayor in June. He bears a passing resemblance to Ronnie Wood, though he's in better physical condition, on account of his habit of biking as many as five hours a day. "A lot of communities struggle with things like budget cuts, crime, and school shootings. Civic leaders don't have much time to consider the environment. Here, our basic needs are met, so we're able to take action on larger issues. We're obliged to lead by example because we can."

This idea of Aspen as a model for the world – a shining city at the bottom of a hill – was introduced to the public in 2005 when the city proposed a series of ambitious environmental resolutions called the Canary Initiative. "The goal," wrote Aspen's mayor in 2007, when the Initiative's first regulation was enacted, "is to aggressively reduce Aspen's carbon footprint to protect our community's future, and to contribute to global reduction of global warming pollution." One of its chief resolutions was to eliminate coal-fired power as an energy source by 2015. Under Ireland, the share of the city's energy that came from renewable sources rose to 75 percent, with contributions from solar, hydroelectric, and wind power. By spring 2014, with the city's purchase of power from a new hydroelectric plant, that number will rise to more than 89 percent. By comparison, the neighboring utility, Holy Cross Energy, which serves most of the homes in the hills above town, draws 12 percent of its power from renewable sources. Since the Canary Initiative, water conservation – a crucial priority for a city that relies mainly on snowpack runoff for its water supply – has been fortified by the renovation of the town's water treatment facilities and a $5 million retrofitting of the city's pipes. And thanks to the high-tech bus system, which is free to ride within 15 miles of Aspen and serves 4.5 million passengers a year, Aspen has the same volume of automobile traffic as it did 20 years ago.

"Leadership by example is not only the best way," says Ireland. "It's the only way. You have a stage here, a bully pulpit. If this were Carbondale" – a city 30 miles up the valley – "people like Bill Clinton wouldn't be asking me to lunch."

But the sense of enlightened sacrifice, of noblesse oblige, can be traced further back than the Canary Initiative, all the way to the spring of 1945, when Walter Paepcke, a cardboard-box magnate from Chicago, came to town. There were no paved roads or stoplights then, and the population had dwindled to 700, but Paepcke found a dilapidated grand hotel, the charred remains of an opera house, brick-and-sandstone country stores, and Victorian mansions – the legacy of a silver mine that during the 1880s was one of the richest in the world, with a 40-mile-wide mother vein. In 1892 alone, the equivalent, in today's dollars, of $2.6 billion worth of silver was removed from Aspen's mountains. The following year, the Sherman Act was repealed; silver was demonetized, and the metal's value crashed. Nearly all 15,000 residents fled, leaving behind many of the city's treasures. Most valuable of these was a hydroelectric plant, built in 1893, on the edge of Castle Creek, in part to provide electricity to the mining tunnels. From a small reservoir 300 feet above town, water descended a flume – like a waterslide made out of wooden planks – and fed five 270-horsepower turbines. Aspen was one of the first cities west of the Mississippi to be fully electrified – earlier, even, than Denver. Incandescent lamps soon appeared in every home and office, and on the streets. The plant supplied all the city's power until 1958.

Paepcke, a Yale graduate who incorporated modern art into his company's advertising campaigns and sought to enrich himself by taking the Great Books seminar at the University of Chicago, dreamed of re-creating Aspen in his own image. After founding the Aspen Skiing Company in 1946, he grew more ambitious. "He saw it first as a ghost town worth preserving as such," said Robert Maynard Hutchins, who served as president of the University of Chicago. "He then began to think of it as an American Salzburg." In 1949 Paepcke invited artists, scholars, businessmen, musicians, and politicians to Aspen for a festival in honor of Goethe's 200th birthday. The Goethe Bicentennial served as a model for the Aspen Institute, which Paepcke founded in 1950, as well as the Aspen Music Festival and School and the International Design Conference. It wasn't so much a city that was emerging but a grand humanistic experiment – what came to be known as the Aspen Idea, defined by a "harmony between mind, body, and spirit." By 1953, two bookstores had opened in downtown Aspen, along with boutiques selling Venini glass, Pucci dresses, Gucci leather, and drawings by Andy Warhol. Paepcke had turned "a shattered town into a kind of national treasure of arts and ideas," wrote journalist Peggy Clifford in her 1980 memoir, 'To Aspen and Back.' "It was not an act of philanthropy. It was an act of passion – and hubris."

"Aspen has always attracted people who think they can do whatever they want to do," wrote Hunter S. Thompson, who first visited this "experimental behavioral tank" in 1960 and later settled 15 miles away. "Of course," he added, "you can't create a valley for the rich and then expect to live in peace with them. The rich are monsters."

I thought of Thompson one afternoon while I waited for the free public bus to take me back to my hotel. The evidence of Aspen's enlightened environmental awareness was visible all around me: recycling bins; a stand offering complimentary biodegradable doggie bags; a water fountain and plastic-bottle refilling station with signs urging passersby to drink Aspen tap; advertisements for RFTA, the nation's first rural rapid transit system, and its fleet of clean diesel buses; a rack of WE-cycle bicycles, positioned near a parking area for Car to Go, Aspen's car-share program. Maria Shriver walked by with two friends. She looked happy. Everybody in Aspen looked happy. The Aspen Idea was thriving. It was the week of the Aspen Institute's annual Ideas Festival, and the private jets lowering overhead contained many of the world's most prominent intellectuals, businessmen, and politicians. There were talks with titles such as "Fear and Hope: Climate Change and Policy Solutions" and "What Is the Right Energy Mix?" By all appearances, Walter Paepcke's dream has been achieved.

There is only one problem. No matter how successfully the town curbs its carbon emissions or protects its pristine natural environment, Aspen, as we know it, is doomed.

"The winter lasts forever," wrote James Salter in a 1981 ode to the town where he has spent his winters since 1969. "Skiing begins in late November and continues until mid-April."

Not anymore. About 15 years ago, Chris Davenport, the world-champion skier, was hiking to Maroon Bells, Aspen's most iconic landmark. Near the end of that hike, as you reach an altitude of 14,000 feet, Aspen's second-most-iconic landmark comes into view: the massive snowfield that gives Snowmass Mountain its name. Snowmass, long considered the largest permanent snowfield in Colorado, descends the mountain's eastern slope like a billowy white apron. It is a popular local tradition to hike the slope in July or August, have a picnic near the summit, and occasionally ski down. But when Davenport, 200 feet from the summit of North Maroon Peak, looked for the familiar view, he became confused. Snowmass was missing. Had it moved? No, it dawned on him, the mountain was still there. Only the snow was missing.

"I speak the language of the mountain," Davenport tells me. "She doesn't hide anything. When she speaks, it's not subtle."

There are a number of ominous signs beyond the shrinking ski season, none of them subtle. Kit Hamby, district manager of Snowmass Water & Sanitation District, has never seen water levels so low on Snowmass Creek, which provides water to nearby Snowmass Village. Like all local streams, the creek is fed by snowpack. "The averages are going down."

Jeff Pogliano, a 30-year Aspen resident who sells real estate at Sotheby's downtown, has been surprised at the unpredictability of the weather in the past 15 years, though he insists he is "not a climatologist." He is especially concerned about the increase in frequency and vehemence of forest fires across Colorado. "The conversation is always whether or not we'll have Fourth of July fireworks," he says. Later that week, blaming the extreme drought that had ravaged the state, the Pitkin County sheriff canceled the fireworks for the second consecutive year.

"Winters are shorter, no question," says Ireland, who has lived in Aspen for 34 years. "This community has to start thinking about what we're going to do post-snow."

Aspen's temperatures have increased by approximately three degrees Fahrenheit in the past 30 years – a finding consistent with the fact that the American West has warmed more quickly than global averages. A study commissioned by the Canary Initiative projected that in a medium-emissions scenario, temperatures will rise an additional 3.2 to 4.5 degrees by 2030. In high-emissions scenarios, there will be no more skiing in Aspen by 2100, possibly well before then, and Aspen's climate will resemble that of Amarillo, Texas. Amarillo by that point should resemble Venus.

Aspen will have problems more dire than hotter weather, however. Even in the worst-case scenarios, Aspen and the other mountain towns in the American West will still be more habitable than cities in the plains. When Denver turns into desiccated, sunbaked desert, Aspen and the towns in the Rocky Mountains will seem balmy by comparison. But Aspen is not immune to the great curse of the American West: It, too, has a water problem. Its streams and creeks, which provide some of its energy and all its drinking water, are fed largely by snowmelt. Snowpack melts gradually, working as a natural pipette, supplying the streams with a steady trickle of water.

It is not known whether the amount of annual precipitation will be changed by warmer temperatures. But even if precipitation remains constant, it won't be distributed in the same way. "In midwinter," says Kevin Trenberth, from the National Center for Atmospheric Research's Climate Analysis Section, "warmer conditions actually mean more snow, because the atmosphere holds more moisture at a rate of about 4 percent per degree Fahrenheit warming." The winter will be shorter, however, and the snowpack will melt more quickly. Without a snowpack, water levels in the streams will drop precariously as summer progresses. During rains, stream levels will spike, but they will fall immediately afterward and risk drying up entirely. The longer summers will lead to more severe wildfires and droughts, while there will be more floods in the early spring and autumn.

The streams are the mountains' arteries, responsible for supporting not only the fish and aquatic species that live in the river but the animals and plants that drink from it. Among the animals that rely on the streams for their drinking water are human beings.

The people who best understand what is happening to Aspen – and what is going to happen to the American West in the years ahead – live just over the mountains, in a former ghost town called Gothic.

You can drive to Gothic from Aspen, but it is nearly as fast to walk. If you hike to Maroon Bells and keep going, over West Maroon Pass and down the other side, you descend, several hours later, into East River Valley. This valley, widening and deepening as it goes, follows its river four miles to the Crested Butte Mountain Resort, and in another four miles spills into the town of Crested Butte. Gothic is hidden at the top of this valley, 9,485 feet above sea level and invisible to the rest of civilization. It lies near the end of a dirt road that is impassable for six months a year. The rest of the year it serves as the campus of the Rocky Mountain Biological Laboratory (RMBL, pronounced "rumble"), one of the leading research field stations in the world – "geek camp for scientists," as one put it. Every summer some 40 scientists and 40 graduate students gather to conduct experiments in the valley and mountains surrounding the campus. Although the scientists come from many disciplines – particularly botany, ecology, and evolutionary biology – those who have spent enough time at RMBL have inevitably found themselves becoming experts in a new discipline: climatology.

David Inouye, a pollination biologist who teaches at the University of Maryland, has for 43 consecutive summers come to Gothic to observe its wildflowers. Inouye's goal, when he began the experiment as a graduate student, was to understand how flower populations change over time – how many flowers each species produces, when they bloom, and how the populations vary each year. "Nobody ever thought about climate change in the early Seventies," Inouye tells me. "But the context of the study has changed." We were inspecting one of his 48 test plots, a dense thicket of lupine, American vetch, meadow rue, and bluegrass. Every day his student assistants count every flower in every plot. As the summer has crept earlier, the flowers have been blooming sooner. The trigger, Inouye has discovered, is the date of snowmelt. He used to be able to travel to Gothic once his semester ended. Now he has to send an assistant to Gothic weeks ahead of him, since the melt occurs while school is still in session.

When Inouye's assistant arrives in the spring, she is greeted by Gothic's only permanent resident, Billy Barr, who has lived here since 1973. Barr looks exactly how you might imagine a man to look if he had spent 40 years in a cabin in the middle of the Rockies, surrounded by mountains and snow. He looks like mountains and snow: craggy features, with stringy white hair that hangs to his shoulders, and a stringy white beard. He lives in the most distant of Gothic's several dozen wooden cabins, some of which date to the 19th century. At the end of autumn, Barr stockpiles enough food to last the winter. When he desires a vacation, he skis four miles to the paved road, where he waits for a bus to Crested Butte, and then switches to another bus to Gunnison, where he spends the night. But he doesn't leave Gothic often. "Everyone has this idea," he tells me, "sitting in a comfortable chair in your cabin, reading a book, with the snow falling softly outside. The truth is, it's boring as shit. But I like it."

Barr, who is now RMBL's accountant, has accidentally managed to create one of the most valuable climate databases in the world. Ever since his arrival in Gothic four decades ago, he has kept a weather journal. He makes observations about the quality of light, cloud cover, and wind strength, using a numerical rating system of his own invention. With a pole he measures the depth of snow, and with a snowboard, which he clears twice a day, he measures the daily snowfall; he weighs the snow with a hanging butcher's scale in order to determine its density. Each spring he notes the first appearance at Gothic of the ground squirrel, chipmunk, robin, and red-shafted flicker. For more than three decades, in a separate journal, he kept detailed notes about the avalanches he observed in the valley, about 400 on average each winter. Barr's notes are the most comprehensive data on natural avalanches in the world. Taken together, his journals describe the radical transformation that Colorado's high alpine landscape has sustained in the past 40 years.

Barr's studies are not Gothic's longest-running. Since 1962, scientists have been observing the local marmot population, which has numbered between 50 and 350. Each marmot has, at some point in its life, been trapped and marked with a symbol, using a toothbrush dipped in black dye. Graduate students hike into the hills every day, where they spend hours staring through binoculars at the marmots. They make notes about the animals' behavior, referring to each one by its mark: Smiley Face rubs its cheek on rock. Musical Note pushes Mickey Mouse off rock. Lollipop mounts Sail Boat. There are 51 years' worth of notes like this.

The current director of the marmot study is Dan Blumstein, an evolutionary biologist at UCLA who was born two years after the experiment began. His interest in the study derives, in part, from its duration. We tend to think of evolution as a process that occurs over millennia, but after more than 50 years, natural selection begins to reveal itself. And the marmots are changing. They're getting fatter. During the past 40 years, their hibernation time has decreased by 40 days – one fewer day per year. With longer time aboveground, the marmots eat more, which makes them more likely to survive the hibernation, but also more likely to be nabbed by a coyote.

Gothic is also the site of the world's longest-running experiment on the effects of global warming. On a sloping meadow several hundred yards above the road, a series of heat lamps dangle from cables over a small plot of land. The lamps warm the ground by two degrees Celsius, the minimum amount by which the planet's temperatures are expected to increase this century. The lamps, which have been on continuously for 23 years, play a trick on the wildflowers. In early spring, the flowers emerge from the ground prematurely, only to wither before the summer rains come. Some species have dwindled, and hardier ones, like sagebrush, have annexed territory, but overall there are fewer flowers. Crested Butte, the so-called wildflower capital of the world, is losing its wildflowers. Colorado is losing its forests. And Aspen is losing its snow.

It is Auden Schendler's conviction that in order for Aspen to inspire a global energy revolution, it can't only tout its successes but must be honest about its failures. He was well prepared for failure. What he wasn't prepared for was the way in which Aspen recently has failed – a failure so spectacular that it threatened to undo all the good work of the past decade. In the past two years, Aspen's environmentalists have set an example for the world, and it's not a positive one. "Enviros are fighting other enviros," Schendler tells me. "We're eating ourselves alive." The internecine crisis has become so bitter that in Washington political circles, the Aspen Idea has been replaced by a new term: the Aspen Problem.

Like all Western problems, Aspen's comes down to water. For Aspen to rid itself of coal-fired energy – in order to fulfill the Canary Initiative's promise and increase its 75 percent share of renewable energy to 100 percent – the city determined that it needed to build a new hydroelectric plant. There was an obvious location: the bank of Castle Creek, where one of the city's original hydroelectric plants had stood for more than 100 years. Schendler was among the plan's most aggressive boosters. The city hired ecological consultants to study the proposal, write environmental impact statements, and develop regulations to ensure that the plant would not harm the health of the creek. In a 2007 referendum, more than 70 percent of the town voted to fund the construction of the hydro plant. But four years later, after a $1.5 million turbine had been purchased and 4,000 feet of penstock laid in the ground, a group of local residents and companies filed a lawsuit to halt the project. Among the complainants were several landowners with multimillion-dollar properties that abutted or drew water from Castle Creek. One of them, cloaked by four limited-liability companies that he controlled, was Bill Koch – younger brother to Charles and twin to David, who have donated more than $100 million to libertarian groups and organizations that promote global warming denial. Bill, though a pauper in comparison to his brothers, has an estimated net worth of $3.8 billion. He is the founder and president of energy conglomerate Oxbow Carbon, which operates a coal mine in nearby Somerset. "There are a lot of obstacles to renewables in this town that are not apparent to the naked eye," Mick Ireland tells me.

Opponents of the plant argued that the city had lost some of its water rights to the creek, and that the hydro project would cost taxpayers too much. But their most effective strategy was to appeal to the anxieties of the city's environmentalists. They claimed that the plant, despite the assurances of ecological consultants hired by the city, would threaten the survival of the creek. Fliers showing images of dry streambeds and polluted water appeared in every Aspen mailbox. "It's Not Green to Kill a Stream," they read. "Aspen's Water-gate." The ads were paid for by anonymous shell organizations like the Aspen Citizens Committee and Friends of Castle and Maroon Creeks, registered in Denver and Colorado Springs.

At Lance Armstrong's 40th birthday party, held in Aspen two years ago, Mayor Ireland was confronted by a heavy-set stranger with round wire-rim glasses and a jaunty wave of white hair. The stranger – hearty, bluff, red-faced – grabbed Ireland "like a football player" and shook him.

"You're a liar!" he shouted in Ireland's face. "I'm not building a pipeline!"

Extricating himself as gently as possible, Ireland concluded two things. One: The man was Bill Koch. Two: Koch was planning to build a pipeline from Castle Creek to his properties on the other side of the Elk Mountains – the Somerset coal mine and an Old West town that Koch is building for his personal amusement.

"Bill Koch spent huge amounts of money fighting the city's water rights," Ireland said when asked of Koch's motives. "He's not going to invest huge amounts of money without a purpose." (A spokesperson from Koch's company denies this, calling Ireland's pipeline claims "absurd" and a "total fabrication.")

Western water law, which has not changed greatly in the past two centuries, can be distilled to two core principles. "First in time, first in right" means that the first person to draw from a body of water has priority over later claims. "Use it or lose it" is just as self-explanatory; should a claimant not draw the water allotted to him, he forfeits his rights. Koch has several legal claims on Castle Creek, but his claims rank lower than those of the city of Aspen, some of which predate Koch's by more than a century. It is Ireland's theory that Koch, by thwarting the hydro plant, hopes to build a stronger legal case that the city, by failing to exercise fully its water rights, deserves to lose its claim. In theory this could allow Koch to drain a greater share of the water from Castle Creek. (Koch, meanwhile, has publicly stated that he would never divert water from the creek.)

Two years ago, a petition supported by Koch collected enough signatures to require a new referendum on the hydro plant. In the last election, voters expressed their disapproval by a margin of 110 votes. Though the referendum was nonbinding – the plant had already been authorized – the city suspended its plans. The opposition, largely through anonymous fundraising, spent more than $300,000 on ads and mailings; supporters barely raised five figures. "It wasn't a fair fight," says Ireland, still rueful today. "Aspen could have been the first city in America to run entirely on renewable energy." He shakes his head. "All you have to do is go rent Chinatown."

In his fight against the hydro plant, Koch had unlikely allies. A number of Aspen's old environmental guard – conservationists who have fought to protect the region's streams, open spaces, and forests – were concerned enough to demand additional analysis of the plant's impact on the creek. A rift opened in Aspen's environmental movement between, as one hydro supporter put it, the "Rachel Carson, Silent Spring–type" and the newer generation of activist, personified by Auden Schendler, who argues that every creek will dry up if radical measures aren't taken to curb the warming of the atmosphere. "Look, nobody wants to be against Auden Schendler," says Chelsea Congdon Brundige, the stream conservationist. "He's the environmental playboy." But she points out that the stream will assume greater importance in the local ecosystem as the weather gets warmer, which is a reason to protect it vigilantly. Besides, adds Brundige, Aspen's quest to ban coal-fired power is largely symbolic; it will have no impact on global weather patterns.

"It's an odd debate in many ways," says William Dolan, the city's utilities specialist. "Both sides could describe themselves as extremely environmentally conscious, and they'd be right." The hydro-plant project has been Dolan's focus since he began his job two years ago, after having received a master's degree in water science, policy, and management from Oxford. "The vast majority of people on the other side of the issue had pure intentions," he says. "Whether their concerns are founded in reality is another question."

Schendler takes a different lesson from the failed fight over the hydro plant – a lesson with ramifications that extend beyond Aspen, and even beyond the American West. "If we want to solve climate change, we have to break some stuff," he says. "We're going to fracture alliances. We're going to have to start doing some difficult things. And those things are going to hurt."

This is how Schendler justifies his most daring gambit yet. Recently he has entered into a partnership that is as uneasy as it is unlikely – with Bill Koch.

After 10 years of entreaties, Schendler and his partners finally managed to arrange a meeting with Oxbow Carbon to discuss the possibility of capturing the methane vented by their Somerset coal mine. The law requires mines to vent methane gas in order to protect their workers and prevent explosions. That methane rises into the atmosphere, where it traps radiation 21 times more efficiently than carbon dioxide. But methane can also generate energy, and Schendler favored outfitting the mine with a methane-capturing system. That methane would generate as much energy as Skico needed each year for all its properties. And by capturing the methane, it would eliminate three times the carbon pollution created by Skico each year.

"Wait," said the mine's representative, holding up his palm. "We don't believe methane is a pollutant. We don't believe coal is, either. We think burning coal is good for society."

Schendler paused. What could he possibly say to win these men over? "Why did you take this meeting?" he asked finally. "I'm a resource guy," said the mine rep. "I hate to see resources wasted."

The methane-capturing plant opened in November 2012. At the grand opening, Schendler posed for pictures with Oxbow executives. Mick Ireland was not in attendance. It was one of Koch's conditions that Ireland not be invited.

"We have the ability in Aspen to reach the world," says Schendler. "The downside is that there's a temptation to think we're the center of the universe, and we're not. We're a bubble. Lose that awareness and you're doomed. We've fucked up. Don't get me wrong. But if we don't lead, who will?"

We are halfway up Fanny Hill, the beginner ski slope at the base of Snowmass Mountain. At the side of the trail, a small shack is loudly humming. Behind the shack lies a pool of turquoise water, a retention pond for snowmelt; it is filled by a pipe that drains water from West Brush Creek some 800 feet farther up the mountain. During the winter this water is used to make snow. About 10 years ago, Schendler realized that the snow-making system, one of Skico's largest energy consumers, could itself be used to generate electricity. For $200,000, Skico built the powerhouse and installed within it a 115-kilowatt turbine. This micro-hydroelectric plant now generates approximately $15,000 worth of energy each year, enough to power 15 homes year-round. But the plant's long-term financial benefits mean little to Schendler. Nor do the energy savings, which, in the broader scheme of things, are infinitesimal.

"None of that matters," says Schendler. "But this matters." He points to a sign on the side of the powerhouse. It explains what the Fanny Hill plant does and promotes its environmental benefits. A diagram shows how the turbine, with the help of a Pelton wheel, a waterwheel invented by a gold miner, turns water into energy.

"Seven hundred thousand people ski down this hill each winter," says Schendler. Some of them, he figures, will take a break at this point on the slope, or fall down, and read the sign. Some of those people, just maybe, will be encouraged to finance hydroelectric plants of their own – or more ambitious projects.

But nobody was looking at the informational sign now, because it was summer and there was no snow on the ground, only grass and rocks. In the stillness of the afternoon, it was difficult to imagine what the slope looked like when it was covered with snow and thousands of young skiers practicing their snowplows and J turns. But it was easy to remember that before long, the slope will be snowless year-round. Then nobody will have the chance to read the sign except, perhaps, the occasional hiker, trying to escape the heat of the valley.