WIND SWEPT ACROSS the mountains and a bitter chill hung in the air. Snow blanketed the landscape, having fallen overnight. Six of us trudged through it single file, heads down, stumbling occasionally in the gales. Above us, clouds sped, blanketing the stone walls and peaks of the Continental Divide. Below us, the North Fork of Middle Boulder Creek flowed eastward through a U-shaped valley, from its headwaters to the reservoirs of Boulder, Colorado, 20 miles away.

It was August, but the chilled conditions were typical of an altitude of 13,000 feet in the Rockies. Our destination lay above, at Arapaho Saddle, where we hoped to get a view of an alpine glacier tucked in a cirque between two peaks. Not just any glacier though: Arapaho Glacier is the largest and, as some would say, the last alpine glacier in the state of Colorado.

Ahead of me hiked Ted Scambos, senior research scientist at the University of Colorado Boulder’s Earth Science and Observation Center. Beside Scambos was Mike MacFerrin, a research glaciologist at the university who specializes in the Greenland Ice Sheet. Next to him strode Gabi Collao Barrios, a postdoctoral researcher at Scambos’s lab who studies snowpack changes in the Rocky Mountains and ice flow dynamics in Antarctica. To her left was Naomi Ochwat, a PhD student in geology who was also working with Scambos, and an electrical and electronics engineer from the university named Jorge Cañardo.

As we crested the pass, Scambos scanned the view, looking for the glacier through a pair of black polarized sunglasses. “Look at it!” he exclaimed. “It’s beautiful!” I chuckled at his sarcasm. All we could see was a wall of ghostly silver clouds. We huddled under an overhanging slab of granite where a small wall of stones has been amassed to shield hikers from the elements. Ochwat passed out espresso candies and tortillas with cheese. “It’s ten ’till noon,” Scambos said. “Might as well wait a while and see if the weather clears up.” His nonchalance spoke to his three decades of fieldwork in these types of conditions, from the frigid ice rivers of Greenland to the glaciers of Antarctica. A glaciologist, Scambos studies how climate change affects the cryosphere, the part of Earth’s surface characterized by ice. And, for much of the last two decades, he’s studied the Arapaho Glacier.

Alpine glacier ecosystems like the one we were in are “sensitive indicators of climate,” Scambos and his colleagues wrote in a 2010 paper in Arctic, Antarctic, and Alpine Research. And these glaciers are quickly melting. “If recent trends in area loss continue,” the paper noted, “Arapaho Glacier may disappear in as few as 65 years.”

What we were seeing — or rather, what we weren’t seeing — didn’t seem to compute.

The ecosystems of the Rocky Mountain high country live and die with the seasonal ebbs and flows of the cryosphere. Runoff from snowpack and glaciers provide a seasonal influx of water on which resident flora, fauna, and humans depend. Water from Arapaho Glacier runs into the Silver Lake watershed, which accounts for 40 percent of Boulder’s water supply.

Without the glacier, Boulderites would lose a valuable resource, at a time when the city’s entire water portfolio is facing various threats related to climate change. A report from the City of Boulder Water Resources Advisory Board projects that by 2070 Boulder’s climate may be eight degrees Fahrenheit warmer and 10 percent drier than today’s climate. Annual water demands may rise as much as 5,000 acre-feet, and simultaneously, Boulder Creek’s water volume may face 42 percent declines as a result of shrinking snowpacks.

“Hey! We might have a view of the glacier now,” Scambos said after about an hour.

We emerged from our shelter and hiked a few hundred feet east on the ridge, where the glacier usually comes into full view beyond the upper reaches of South Arapaho Peak. We stopped and, with great anticipation, looked toward where the glacier should have been. Then we peered harder.

What we were seeing — or rather, what we weren’t seeing — didn’t seem to compute. We were all silent for a moment.

“Where is it?” someone asked finally.

GLACIOLOGISTS ARE NO STRANGERS to loss. For decades now, they have been observing the objects of their study dissolve at historically unprecedented rates all across the world. The Arapaho Glacier, in particular, has long been known as especially fragile. Even the first scientists to study the glacier knew it was quickly disappearing.

In August 1897, two botanists named Herbert N. Wheeler and Darwin M. Andrews embarked on an expedition to the valley floor downslope of the Arapaho Glacier to collect dogtooth violet bulbs. Specimens in hand, they decided to keep hiking — driven by curiosity “to see what was at the head of that valley,” Wheeler later wrote in his journal. They marched on, beneath the eastern face of the Continental Divide, up a steep slope of rock and ice toward a ridge between two peaks. When they reached the saddle, they saw a bowl-shaped cirque filled with ice. The slopes, ringing the cirque in a semicircle, were a mass of snow, stone, ice, and the occasional protrusion of tundra. Beneath the glacier, mounds of snow and rock trailed like stepping-stones across the valley floor to a series of bright blue lakes left in the wake of the glacier’s melting. The valley itself was carved by the glacier’s movement. Eroded talus stones piled upon the landscape, remnants of the glacier’s bygone power to erode mountains into piles of scree and a fine, sedimentary dust.

Even then, the glacier was just a remnant of its former self.

Since the Pleistocene, some two-and-a-half million years ago, much of what is now Colorado has been shaped by glaciers. Slow-moving rivers of ice carved valleys out of mountains and deposited massive, glacial erratic boulders across the basins and ranges of the state. They sculpted ridge lines and arêtes, and textured the landscape with felsenmeer (fields of boulders) and hanging lakes.

During the Last Glacial Maximum, more than 20,000 years ago, Colorado’s Front Range was inundated by ice. Present-day Rocky Mountain National Park was covered by an icecap, and the region’s largest glacier at the time, located in the valley of the Cache la Poudre River and home to the current headwaters of the Colorado River, was 28 miles long. Back then, Arapaho Glacier may have been 9 miles long, according to a 1902 report by glaciologist N. M. Fenneman.

What triggered the end of the last Ice Age isn’t entirely clear, but about 18,000 years ago, a period of rapid deglaciation began. Colorado’s glaciers began to melt.

By the time Wheeler and Andrews trekked up the valley floor and found Arapaho, the glacier had melted considerably. (Arapaho was officially “discovered” in 1900 by a Boulder-based pharmacist named Eben G. Fine, since Wheeler had not published his journals from 1897 by then.) Even at a fraction of its historic size, the massive glacier impressed Wheeler and Andrews. “After reaching the top,” Wheeler wrote, “we walked toward the north and soon came upon cracks in the ice, at first a few inches wide and then several feet wide, rather terrifying … We dropped rocks down into the crevasses but didn’t hear them strike bottom.”

STANDING ON THE RIDGE almost exactly 124 years later, Scambos’s team and I saw a very different view.

Earlier that morning, at his invitation to tag along on an expedition to determine whether the Arapaho was still a true glacier, I had met Scambos at a trailhead in the Indian Peaks Wilderness of the Roosevelt National Forest. When I arrived, Scambos was already there with a team of 15 researchers from the University of Colorado Boulder, the Colorado School of Mines, and Colorado State University.

After I introduced myself to the team, Scambos dug through his pickup truck and emerged with an ice axe. He handed it over to me, and I strapped it to my backpack. Around me, everyone readied their own gear. Equipment varied from researcher to researcher, fine-tuned to their respective fields of scientific inquiry. There were cameras and drones, crampons and ice axes, ground-penetrating radar equipment and ice drills. Scambos assigned me to the hand drilling team, led by MacFerrin, who outfitted me with a pair of crampons to be used once we got to the glacier. On his back was a kind of pack I’d never seen before. It looked like a stretcher with a set of backpack straps attached to the base of one side, long-side up. Strapped to the stretcher portion of the pack was an ice axe and a hand auger ice drill. The drill looked “heavy as shit,” another researcher at the trailhead observed. Other members of the team carried pieces of a solar-powered ice drill, a new kind of equipment that would help them collect ice core samples.

A glacier, by definition, has to be flowing beneath its own mass. It has to be massive enough to move.

In all, the expedition would contribute to Scambos’s mission to learn the glacier’s size and movements, to see how much and how quickly the glacier is melting. These details from Arapaho Glacier would give clues to how climate change has altered similar alpine glaciers throughout the state — glaciers that may already be gone.

A Google search will tell you that Colorado is home to 16 glaciers. These “glaciers,” however, are glaciers only in name. “While there is no global standard for what size a body of ice must be to be considered a glacier,” reads a white paper from the United States Geological Survey (USGS), scientists typically “use the commonly accepted guideline of 0.1 square kilometers (about 25 acres or the size of 15 city blocks) as the minimum size of a glacier. Below this size, ice is generally stagnant and does not have enough mass to move.” So a glacier, by definition, has to be flowing beneath its own mass. It has to be massive enough to move.

In the mid-1980s, the USGS identified seven glaciers in the state of Colorado that fit these criteria. Arapaho Glacier was one of them. But in recent decades, glaciologists have watched the other six melt away or outright vanish. Arapaho Glacier remained, with enough mass to move. It was a full-on, bona fide alpine glacier, the only true glacier left in the state of Colorado.

Arapaho’s size and rate of decline has been a question that has vexed scientists since Wheeler and Andrews first dropped rocks in its crevasses. In 1902, just a few years after it was discovered, Fenneman was already concerned with the glacier’s rapid decline: “The snowfall for the past three winters has been deficient, and the melting in the ensuing summers has been excessive,” he wrote.

Half a century later, in 1951, a glaciologist named Ronald L. Ives measured the glacier’s thickness and reported a range between 25 and 130 meters. It’s a rather wide spectrum — somewhere between the distance from first base to second and the height of the Great Pyramid of Giza. By 1979, researchers narrowed the glacier’s thickness down to between 30 and 50 meters, while others estimated that the glacier had lost more than half of its ice in the preceding two decades.

Still, according to Scambos, these measurements were imperfect, calculated without the benefit of modern technology. “These area and thickness measurements were highly uncertain, and thus should be considered educated estimates at best,” Scambos and his colleagues wrote in 2010.

In 2007, Scambos teamed up with W. Tad Pfeffer and other glaciologists from CU Boulder to determine Arapaho Glacier’s melting over the last century. Pfeffer brought ground penetrating radar and GPS equipment to the glacier to create an accurate map of the cirque. The team then used aerial photographs and historical photographs to overlay past surveys of the glacier on the updated digital map. The results were staggering. Between 1900 and 1999, Arapaho Glacier lost 52 percent of its area. The glacier also lost about three-quarters of a meter of ice thickness per year between 1900 and 1960, and a tenth of a meter per year from 1960 to 2005.

Scambos and Pfeffer pointed to a fortuitous circumstance of geography to explain the deceleration of melting. In their 2010 paper, they wrote that “the region of Arapaho Glacier that still exists occupies the basin of the cirque adjacent to the western headwall because it is this region that receives both the most snow and least solar radiation.” The Arapaho Glacier is shaded by mountains, shielded from the heat of the sun. If the climate remains stable, they wrote, the Arapaho Glacier may be “on its way to a smaller but sustained existence” that would “require much higher rates of climate warming to alter.” But the researchers also noted that “although it may be able to retreat into a region of the cirque where it is stable, it is also possible that continued climate forcing will destabilize the glacier enough to cause its complete disappearance.” Even so, they estimated that the glacier might last until about 2075, if not longer.

WITH AN ARRAY of scientific equipment on our backs, we set forth up the Fourth of July Trail, which leads to the glacier. Trekking poles clinked against stones. Boots crunched on rock and soil. Birds sang in a forest of Engelmann spruce and subalpine fir. Mountain bluebells, fireweed, Indian paintbrush, and showy fleabane poked through the snow. We were surrounded by high peaks, their summits hidden in billowy gray clouds.

As we hiked past steep, fast-flowing streams and lichen-speckled outcroppings of granite and gneiss, we kept an eye on the clouds above. By the time we reached the treeline, about two hours into our hike, the weather took a turn for the worse. “It’s just way too cold up there!” said a group of hikers on their way down from Arapaho Saddle. The wind blew ever more powerfully. Some of us began to shiver. We twisted and turned, jumped up and down, warmed our hands with our breath. Some were dressed in the spirit of a summer hike in the high country. It had been a long, hot summer, after all. Thankfully, I wasn’t one of them.

“It’s going to be hard to get much done in this weather,” Scambos said, but we waited another hour in a thicket of fir before he officially called off the expedition. The research team would have to return at a later date. Most of the team turned around. A small group of us, including Scambos, decided to stash the survey gear in the trees and continue on.

The Marshall Fire closed out a year of severe drought in Colorado.

In the high country, with temperatures near freezing in August, it was easy to forget that climate warming is causing rapid changes in this ecosystem and all of Colorado. Since the Arapaho Glacier was first recognized as a glacier in 1900, Earth’s average surface temperature has risen about 1.8 degrees Fahrenheit. From Scambos and other geologists’ perspective, Colorado’s cryosphere has borne the brunt of that change.

But you don’t need to be a glaciologist to recognize the direct impacts of climate change in this region. In the last few days of 2021, dry conditions and high winds fanned a wildfire that burned thousands of acres and destroyed hundreds of homes in the towns of Superior and Louisville, just outside of Boulder. The Marshall Fire closed out a year of severe drought in Colorado and unprecedented water shortages across the American West.

As we leaped from rock to rock, avoiding pools of mud on the trail, I struck up a conversation with Scambos. “How would Arapaho’s absence affect Boulder’s water supply?” I asked.

The glacier isn’t the only source of Boulder’s water, Scambos reminded me. But each water source is impacted in one way or another by climate change. Another 40 percent of Boulder’s water comes from Barker Reservoir near the town of Nederland. This reservoir is fed by snowmelt via Middle Boulder Creek.

Globally, nearly two billion people are reliant on snow-packed mountains and alpine glaciers for their water supplies — and that snow and ice is fast disappearing. According to a study funded by the US National Oceanic and Atmospheric Administration, as the planet warms, mountain snowpack is expected to melt earlier and earlier each spring. In some mountain regions, like the Swiss Alps, parts of the Himalaya, and the Cascades, each degree Celsius of warming above pre-industrial levels results in the snowpack disappearing as much as 27 days earlier.

If greenhouse emissions continue unabated, Colorado’s climate is projected to warm between 2.5 and 5 degrees Fahrenheit by 2050, relative to a 1971-2000 baseline. As a result of this warming, Colorado’s high-elevation snowpack is projected to decline nearly 20 percent by the midpoint of the century. That means that four-fifths of Boulder’s current water supply could be facing shortages in coming decades.

The remaining 20 percent flows to Boulder from the Colorado-Big Thompson diversion, a 250-mile-long chain of dams, reservoirs, and pumps that “stores, regulates, and diverts water from the Colorado River on the western slope of the Continental Divide to the eastern slope of the Rocky Mountains,” according to the US Bureau of Reclamation.

However, the Colorado River — wrung out by drought, extreme heat, and over-drafting for farms and cities throughout the Southwest — is facing severe shortages as well. In August 2021, the US Department of Interior declared the first-ever water shortage in the Colorado River Basin at Lake Mead, one of the river’s main reservoirs. In Colorado, the river’s flow is projected to decline some 55 percent by 2100, resulting in drastic water shortages for the 40 million people dependent on the river — Boulderites included.

The Arapaho Glacier’s disappearance may not deplenish Boulder’s water supply entirely, but the glacier’s melting is symptomatic of a larger climatic trend, one sure to impact the lives of Boulderites, Coloradans, and billions of other human beings around the planet.

AT THE SADDLE, once we got over our initial shock, we surveyed the gloomy view. Arapaho had shrunk to little more than a sledding hill. The glacier’s remaining ice was thin and darkened by settled particulate matter and rocky debris. Along its perimeter, rock outcroppings emerged from the ice — outcroppings not seen in historical photographs. We hiked around the ridge for a time, searching for vantage points from which the glacier has been photographed over the past 120 years. Given the cloudy view, however, the photos would have to be snapped another day.

We descended from the alpine. By the time we reached the thicket of spruce and fir where we had left our more cumbersome gear, the wind had died down and the weather was warmer. We sat in silence in the grass of a montane meadow, snacking on apples and granola and trail mix, contemplating the glacier’s future and what we might learn from it. Clouds coasted across a pale blue sky. Birds sang in the high country.

“So, the Arapaho Glacier. It’s just … not a glacier anymore?” I finally asked, seeking some kind of closure.

“Are we all ready to go?” Someone asked.

We rose and trekked down the single-track trail, across meadows and through woods of aspens and evergreens, back to the trailhead where we’d begun our hike that morning. We reached our respective vehicles. I handed Scambos his ice axe and returned the crampons to MacFerrin. “Thanks again for lending these, Mike,” I said. “It’s a shame we couldn’t put them to use.”

“No problem,” he replied with a sigh. “I certainly wish we could have used it, too.” He took the gear and began packing it away.

Scambos and I shook hands. We discussed dates for the upcoming historical photographs and drone survey of the glacier. I told him I’d do my best to be there. “So, the Arapaho Glacier. It’s just … not a glacier anymore?” I finally asked, seeking some kind of closure.

Scambos looked up at the steep, timbered slopes of the glacial valley that enclosed us. He still needed to complete his surveys, to collect data on the glacier’s flow. But he also couldn’t doubt his own eyes. “That ice doesn’t appear to be flowing,” he said. And it certainly wasn’t the required 25 acres in size.

“I’d say the Arapaho Glacier has safely entered permanent ice field status,” MacFerrin chimed in as he loaded gear into the back of his crossover.

“Yeah,” Scambos agreed. “It’s really just an ice field now.”