Annual expeditions to Chhota Shigri began only fourteen years ago, so relatively little is known about its climatic history. Chhota Shigri and the other glaciers of the eastern Himalayas are unusual, in that, unlike the majority of the world’s glaciers, which get most of their snow from winter storms, they get much of theirs from the summer monsoons, which tend to insulate them from more rapid melting. (Most of the glaciers of the Karakoram Mountains, in Pakistan, are not receding at all; it’s one of the few places in the world where this is the case.)

The data are also limited by the uneven quality of the expeditions. Glaciologists can spend hundreds of thousands of dollars on research trips, but Azam and Ranjan had only a few thousand dollars to buy equipment and to pay porters. Some glacial expeditions extract ice cores using cranes and ferry them home by helicopter. The Indian scientists would transport their cores in dry ice, using a portable cooler, of the kind you might use to chill beer for a picnic, driving them by car back to Ranjan’s laboratory, in New Delhi—a sixteen-hour trip. Some of the experiments that they planned to perform on Chhota Shigri seemed comically rudimentary. In one, to measure the volume of meltwater flowing out of the glacier, a graduate assistant would toss a wooden block into the water and time its float downstream.

In the morning, the sun rose over the mountains, but for hours the high-walled valley remained shaded and bitterly cold. Unlike glaciers in other parts of the world—Greenland, say, or the Alps—many of those in the Himalayas lie at the bottom of narrow valleys that get only a few hours of direct sunlight each day. As a result, they are melting more slowly than they would on flatter ground. It was not until 8:20 A.M. that the sun shone on our camp; by midafternoon the valley was in shadow again.

Markus Engelhardt’s first task was to check the camp’s weather monitor, which had been planted four months earlier, and recorded temperature, solar radiation, and barometric pressure. There was an array of similar instruments installed throughout the camp; one of them, a five-foot-tall aluminum thistle with a crown of flaps, looked like something you might find in a Santa Fe sculpture garden. Engelhardt had two other weather stations on the glacier, and he was eager to download their data, which would allow him to construct a precise record of fluctuations in the local climate. As he watched information scroll across the screen of his laptop, Engelhardt, who had been stoic during our long ascent, could barely contain his enthusiasm. “I want to go back to the office right now and start studying the data,” he said.

For the people who live on the Indian subcontinent, the future of the high-mountain climate is of more than academic interest. The three great rivers that ﬂow from the Indian Himalayas provide water for more than seven hundred million people in India, Pakistan, and Bangladesh. Photograph by Simon Norfolk / Institute for The New Yorker

The team set out into the valley, following a stream that was flowing from the glacier. There were nine of us, including three graduate assistants who’d come with Azam and Ranjan. I had imagined a smooth carpet of ice that led to the top of the glacier. Instead, there was a rough track of boulders, a destructive path that marked Chhota Shigri’s retreat. Thousands of years ago, as the glacier moved forward, debris from the valley walls was torn loose by the advancing ice and tumbled onto its face, creating a craggy obstacle course.

Azam had not visited since 2013, when he was completing a doctorate at the University of Grenoble, in France. (His thesis topic: the effect of the climate on Chhota Shigri and the surrounding glaciers.) Like many of the glaciologists I encountered, Azam entered the field not because he was drawn to science but because he loved the outdoors. Born in the plains state of Uttar Pradesh, he grew up seeing the Himalayas on television and dreamt of going there. In college, he took a sensible path, studying chemistry, but he was also athletically inclined; he won several bodybuilding titles, including Mr. Jawaharlal Nehru University. After he finished a master’s degree in chemistry, his teachers urged him to go into medical research. But, he said, “I was being pulled by some invisible force.”

That same year, he had signed up for a mountaineering course offered by the Indian Army, which took place on the Dokriani Glacier, near the Chinese border. During the course, Azam noticed a series of bamboo rods protruding from the snow: ablation stakes, basic instruments of glaciology. “Until then, I didn’t realize you could work on a glacier,” he told me. Not long afterward, he went to Grenoble, where he spent the next three years studying ice, making field trips to India every summer. “When I am in the mountains, on the glacier, I feel close to myself—I’m far from everybody, there’s no technology, and I can think,” Azam said. “Only recently has the science become more important to me.”

Ranjan, who is thirty-one, spent years examining glaciers as a graduate student in Switzerland, but he had never been to one in India, where the terrain is much more rugged. On the trail, in his heavy clothes—layers of thermal underwear and fleece and a down jacket—he cut a husky figure. As we started off, he worried that he was not fit enough to complete the expedition. “I am not sure that I can do this,” he said. He moved slowly, panting heavily. The porters practically skipped across the rocky ground as they carried several hundred pounds of our equipment, as well as dozens of eggs.

At higher elevations, the valley deepened; the walls rose a thousand feet on either side, in layers of colored sediment, each representing a different mineral and a different epoch. The landscape was desolate, but occasionally there was a surprise: a golden eagle, a butterfly with orange wings. A solitary black crow followed us the length of the glacier.

Rounding a bend in the stream, we arrived at the glacier’s snout, a cave of ice with water rushing from the entrance. Behind it, Chhota Shigri spread upward into the peaks, a vast shoehorn of snow and ice covered with sharp-edged boulders, most of them the size of a car. The glaciers of the Himalayas are scattered with geological debris, which, along with the lack of direct sunlight, slows melting. Yet, since Azam’s last visit, two years earlier, Chhota Shigri’s snout had receded more than sixty feet. At its largest, the glacier sat almost atop the Chandra, slowly filling it with frigid meltwater; now it is barely visible from the banks. “It’s going very fast,” Azam said, standing on a ridge above it. The shrinking snout had left behind enormous hunks of what glaciologists call “dead ice,” which were melting on the glacier’s trail. A single glance belied the reports that India’s glaciers are stable. After this, all the activity would consist of taking small, precise measurements, to find out exactly what was changing and how much.

The opening of Chhota Shigri’s snout was five feet high, large enough for us to enter. Pressing ourselves against the interior walls and shimmying along the narrow banks of the rushing water, we worked our way into a vaulting palace of ice, where ten-foot-long icicles hung from the ceiling like giant fishhooks. Underneath the roar, you could hear the drip of melting ice. In the walls and the ceiling, water and earth streamed behind sheets of clear ice, the sediment tinting the walls orange and pale green. Air bubbled in the water, trapped when the glacier’s ice froze around it, more than two hundred and fifty years ago. “It could collapse at any moment,” Azam said. “When we come back next year, it will be gone.”

The glaciologist Farooq Azam, a thirty-three-year-old former bodybuilding champion, has made more than twenty trips to Chhota Shigri. On this trip, he came to measure three things: the mass of the glacier, its thickness, and the speed with which it was moving downhill. Photograph by Simon Norfolk / Institute for The New Yorker

On one of Azam’s early trips to Chhota Shigri, in 2008, he and a French scientist, accompanied by a porter, trekked to the head of the glacier. When they started back, the next day, Azam fell behind the others. Then the sun went down and the temperature dropped. There was no moon, and the way through the boulders disappeared in the darkness. Alone and disoriented, Azam tripped and fell into the glacial stream. On his knees, he crawled alongside the water—his only clear path—wondering if he would survive. Several hours later, another member of the team found him not far from the base camp, shivering and numb, and helped him make his way back. At the camp, the French scientist apologized for leaving him behind. Azam, worried that his legs were frostbitten, dunked them in a barrel of steaming water. “What I learned was nature is always stronger,” he said.