HUARAZ, Peru >> At 50, Americo González Caldua has lived a life that coincided with the retreat of the glaciers of the high Andes. With each passing year, as the cold mountain temperatures rise, the ice moves uphill another 20 yards.

In the dry season, when the storms break and the research season begins, González heads to the icy heights of the nearby peaks with survey prisms and markers. He brings heavy drilling augers that bore core samples deep below the surface of the glaciers and reveal a picture of the atmosphere from a century ago.

He knows the ice sheet as well as anyone. Yet, González is neither a mountaineer nor a scientist: He’s the man most often found trailing behind them, carrying their equipment.

Mount Everest has the Sherpas. The Cordillera Blanca, a snowy mountain range in northern Peru, has the ayudantes de campo, or field helpers, in Spanish. They are the mountain men, mainly indigenous, who have watched a huge expanse of ice that was known to them for centuries shrink drastically in the space of one generation.

“Before, we saw our glaciers as beautiful, our mountain range covered in a white sheet that was stunning,” González said on a recent day at a small mountain-climber’s hostel near the base of an 18,000-foot peak. “But today, we don’t see that anymore on our glacier, which we’re losing more of every day. Instead of white, we are seeing stone.”

Of all the glaciers in retreat throughout the world, those in this part of South America are the most likely to disappear first. Scientists call them the tropical glaciers, ice caps found in places as warm as Ecuador and Indonesia, where high mountain peaks have shielded them for thousands of years from the heat of the jungle below.

Yet now, even these high perches have become precarious. Climate scientists say the ice cap here has been reduced by nearly a quarter in the past 40 years because of rising temperatures. With the rate of melting increasing each year, some scientists predict that within 50 years many of the peaks here will no longer have glaciers.

“It’s not Antarctica, where you have a rupture of a mile and everyone notices,” said Justiniano Alejo Cochachin, a glaciologist who works for the Peruvian government. “It’s 19 meters a year, it is bit by bit.”

On his many journeys, González has spent decades looking over the shoulders of scientists like Cochachin, shaping his own intimate view of a landscape altered by climate change.

He watched the expanding rocky fields around the Pastoruri Glacier, where the melting ice uncovered fossils that had not seen daylight in ages, including those of ferns and other plants. He has seen rivers turn red as other glaciers melted and exposed heavy metals that poison the water downstream.

“If there is no water, there is no life,” González said.

His work begins early, well before sunrise, when he packs crampons used to walk atop the glaciers, large boring drills and topographical instruments, helmets, gloves and the gear to build a shelter, all in a backpack nearly as large as he is.

The food often goes on a mule — provided the mule can make the climb. If not, González carries that, too, on several trips in and out of the camp over the course of several days.

González said the path on a recent climb to a glacier called Yanamarey would not be so taxing, by his standards — a round-trip journey of 10 hours. And so we headed out one morning with Rolando Cruz, a researcher in the nearby town of Huaraz who came to take some measurements at the base of the glacier.

The long hours up are often quiet ones, where González searches for what he calls the “perfect route” through the unmarked boggy landscape of mist and fog where jagged peaks rise up on either side and hawks soar above. Vast plains stretch for miles, former lake beds from the ice age, where cows graze.

“The cows weren’t here before,” noted González, saying they now graze at higher altitudes as they follow the grasses as the temperatures have warmed.

The route was one that González has crossed countless times over the decades, since he first visited the Yanamarey glacier in the early 1990s. His descriptions of it from that time vary. At times he evokes a building — it had “blue walls,” he said. Sometimes he spoke of the glacier’s “beautiful long tongue,” and it sounded more like an animal.

“Yes, it is alive,” he said, describing the glacier’s slow movement below his feet.

In the 1990s, the hikes could be an escape from the conflicts taking place below, when the Shining Path, the Maoist rebel group that terrorized Peru for decades, attacked politicians in Huaraz and planted three car bombs. Despite the unrest, U.S. researchers would come each year, and González would lead them up as the ice sheet continued to melt.

“When you go out into the field, your mind clears,” he said.

It was the sound of the cracking, heard on nearly every ice sheet the scientists came to study, that bothered him most. “Tac,” he said, “like a huge sound.” And every year he came, Yanamarey was farther away than it had been the last time.

Our climb continued. The landscape turned into a rocky stretch of boulders. Then the glacier came into view.

It looked very different that day from the place González had described. The ice sheet, having once spilled into the lake below it, had retreated halfway up a rocky mountainside, a small spit peeking behind the rocks. There were no “blue walls,” no “tongue,” just a thin coat of ice over a bare rocky stretch.

“It looks gray, like the color of lead,” González said several times.

Cruz climbed up, took his measurements in the distance and returned some time later. The two men looked at each other with the same resigned glance, then headed back down the hill.

At his age, González knows these journeys will not continue forever. His knees have begun to give out, particularly as he walks downhill with large amounts of gear. “You don’t have the same strength,” he said.

González looked over at his son Álvaro, an 18-year-old who had joined us that afternoon back at the hostel in Huaraz. The boy told me he would soon study climate science in college, inspired by his father who had taken him to see the ice sheet for the first time some years ago.

Who had shown González the glaciers first? It was his mother, he said, on a chilly day when the two were looking out at the peaks from a nearby farm.

“You could see those white glaciers in the distance,” he said. “And our mother pointed to them and said in her language ‘raju,’ which is the Quechua word, which means ice.”

Back then, the ice seemed as permanent as the mountains themselves.

“No, I never imagined this,” said González, describing the ice today. “As a child, you can never picture the things which might happen.”