Carlos Flores, an anthropologist and former Jesuit priest who accompanied the Qoyllur Rit'i pilgrimage for several decades, recalls people commenting on glacial retreat as long ago as the 1970s. Some saw it as a sign of the end of the world.
The Rev. Antonio Sánchez-Guardamino, the Catholic priest in Ocongate, who has also worked among remote Andean communities for decades, is more cautious. "The snow-capped peaks are not the only apus," he says. "There are many apus that are not snow-capped, and people make offerings to them."
Nevertheless, the vanishing glaciers may still signal the end of the world as the Quechua farmers know it.
"If the snow disappears, the people will disappear, too," Sánchez-Guardamino says. "If the snow disappears, we will be left without water. The pastures and the animals will disappear. Everything is interconnected. The problem of the melting of the glaciers is that the source of life is drying up."
Andean farmers struggle to understand the changes. Some say the mountains are turning black because they are angry or sad. Some blame pollution. Carmina Sicusta has another explanation.
"The earth itself is sick," she says.
Sicusta, 48, lives in Amaru, a village of small adobe houses on a mountainside above Pisaq, a picturesque town near Cusco that is best known for Inca ruins and a Sunday market that draw tourists from around the world.
In the past decade or so, Amaru's farmers have watched the pattern of hillside fields change. On the frigid hilltops, the tundra-like pasture suitable only for llamas is receding. Fields of grain blanket high hillsides that were once too cold for anything but animals. Families that used to own dozens of llamas now have only a handful.
"The earth is warming. The waters are warming. The springs are drying up," Sicusta says in Quechua, looking up from her weaving. "There is going to be a shortage of food. Our children will have less to eat."
Her husband, Eugenio Palomino, 46, adds, "There's less and less rain. There won't to be a good harvest."
Farmers say weather patterns are changing, rain and frost come out of season, and the signs they always used to tell when it was time to till or plant are no longer reliable.
Agriculture depends on predictability, Bury says. Early rains wash seeds away, a dry spell during the growing season keeps potato tubers from developing, and rain at the normally dry harvest time rots grain. All spell disaster for subsistence farmers.
While physical scientists may consider people's perceptions of climate change subjective and unreliable, Bury insists it is important to see the world as mountain people do. "When you lose your crops, it's not a subjective event," he says. "People have a good 10-year memory of how things have changed."
In some cases, perceptions may run ahead of scientific evidence, he says, because people could see very local changes that do not show up on computer models with a 100-kilometer resolution. This is not the first time people have had to adjust to climate change in the Andes. Historian Mark Carey of Washington and Lee University has heard legends referring to glacial retreat and lake formation. Based on pollen from lake sediment cores, French climate researcher Alex Chepstow-Lusty believes gradual warming beginning in 1100, after a long arid spell, facilitated the rise of the Inca Empire.
But it is not easy for Andean farmers to conceive of life in a radically different environment. People in Copa Grande, a village in the snow-capped Cordillera Blanca in central Peru, cannot imagine living like farmers in the bare Cordillera Negra across the valley, who depend only on rainwater for irrigation.
"People generally have a very bleak outlook, and most are thinking on a very short time scale," says anthropologist Katherine Dunbar of the University of Georgia, who is doing doctoral research in Copa Grande. "People say, 'The glaciers are going to go, there's not going to be water and we're all going to die.'"
A generation ago, the glacier above the village was the place where teenagers spent time with friends and courted. Fewer go now, because the glacier is farther away and the ice at the edge is soft and dangerous.
"The loss of the glacier is the loss of a social scene," Dunbar says.
Because environmental changes have a social and cultural impact, technical solutions alone are not enough, says Lino Loayza of ANDES, a Peruvian non-profit organization working with residents of Amaru and neighboring communities.
"Our first priority is food security, so people eat well and have enough food," Loayza says.
Besides planting a variety of staple crops, the communities have established the Parque de la Papa, or "Potato Park," to preserve some 700 varieties of native potatoes adapted to different altitudes. They prepare medicinal plants and are branching into tourism, with hiking circuits, a restaurant specializing in potato dishes, and crafts workshops. As farming becomes more unpredictable, they hope the alternatives will enable them and their children to stay on their land.
Further north, the snow-capped Cordillera Blanca has long been a draw for Peruvian and foreign hikers and climbers. In the communities Cary has studied, about 25 percent of the people work in tourism. The area is losing about 10 percent of its snow cover per decade, and guides say softer snow is making some climbing routes more dangerous.
Worldwide, studies predict the migration of between 25 million and 1 billion people because of climate change and related disasters, but economics also plays a role. A sagging tourist industry in the Cordillera Blanca could mean fewer jobs, spurring migration to cities even before the glaciers disappear. And most of Peru's large cities are in the coastal desert, where water stress is likely to be greater.
Nevertheless, the pilgrims at Qoyllur Rit'i pilgrims faced the future with faith. Awaiting sunrise on a ridge below the sanctuary, a tall, young ukuku with a short, braided beard and a single silver earring - himself an emblem of cultural change - said the rituals will continue even if the glaciers are gone.
"These people are very resilient," Orlove says. "They're in it for the long haul. They're very committed to their land. They're able to come up with remarkable responses."