Nearly three miles high on a massif in the far north of Colombia, 18 men and women clamber up a steep, rocky slope. Members of a local indigenous group, the Arhuaco, they are dressed in white tunics, with intricately woven bags slung across their chests, the men’s heads covered by conical white hats symbolic of snowy peaks. They pause near a depression, chests heaving in the thin air, to peer over the edge. Deep inside, flocks of birds swoop around a single, gnarled tree, rivulets of water flowing from its base. The Arhuaco say that when the world was created, they emerged from this very spot. They call it the Mother. Seen from space, the Sierra Nevada de Santa Marta—the world’s highest coastal massif, its peaks brushing the sky at nearly 19,000 feet—resembles a gigantic pyramid rising from the blue waters of the nearby Caribbean Sea. The highest summits of this compact mountain range are known to the outside world as Simón Bolívar, Cristóbal Colón, Guardian, and La Reina, but the Arhuaco call this realm above the clouds Chundua, meaning, loosely, heaven. View Images As the world’s highest coastal massif, the Sierra Nevada de Santa Marta represents a microcosm of the planet, ranging from coral reefs to glaciers. More than 92 percent of the ice in its upper reaches has disappeared, and rivers fed by glacial meltwater that provide water to millions of people down below are drying up. Photograph by Stephen Ferry, National Geographic In a way, the Sierra Nevada is a microcosm of the planet: Within an area smaller than the state of Massachusetts are coral reefs, sandy beaches, deserts, rainforests, tropical dry forests, savannas, paramos, tundra, alpine lakes, glaciers—all connected in a seamless gradient of life-forms that seem to change with each upward step. Here are more endemic plants and animals—species unique to this place—than almost anywhere else on Earth. The catalog includes the blue-bearded helmetcrest hummingbird, the Santa Marta parakeet, plants such as Libanothamnus glossophyllus (a high-altitude, hairy-leaf succulent), two species of palm, and at least four separate species of harlequin frogs, which scientists consider to be the world’s most threatened amphibians. (Here's how former Colombian FARC rebels are helping scientists discover new species.) View Images Groups of Arhuaco make regular treks in the Sierra Nevada to carry out spiritual work but rarely in the company of “younger brothers,” as they call outsiders. Here, spiritual elder Adolfo Chaparro (left, back to camera) presides over a ceremony in which meditating residents of the village of Sogrome direct their thoughts into pieces of colored paper and thread he'll leave at sacred sites. Photograph by Stephen Ferry, National Geographic But this contained landscape faces trouble. As the planet heats up, the glaciers are disappearing. During the past 150 years, the massif has lost more than 92 percent of its ice, and scientists predict that the rest will be gone within the next 30 years. If that happens, the 35 life-sustaining rivers that flow from its peaks will begin to run dry, imperiling the animals and plants in the varied ecosystems and jeopardizing the lives of not only the Arhuaco but also millions of people in the region below. At a time when many of us see ourselves as separate from nature (and destroyers of wilderness), it’s tempting to imagine that such abundance could persist only in the absence of human activity. But in this case, the region’s human inhabitants, the 35,000 Arhuaco—along with the indigenous Kogi, Wiwa, and Kankuamo, who collectively number about 50,000—have been its bulwark. For as long as anyone can remember, they have protected the Sierra Nevada by keeping outsiders—us—out. Groups of Arhuaco regularly make treks up the Sierra Nevada to carry out spiritual observances and pay their respects—but never in the company of “younger brothers,” as they call outsiders. They see themselves as the older brothers, nature’s caretakers in a world gone astray, responsible for rectifying the transgressions of their often irresponsible and careless kin. View Images Seynekun Villafaña coaxes her mule forward through dwarf forests and shrubs that live at about 10,000 feet above the sea. The Sierra Nevada is home to a remarkable variety of species of plants and animals found nowhere else on the planet. Photograph by Stephen Ferry, National Geographic The clarity with which the Arhuaco perceive the galloping transformation of the Sierra Nevada must seem like a curse. For them, the changing climate is more than an environmental crisis—it’s an existential one too. If what’s happening now goes on unchecked, “indigenous people won’t be the only ones who will suffer,” says Amado Villafaña, a photographer and the director of Yosokwi Productions, a media team composed of Arhuaco photographers and filmmakers. “All of us will be affected.” This is why, after months of intense deliberation, the Arhuaco elders (known as mamos) took an unprecedented step. Breaking with their rigidly isolationist past, they invited photographer Stephen Ferry and me to join them on a spiritual journey from the base of the massif all the way up to a sacred lake called Naboba, fed by glacial melt at nearly 16,000 feet. They want us to be their megaphone to the wider world about the threats to the Sierra Nevada, to their way of life—and to humanity. View Images An Arhuaco woman walks alongside the Guatapurí River outside Sogrome. In this otherwise arid region, the river is a crucial water source for the city of Valledupar, which has a population of nearly half a million. But as the massif’s glaciers have shrunk, the Guatapurí’s headwaters have slowed to little more than a trickle. Photograph by Stephen Ferry, National Geographic The Arhuaco imbue all plants, animals, and rocks with metaphysical attributes and even personalities. They regard harlequin frogs—mostly seen along the edges of glacial lakes—with special admiration and respect. “Everything has life and spirit,” Villafaña says. “But frogs are particularly sacred because they sing to the water.” View Images The tiny village of Meywaka nestles at about 12,000 feet below a depression in the side of a moraine left by a retreating glacier. The Arhuaco call the sinkhole-like feature the Mother because it resembles a woman’s uterus and birth canal. They believe that when the world was created, their people emerged from here. Photograph by Stephen Ferry, National Geographic The cosmology of the Arhuaco, steeped in symbolism and allegory, emerged deep in the past and embodies a central idea: that the Sierra Nevada is sacred ground. To them, the massif is a person, complete with feet, hair, and intimate creases like those at your hip. It has breasts, veins, and—most crucial—the faculty of thought locked in its snow and ice. Just as the human brain serves to regulate body temperature and the rhythmic pulses of the circulatory system, meltwater from the glaciers is lifeblood, a dependable supply of the elixir in a land where periods of wet and dry fluctuate wildly. “In Colombia and the outside world, this place is known as the Sierra Nevada de Santa Marta,” Villafaña says, glancing up at the towering peaks. “But for us, it’s the heart of the world.” View Images From left to right: Amado Villafaña, Diego Chaparro, and Eulogio Villafaña pause at a homestead several miles below Meywaka. Photograph by Stephen Ferry, National Geographic Safeguarding the heart of the world is not just woven into the lives of the Arhuaco—it’s the very fabric of their culture. Caring for this place is a sacred obligation—an obligation they’ve been able to fulfill by sealing themselves off in their mountain redoubt from time immemorial. Until now. “The ice is melting,” Clementina Villafaña says softly, a forlorn expression clouding her face. Clementina was born and raised in Meywaka, at 12,000 feet the highest Arhuaco village in the Sierra Nevada. Perhaps just shy of 40 years old, she speaks of the abundant snow and ice decades ago, of the gushing rivers now slowed to a trickle, and of shrubs, flowers, and birds from lower altitudes that have been migrating upslope as temperatures have warmed. “All of this used to be covered in snow,” she says, sweeping one hand across the landscape as she fiddles with a spindly young plant clinging to a nearby rock with the other hand. “The little trees and shrubs you see around here didn’t use to exist in this place—it was too cold. You would only see these farther down the mountain, where it’s warmer.” Glacial change in Sierra Nevada de Santa Marta 1 mi 1 km Colón Bolivar Reina Meywaka Guardián 3 mi Glacial change in Sierra Nevada de Santa Marta 3 km Colón Bolivar Reina Meywaka Guardián Glacier Area Year Brian T. Jacobs, NG Staff. Sources: Instituto de Hidrología, Meteorología y Estudios Ambientales (IDEAM), USGS/NASA

Of all the ice present on Earth, it’s the tropical glaciers in the equatorial belt—99 percent of which are found in South America—that are most vulnerable to climate change, says Jorge Luis Ceballos, head glaciologist at Colombia’s Institute of Hydrology, Meteorology, and Environmental Studies, in Bogotá. Ceballos has spent nearly 20 years studying the retreat of the Sierra Nevada’s glaciers.

“While I started my career as a glaciologist,” Ceballos says, “I’ll end it as a historian, because these glaciers will likely vanish within our lifetimes.”

In their fervor to keep younger brothers off the massif, the Arhuaco have never allowed Ceballos to see the shrinking glaciers for himself. Instead, he’s had to monitor the vanishing ice from his desk by analyzing satellite images provided by the Colombian Air Force. (Here's why Venezuela's last glacier is about to disappear.)

Mule train: an unruly convoy

On our 12-day journey up the massif, we make many stops along the way—sometimes several in a day—as the Arhuaco pilgrims carry out solemn devotions to restore balance to the natural world.

We rise before dawn to saddle the mules. Then, all day long, we wind one by one along precarious cliffs, through mossy forests, up lush, mist-cloaked valleys, over ice-blue rivers rushing down the mountainside. Most in our group, like Ferry and me, have never climbed to the upper reaches of the massif, and all our senses are awakened as we absorb the unfamiliarity of this place.

During the climb, our long conversations and silences are sometimes interrupted by outbursts of exhausted laughter provoked by the eternal struggle of keeping our convoy of unruly mules in order. The journey is a communal endeavor. We sweat together under the tropical sun, shiver together at night, huddled around the campfire—and marvel at our constantly changing surroundings.

Six days into the trek, we reach Meywaka, Clementina Villafaña’s village. The tiny cluster of stone and straw houses nestles against the base of a ridge of rocks and sediment seven stories high—detritus deposited by a retreating glacier more than 150 years ago.

View Images Arhuaco gather colored stones to be used as spiritual payments. Each color represents a different aspect of the natural world: green for coca leaf chewed by the men, white for snow and ice, gray for water. Photograph by Stephen Ferry, National Geographic

It’s just above Meywaka that we gaze into the mysterious birthplace of the Arhuaco before continuing over the top of the ridge. There, in an ice-gouged valley some 300 feet below, a glacial lake shimmers in the muted afternoon light. Its edges are hemmed with the iridescent green fringe of new plant life—a sign that the lake is shrinking.

In single file, the group descends. Then, in silence, the Arhuaco busy themselves along the water’s edge, digging their fingers into the earth in search of small colored stones.

View Images Valleys in the upper reaches of the Sierra Nevada are lined with detritus from glaciers that enveloped this region during the Little Ice Age, which ended here in the mid-1800s. Photograph by Stephen Ferry, National Geographic

Few creatures survive at this altitude, yet the entire landscape seems to breathe. I crouch next to Marcelino Villafaña—a skilled accordionist of traditional chicote music who is as soft-spoken as he is indefatigable during our arduous climb—close enough to feel the heat radiating from him. I watch him carefully select small stones and place them in the bag slung across his chest. Each stone’s color has meaning: white for snow and ice, green for the coca leaves traditionally chewed by the men, gray for water.

It may seem far-fetched to think that gathering pebbles from a lakeshore constitutes an act of conservation, yet this small observance represents the sensibility that pervades Arhuaco life—and helps explains the people’s effectiveness as nature’s caretakers.

View Images Gladys Martínez (center) makes warming coffee with powdered milk for Eulogio Villafaña (left) and Ever Maestre at the edge of Lake Naboba. The night before, temperatures had fallen below freezing. Photograph by Stephen Ferry, National Geographic

For the Arhuaco, nature and society exist as one in a union that needs constant rebalancing through intricate processes of spiritual work. From a young age, boys and girls are taught to pass their reflections about the natural world to everyday objects such as pieces of wool, cotton, or string. These tokens, imbued with their thoughts and gratitude, are packaged together with natural objects—pebbles from the lake, for example—and left as “payments” along a network of sacred sites on the massif.

Later that day, people approach Mamo Adolfo Chaparro, who’s perched on a boulder deep in thought, a shock of black hair flowing wildly from beneath his white cap, to hand him their stones. Mamo Adolfo is the group’s leader and the sole keeper of knowledge pertaining to the Arhuaco’s commitments to the sacred sites in this part of the Sierra Nevada. He’s a man whose profound, almost detached, demeanor seems to reflect a lifetime spent fixated on the monumental task of maintaining order in the natural world. Mamo Adolfo will carry the stones back down the massif and deposit them as payments around the base.

View Images Under the guidance of Mamo Adolfo Chaparro (right), Arhuaco pilgrims carry out spiritual work. Here, he prepares to place packages containing spiritual payments beneath a sacred rock. Photograph by Stephen Ferry, National Geographic

Why, I ask Ever Maestre, 25, who does odd jobs in a village near the city of Valledupar, do the Arhuaco think of these offerings as payments?

“Down below in the cities where the younger brother lives, people pay bills for the things they need to survive, like electricity, water, and gas, using money,” he says. “This is our way of paying our bills to the mountain and the Earth for the things we must take to survive.”

A devout brand of conservation

Humans have always felt a need to understand and relate to our surroundings in meaningful ways—to connect with something bigger than ourselves. In antiquity, we sought—and found—this spirituality in nature.

For the Arhuaco and other indigenous peoples, the landscapes, ecosystems, and biodiversity that sustain their lives and cultures are seen as sacred—no less worthy of veneration than a church, mosque, or other house of worship.

Recent studies have shown that areas managed by local communities and indigenous people hold as much as 80 percent of the Earth’s biodiversity, and sacred natural landscapes such as the Sierra Nevada de Santa Marta are considered to be the world’s oldest conservation areas.

View Images Lake Naboba and the summits of Bolívar and Colón are seen from halfway up the northern flank of Guardian Peak. The Arhuaco know this part of the Sierra Nevada as Chundua, which means, loosely, heaven. Photograph by Stephen Ferry, National Geographic

While that may make them seem rare and intriguing, they’re widespread—likely in every country on Earth. These places resonate at the depths of human emotion. The belief that a mountain, river, forest, or lake can and should be considered sacred and therefore deserving of profound respect and protection is at the core of a devout brand of conservation known as “indigenous environmental stewardship.”

“We see the natural world as a living being with rights,” Amado Villafaña says. “The rights of the natural world—of the air, the water, the moon, the stars—always take precedence. Respecting these rights is what allows us to exist alongside everything else on the planet. For us, human beings are secondary—we have a very clear understanding that humans come, we spend a bit of time here, and then we leave. The natural world must prevail.” (Here's what happened when a river, forest, and mountain were given legal rights in New Zealand.)

It was a leap of faith on the part of the Arhuaco elders that by revealing through Ferry and me the sacred work they do to protect nature, they would be able to reawaken in the “younger brothers” our innate human capacity to sense the divine in nature. Only then, they believe, will we be stirred to carry out our responsibility of protecting Earth.

Following my return from the Sierra Nevada, the scent of earth and smoke from the campfires faded from my hair and clothing. What has stayed with me, thanks to my time with the Arhuaco, is a new appreciation of the natural things around me—of the intimation of the divine in objects as seemingly mundane as a tree or a bird or a flower.

This story was created in partnership with the National Geographic Society and the Wyss Campaign for Nature, which seek to inspire the protection of 30 percent of the planet by 2030. Learn more at campaignfornature.org .

Gena Steffens is a writer, photographer, and National Geographic explorer based in Bogotá, Colombia. Follow her on Instagram.