Over the past several decades, the effects of climate change, overgrazing, and human activity have led to widespread desertification on the plateau. To make matters worse, the region’s glaciers have receded 15 percent over the past 30 years. Hundreds of plant and animal species face imminent danger as a result, including the area’s most famous inhabitant, the elusive snow leopard.

Now the Chinese government is undertaking one of the most ambitious conservation experiments in the world to halt the degradation. It intends to combine three separate regions of Sanjiangyuan to create China’s first national park – setting aside an area the size of Pennsylvania. 

At the same time, China is working to set up a series of other trial national parks around the country. Thirteen projects have been established in 10 provinces so far. They include a national park for giant pandas and a separate one for Siberian tigers and Amur leopards.

Gretchen Daily, a conservationist and biology professor at Stanford University, says these initiatives, combined with other large-scale environmental projects Beijing is already pursuing, represent “a level of investment in nature that’s completely unprecedented.” 

The new thrust is part of an effort by President Xi Jinping to transform China into an “ecological civilization.” More than six decades after Mao Zedong declared that “man must conquer nature,” Chinese leaders have signaled a fundamentally different approach to the natural world. The change in attitude reflects a growing realization of the damage China’s rapid economic rise has done to the environment.

“Xi Jinping believes the past model of economic development is no longer sustainable,” says Rose Niu, chief conservation officer at the Paulson Institute, a Chicago-based research center that focuses on United States-China relations and is working with Beijing on the trial parks. “He is fully aware of the risk of not taking corrective action.”

The new parks movement is audacious – and risky. Scheduled to open in 2020, Sanjiangyuan National Park will, at 47,000 square miles, become the world’s second-largest national park (after Northeast Greenland National Park, which is bigger than all but 29 countries). The animal parks will both be at least one and a half times the size of Yellowstone, the crown jewel of the US park system. 

“It took the US 100 years to get to where we are with our national park system,” says Destry Jarvis, a founding member of Global Parks, a nonprofit consultancy started by retired US National Park Service managers. “If the Chinese keep it up, they could get to the same place in 25 or 30 years.”

Yet in a country of almost 1.4 billion people, Mr. Jarvis cautions, creating harmony between humans and nature will be a mammoth task. For both China and the world, the experiment is important for what it means for protecting the environment, for combating global warming, and for Chinese social cohesion, since tens of thousands of people will have to be relocated to make room for one of the most expansive conservation efforts in modern history. 

National parks have long been regarded as temples of nature in the US. President Theodore Roosevelt said as much after camping in Yosemite with the naturalist John Muir in 1903. “It was like lying in a great solemn cathedral,” he later wrote, “far vaster and more beautiful than any built by the hand of man.” Transcendentalists such as Ralph Waldo Emerson and Henry David Thoreau extolled unspoiled wilderness for its ability to rejuvenate the soul. Nature was intrinsically valuable in their eyes, an idea that still influences the debate over what to do with America’s most pristine natural sites. 

The scientists and bureaucrats at the forefront of China’s national park program rarely speak in such soaring rhetoric. For them, natural areas are first and foremost providers of “natural capital,” a precise but uninspiring term that includes biodiversity as well as ecological services that are essential for human life. The Chinese government has even developed a monitoring system for tracking the country’s natural capital and quantifying its value.

In 2012, it launched its first national ecosystem assessment. With the help of more than 20,000 satellite images and 100,000 field surveys, a team of researchers measured how much natural capital China lost or gained between 2000 and 2010. A study published in the journal Science last June summarizes their findings: Water retention, food production, carbon sequestration, soil retention, sandstorm prevention, and flood mitigation were all up 4 to 38 percent; biodiversity conservation was down 3 percent.

“It’s like measuring GDP,” says Ouyang Zhiyun, a researcher at the Chinese Academy of Sciences and one of the authors of the study, referring to gross domestic product. “We call it gross ecosystem product.”

Dr. Ouyang, who is overseeing the planning process for the new parks, is one of China’s most distinguished scientists in the field of ecology. He was born and raised in the Luoxiao Mountains in the southern province of Hunan, where, as a young boy, he spent his free time climbing trees and exploring the nearby woods. Earlier this summer, I caught up with him in his large, cluttered office on the north side of Beijing. 

“My home village was surrounded by nature. There were even tigers there in the 1970s,” he says with unfeigned excitement. Now in his mid-50s, Ouyang wears glasses and has short salt-and-pepper hair. He exudes an almost insatiable, childlike curiosity about the natural world. 

When Ouyang began his studies at Hunan Agricultural University in 1979, the Chinese economy was only starting to take off under the reforms instituted by Deng Xiaoping. Ouyang had no idea China would grow to become the world’s second-largest economy over the next three decades, nor did he anticipate the scale of environmental destruction the country’s rise would bring. It wasn’t until the summer of 1998, when devastating floods along the Yangtze killed 4,150 people, that he came to fully grasp the Faustian bargain at the center of China’s economic boom. Although extensive rains linked to El Niño were the primary cause of the floods, they were intensified by decades of logging along the river – making them the worst in 44 years.

The floods were a wake-up call for China. In the weeks that followed, the central government enacted logging bans in 13 provinces to better protect the Yangtze and Yellow Rivers, and the next year it launched the largest reforestation effort in the world. “It was a turning point,” Ouyang says. “The floods forced the government and the public to really start paying attention to ecological conservation.”

China has since spent more than $100 billion on planting trees; an estimated 21.7 percent of the country is now covered in forest, up from 18.9 percent in 2000. It has also expanded the number of nature reserves, forest parks, and other protected areas in an attempt to strike a balance between economic growth and environmental conservation. By the end of 2014, some 2,729 nature reserves and thousands of other parks had been established by all levels of government. A central goal of the national park program is to make these lands easier to manage and better ensure their preservation.

“The ecological environment has irreplaceable value,” President Xi told a group of lawmakers from Qinghai province in March 2016. “We should treat it as our lifeline and protect it like the apple of our eye.”

This mission is considered particularly vital for places such as Sanjiangyuan, which is located in Qinghai. At more than 12,000 feet above sea level, it harbors one of the highest concentrations of biodiversity of any high-altitude region in the world.

Yet some of its key wildlife face pressure from habitat destruction and poaching. No more than 7,000 snow leopards remain in the wild, and 90 percent of all Tibetan antelope, or chiru, have been wiped out over the past century. Shawls woven from their wool, known as shahtoosh, are a coveted accessory in Europe, where they can sell for as much as $20,000 on the black market. Now only about 100,000 to 150,000 chiru can be found on the Tibetan Plateau.

Equally ominous, climate change is melting whole swaths of Sanjiangyuan at an alarming rate. A government report published in 2015 estimates that more than 80 percent of the region’s permafrost could disappear by the end of this century, releasing large amounts of carbon as it thaws and accelerating global warming.

“What everybody hopes is that the awakening China’s experiencing now ... continues,” says Dr. Daily, the Stanford professor and a pioneer of the natural capital movement. “There’s no guarantee that it will. It’s a huge experiment. No one has ever experienced this set of circumstances in the world before, with so many people pressing up against the very limits of Earth’s boundaries and life-support systems. Everybody also hopes that with China’s leadership, other countries will experience this awakening, too.”

Ouyang and his fellow planners, however, still face significant challenges. Earlier this summer, Chinese officials visited Yellowstone and the Grand Canyon for advice on how the US manages its parks. Doug Morris, another member of Global Parks who accompanied them for two weeks, says that while the trip was a useful guide for the Chinese, they will have to address some pressing problems. One is how to ensure that the tourism boom expected to come doesn’t endanger the parks’ ecosystems and wildlife.

“There’s a lot of worry that the parks will turn into amped-up Disneylands,” says Daily, echoing a concern mentioned by almost every researcher I interviewed. 

Then there’s the question of what will happen to the people who live in the areas designated to become parks. “Ecotourism is big business now,” Judith Shapiro, author of the book “China’s Environmental Challenges” and a professor at American University, says in an email. “Especially as the pollution in the developed eastern part of the country, and the rising disposable incomes of the middle and upper classes, have created a huge influx of Han tourists in vulnerable regions in the west.”

A contentious issue is whether the influx of outsiders will benefit local people. 

People like Gongson Zhuoma.

Early one morning at 3:30, Ms. Zhuoma and her sister-in-law wake up to milk their family’s yaks. They tie woolen aprons around their waists and put on heavy jackets and stocking caps before stepping outside their white tarpaulin tent into the cold, cloudless night. Each carries a five-gallon bucket for the work ahead.

The Milky Way is visible overhead as they start to make their way through the rows of yaks. By the time they finish three hours later, the sun is beginning to rise. The two women return to the tent to help Zhuoma’s mother churn butter by hand. Once that work is over, they head back outside to shovel dung into large piles, which will be used to fuel the stove. It is their morning routine, one they repeat day after day. 

Zhuoma and her family live in the far western reaches of Sanjiangyuan, a half day’s drive from the headwaters of the Yangtze and just east of a biodiverse region known as Hoh Xil or Kekexili. Out here the Tibetan Plateau reaches more than 15,000 feet above sea level. Windswept grasslands extend for miles in every direction. Some call it “no man’s land,” but for Zhuoma and her family, it’s been their home for generations. “It’s a hard life,” says her husband, Ciren Gongbu. “But it’s the only life we’ve known. We don’t want to move.” Despite his insistence, he knows that the Chinese government might not give them a choice. 

Hundreds of thousands of nomadic herders across the Tibetan Plateau have been relocated into drab townships – so-called New Socialist Villages – over the past two decades. The “Ecological Relocation” program, launched in 2003, has focused on reclaiming the region’s fading grasslands by curbing animal grazing, but critics say its main purpose is to give the Chinese government greater control over people on the margins of Chinese society.

“Chinese authorities are coming to this issue with very set preconceived notions about what development means to Tibetans,” says Bhuchung Tsering, vice president of the International Campaign for Tibet, a Washington-based advocacy group critical of China. “They need to listen to local people. Otherwise it will be a tragic end to one of the unique features of Tibetan cultural life.”

The Chinese government, for its part, says the Sanjiangyuan National Park will create 17,000 jobs for local people. It has even promised to hire at least one member of each family as a park ranger. Yet the costs are considerable; more than 20,000 people live in the Yangtze area of the park alone. While many have relocated to prefab villages, others, like Zhuoma and her family, have no intention of leaving the land.

“We would lose our yaks and have nothing to eat,” says Rishan, Zhuoma’s father, who like many Tibetans uses a single name. “How would we make a living?”

For now, the government has allowed them to stay and pays Mr. Gongbu 1,800 yuan (about $265) a month to work as a ranger. His job is to keep a daily record of local animals and human activity, such as fishing and hunting, in an official-looking blue notebook, which he turns in to government officials a few times a year. 

Other nomadic families have been less fortunate. In a shabby concrete house in the town of Yuegaizhen, 170 miles east of Hoh Xil, Cichengji and his wife, Duoji Zhuoma, are despondent. They moved here in 2015 at the request of the government and in the hope of starting a better life. Things went well at first. Shortly after they arrived, Cichengji was hired as a park ranger. He didn’t mind the work: picking up trash and counting wild animals twice a month in a region of Sanjiangyuan. Then the paychecks stopped coming. He received his last one in December and is now running out of money.

“We called the government but no one answered,” he says, noting that he plans to quit if he doesn’t get paid by the end of the year. “We can’t live like this.” Cichengji says he wishes he could return to his life as a yak herder, but he reluctantly acknowledges that the government is unlikely to allow that. Instead, his backup plan is to work in construction. “It’s difficult to find work here,” he says “There’s nothing else I can do.” 

Sanjiangyuan isn’t the only national park location where the Chinese government faces the dilemma of what to do with local people. In the southwestern province of Sichuan, the provincial forestry department announced in March that 172,000 people would be relocated to make room for the giant panda park. Ouyang and his colleagues have recommended allowing people to stay in areas of the parks where they won’t threaten key ecosystem services. In cases when they do have to relocate, they’ve advised the government to provide long-term subsidies and support. It’s perhaps too early to tell how far the government will take their suggestions. 

But if what’s happening in Sanjiangyuan is any indication, relocations remain controversial.

I flew home to Beijing after seven days on the Tibetan Plateau. The sky was dark as I took a taxi to my apartment near the northeast corner of the third ring road. Beijing officially has six roads that circumnavigate the city in uneven concentric circles. 

A seventh unofficial ring road – unofficial because only 24 miles of it pass through Beijing – opened last December. By connecting 13 cities around the capital, this 620-mile expressway is part of the government’s plan to make Beijing the center of a new mega­city of 130 million people – more than one-third the population of the entire US. And all of this is happening in one of the most water-scarce corners of China (Beijing’s per capita water availability is on par with that of Saudi Arabia).

As I stared out the window at the endless layers of concrete, steel, and glass, I found it hard to imagine a place more different from Sanjiangyuan. Which is perhaps the point: nature as an antidote to the irrepressible presence of humans. Certainly that is one rationale behind America’s century-old experiment with national parks and, to a certain degree, behind China’s new experiment.

“Nature can exist without man, but man cannot exist without nature,” Ouyang told me earlier this summer. Did he mean that man can’t survive without nature solely because of the ecological services it provides, or because of something more profound – the enrichment of the spirit that Thoreau and Emerson and Roosevelt rhapsodized about? I went back to his office the day after I returned from Sanjiangyuan to ask him, and I left with the impression that he had meant what he said literally.

Still, the question lingers as to whether there is value in nature beyond that which can be measured by even the most advanced computer models and rigorous field studies.

As I contemplated this, I remembered one afternoon driving through Sanjiangyuan in a rented SUV when, out of nowhere, a sparrow flew into the windshield. It fluttered its wings for a brief moment, then died. The driver, a 22-year-old Tibetan man who had spent much of the previous hour singing along to Chinese pop music and 1990s American rap, suddenly became solemn. He turned off the car stereo, removed his wooden prayer beads from around his wrist, and started to pray.

Xie Yujuan contributed to this report.