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Climate and the Khan

A fortuitous shift in weather patterns fueled the Mongol Empire's explosive growth 800 years ago. But will a less favorable change, currently underway, result in catastrophe?

By Russ Juskalian
May 28, 2015 5:00 AMJun 15, 2023 7:51 PM
Inside the park’s boundaries, a fence protects a study plot of thriving native grasses (left) as skyscrapers loom above the ger slums of Ulaanbaatar (right). | Russ Juskalian


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Dense clouds suffocate the sky over Mongolia’s Khangai mountain range, and Amy Hessl, by her own admission, is about to cry. She sprawls on the dry, scrubby ground, defeated. As the temperature drops on this early June day and the clouds give way to icy raindrops, all Hessl can mutter is, “I feel sick.”

Hessl, a geographer from West Virginia University, studies tree rings for what they can tell us about climate and past environments. She’s come to Mongolia to investigate one of history’s most enduring puzzles: how Genghis Khan set forth from such an inhospitable place to beget the largest contiguous land empire the world has ever known. Her team, working to unearth this ancient mystery, has found clues of another climate-driven transformation — one that’s still underway. It’s a tale in which herders and nomads are streaming to urban centers while resources are being exploited without long-term environmental planning, and people, individually and as a society, have no choice but to adapt.

In the past 75 years, Mongolia’s temperature has increased more than 2 degrees Celsius, more than twice the global average, and its weather has changed in curious and counterintuitive ways. The country is like a petri dish in which we can see the complex interplay of social, environmental and economic challenges the rest of the world will be dealing with in the coming decades.

On this blustery June day, for Hessl to continue her scientific sleuthing, she needs access to a specific sort of research site, one where trees that died hundreds of years ago have been preserved without rotting or insect infestation. In Mongolia, that means one thing: old lava fields. After two days and about 200 miles of rough travel, the location Hessl chose is tantalizingly close. But there’s a problem.

The expedition’s drivers say the washed-out track between the team and the site is risky in good weather, and impassable when glazed with ice — a real possibility in the freezing rain. Hessl despairs that a year of planning and a huge outlay of money — $30,000 in travel expenses alone — will have been for nothing if she’s forced to turn back now.

Hessl has to make a choice, and fast, to save the expedition. She decides that her target destination, so close, will have to wait another year. Instead, they will travel to Khorgo, a lava field her team has visited in the past. It’s on the far side of the mountain range, more than 10 hours away, but it will allow them to make the most of what’s left of a two-week research window. Vodka is ceremoniously offered to the elements for protection, and we’re on our way again.

Nature Set the Table

According to legend, Temujin — the man who would become Genghis Khan — was born around 1162, to a woman his nomadic father kidnapped from another tribe. After his father’s murder by rivals, and lean years of exile subsisting on scavenged food and steppe rats, Temujin began climbing the tribal ladder with a cunning strategy: He paired pragmatic alliance-making with unbridled use of force. In 1206, he conquered the nomadic tribes of the steppe and became Genghis Khan (or Chinggis Khaan, as Mongolians transliterate the title), great leader of the nascent Mongol Empire. He then led his relatively small force of mounted archers east to China and west to the Caspian Sea in a conquest of unmatched velocity. Before his death in 1227, Genghis had built an empire eclipsing that of Rome — and in a fraction of the time.

Horses were the dynamo of Genghis’ army. The animals provided speed and agility in fighting, transportation for people, dried dung for heating fuel and nourishment in the form of milk and meat. But researchers have long sought to understand not only the pace of Genghis’ conquest, but that it happened at all. The Mongolia of the late 12th century, when he began his meteoric rise, was engulfed in drought. It was an unlikely starting point for a horse-based campaign of world domination.

Genghis, a follower of the shamanistic belief known as Tengrism, credited his success to the Eternal Blue Sky. And as it turns out, he may have been right.

Research by Hessl and others has revealed Genghis happened to be the right man in the right place at the right time. His conquest coincided with the most consistently wet — and likely resource rich — period in Mongolia in more than a thousand years.

“Nature set the table, and Genghis Khan came to eat,” says Hessl.

In the summer of 2010, Hessl and her colleague Neil Pederson, a forest ecologist then working at the Lamont-Doherty Earth Observatory of Columbia University, were in Mongolia sampling larch trees. Using dendrochronology — analyzing tree rings to date past events — the team was building a record of regional fires and droughts going back about 650 years.

They spotted some Siberian pines in an area where they’d only ever seen larch. The researchers took more than a dozen samples of the pines, both living and long dead. “We really had no idea what we were doing,” Hessl says. Pederson had a similar reaction. “In the back of my mind, it was just like, ‘This is cool. I can’t wait to work these up later,’ ” he says.

Pederson finally got around to taking a closer look at the slices of dead pine months later. He put a cross-section of the sample KLP0010 under a scope and watched as its fine lines came into focus. He saw many more tree rings than expected. KLP0010 was old — really old.

For a place like Mongolia, where historical records are scarce, the significance of the discovery was immense. In a hasty, sloppily enthusiastic email to Hessl, Pederson couldn’t contain himself:

“yes, i can see the yr Chinggis was born. i can see the yr he died. i can see the yrs Mongolia rose to rule Asia!”

Pederson knew the team’s research was about to change. If they could collect enough samples, they’d be among the first scientists to find local evidence of the climate’s ebb and flow during Genghis’ time. The tree rings would hold secrets about weather, moisture and productivity in the patterns of their growth. The first trip back to Khorgo, in 2012, found evidence of the wet period, or pluvial, that Genghis rode to fame. The next expedition, in summer 2014, would confirm it.

Location, Location, Location

The team was in better spirits when we finally reached the lava field at Khorgo, the site hastily chosen as a backup after the weather drowned our initial plans. The next morning was cold but cloudless, and as we walked through sparse, boot-high grass, the dried earth crunched with each step. After a few minutes, the terrain gave way to dusty, black, pockmarked volcanic rock. I spotted a sun-bleached skull. “Sometimes, horses wander in and get lost,” says one of the Mongolian scientists. “Some die.”

Location is the key to using trees to determine an annual record of soil moisture. You want to be at the edge of a species’s range where, in Hessl’s words, the trees are “very stressed, very unhappy, depressed” and therefore likely to respond to changes in water balance. The concept grew out of Liebig’s law, a centuries-old principle in agriculture: Growth is regulated not by total resources, but on the availability of the resource that is the most scarce. Where the limiting resource for growth is moisture, the drier years will produce exceedingly narrow growth rings — less than a tenth of the thickness of a sheet of paper — and the wetter years will produce fatter ones.

Dendrochronologists can construct thousand-year histories using trees that, individually, may have lived only a fraction of that time. As Hessl puts it, it’s as if the trees are all listening to the same song of the climate, recording the tune in tiny, concentric rings of cellulose. Where the music overlaps, two trees were alive at the same time. Beginning with cores from live trees, the researchers can reconstruct the climate record in reverse, all the way back to the lifetime of trees now long dead.

At the Khorgo site, Hessl was searching for the oldest possible specimens to strengthen the data from the time of Genghis Khan, and to push the record back even further for a more complete understanding of the area’s climate patterns. Her team hunted for the signs of a promising candidate: a gray, weathered trunk, no bark and few remaining branches.

As we walked the lava field over the next few days, Hessl explained that a colleague’s computer models showed how a wet period would have resulted in highly productive grasslands and healthy livestock — crucial to Genghis’ ability to mount a long-term campaign across the expansive Eurasian steppe. Perhaps he even interpreted a favorable turn in the climate, around the year 1211, as proof that the Eternal Blue Sky chose him to conquer the world. Nicola Di Cosmo, a historian collaborating with Hessl, later told me that wetter, milder conditions than the previous decades of drought would have given Genghis and his army significant advantages, including a constant supply of horses, increased agricultural production and other resources needed to support a centralized government and large military.

On my last day with the team, I joined a Mongolian forestry graduate student named Badar-Uugan as he wielded a chain saw to cut samples. A few days earlier, Badar-Uugan’s father, who lived 20 minutes down the road in the dusty town of Tariat, told us that small bodies of water, including the one at the bottom of Khorgo’s volcanic crater, had been disappearing over the past few decades. I asked Badar-Uugan if he had observed the same things. “The amount of rain is the same,” he tells me. “But the biggest difference is the variability. We used to get more consistent precipitation, but now it rains all at once, and then maybe it won’t rain for another month or two.”

Late that afternoon, as Hessl sat on the black rocks and stretched her bad back, she told me she’d seen something foreboding in the climate record. As Mongolia warmed during the 20th century, it experienced some wet years, similar to those during the early 13th century.

Instead of the rise of a khan, this modern pluvial overlapped with the country’s transition from Soviet satellite to market economy. Livestock capacity exploded, and herding shifted from traditional yaks and sheep to more voracious goats, valued for their cashmere.

But in 1999, “the bottom dropped out,” Hessl says. The next 10 years were marked by drought, massive herding losses, rapid soil degradation and wave after wave of nomads migrating to the capital of Ulaanbaatar. Here’s the scary part: If the late 20th century pluvial turns out to be an anomaly — and it looks like it might — decades of expansion were built on a new normal that was anything but. Mongolia’s struggles could be just getting started.

Back to the Future?

The next morning, I caught a 14-hour bus ride to UB, as locals often call Ulaanbaatar, and passed the time watching the parched steppe with new eyes. I saw patches of grassland turned sandy and beachlike, and huge curtains of dust raised by strong winds. In UB’s modern core, Chinggis Khaan Square, children zipped around on toy electric cars amid a profusion of hipsters. Depictions of the khan were everywhere, on dozens of bottles of vodka, on the steps of the Government Palace, on signage for banks and the Grand Khaan Irish Pub.

I rushed to the National University to catch the end of a talk by Clyde Goulden on the country’s changing climate. Goulden is something of a superstar here. The American scientist, now in his 70s, has conducted climate research in Mongolia for 20 years. He was recently awarded the highest honor the country gives to foreigners, the Order of the Polar Star.

As Goulden parsed meteorological records and the results of more than 100 interviews he and his Mongolian wife, Tuya, had conducted with nomadic herders in the northern provinces of Hovsgol and Khentii, he paused and apologized to the audience: “I’m sorry to bring all this depressing news to you.”

The herders, Goulden says, were so distressed by the growing unpredictability of the weather that many had talked about giving up. They spoke of hot days “burning” the grass, winds scouring the soil and rapidly fluctuating temperatures.

Just as Inuit dialects have many ways to describe snow, modern Mongolian puts an emphasis on describing nuances in rainfall. For a herder in a dry country, survival depends on the rains. According to Goulden, nearly 98 percent of the herders said that lighter, longer rains — shivree, namiraa and zuser — were increasingly being replaced by shorter, high-intensity rains called aadar.

Instead of a drizzle that would last for days and be slowly absorbed by the steppe grasses, the same amount of rain was falling in 20 or 30 minutes. Aadar was problematic, the herders told Goulden, because its intense precipitation fell on small areas, eroding the soil and spilling off the steppe faster than it could be absorbed.

Outside Hustai National Park, a woman milks cows in a buffer zone where reduced rainfall and overgrazing have desertifed the land. | Russ Juskalian

After the talk, Goulden told me his research had implications far beyond the steppe lands.

“I want to know what it’s like,” he says, “to see what happens in Philadelphia when it warms 2 degrees Celsius, or in Kansas, where I grew up.” We might learn from Mongolia’s effort to adapt to its environmental challenges, he says.

So far, the lesson is a cautionary one. Since Mongolia’s democratic revolution in 1990, the country’s livestock numbers have more than doubled, intensifying environmental stress. More than 70 percent of Mongolia’s land is already degraded. In a dangerous feedback loop exacerbated by overgrazing and poor resource management, whole regions are losing biodiversity. Soil is releasing stored carbon dioxide and beginning to desertify. Destabilizing forces of poverty and large environmentally aggravated migrations are rising.

According to UNICEF, up to 70,000 herders can flee unproductive lands in particularly difficult years in Mongolia. Almost all head, permanently, to UB’s interconnected slums. From the air, the city’s so-called ger district looks a lot like a plant under a microscope. Each small, wooden-walled plot of land, like a cell, butts up against its neighbor, with a white ger — the traditional wood and felt tent of nomadic Mongolians — at its nucleus. More than simply a district, its 750,000 residents represent about 60 percent of the capital’s population, and more than a quarter of the entire country. The shantytown’s concentric bands of humanity can be read in the same way scientists like Hessl read the rings of a pine tree. Instead of moisture, the district’s onion-like growth measures the movement of people in response to ecological breakdown.

Genghis Khan’s face has become a marketing gimmick for everything, even vodka, as Mongolia moves further from its nomadic roots. | Russ Juskalian

As one travels away from the city’s core, the ratio of gers to more permanent structures increases. About 6 miles northeast of downtown UB, the city runs out, and beyond the last wooden fence there is nothing but steppe and mountains and desert. It was here where I saw 62-year-old Dolgorsuren Chimeddulam stacking dried dung to fuel her stove.

Chimeddulam erected her ger the month before in this narrow, treeless valley, framed by a dump on one side and a cemetery one ridge over. She squinted her weathered face and waved me inside. Chimeddulam had hunched shoulders, and she wore rubber shower sandals, a bright turquoise headscarf decorated with images of flowers and a burgundy deel — the traditional neck-to-ankle tunic that Mongolians have donned for centuries — embroidered with geometric designs and detailed with gold thread. Inside her ger were a few painted dressers, a frame filled with photos and a small shrine.

Chimeddulam offered me candy from a bowl and apologized for not being able to pour me a cup of salty milk tea, a staple of nearly every guest-host interaction in the country. “I lost my livestock in the dzud,” she says, by way of explanation. “I lost them all.”

If you ask five people to define dzud, you’re likely to get five answers. Most describe a brutal winter or spring storm in which the temperature plummets as low as minus 40 degrees Fahrenheit, fodder is inaccessible and animals die en masse. Herders will tell you dzud starts earlier, with a summer drought that prevents animals from thriving. Others, like Hessl and researchers at the World Bank, refer to a social component — a sort of collective narrative of hardship and loss that reifies the dzud as a national phenomenon. It’s unclear whether dzud can be linked to climate change. What is clear is that overworked grasslands and worsening weather conditions are making dzud harder to mitigate.

For Chimeddulam, the calamity meant the loss of wealth, income and lifestyle. Without animals, she had no milk for her tea, and nothing to sell. So she traveled more than 200 miles to the capital — one of the city’s latest arrivals, judging by her spot on its outskirts. As I talked to other residents of the district, I heard Chimeddulam’s story repeated with slight variations:

“The grass used to be tall, up to my waist, you could get lost in it.”

“The rain used to be regular and predictable, but now it’s confused.”

“The soil never used to blow away in the wind.”

“My animals died, and I have nothing left.”

Losing Ground

Most people visit Hustai National Park — an expanse of more than 123,000 acres about 90 minutes west of UB — to see the takhi, or Przewalski’s horse, the last truly wild horse left on the planet. But after hearing about the changes to Mongolia’s steppe, I came to stare at the ground with Tserendulam Tseren-ochir, a biologist studying grassland degradation and recovery.

The rolling hills surrounding the park were covered in greenish-gray vegetation. “Artemisia and Carex dominate this area,” Tserendulam says, referring to the plants in a buffer zone between the unprotected steppe and the sanctuary of the park. “That is a sign of degradation,” she explains. Overgrazing has led to imbalance: Some native plants thrive while others diminish.

Nearby, a fenced plot of meter-high, flaxen grasses looked like something from the American plains. The fencing, built a decade ago, was a simple experiment to keep out grazing animals and allow biologists to study the undisturbed area. Carex and Artemisia still grew inside the fence, but the species balance was healthier; native grasses, preferred by livestock, were able to compete when allowed to grow to full height.

Tserendulam led me to the center of the park, where clumps of native grasses, like Stipa krylovii and Achnatherum splendis, were healthier and more abundant, no fencing required. But even here, the changing climate was having an impact. Over the past 15 years, Tserendulam says, streams that were once consistently wet often flowed only after a storm, erosion was accelerating, and some plants were blossoming at different times than in the past.

On the far side of the park, along a buffer zone near the Tuul River, we stopped at a lone ger. A young couple inside served us milk tea and heaping bowls of homemade noodles with chunks of mutton and fat. Thick vegetation grew next to the riverbank, but the land by the ger was in rough shape. Even species that thrived in areas of moderate degradation were struggling to survive here — a sign of impending desertification.

“Look, this is Carex,” Tserendulam says, crouching to measure a stalk with her finger. “It is normally 8 to 10 centimeters, but here it is only 1 to 2 centimeters. When it is totally degraded, it will be almost all just dust.” It was still possible to reverse the damage, she says, but recovery would take decades. Back in the park, a plot of land similarly degraded more than 20 years ago still hadn’t returned to full health.

By the time I returned to UB the next morning, Hessl had emerged from the field with about 140 new tree ring samples. We met over a beer to discuss the parallels between Genghis’ time and our own. Earlier, Hessl had told me that the two periods were, in broad ways, “mirror images of one another”— each marked by changing climate, urbanization and societal reorganization. Now, sitting among UB’s rising middle class, she warned against interpreting her findings in an environmentally deterministic way. The climate did not make the khan; the khan made use of the climate.

Later that evening, I took an elevator to the top of Mongolia’s tallest building. Peering out past the glass, I could see the twinkling lights of the new Mongolia in the square below, and further beyond that, the faint outlines of the old Mongolia on the dark hillsides of the ger district. I thought about Chimeddulam without her milk tea, and the trees recording the climate’s tune, and Genghis Khan’s remarkable insight to break from tradition when it no longer served him and seize a new opportunity served up by nature.

The climate may not pick winners and losers, as Hessl said. But in her tree rings is ample evidence that a changing climate can shift our story, creating a set of conditions that we can adapt to and take advantage of in order to thrive. Or ignore, to our detriment.

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