The weather in Mongolia is a constant presence – cruel, beautiful and extreme. Climatically, the country belongs to the category known as ‘harsh continental’. In Ulanbataar, the world’s coldest capital, the temperature can drop as low as minus forty-five degrees Celsius. There are places in the country, and not just in the Gobi desert, where you can experience a temperature range of thirty-seven degrees Celsius in a single day. Winds race across the treeless steppes like an invading horde, cruel and sudden and full of face-lashing grit. They are either very cold or very hot or very dry.

But Mongolia also has one of the sunniest of the world’s climates. On average, it receives more than eight hours of cloudless sun every day. Far from the influence of the oceans, blocs of intense high pressure build up over the country, particularly in winter. Unhindered by cloud cover, the land’s residual warmth disappears into the atmosphere. It is an atmosphere almost entirely without humidity, leaving the sky so blue that if you fired an arrow up into it, you would get the sense that it might just stick there.

Blue is everywhere in Mongolia. The flags that fly at ovoos, the cairns erected to propitiate the spirits of significant places, are blue. In the herds, you can often spot certain animals with blue tags tied around their necks. Khatags are the blue scarves sold at monasteries, presented to the various representations of the Buddha or used for more earthly purposes, draped over the tops of televisions in Ulanbataar’s apartments, or stuffed for protection inside the windscreens of cars – it is the few metalled roads around the capital that are most dangerous; as they are increasing, so are the fatalities. And the supreme presence in the traditional Mongolian pantheon is blue. Even after a savage half-century of Stalinist repression, even after a half-millennium of imported Buddhist rites, Mongolians have never really relinquished the animistic reverence in which they hold Kokh Mongke Tenger, the Blue Eternal Sky.

For me it began as an indulgence. During a desk-bound year writing fiction, I developed a hankering for wide open spaces, landscape, movement, physical exhaustion at the end of the day — in short, a ride across the Mongolian steppe. But such formless impulses have a habit of taking on their own shape. I began to read. I read about the timeless habits of Mongolian pastoralists, about the country’s recent history which during most of the twentieth century had mirrored that of its parent state, the Soviet Union. I read about the chaos of the 1990s — the same pattern of unemployment, insecurity and inflation that had dogged all those living between Belgrade and Vladivostok. And I read too about the enduring, poetic world of Mongolian belief.

The Mongolians’ cosmology expresses both the extreme severity of the environment and their absolute dependence on its forces. Thus the word for ‘god’, ‘sky’ and ‘weather’ is the same – tenger. Beneath the Kokh Mongke Tenger, the Blue Eternal Sky, are ninety-nine lesser tenger who each control an important aspect of the herding life. They include the tenger of heroes, tenger riding on the clouds, cattle tenger, eggs tenger, billy goat tenger, tenger who increases the fruits of the field and tenger who makes the rain fall. If there is a moral aspect to the traditional Mongolian belief system, it has to do with tegsh or ‘balance’. Misfortune arises from imbalance – whether for an individual, a group, a herd or within the wider environment. As to restoring it, the use of a blue scarf can help, as can a visit to a holy mountain, or to an ovoo. In extreme circumstances, a shaman can be called on to intercede.

In the spring of 2001, I noticed reports from Mongolia in the British press: ‘White-outs threaten Mongolia’s herds . . . Snowstorms play havoc with Mongolian Pastoralists.’ The reports talked of the zud – the winter famine – and were invariably illustrated with a foreshortened picture of a dead animal, stretched out on the steppe; the unseasonal covering of snow had prevented it from feeding.

In Mongolian lore, winter lasts precisely eighty-one days: nine periods of nine days, each signified by particular conditions (first nine, the drink koumiss congeals; second nine, arak congeals; third nine, tail of three-year-old yak freezes; fourth nine, horns of four-year-old yak freeze, etc.). But recently this pattern has been disturbed. The weather in Mongolia is changing. The rains in summer are lighter. The permafrost is melting. Spring is capricious. Violent weather has become more frequent and more widespread. Heavy snow is now falling as early as September. Zuds – traditionally a three-times-a-century occurrence – are now disturbingly regular. Every March great dust storms sweep south over China. A couple of years ago they affected 130 million people; at times the air was so clogged with Mongolian dust that the people of Beijing found themselves wandering blind through it.

Few other places on earth retain such an ancient way of life over so wide an area, and one so precariously sensitive to the weather. Of course, the threats to Mongolia’s herders are not just climatic. The country has been thrown out of sync by the withdrawal of Soviet support. But the change in weather is emblematic of a more general malaise, a sense that something is not quite right, that tegsh has been damaged in some profound way.

In May, I contacted Graham Taylor, an Australian whose lone five-month ride through Mongolia a few years earlier had had such an effect on him that he stayed on. He set up a tour company in Ulanbataar and called it Karakorum Expeditions. I emailed him: could he provide me with a guide?

‘Sure,’ he replied. ‘No worries.’

So, after an all-night flight from Moscow, I stumbled into the arrivals hall of Buyant-Ukhaa International Airport and spotted a handwritten cardboard sign: philip madsed. Behind it was a tall, lithe-looking figure who smiled when he saw me. It was a charming smile, one that I came to know as characteristic of him, a smile that made his eyes disappear completely.

Narmandakh Baatarjambyn was twenty-four. He had been born and brought up in Ulanbataar. He had spent his childhood summers, like many young urban Mongolians, with his grandparents, helping out with the herds and living in gers, the white, conical-roofed tents that dot Mongolia’s steppe. He was now studying tourism at Ulanbataar’s university. He had a wife called Lkhagwadelger and a three-month-old son called Dulguun. Over the coming weeks he proved the best of companions – good-natured, competent and with an infectious love for Mongolia’s wilder places. With people like him, I thought, Mongolia’s future was brighter than it appeared. It was only a week since he had contacted Graham Taylor for the first time, looking for work – and here it was, stumbling into the airport, shaking his hand.

He took me straight to the market where I bought three saddles (a Mongolian saddle, a pack saddle and a Russian cavalry saddle), three hobbles, three stakes, fifteen metres of leather strap, a quantity of food, and a silver bridle studded with tiny pieces of turquoise.

Next we called in on the National Agency of Meteorology, Hydrology and Environment Monitoring. The director sat in an office trailing with flowering succulents. Every day he received a mass of information from meteorological stations around the country. But when I started to ask him about the changes in Mongolia’s weather, he held up his hands.

‘Excuse me – but everything is in here,’ he explained, patting the cover of the agency’s own book. When we left him he was watering the roots of his plants with a miniature watering can. I took the book back to my hotel.

Climate Change and its Impact in Mongolia makes disturbing reading. No single statistic dominates the picture but each detail contributes to an alarming overall impression. For every degree that the temperature rises, water resources decline by up to six per cent; this reduces the pasture land, pushes herds into a smaller area and results in further overgrazing. Meanwhile the desert is projected to grow by more than three times in the next fifty years, by which time nitrogen levels in the grasslands will have diminished by sixteen per cent and permafrost will be less than half what it is now. The shrinking of the permafrost will convert good pasture into marsh. It will also undermine the foundations of roads, bridges and the high-rise apartment blocks that ring the skyline of Ulanbataar.

Seventy per cent of Mongolia’s grassland is already overgrazed, one third of the country’s water resources is deemed ‘highly vulnerable’. The production of fodder has diminished by two thirds since the withdrawal of Soviet support fifteen years ago; in the same period the number of livestock has increased from twenty-five million to thirty-two million. It is also estimated that by 2020, Mongolia’s human population will have doubled to five or six million, thereby placing a greater strain on her natural resources.

The province of Dzavhan, to the west of Ulanbataar, had been particularly hard hit by the winter’s zud. Its herders had lost about twenty-three per cent of their livestock. That evening, fresh from the state department store, Narmandakh arrived with a map of Zavkhan. We traced a route east from Uliastay, the capital of Zavkhan, up across the mountains and into the neighbouring province of Arhangay. The shading darkened across the spine of the Khangai mountains and at one point was dabbed with white – the peak of Otogen Tenger.

‘What does ‘otogen‘ mean?’ I asked.

‘Younger sister,’ he said. ‘A sacred mountain – the younger sister of the sky.’

The plane dropped through islands of thin, scattered cloud. A man was pointing through the window. ‘Look! Look!’

Rising from their seats, the passengers crowded the aisle to see – and for a moment, in its approach to Uliastay, the small plane wobbled. Between them, some fifty miles to the north, I glimpsed the snowcap of Otogen Tenger.

Sitting on my other side was a doctor. He was pointing through the window on his side. ‘Every year it gets closer.’ Beneath the bronze treeless hills, to the south, a tongue of desert sand was stretching towards Uliastay.

The weather station for Zavkhan was at Uliastay’s airport – a low, concrete building. Most of the rooms were empty. The director was not there but we did manage to reach him on a crackly phone.

‘Zavkhan? Yes, we are one of the coldest places in the world . . . also we have one of the highest barometric pressures,’ he said proudly. ‘Over the last fifty years average January temperature is minus forty-two C . . . last ten years it has dropped by one or two degrees . . . rainfall has been falling also . . . the Gobi is now only forty miles away –’ Then the crackles took over and he was gone.

Uliastay was a two-horse town and neither of them was for sale. So we took a jeep and followed the course of the Bogd river up into the mountains. Three times we stopped at clusters gers – but no one had horses to spare. In the end, the driver lost patience. He dumped us beside the river. ‘Maybe here you will find your horses.’ We watched him go. He turned back down the valley, the jeep disappearing into nothing before a pale parachute of dust. The wind soughed in the grass. A mile away was a group of gers. It was getting dark.

We collected dried dung and made a fire. After a meal of noodles we crawled into our tent and I rolled out my sleeping bag. ‘Where’s yours, Narmandakh?’

‘It’s okay.’

‘What do you mean? You’ll freeze!’

‘It is the Mongolian way. I have my del,’ he fingered his knee-length cloak, the serge uniform of the herders. ‘If I am to be a good guide, I must make myself tough.’

In the end, neither of us slept much. At about two, the wind freshened, the tent collapsed and we had to struggle out through billows of canvas. Low clouds were racing across the moon. The ground was cold underfoot but we were laughing as we fetched rocks from the river, re-erected the tent and weighed down its rim with the rocks.

‘Perhaps we fly in it!’ shouted Narmandakh above the noise of the wind. ‘Up to Otogen Tenger, like in a balloon!’

Word travels fast in these high valleys and at dawn a man rode up to the tent leading three horses. Two of the horses stood with their heads down. Ribs striped their sickly-looking flanks. The third was a lively bay gelding and when we tried to saddle him, he reared up and showed his teeth.

‘What do you think?’ I asked Narmandakh.

‘He is an angry horse.’

‘I can see that.’

‘An angry horse is good.’

‘Really?’

‘He is a good horse.’

‘Okay – we will take this one,’ I told the man. ‘But not these two.’

He looked at me sadly. ‘Please?’

‘No. They’re practically dead.’

‘I am getting married. I need to buy a flat in Ulanbaataar.’

I shook my head and we watched him hobble the horses – though it was hardly necessary – and ride off. He would collect them later, but now he was going to the Naadam Festival.

Staking our new gelding, we made our way over to the gers. There too they were preparing to go to the Naadam, the annual festival of Manly Sports. They were grooming a palomino, quiffing up his mane and tying it with a red ribbon. The family were champion herders. Three herding medals were nailed to the ger’s lintel, dated 1981, 1983, 1987 – the good years.

We sat in the ger and talked. We talked about the dry summer and the snowy winter. They had lost a good number of animals in the desert and when we asked if we could buy a horse, they said: ‘We are sorry – we have no horses to sell.’

So we walked back across the steppe to our tent, towards our mound of equipment and our one angry horse.

‘Don’t worry. Something will happen.’ Narmandakh smiled. His optimism was unfailing.

We lit the fire and made tea. Then came a distant, insect-like whine. A motorbike was bouncing towards us from the gers. Its rider had been sitting in the corner of the ger we had just visited.

‘I have made a decision,’ he said, propping his bike on its stand. ‘I will sell you my mare.’ She was his last horse. He was an accountant in Uliastay. His son was doing a teaching diploma and he needed money to pay the fees. In previous summers he had kept twenty horses and forty cows up here with his brother. That winter they had gone to the Gobi and the snow came early and the horses tried to eat but their muzzles had frozen and they died. He pointed across the river to a group of a dozen horses. ‘That is her, on the left.’

‘Aren’t you sad to sell her?’

‘Look – she is fat. In the autumn she might be stolen and killed for her meat. Then I would have nothing.’

In the early afternoon we left the main valley and headed south-east – towards Otogen Tenger. With only two horses, we loaded the mare with our equipment and Narmandakh and I took it in turns to ride the gelding.

Narmandakh was wearing a denim baseball hat, embroidered with the name shiva, and his pale-blue del with an orange sash belted around it. He looked around him. He began to sing. He sang a great deal during our journey. ‘It is the countryside,’ he said, ‘I cannot stop myself.’ He sang ‘The Beautiful Deer of Khangai’ and ‘The Tall Brown Horse’. He used to perform the songs in Japan where he had worked for a couple of summers.

‘The Japanese loved those songs. Too many come now to look at our land – they say that Japan is a very crowded place and they like to look at our empty steppe!’

We heard the riders long before we saw them, the beating of hoofs behind us and the dust and we climbed the slope to let them pass. Thirty horses and their child-jockeys galloping up towards the finishing line. Three races passed us by the time we reached the Naadam crowd, sitting on the grass at the head of the valley.

The wrestling had just begun. Dressed in boots, coloured trunks and ornamental sleeves, the participants lumbered out into the circle of spectators. They were big and bull-necked. Lips of fat spilled over their trunk tops. Before each bout, they performed a dance – the devekh, the eagle dance – and for a moment these two thugs, swaying and dipping with outstretched arms, seemed as weightless as steppe eagles.

It was already late afternoon when we left the Naadam to walk and ride the ten miles to Kokh Nuur, the Blue Lake. We ate a meal of bread and dried fruit and put up our tent in the dark.

In the morning the sun rose and filled the tent with its buttery glow. Narmandakh was still asleep in his del, head propped on his saddle in the Mongolian way. Outside it was very cold. I peeled away frosted socks from my frosted boots and walked out to the lakeside. For two miles the water stretched north, a flat sheet of grey in the morning sun. Smoke rose from a group of distant gers but otherwise nothing moved in that vast arena of mountains.

In the gers above the lake was a man named Baatar Tsimbingsereng. He was a young grandfather who lived with his extended family. Normally they spent the summer close to Uliastay but in recent years the number of other herders had forced them higher. They had a horse for sale, a light-stepping ginger mare.

‘Her mother was a very beautiful horse.’ Baatar patted her neck. ‘She had one blue eye and a white streak down her face and a walk like a limousine.’

She proved the best of our three horses. She never slipped or stumbled. She was the easiest to coax across girth-deep rivers, the easiest to lead through boulder fields, or down narrow cliff paths.

We closed the deal with Baatar in his ger with a bowl of tea. He spoke slowly: ‘We asked the lamas: “What can we do to stop the animals dying?” and they said you must choose one animal in each of the herds and tie a scarf on it and this animal must not be slaughtered, and as long as he lives the herd will have good luck.’

In September they had arrived on the edge of the Gobi desert. One morning they felt a blast of cold air from the north and saw the first spots of snow against the mountains. They had not even started wearing winter clothes. They lost half their horses within a couple of months, half their goats and sheep and every one of their yaks. But it was the black zud that did for them. The white zud was the blanket of snow and it didn’t last too long. Then the snow went and in its place was the black zud. The earth was black, he said, black as the night with not even a ‘foal’s hoof’ of grass to cover it.

Baatar looked out of the open door. ‘Yes, I know why it is. I have heard there is a big hole in the north and that is what is making it different. It is because of a big hole in the sky.’

Wherever you go in this half-continent of a country, you can walk into a ger and everything will be in exactly the same place – kitchen and food to the right, saddles to the left, the stove dead ahead. Beyond that, on the left, is the guest area and you must make your way there at once and drink the bowl of tea given to you. Even if you are a complete stranger, even if you have already placed your saddlebags inside the door for the night, only then might you attempt some sort of introduction.

As Mongolians worship the land and sky around them, so gers, their shelter against the climate, have become microcosms of these elements. At the apex is the tono, the smoke hole through which can be seen kokh tenger, blue sky. From there radiate uni or roof supports, painted orange to represent the rays of the sun (itself one of the eyes of the Father of Heaven, the other one being the moon). Because gers always face in the same direction, you can tell the time simply by seeing on which of the uni the sunlight is falling. When the country’s holiest statue, the enormous bronze Migjed Janraisig in Ulan Baatar’s Gandan monastery, was recently rebuilt – the original was smelted down for arms during the 1937 purge of the lamas – a ger, with its furniture, was placed inside it.

As the gers have come to represent the larger cosmos above, so the sky itself is seen as a great tent. The Milky Way is the seam while the other stars are light-holes in the canopy. Meteors occur when the gods open the tent to peep inside; winds come through gaps in the horizon, when the foot of the tent is not completely fixed to the ground.

Anyone who sees the gers and spends enough time with the herders to witness just a little of their harsh nomadic life, comes away astonished by their toughness, their ability to live without superfluous possessions let alone luxuries. But the herders’ way of life is not as robust as it seems. They have been unable to develop the Darwinian virtue of adaptability. Shift the tent poles of their life, shift any of the parameters on which they depend, and these often heroic pastoralists look distinctly exposed.

That evening, Narmandakh and I took the new mare and the gelding up to the local ovoo. Baatar stood with his back to the lake and raised his arm. ‘Follow that slope and you will see it, on top of the hill.’

Shortly below the top, we hobbled the horses and continued on foot to the shrine. The summit was flat and broad, a field of frost-shattered rock. Each slab wobbled as we stepped on it, and let out a hollow knocking sound. The ovoo itself was a pile of stones and several ragged blue khatags. Broken vodka bottles lay between the rocks.

It was dusk. Muddy-brown cloud had brought the day to a premature end. A cold wind brushed at our ears. As we turned back, I saw something moving.

‘Look!’ I pointed.

‘What is it?’ asked Narmandakh.

‘I don’t know. Maybe a dog.’ It was already gone.

But it wasn’t a dog. When it reappeared there were others, five of them, five wolves padding across the rocks. One of them stopped suddenly and looked at us.