The railway to Tibet is one of the greatest symbols of that spirit. Since it was built in 1984, the route from Xining, the provincial capital of Qinghai Province, to Golmud, the garrison town in China's wild west, has been the train to nowhere. No one, it was believed, could build a line any further across the Qinghai plateau, certainly not one all the way to Tibet. It was too bleak, too cold, too high, too oxygen starved. Even the best Swiss tunneling engineers concluded that it was impossible to bore through the rock and ice of the Kunlun mountain range.

If that were not enough, even the flats were filled with perils. A meter or so below the surface was a thick layer of permafrost; above this, a layer of ice that melts and refreezes with the seasons and the rising and setting of the sun. How could anyone build a track on that? And how could a regular service be run in an area plagued by sandstorms in the summer and blizzards in the winter?

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Soon after leaving Golmud, we hit the start of the Kunlun range. The craggy slopes on either side are so steep and barren that it is like driving through an alien planet. This is where engineers started blasting and building the first of the seven tunnels and 286 bridges on the 1,110-kilometer-long stretch of new line. At its maximum altitude in the Tanggula Pass, the track runs 5,072 meters above sea level -- higher than Europe's greatest peak, Mont Blanc, and more than 200 meters higher than the Peruvian railway in the Andes, which was previously the world's most elevated track. The longest tunnel -- at Yangbajin -- stretches 3.3 kilometers. The longest bridge spans 11.7 kilometers over the Qingsui River.

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From Xidatan, the railway climbs steadily toward Kunlun Pass (4,776 meters). This is one of the great doorways to the top of the world. It is also the northern shore of a vast sea of permafrost that stretches more than 600 kilometers across the plateau toward Tibet and the Himalayas, prompting some to describe this area as the third pole of the world.

This barrier of ice and rock had been considered impassable, but China's scientists believe they have overcome the challenge. Their big technological breakthrough has been to insulate the track from the top level of ice, which thaws every summer day and freezes by night. On a normal line this would buckle the rails, collapse bridges and cave in tunnels. But for the new railway, engineers have pumped cooling agents into the ground so that the earth around the most vulnerable tunnels and pillars remains frozen and stable. It is not cheap. Largely because so much of the line has been built on viaducts rather than the semifrozen surface, the budget for the railway is 26.2 billion yuan ($3.24 billion).

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This is the dark and dirty side of China's development. Pan Yue, the deputy minister of the environment, says the Qinghai Plateau and the western region of China are so ecologically stressed that they can no longer support their current populations. Because there is not enough space for them all to be resettled quickly, he estimates that the country will soon have more than 150 million environmental refugees.

The problems are evident throughout the country. When the railway is finished, travelers on the train from Beijing to Lhasa will pass through some of the most polluted cities and overexploited farmlands in the world. Acid rain now falls on a third of the Chinese landmass. According to the World Bank, 16 of the planet's 20 worst polluted cities are in China.

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