It is one of the world's last great wildernesses, a 435-mile long peninsula of lakes and squelching tundra stretching deep into the Arctic Ocean. For 1,000 years the indigenous Nenets people have migrated along the Yamal peninsula. In summer they wander northwards, taking their reindeer with them, across a landscape of boggy ponds, rhododendron-like shrubs and wind-blasted birch trees. In winter they return southwards.

But this remote region of north-west Siberia is now under heavy threat from global warming. Traditionally the Nenets travel across the frozen Ob River in November and set up camp in the southern forests around Nadym. These days, though, this annual winter pilgrimage is delayed. Last year the Nenets, together with many thousands of reindeer, had to wait until late December when the ice was finally thick enough to cross.

"Our reindeer were hungry. There wasn't enough pasture," Jakov Japtik, a Nenets reindeer herder, told the Guardian. "The snow is melting sooner, quicker and faster than before. In spring it's difficult for the reindeer to pull the sledges. They get tired," Japtik said, speaking in his camp 25kms from Yar-Sale, the capital of Russia's Arctic Yamal-Nenets district.

Herders say that the peninsula's weather is increasingly unpredictable – with unseasonal snowstorms when the reindeer give birth in May, and milder longer autumns. In winter temperatures used to go down to -50C. Now they are typically -30C, according to Japtik. "Obviously we prefer -30C. But the changes aren't good for the reindeer and ultimately what

is good for the reindeer is good for us," he said, setting off on his sled to round up his itinerant reindeer herd.

Japtik lives on the tundra in a reindeer-skin tent or chum (ital) with his wife, mother, and three-year-old nephew Albert. There is also baby Pasha. The Japtiks live with three other families; the group has around 600 reindeer. The family slaughters a reindeer every couple of weeks, eating it raw and with pasta. They also catch fish – slicing off filets of sushi-like whitefish, taken from the thousands of virgin-lakes across the peninsula.

Here in one of the most remote parts of the planet there are clear signs the environment is under strain. Last year the Nenets arrived at a regular summer camping spot and discovered that half of their lake had disappeared. It had drained away after a landslide. While landslides can occur naturally, scientists say there is unmistakable evidence that Yamal's ancient permafrost is melting. The Nenets report other curious changes - fewer mosquitoes and a puzzling increase in gadflies.

"It's an indication of the global warming process, like the opening of the Arctic waters for shipping this summer," says Vladimir Tchouprov, Greenpeace Russia's energy unit head. The melting of Russia's permafrost could have catastrophic results for the world, Tchouprov says, by releasing billions of tonnes of carbon dioxide and the potent greenhouse gas methane, that was previously trapped in frozen soil.

Russia – the world's biggest country by geographical area - is already warming at one and a half times the rate of other parts of the world. If global temperatures do go up by the 4C many scientists fear, the impact on Russia would be disastrous. Much of Russia's northern region would be turned into impenetrable swamp. Houses in several Arctic towns are already badly subsiding.

Many Russians, however, are sceptical that climate change exists. Others rationalise that it might bring benefits to one of the world's coldest countries, freeing up a melting Arctic for oil and gas exploration, and extending the country's brief growing season. Russia's scientific community seems sceptical of global warming and the Kremlin doesn't appear to regard the issue as a major domestic problem; public awareness of climate change in Russia is lower than in any other European country.

Western politicians, however, point out that it is in Russia's interests to take action on climate change and to push for ambitious targets at December's Copenhagen summit. "There is 5,000 miles of railway track built on permafrost. It could crumble as a result of melting," Ed Miliband, the secretary of state for climate change, pointed out during a recent visit to Moscow.

However, even Russians working in the Arctic are unconvinced that their country faces a serious climate-change problem. "It's rubbish. It's invented. People who spend too long sitting at home have made up climate change," Alexander Chikmaryov, who runs a remote weather station on the Yamal peninsula, said, standing in his dilapidated station strewn with rusting engine parts and a broken-down wind turbine.

Chikmaryov lives in Marresale, an outpost on the Yamal peninsula's north-west coast overlooking the Kara Sea. A small community of Nenets hunters live nearby; otherwise there's nobody for a hundred kilometres. The weather here is, not surprisingly, bitterly cold; the sea freezes nine months of the year. The word Yamal means "end of the world" in Nenets language, and in Marresale you see why.

In fact, Chikmaryov's own data suggests that global warming is a real problem here too. In 2008 the ice was 164cm thick; this year it is 117cm. Winter temperatures have gone up too – from lows of -50C in 1914, when the station was founded, to -40C today. Every year large chunks of the coast on which the station is precariously perched fall into the sea. On the beach there is a jagged layer of thawing permafrost.

And there are other unnatural signs. On 15 August a large polar bear ambled into Marresale and started rooting through the station's rubbish bin. "It was 7pm. The bear was enormous. We set off a flare. It ran off," she recalled. Polar bear sightings are becoming increasingly common – with the bears apparently venturing south from their far-northern habitat in search of food. "They are an impudent lot. They aren't afraid of humans," Ludmilla says, gleefully recalling how one polar bear ripped the scalp from a Russian scientist living on Franz Josef Land.

Back on the tundra Japitik was rounding up his reindeer. Some were already back at the camp; their munching resembled the soft clicking of a thousand knitting needles. "I've lived all of my life in the tundra," he said.

"The reindeer for us are everything – food, transport and accommodation. The only thing I hope is that we will be able to carry on with this life."