It's been a race against time to bring in the reindeer from their mountain summer grazing ground, but today Per-Martin Kuhmunen, a 39-year-old Sami herder is triumphant.

"We brought them in today," he grins as he and two other members of the Gabna herding district sit exhausted, bruised and battered, in a cabin on the outskirts of the village of Abisko in the far-northern corner of Swedish Lapland.

The herders, like those from other districts across Sweden, have this year been forced to bring their 6,500 reindeer in from their mountain pastures a month earlier than normal, after unusually early and heavy snowfall linked to climate change meant their animals could not find food.

"The problem comes when the ground is still warm," explains Tomas Svonni, the district's chairman. "When you get snow on warm ground, you get ice at the bottom, and the food which the reindeer eat becomes frozen."

Inside the cabin, there's a fug of sweat, wet clothes and boiled reindeer meat. Parked outside are the snowmobiles, day-glo lassos hanging from the handlebars, on which the men have spent four days ranging over the slopes in search of their animals.

Christer Johansson is busy sawing and screwing planks in darkness, even though it's only the early afternoon. He is racing to finish the complex arrangement of wooden pens where the deer will be separated by owner over the coming days.