They lived through the ice age. Can the mighty musk ox survive the heat?

Rising temperatures are pushing these Arctic mammals ever farther into Greenland's north. But eventually there will be nowhere left for them to go

Built like a small bison, weighing as much as a grand piano and covered in thick, shaggy coat, the musk ox is one of the most distinctive species in the high Arctic. But from a hill on Greenland's tundra, they seem impossible to find.

Each bush, rock and clump of grass resembles a mass of wool and horns in the blustery chill on the edge of the island's enormous polar ice cap. Scanning the shimmering landscape with binoculars, Chris Sorensen looks for signs of movement.