American Arctic

The Arctic National Wildlife Refuge in Alaska has long protected survivors of the Ice Age, but this frozen fortress is melting due to climate change. For the caribou, musk oxen, polar bears and Arctic foxes, the Ice Age is slipping away.

Within hours of being born, a muskox calf is ready to start exploring. Meanwhile, its mother keeps a careful eye on her newborn. Muskoxen were hunted to extinction in Alaska by 1860 but were reintroduced in the 1930s. There are now a few thousand in the state.

The caribou migration is a veritable feast for grizzly bears — if the bears can catch them. Grizzlies hunt all the way to the Arctic Ocean in the summer, but caribou are faster than bears on the open plain.

A polar bear mother and her cubs search for scraps during a too-hot summer. In the Southern Beaufort Sea, there are only about half as many polar bears as there were 35 years ago. North Alaska has the largest oil field in America, and its effects can be seen in the changing landscape and climate.