Kate Humble and Patrick Aryee follow the changing seasons in one of Earth's harshest environments...

In the far north-west of the USA, the vast wilderness of Yellowstone National Park is home to some of North America’s most iconic animals, including grizzly bears and bison.

It’s a vitally important ecosystem, but tough to live in: temperatures range from -40°C in winter to +40°C in summer. Kate Humble and Patrick Aryee are in Yellowstone for this three-part documentary following 2016’s great thaw, when the unpredictable weather broke records.

Patrick witnesses how animals must adapt to survive a changing climate, while Kate joins scientists to learn more about the science of the thaw. Continues tomorrow.