Frozen Worlds showcases the variety of cold habitats on Earth, explores why they are cold, and examines the incredible ways in which animals have overcome the challenges of survival there.

In this episode we begin our journey in the frozen continent of Antarctica in the far south, the most hostile place on Earth. After being raised on the ice in winter, in spring emperor penguin chicks find themselves abandoned by their parents. To survive they must find their own way across the treacherous sea ice to the rich waters of the Southern Ocean.

The waters surrounding Antarctica may be the richest of all but they also home to the killer whale, an exceptionally sophisticated predator. To reach Weddell seals - their favoured prey - a family of killer whales have learnt to generate their own waves, washing the seals off their ice floes. ‘Wave-washing’ is a technique that has been passed down over generations and is coordinated by the family matriarch who can be over 100 years old.

Leaving Antarctica and traveling north, we discover frozen habitats that are created by altitude. The greatest of these is the Himalaya - the tallest mountain range on earth. It contains so much ice and snow it is known as the ‘third pole’. In the shadow of the Himalaya lies a vast frozen grassy plain that is home to the Pallas’s cat, also known as the grumpiest cat. It may have extremely dense fur but, if it’s to survive the Mongolian winter, it needs to catch lots of gerbils and voles. Easier said than done when you only have short legs and paws sensitive to the cold.

North of the Great Steppe lies the boreal forest which encircles the continents of North America, Europe and Asia and remains frozen for six months of the year. Prowling these forests in the Far East of Russia is the Siberian tiger, the largest cat in the world. In winter it is on the lookout for black bears hibernating in caves, a high-risk strategy that only a cat of this size would attempt.

Above the boreal forest we cross into the Arctic Circle where conditions become so extreme that trees can no longer grow. This is the tundra. The musk ox - a relic of the last ice age - lives here. In spring their calves must face a far greater danger than the cold. Encounters with grizzly bears can be brutal but if just a few calves survive, the herd’s future is secure.

To the north of the tundra is the Arctic Ocean, the only ocean that can completely freeze over. Living here is the hooded seal, one of the most peculiar animals on Earth. Males have extraordinary inflatable noses producing a bright red balloon out of their left nostrils; something one male hopes will make him irresistible.

All of the frozen habitats share one thing in common - the threat posed by today’s climate change. Greenland is home to the largest body of ice in the northern hemisphere. Traveling there we witness how global warming is melting its icecap at faster rates than ever before with profound consequences for global sea levels. And lastly we meet the polar bear, the Arctic’s most iconic resident, as a mother struggles to provide for her cubs in a world of shrinking sea ice.