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"The Polar Sea" begins in Reykjavik, Iceland with Richard Tegner, an ordinary Swedish man embarking on an extraordinary expedition to cross the Northwest Passage with his friends.

It is late July and the Northwest Passage is still choked with ice. In the small village of Ilulissat, Greenland, a motley collection of Arctic voyagers assembles to prepare for their expeditions while they wait for the sea to melt.

The explorers cross Baffin Bay to the tiny Inuit village of Pond Inlet. The new accessibility of this region has brought an unprecedented wave of tourists to Pond. For residents this is one of the many mixed blessings of climate change.

We depart coastal civilization for Lancaster Sound, a wilderness teeming with whales, birds and bears which is now being swarmed by scientists racing to understand the biological effects of climate change.

Crossing the Northwest Passage remains an immense challenge despite the melting ice. Halfway through their journey, some explorers break down and fall back, leaving others exiled.

In the little coastal village of Gjoa Haven deep in the Northwest Passage, modern life - driven by Canada's ongoing efforts to dominate this territory - has led to very mixed results.

Late August finds our explorers at the halfway point of the Northwest Passage in Cambridge Bay, racing against the return of winter. Undiscovered until the 20th century, this is an ancient crossing place where surreal contrasts abound.

Richard Tegner has hitched a new and luxurious ride and is sailing west along a melting coast. Climate change is turning the Arctic green and the consequences are as complex as they are frightening.

Entering Alaska, USA, the Northwest Passage transforms from wild terrain into an industrial corridor lined with oil rigs. As ice melts, newly revealed oil and minerals create a bitter divide between petrol politics and reality.

Two months after they began their journey, our explorers finally exit the Bering Strait and complete the Northwest Passage, but not before passing one last astonishing impact of climate change: an entire community sinking into the sea.