Our journey begins with David Attenborough at the North Pole, as the sun returns after six months of darkness. We follow a pair of courting polar bears, which reveal a surprisingly tender side. Next stop is the giant Greenland ice cap, where waterfalls plunge into the heart of the ice and a colossal iceberg carves into the sea. Humpback whales join the largest gathering of seabirds on earth to feast in rich Alaskan waters. Further south, the tree line marks the start of the Taiga forest, containing one third of all trees on earth. Here, 25 of the world's largest wolves take on formidable bison prey. At the other end of our planet, the Antarctic begins in the Southern Ocean where surfing penguins struggle to escape a hungry sea-lion and teams of orcas create giant waves to wash seals from ice floes -a filming first. Diving below the ice, we discover prehistoric giants, including terrifying sea spiders and woodlice the size of dinner plates. Above ground, crystal caverns ring the summit of Erebus, the most southerly volcano on earth. From here we retrace the routes of early explorers across the formidable Antarctic ice-cap - the largest expanse of ice on our planet. Finally, we rejoin David at the South Pole, exactly one hundred years after Amundsen then Scott were the first humans to stand there

It is high summer in the Polar Regions, and the sun never sets. Vast hordes of summer visitors cram a lifetime of drama into one long, magical day; they must feed, fight and rear their young in this brief window of plenty. Summer is a tough time for the polar bear family, as their ice world melts away and the cubs take their first swimming lesson. Some bears save energy by dozing on icy sun beds, while others go egg-collecting in an Arctic tern colony, braving bombardment by sharp beaks. There are even bigger battles on the tundra; a herd of musk oxen gallop to the rescue as a calf is caught in a life and death struggle with a pair of Arctic wolves. But summer also brings surprises, as a huge colony of 400,000 king penguins cope with an unlikely problem - heat. The adults go surfing, while the woolly-coated chicks take a cooling mud bath. Nearby, a bull fur seal is prepared to fight to the death with a rival. Fur flies as the little pups struggle desperately to keep out of the way of the duelling giants. Further south, a minke whale is hunted amongst the ice floes by a family of killer whales. The dramatic chase lasts over 2 hours and has never been filmed before. The killers harry the minke whale, taking it in turns to wear it down. Eventually it succumbs to the relentless battering. Finally, comical adelie penguins waddle back to their half a million strong colony like clockwork toys. The fluffy chicks need constant feeding and protection as piratical skuas patrol the skies. When an unguarded chick is snatched, a dramatic "dogfight" ensues.

There is no greater test for life than winter, as temperatures plummet to 70 below and winds reach 200kph. Darkness and ice extend across the polar regions and only a few remarkable survivors gamble on remaining. We join a female polar bear trekking into the Arctic mountains to give birth as the first blizzards arrive. Out on the frozen ocean, the entire world's population of spectacled eider ducks brave the winter in a giant ice hole kept open by ferocious currents. Arctic forests transform into a wonderland of frost and snow - the scene of a desperate and bloody battle between wolf and bison, but also where a remarkable alliance between raven and wolverine is made. Beneath the snow lies a magical world of winter survivors. Here tiny voles dodge the clutches of the great grey owl, but cannot escape the ultimate under-show predator - the least weasel. Midwinter and a male polar bear wanders alone across the dark, empty icescape. Below the snow, polar bear cubs begin life in an icy den while fantastical auroras light the night skies above. In Antarctica, we join male emperor penguins in their darkest hour, battling to protect precious eggs from fierce polar storms. Weddell seals escape to a hidden world of jewel-coloured corals and alien-looking creatures but frozen devastation follows as sinister ice stalactites reach down with deadly effect.

Spring arrives in the polar regions, and the sun appears after an absence of five months; warmth and life return to these magical ice worlds - the greatest seasonal transformation on our planet is underway. Male Adelie penguins arrive in Antarctica to build their nests - it takes a good property to attract the best mates and the males will stop at nothing to better their rivals! But these early birds face the fiercest storms on the planet. In the Arctic, a polar bear mother is hunting with her cubs. Inland, the frozen rivers start to break up and billions of tons of ice are swept downstream in the greatest of polar spectacles. This melt-water fertilizes the Arctic Ocean, feeding vast shoals of Arctic cod and narwhal. The influx of freshwater accelerates the breakup of the sea-ice - an area of ice the size of Australia will soon vanish from the Arctic. On land, a woolly bear caterpillar emerges from the snow having spent the winter frozen solid. Caterpillars normally become moths within months of hatching, but life is so harsh here that the woolly bear takes 14 years to reach adulthood. Once mature it has only days to find a mate before it dies! Alongside the caterpillars white Arctic wolves race to raise their adorable cubs before the cold returns.

The coast is the dynamic border between land and sea; powered by the tides and thrashed by waves, this is a world of continuous change. Opportunities never last long here, so hunters are always in a race against time. The coast is the only place on the planet where predators from air, land and sea come together. Dolphins that leave the safety of the sea to fish, walking octopuses, ingenious monkeys, fishing wolves and the greatest gathering of feeding humpback whales come to the coast to hunt. For all, timing is everything.

Every year grizzly bear families in North America depend for their survival on a spectacular natural event: the return of hundreds of millions of salmon from the Pacific Ocean to the mountain streams where they were born. The salmon travel thousands of miles to spawn and then die. The great run not only provides food for bears, but for killer whales, wolves, bald eagles, and even the forest itself. The question is: will the salmon return in time to keep hungry bears alive?
A mother grizzly and her cubs emerge from their den high in snowy Alaskan mountains. Filming from the air the team capture a TV first, following the bears as they negotiate a near vertical slope on their journey to the coast where they await the return of the salmon. Meanwhile, the salmon are making their way to the to river mouths where they must swim upstream and against the current. The programme reveals how they tackle the torrents and leap over waterfalls, a feat equivalent to a human jumping over a house. Dozens of hungry bears eagerly await the salmon that make it up river. In another TV first, underwater cameras record the ingenuity and fancy footwork they use to collect dead salmon from the bottom of deep pools.