"DAVID ATTENBOROUGH:" "The power of the sun drives the seasons, transforming our planet." "Vast movements of ocean and air currents bring dramatic change throughout the year." "And in a few special places, these seasonal changes create some of the greatest wildlife spectacles on Earth." "Here in the Arctic each summer, the sun begins to melt the winter ice." "Nearly three million square miles of ice will disappear," "opening up a narrow window of opportunity for millions of animals." "For many, it's their best chance to feed and breed." "But for polar bears, it's the hardest time of the year." "They have to survive the greatest seasonal change on the planet." "Winter in the Arctic." "The northern lights flicker across the sky." "It's a land of continuous night where temperatures plummet to minus 40." "Polar bears are in their element, hunting for seals on the frozen sea." "But the long night is coming to an end." "In February the sun rises for the first time in four months." "In the coming weeks the strength of the sun will power an enormous change." "But for now its rays offer only a little warmth." "Despite the sun's return, six million square miles of the planet's far north is still cloaked in ice." "Deep snow covers the mountains." "Even the sea is frozen solid, many metres deep." "Groups of ringed seals haul out through holes in the ice to bask in the weak sunlight." "(YELPING)" "But they are vulnerable and have to keep a lookout." "With the sea still frozen, it's easier for predators to get close, and the seal's greatest enemy is the polar bear." "A mother bear and her four-month-old cub are hunting." "Seals make up most of the bear's diet, and to find them she must lead her youngster out onto the ice for the first time." "Scientists, looking at how a changing climate is affecting bears, have fitted the female with a radio collar." "The ice here is thinner, and she must spread her weight to avoid breaking through." "For her cub, it's all just a game." "By sticking close to Mum, he'll learn how she hunts for seals, a critical lesson for his future survival." "At this time of year the frozen Arctic is empty of life and only a few hardy residents can survive." "For a female arctic fox, the winter has been a time of hunger." "Food is scarce and she's had to wander far and wide, scavenging from the remains of bear kills." "(YELPING)" "But her fortunes are changing." "A dead reindeer is a lucky find." "If no other scavengers come along, this could sustain her for the rest of the winter." "With the sea frozen, polar bears are busy hunting." "This bear has caught a seal." "He waited for it to surface through a hole in the ice and his patience has been rewarded." "He must catch a seal about once a week, and this is the best hunting season." "As long as there is sea ice the bears won't go hungry, as walking on the ice is the easiest way for a bear to get close to a seal." "But the ice will soon start to break up and hunting will get harder." "The calories the bear takes in now will have to see him through hard times ahead." "For polar bears it's the survival of the fattest." "At this time of year there are still only five hours of daylight." "But as the sun rises higher, each day lasts 40 minutes longer." "It's March, and with increasing sunlight the first in a huge wave of migrants are arriving." "Millions of seabirds are travelling north to reach the frozen coast." "Huge flocks of little auks and guillemots fly across many miles of ice from the nearest open water." "Their destination is the still-frozen sea cliffs." "It's an inhospitable place, but in a few weeks everything here will change." "It pays to be early, even though the snow has yet to melt." "The first arrivals get the best nesting ledges and a head start." "(SQUAWKING)" "They have just 50 days from laying their eggs to raise their chicks." "(SQUAWKING)" "The Arctic's silent wilderness is coming to life." "It's three months since the sun's return and its power is growing daily." "The air temperature rises slowly and once above zero, at long last, the melt begins." "Melting snow feeds freshwater streams which pour off the land." "In just a few short days, the melt unveils a whole new landscape." "The coastal cliffs now teem with nesting seabirds, and it's not long before they attract unwelcome attention." "The fox's white winter coat has disappeared with the snow." "Her new camouflage will allow her to change from scavenger to hunter." "The short summer will be her best chance to raise a family." "The snow may be disappearing from the land, but the sea ice has yet to melt." "The coastline is still locked in ice." "The islands of the Arctic are surrounded by thousands of miles of white frozen ocean." "Because the sea ice is so thick, it won't begin to break up until the temperature stays above zero for a number of days." "Until then, few creatures can penetrate this icy barrier." "The sun reflects from the white frozen sea, creating a desert of icy mirage." "The bear can still walk on the ice to hunt for seals, but not for much longer." "It's getting warmer by the day." "The bear's world is about to melt away." "It's now June and the sun beats down 24 hours a day." "The temperature remains constant above zero degrees." "The frozen sea begins to melt." "Pools form across the surface, absorbing more of the sun's heat, speeding the thaw." "Sunlight penetrates the frozen surface, illuminating a strange world beneath the ice." "The frozen barrier has split." "Mysterious voices echo against the icy ceiling." "Giant cracks, or leads, form at weak points, creating a pathway for new arrivals." "Narwhal." "Known as the arctic unicorn because of their strange spiral tusks, narwhal are some of the most secretive and elusive animals in the world's oceans." "The leads provide passage for thousands of these mysterious whales." "Each summer they travel 600 miles north, navigating through the ice to reach rich fishing grounds." "More whales travel along the edge of the ice where it meets the open sea, to search for the openings of leads." "It's a hazardous journey." "As mammals, they need air to breath and if the ice closes above them they could suffocate." "They're looking for holes in the ice where they can surface." "A single breath will last them for 1 5 minutes." "The further they travel, the harder it becomes to find holes in the ice." "They snatch a breath and then travel on." "But ahead, the ice forms an impenetrable barrier." "The narwhal use their heads and their long tusks to break the ice and enlarge the breathing holes." "For now they've reached a dead end and must wait." "The ice will need to melt further if they are to continue." "All across the Arctic the sea ice is beginning to retreat." "The leads widen, forming tracts of open water." "Wind and ocean currents shift the loosening ice, breaking it up." "As the ice melts, thousands of miles of open ocean become accessible, providing a bonanza for millions of seabirds." "In just four weeks a colony of guillemots can devour one and a half million tonnes of arctic fish." "As the ice melts, their journey to their feeding grounds in the open sea shortens by the day." "They gather at the edge of the retreating ice and dive to hunt for arctic cod and capelin." "The shoals are found 80 metres down in the murky depths, and the guillemots must hold their breath for nearly two minutes." "With their crops stuffed with fish, they return to the colony to feed their hungry youngsters." "(YELPING)" "With 24 hours of daylight, they go on fishing around the clock." "Warmed by the sun and driven by winds and currents, the sea ice is now fragmenting." "That is a big problem if you need the ice to hunt from." "A polar bear can smell a seal from over a mile away." "(SNIFFS)" "But the prey he depends on is hard to find in this constantly moving landscape." "He must take to the water to navigate through the drifting maze of ice." "Bears are excellent swimmers, but he's no match for a seal." "As the ice melts, finding seals gets harder and with more open water, it's easier for a seal to escape." "The melt has caused a shift in power." "Now it's "advantage seal"." "The bear's chance has slipped away, and his hunger grows." "The ice barrier broken, strange marine visitors begin to arrive." "They've swum 600 miles to get here, and with the ice gone they can make their way into the shallows of freshwater estuaries." "(CLICKING)" "Beluga whales." "As more and more belugas arrive, a strange annual ritual begins." "For belugas, this is a very special event." "The violent thrashing against the river bed loosens their year-old skin and rids them of unwelcome parasites they may have picked up on their journey." "In freshwater, warmed by the strengthening sun and with the smooth pebbles in the shallows to rub against, the whales whistle with pleasure." "(ALL WHISTLING)" "But the ice-free summer will be short." "The whales can only enjoy their arctic spa for two weeks." "Soon the belugas must leave the shallows and make the most of what's left of the summer to hunt the shoals of arctic fish." "It's early July, and at the bird cliff the fox has caught a nesting fulmar." "She has a family now, eight tiny mouths to feed, and one bird is not enough to go round." "The cubs bicker over their dinner." "They're only three weeks old and in just another two weeks they'll have to be ready to fend for themselves." "(YELPING)" "The winter ahead will be so harsh that only two of these eight cubs are likely to gain enough weight to survive." "Their lives depend on every mouthful." "(YELPING)" "When food is scarce the most dominant cub will feed." "And the smallest will go hungry." "The seabirds have been working round the clock to keep their chicks fed and to prepare them for the first big challenge of their lives." "If they are to escape the winter, they'll have to leave the cliffs right away, and get far out to sea." "But it's only been 20 days since they hatched and their wings are still too weak for them to fly." "So far their feet have never left the ground and there is only one way down to the safety of the sea," "300 metres below." "Reluctantly, the chicks take a few nervous steps towards the edge." "Encouraged by a gentle nudge, he leaps into the unknown." "Dad follows right behind him, reassuringly calling to his chick." "(SQUAWKING)" "Made it." "The landings may not be stylish, but at least they're on target." "(SQUAWKING)" "It's easy to misjudge the distance and some fall short of the water." "But even now, Dad sticks close by." "He encourages his chick to take the last few steps towards the safety of the waves." "But some chicks land a long way from the water." "They're sturdy enough to survive the fall, but this is no place to be left alone." "For the mother fox it's easy pickings." "With so many free meals falling from the sky, she runs from one kill to the next." "The chicks will be jumping for only three days, so she must make the most of this bonanza." "The survival of her own family depends on it." "With more chicks than she can possibly carry, the mother fox has to be clever." "What her family can't eat now, she buries." "For the days ahead she'll have a well-stocked larder, enough for all eight of her cubs." "Their bellies now full at last, the cubs can relax in the sun." "For the guillemot chicks that survive, the ordeal has only just begun." "They must retreat south 600 miles, beyond the reach of winter." "But the youngsters can't fly yet, their wings aren't strong enough." "So, led by their parents, they'll have to swim." "(SQUAWKING)" "At the height of summer even the permanent ice caps are touched by the power of the sun." "Melt-water, channelled down from high on these ice caps, pours over a precipice where the ice meets the ocean." "Along this 200-mile wall of ice, a thousand freshwater cascades plummet into the sea." "As July draws on, the great melt reaches its peak." "The greatest seasonal change on the planet has taken place." "The sea ice that once extended all the way to the horizon is now open ocean." "In just three months, the sun has won its battle with the ice." "Over two and a half million square miles of ice has melted away, uncovering thousands of islands surrounded by open ocean." "But in recent years, the scale of this melt has been growing." "And for one animal this is a critical issue." "A mother bear and her adolescent cub rest on a fragment of sea ice." "With the melt, they're forced to swim ever-greater distances to hunt for seals." "Their arctic home is increasingly vulnerable to a changing climate, and this year there has been even less ice than normal." "If future melts are as extreme as this one, bears like these may starve or drown, lost at sea." "This is one of the last pieces of ice now adrift in the open ocean." "The polar bear's icy world has melted away." "For many others the open water provides the greatest feast of the year." "The narwhal have made it through the ice." "They gather in bays where they can hunt for arctic cod and squid." "Here they are joined by other ocean migrants." "Bowhead whales." "These 1 00-tonne giants feed on millions of tiny plankton that flourish in the sunlit waters." "Belugas have come for the rich fishing and rest on the surface between dives." "Even on the sea bed there is plenty on the menu." "Two tonnes of pulsating blubber forages for clams in the sediment." "Walrus are year-round residents of the Arctic, following the ebb and flow of the ice." "In the open summer waters they can reach huge areas of the ocean floor, rich feeding grounds for these giant seals." "They hoover up clams with their rubbery lips." "A single walrus can eat up to 4,000 clams in one 1 0-minute dive." "Bellies full, they come up for air." "With the sea ice gone, the walrus haul out on dry land to rest." "(BELLOWING)" "They're used to huddling together to keep warm, and even now that it's 1 2 degrees above freezing, they prefer to stick close together." "In the warmth of the sun, the walrus begin to shed their old skin, and they spend hours scratching." "Some places are harder to reach than others." "(GRUNTING)" "These irritations make them bad-tempered and arguments often break out." "(BELLOWING)" "(SNORTING)" "Spitting, stabbing and bellowing iron out any disagreements." "(SNORTING)" "All disputes settled, a peace of sorts returns once more." "Digesting a belly full of clams generates a lot of wind, making walrus colonies very fragrant places." "(FARTING)" "Fed by the abundant supply of guillemot chicks, all eight fox cubs seem to have boundless energy." "Soon they will be ready to face the world without their mother." "In just five weeks she's raised her cubs, making the most of the short summer." "The mother fox has won her race against time." "Between June and July, the Arctic is the land of the midnight sun." "An empty wilderness has been transformed." "(CHIRPING)" "The once-frozen ocean is now bursting with life, as all the animals enjoy the summer feast." "(CLICKING)" "But polar bears aren't so fortunate." "With no sea ice to hunt on, they're now trapped on dry land." "A hungry bear will eat any food it can get its paws on, but for a meat-eater a few scraps of dry lichen won't go far." "It may have been four months since his last kill and he won't find any seals here." "If the yearly increase in the scale of the melt continues, more bears will starve." "Two thirds of the world's polar bears could vanish by 2050." "The great melt has always been difficult for bears, but soon surviving the summer may become impossible." "The scale of the summer melt has changed over the last 30 years." "2007's melt broke all records." "400,000 extra square miles of ice disappeared, the greatest melt ever recorded." "The latest predictions suggest that the Arctic may be entirely ice-free in summertime within 20 to 40 years." "By September, the sun's power begins to ebb." "The summer comes to an end and the Arctic empties of life." "The last seabirds begin their long journey south, leaving only a few hardy residents behind." "The fox cubs now face the changing season alone." "Already, the first snow is beginning to fall." "The full Arctic winter is just six weeks away." "For hungry bears, six weeks may be too long to wait." "The sea ice will not freeze properly till it reaches minus 2 degrees." "For now, it's still too warm." "This ice is no use to the bears." "They can't walk on it to hunt." "The normally unsocial bears gather in groups, trapped on the shoreline." "This is the time of year the male bears spar." "(GROWLING)" "Only the biggest bears have the energy reserves to fight." "After a summer without food, the bear's systems are in low gear." "These aerobics help warm them up, in readiness for the winter hunting ahead." "(GROWLING)" "It's late October, but still the sea hasn't frozen." "For every degree rise in the average temperature, the summer melt is extended by a whole week." "That's more bad news for polar bears." "Smaller, younger bears don't have the energy of the big males." "Each day they are without food, they lose nearly a kilo." "Some have lost half of their body weight." "These hungry bears must now rest in the snow and conserve energy." "All they can do is wait." "At last the wind changes, blowing from the cold north across the sea." "The air temperature plummets to 20 degrees below." "It's now cold enough for ice crystals to form in the ocean." "They knit together forming a greasy layer of surface ice." "This thickens into plates which bump and collide in the swell, forming pancake ice." "These pancakes lock together to form a continuous surface." "At long last the sea has frozen." "Only now can the bears head out onto the sea ice to hunt for seals." "But the new ice has a surprise in store." "(ICE CRACKING)" "This season, for the first time ever recorded, even the winter ice is thinner." "The ice here is too thin to climb out on and he struggles to free himself." "At last, safely on the firmer ice, he rolls in the snow to dry his fur." "In November, the sun sets over the frozen north." "It will not appear again for four months." "The summer melt provides opportunities for millions of animals, but has now become a threat to the polar bear's very survival." "This season, the bear has survived the greatest melt yet recorded and made it through to the Arctic winter."