The end of the Arctic summer, and the sun hasn't set for three months.
It's hard to imagine the bitter cold will soon return.
Some will welcome the chills of autumn, but for most,
time is running out before they will have to retreat to the south.
Early autumn in the Canadian Arctic,
and polar bears are gathering on the coastal strip,
waiting for the sea to freeze.
But a life spent alone on the sea ice
is no preparation for a crowded beach.
Such close contact with other bears must be stressful.
Surely tempers will flare.
Over half a tonne of bear slams into the other.
Polar bears will fight to the death over mates,
but not in autumn.
Now these fearsome predators display
a surprisingly tolerant side to their natures.
Being marooned on land means the bears no longer have access
to the seals they usually hunt
and they have to scrape by on whatever they can find.
Like bears the world over, they're not choosy feeders.
They even turn vegetarian,
delicately picking out berries from between the thorns.
There are plenty to go around
so there's no need to squabble over them.
Any fighting is just for fun.
The bears select sparring partners who are well-matched
and they always pull their punches,
no-one wants to get hurt in a play-fight.
Perhaps these bouts are a way of testing rivals
in case they ever meet again out on the sea ice.
One thing's for sure, the famous loners
are revealing a social, playful side we rarely see.
It's all just boisterous fun but with so many big males around,
the females keep their cubs at a safe distance.
The wary mother will lead her young to a quieter beach
along the coast while she waits for the ocean to freeze.
The sea ice is now at its minimum extent.
In the Canadian Arctic, vast stretches of coastline
are now unlocked and ready to receive visitors.
Belugas - the white whales of the North.
They're relying on open water to reach an ancient rendezvous.
It's a journey they make every year along traditional routes.
Baby belugas ride piggy-back, pulled along by their mother's slip stream.
This one is only a month old,
and won't turn white for another five years.
Thousands of belugas are being drawn to one special estuary
in the Canadian Arctic.
It isn't food that brings them here.
Curiously, it's personal hygiene.
When the tide is low they swim into the shallows
and flail around with great enthusiasm.
They're after a body scrub.
The gravel acts as a loofah
and thrashing their bodies across it
helps to get rid of their old skin.
Presumably the treatment keeps them clean and streamlined,
but it also appears to feel good.
Bliss!
The water in the estuary is warmer and less salty
and that seems to soften the skin making the scrub more effective.
This secluded estuary is only a temporary whale spa,
the ocean will soon freeze again forcing the whales to travel south.
Vast seabird colonies are the jewels of the Arctic.
Brunnich's guillemots have spent the summer months packed together
on vertical cliffs beyond the reach of predators.
They are among the most numerous seabirds in the Northern hemisphere.
This colony alone contains 100,000 birds
and there are many more like it all along the Arctic coastline.
In just a few weeks these cliffs will empty
but before the guillemots can leave, their chicks must fledge.
Their feathers are now fully formed, but their stubby wings
are still too short for them to fly properly - this will be a challenge.
It's a 150 metre drop and they need to make it all the way to the sea.
Here goes.
He falls short and survives the crash landing.
The chicks are manna from heaven for an Arctic fox.
The next chick is accompanied by a parent.
Failed again.
This looks better!
Success!
Aquatic landings are certainly gentler
and foxes can't reach you out here.
The chicks will stay in their parents' care for another month.
The guillemots are not the only ones preparing to leave,
all across the Arctic millions of summer visitors
are beginning to return south.
The guillemot chicks can't fly yet,
so they and their families must swim to their winter feeding grounds.
It's a journey that will take them a thousand miles south
to the open ocean and away from the approaching ice.
The breeding season is over and silence returns to the Arctic.
But as the first storms of autumn
sweep through the deserted nesting grounds,
they bring an unexpected bonanza for the few that remain.
The discovery doesn't remain secret for long.
It's a huge fin whale carcass.
The polar bears have been drawn from several miles away,
guided by their extraordinary sense of smell.
Bears are arriving all the time,
but there's plenty of room at this 18 metre long dining table.
They're surprisingly relaxed,
but with enough for everyone there's no need to argue.
The tastiest morsels are often underwater.
Others prefer some greens with their dinner.
After a well-balanced meal,
there's nothing better than some good company.
Despite their reputation as loners,
it's surprising just how sociable polar bears can be.
All across the Arctic the temperature is now dropping
and the sea is beginning to freeze.
Every day over 20,000 square miles of ocean
turn to ice as the cold spreads south.
At first, a thin, greasy film appears on the surface
Next, pancakes of ice start to appear.
The pancakes lock together and form a continuous sheet.
The Arctic Ocean is freezing again.
At last the bear family can return to the sea ice where they belong.
It's been six months since the cubs first emerged from the den.
They've survived the hazards of melting sea ice in spring
and lack of food in summer
and now, at last, they are in their element again.
As the north of our planet turns away from the sun,
the big chill travels south.
Temperatures on the tundra start to fall.
The shorter days and colder nights trigger a dramatic change
in the willows and blueberry bushes.
They stop producing green pigment that harnesses the sun's energy
and red and yellow pigments build up in their leaves.
The tundra blazes with colour and the whole landscape is transformed.
A bull musk ox marks his territory with scent from glands on his face.
He's preparing for the breeding season.
He shadows his harem of females as they graze
the last of the summer grasses.
He must be on his guard.
An outsider is arriving,
a large male whose intentions soon become clear.
The newcomer circles the resident bull warily.
The resident must take up the intruder's challenge.
This clash of Polar Titans could easily become a fight to the death.
The impact is like a car crash at 30 miles an hour.
A heavy skull and a helmet of horn four inches thick
provides some protection for the musk ox's brain.
Over the next half hour, the advantage ebbs and flows
as each tries to finish the duel.
If one can turn the other and gore its flank, the fight will be over.
The stakes rise as the risk of injury, or even death, increases.
The rival is out-manoeuvred.
And the champion returns to his females.
By now most animals have migrated south, but the musk oxen,
with their thick coats, will stay and face the approaching winter.
As autumn progresses, the moisture in the air freezes
and hoarfrost decorates the leaves.
Ice crystals grow like diamonds on every twig.
All across the tundra, both the rivers and the ground freeze solid.
Glassy cathedrals form as the remaining water
becomes locked up as ice.
Soon even the largest waterfalls will be motionless.
The tundra has been transformed once again.
It appears deserted.
Caribou on their migration.
Unlike the musk ox, caribou do head south for the winter,
but it's a long and difficult journey.
They use the frozen lakes as ice roads - these are flat and firm -
but it seems hooves and ice were never really meant to go together.
The frisky males would be well advised to keep
at least one eye on the road as the mating season begins.
A cow is being closely guarded by a mature bull,
with his much larger antlers.
The females are busy feeding-up for the winter,
but the bull has other things on his mind.
The cow is playing hard to get.
She heads off with her admirer in pursuit.
Several other bulls join in the chase.
She's out in front but the amorous males are gaining on her.
The big bull breaks off his chase to deal with a rival.
But now he's fallen behind the other challengers.
The younger bulls, with their lighter antlers,
keep up with the cow more easily,
but as the pace slows, the older bull catches up.
Again he has to stop and fight.
A decisive victory for the big male.
He's earned the respect of the vanquished bulls
and they now trail in his wake.
It's now become a game of Grandma's footsteps,
one look from the boss and the young-bloods freeze in their tracks.
The exhausted bull guards his prize, but he'll need to recover
before he is able to make the most of his victory,
and the herd continues its journey south
to avoid the worst of the advancing cold.
From the ocean to the tundra,
the north of our planet is now completely frozen.
The Antarctic.
In the far south, autumn can be a particularly savage
and unpredictable time.
South Georgia is a splinter of rock in the middle
of the vast Southern Ocean.
It's only a hundred miles long and is battered by the elements.
This ocean generates some of the largest waves on the planet,
they gain size and power as they travel around the globe,
uninterrupted by land for 12,000 miles.
As they buffet South Georgia, they also bring food.
A seal carcass.
A prize worth braving the surf for.
Giant petrels are the vultures of Antarctica,
and are always the first to the spoils.
The word is out, and the hordes move in.
Like feathered dinosaurs they lock beaks in battle.
These butchers provide a service for some unlikely meat-eaters.
With the carcasses now opened, pintail ducks arrive for a meal.
There's plenty of good food here and none of South Georgia's
inhabitants can afford to be fussy with winter looming.
After the feast it's time for a rinse and spin.
The breeding season is finally over
and the petrels will soon be heading out to sea
to avoid the worst of the winter.
A snowstorm is an omen of things to come.
There is now little left to eat and South Georgia's beaches
will soon be abandoned to the cold and ice.
Further south still,
and the first storms are striking the continent of Antarctica.
The Adelie penguins must rear their half grown chicks
to adulthood before winter hits in just a few weeks' time.
The chicks are only three weeks old.
Their downy coats aren't fully waterproof yet
and they cluster together for warmth.
These creches are essential during bad weather
as most of the adults are away at sea,
fishing for their fast growing families.
When the parents return,
their offspring quickly leave the comfort of their peers.
Both chicks are ravenously hungry.
But there may only be enough food for one.
This race could determine which chick has the better prospects.
Most Adelie pairs will only manage to raise a single chick each season.
And this may not be it.
At least number one is getting stronger by the day.
With one meal delivered, the parents must quickly find another.
To rear their chicks before the onset of winter,
the penguins must work round the clock.
The parents can travel over 100 miles
to reach the best fishing grounds
and may be gone for several days at a time.
They return with a kilogram of fish and squid in their bellies,
feed their chicks, and then go off again to repeat the process.
The job must be finished before the sea freezes over again.
At seven-weeks-old, the chicks are losing the last of their baby down,
and are now fully equipped to take the plunge.
Confidence is all that's lacking.
Perhaps it'll help if the parents lead by example.
There...effortless, and as graceful as any fish.
It seems penguins are not born with a love of water.
Staying submerged is the next problem.
Buoyancy control is clearly a skill that needs practise.
Well, it's a start(!)
And at least they can now reach the ice floes.
Swimming is the first of many lessons.
They must next learn to recognise danger in all its forms.
A leopard seal.
Even high up on an ice floe, the penguins aren't safe.
Each year, leopard seals will take 5,000 of them
from this colony alone.
The Adelies that survive drift out into the Southern Ocean.
They will spend the next five months feeding at sea,
avoiding the great freeze that is about to envelop Antarctica.
The edge of the sea ice advances by up to two and a half miles a day.
Eventually, over 5 million square miles of ice
will surround the continent of Antarctica,
effectively doubling its size.
The great white wilderness is empty.
But not for long.
Bizarrely, it's now that the Emperor penguins arrive,
just as all the other penguins have left.
These giants are now at their heaviest.
They've been feeding at sea all summer and can weigh 40 kilos.
From the edge of the sea ice, they head towards their colony...
..but an obstacle course of jumbled ice blocks stands in their way.
The males are particularly fat at this time of year.
This will be crucial for their survival in the months ahead,
but it doesn't make squeezing through narrow gaps any easier(!)
With the worst behind them,
they start a 20 mile march into the freezer to breed.
The only animals to do so.
By tobogganing they can travel at twice their walking speed
and it takes the weight off tired feet.
Their destination is the thicker ice, closer to shore,
which will stay solid long enough for them to safely rear their chicks
throughout the months to come.
Their colony is in the lee of icebergs trapped in the frozen ocean
which will shelter them from the bitter Antarctic winds.
Newly formed pairs promenade together.
Courtship demands that both partners strike and hold a variety of poses.
It's an important process as the bond between the couple
will have to be an exceptionally strong one.
The final act lacks the elegance of the prelude
but at least it's quick.
The egg is laid a few days later.
It contains the female's last reserves.
She now has nothing more to give
and must pass the egg to the male to incubate.
The couple must be quick.
If the egg rests on the ice for too long it'll freeze.
With their eggs safe in the care of the males,
the females start the long journey back to the sea.
The sun is also leaving and will be gone for many months.
The precious eggs, balanced on the males' feet,
will make the terrible ordeal ahead worthwhile.
With no food and only each other for warmth,
they will attempt to keep the next generation alive
while surviving in the most brutal conditions on earth.
Not all of them will succeed.
At both ends of our planet,
the sun sets for the last time in autumn.
A season of change comes to an end
and one of endless darkness and bitter cold begins.
Next time, winter in the poles.
The harshest and coldest conditions on earth.
Ice takes a grip of the frozen planet.
The spectacular return of the Emperor penguins
was a key event for the Frozen Planet team.
The crew will have to operate
in the most dangerous of all polar environments -
the edge of the sea ice.
They have to fly in everything they'll need for a month
of living on the frozen ocean.
On board are slow motion cameraman John Aitchison.
Underwater cameraman Didier Noirot.
And director Chadden Hunter.
With the plane gone, the team are on their own.
This is home for the next month.
But it doesn't look like much right now.
Their tents should be secure on the permanent sea ice
but they're still miles from the ocean where they hope to film.
The locals are keen to get acquainted
with anything of a familiar shape and size.
The Emperors are welcome neighbours around camp,
but the team need to film them returning from the water
and to do that they face a daunting task.
They must find a path to the open sea
through a shifting landscape of jagged sea ice.
Their first scouting trip doesn't look promising.
Neither maps nor Sat Nav help in this ever-changing environment.
The only clue that the ocean lies somewhere to the east
is a steady procession of penguins.
Any suggestions, Didier? We must find a way.
Yes. And we will find a way.
I like the attitude. The penguins have found a way.
It seems the Emperors will be the key to reaching the ice edge.
OK, let's go.
With their penguin guides leading the way,
snowmobiles are brought in to haul 500kgs of equipment
through the icy maze.
It's tough going for film crew and penguins.
When the ice ridges halt progress,
it's time for some back-breaking work.
The next three days are spent chiselling through mile after mile
of broken sea ice.
Once finally clear of the ice boulders,
they spot their goal - a patch of open ocean with penguins.
John is first in position.
He hopes to capture the most striking images
by using a computerised slow motion camera.
But attempts to film the penguins underwater are halted
by an unwelcome visitor.
We just saw the head of a massive leopard seal
so we'll get closer to see what's going on.
We must be careful because those guys can come out very quickly,
out of the hole, and give a bite,
but being red like that, we should be quite protected, you know?
Being dressed in red may be Didier's idea of safety,
but the rest of the crew have a healthy respect for leopard seals.
They can be fiercely territorial and are not afraid to attack humans.
I think I can run faster than him on land.
That's very exciting.
That's the first time I've ever seen a leopard seal in my life
and he's come straight out of the hole and starts...
walloping towards us.
There's a lot of adrenalin.
With the seal frightening the penguins away
and hassling the crew, it's time to try a new hole.
Oh, hello.
Can you see him?
While the seal's around, there's little hope of filming the penguins,
but now a far greater threat is posed by the changing weather.
That dark headland in the distance is Cape Washington.
That's our last sign of mainland. We can't see anything else.
Once we lose sight of that mainland
that means we're out here on our own on the sea ice.
This visibility is getting lower and lower.
It's started snowing and this wind is just blowing off shore
so, if all this ice heads out, we don't want to be on it.
I think we're going to can filming for the day.
All the signs suggest that a big Antarctic storm is on its way.
Winds pick up to 70mph and everyone retreats to their tents.
High winds then turn to heavy snow.
On the driest continent on Earth, a big snowfall is rare.
White-out conditions take the penguins and film crew by surprise.
Each day they must dig out their buried equipment.
Filming has ground to a halt.
One week and a metre of snow later, the headland is visible again
and the team are raring to get back to the ice edge.
They follow their old route back through the frozen maze
and, with no leopard seal in sight,
it's time for another attempt with the pole cam.
It's cumbersome, but it allows the team to capture underwater images
without having to risk the icy water themselves.
That is OK? That's perfect. They are coming. I can see some.
Oh, wow!
Penguins coming in the hole. This is awesome. This is great.
The aim now is to film the penguins' dramatic exit from the hole.
The only problem...which hole?!
These penguins keep outsmarting us.
We tried to switch holes to film them coming up
and they all just completely came up behind us.
Whatever the crew try there's always someone who hasn't read the script!
John has been filming but he can't view his slow motion shots
until they're downloaded to a computer.
While he waits, Didier seizes his chance.
Come, my friend. Come.
If you can't beat them, join them.
It's time to go scuba diving in the coldest waters on the planet.
I will see you on the other side.
The team are 300 miles from help
and have only a small hole as their lifeline to the surface.
A magical world opens up.
For the first time
Didier now shares the penguins' perspective from beneath the ice.
This is Antarctica at its most enchanting.
For Chadden, after weeks of struggle,
the sequence quite literally falls into his lap.
Whoa!
Sorry!
I think I'm in the way.
Just come a little this way. There we go.
I'm getting run over by penguins(!)
I think it worked. It's very difficult to tell.
John's camera is finally capturing
the super slow motion images of the Emperors' dramatic return.
With the penguins performing perfectly
it was all falling into place.
The team were finally able to capture
Antarctica's most spectacular belly flop.
For a free Open University illustrated poster of polar regions
call the number on the screen
or order online by going to bbc.co.uk/frozenplanet
and follow the links to Open University.
Subtitles by Red Bee Media Ltd
E-mail subtitling@bbc.co.uk