Over one third of our planet is frozen,
and yet, the icy worlds of the Arctic and Antarctic
are as alien to most of us as the surface
of another planet.
They are places of superlatives.
From ice caps that hold nearly 80% of our planet's fresh water
to frozen forests that encircle the entire globe.
These are places that feed our imaginations,
places that seem to be borrowed from fairy tales.
They're dominated and shaped by the ice...
..both by its coming and by its going.
This is our planet's last true wilderness
and one that is changing just as we're beginning to understand it.
In this series, we'll be travelling to all parts of these lonely lands,
both north and south,
to witness its wonders perhaps for the last time
and to discover some extraordinary examples
of survival against all the odds,
as can be found anywhere on the planet.
The poles are permanently capped with ice.
Nowhere is colder, windier or more hostile to life.
I'm standing at the North Pole - the very top of the Earth.
Up here, it's easy to see why the polar regions are so cold.
The sun never rises high enough in the sky to warm my back
and those rays that do strike the surface
are mostly reflected back from this great whiteness.
But the fundamental problem is that there's no sun here at all
for half the year.
The polar winter is unrivalled in its harshness.
A night that lasts for months.
Only the toughest stay,
as temperatures plunge to minus 70 degrees centigrade.
And yet, the greatest challenge to life here is not the cold,
but the extreme swings between the seasons.
When the sun finally returns,
an extraordinary transformation begins.
This frozen world begins to melt away.
The polar spring brings a brief opportunity for life.
By summer, the sun no longer sets
and works its magic for 24 hours a day.
Now it's a race to breed before the sun departs.
By autumn, all but the hardiest abandon the poles
and the ice extends its grip.
Land and sea close down for the long, polar winter,
until, once again, the sun returns.
It's spring in the High Arctic
and the sun illuminates a giant frozen ocean,
the first stop on our journey.
The most powerful land predator is on the prowl.
A male polar bear is searching for a mate.
Willing females are few and far between
and the sea ice on which he travels will soon melt and vanish.
He's running out of time to find a mate in this vast, frozen desert.
Ten miles ahead, a single female without cubs -
exactly what the male is seeking.
He seems to relish her scent, even though she's miles away.
This is an exciting prospect.
She's clearly giving off the right signals.
He locks onto her tracks, eager not to lose her trail.
It's easier to tread in the compacted snow of her footprints.
This pursuit could last for days.
The female eventually comes into view.
The search is finally over.
For the female, only half his weight,
this must be a nerve-racking encounter.
The male could kill her if he chooses.
But he has other intentions...
..and she is ready and willing.
She leads him to higher ground.
It seems that courting polar bears prefer privacy,
often leaving the sea ice and heading for the hills
to avoid the prying eyes
of rival males who might disturb them.
Few have witnessed this moment.
For the male,
his only tender encounter in an otherwise solitary life.
But it doesn't last long -
a rival suitor has also caught the female's scent.
Courtship has to be put on hold. He must fight for his rights.
THEY ROAR
He sees off this first challenger without injury to either party,
but bloodier battles are to come.
THEY ROAR
Another battle won, though he has been slightly injured.
He hurries back to his mate,
but now she seems to have lost her enthusiasm.
Female polar bears are high-maintenance.
Wherever she goes, he will follow, mating with her when she allows
and guarding her at all times.
Over the next two weeks, the male sees off many rivals
but the battles take their toll on him.
He is almost spent,
but he has ensured that no other bears have mated with his female.
It's time for the couple
to go their separate ways.
She will give birth to his cubs, alone, in nine months' time
and he may never see her again.
He returns to the frozen ocean,
no doubt relieved to resume his solitary ways,
and just in time.
The ice beneath his feet will soon be gone.
Each spring, the Arctic Ocean undergoes
an extraordinary transformation.
An area of sea ice the size of Europe melts,
exposing the rich waters beneath.
Short-tailed shearwaters have travelled 10,000 miles
from Australia to be here.
18 million visitors darken the skies,
the largest gathering of sea birds on the planet.
Humpback whales have come all the way from the Equator
to feed in these rich, polar waters.
Their giant tails are five metres across.
Simply raising them above the surface
gives the whales enough downward momentum
to reach the great swarms of krill and herring below.
The shearwaters follow the giants' lead.
For those who can get here, in summer,
these waters provide a feast of epic proportions.
But the good times will be very short -
a problem that faces all life in the polar regions.
Journeying south across the Arctic Ocean,
the first land you reach is Greenland,
the largest island in the world.
Despite its name, Greenland is mostly white,
covered by a giant ice sheet
six times the size of the United Kingdom.
In the middle of the island, the ice is nearly two miles thick.
It's a bleak, quiet world.
Sapphire-blue melt lakes
are the first sign that a dynamic process is underway.
Each lake forms in a matter of days, expanding until it's miles across
and starts to overflow.
The spill water then carves its way through the ice.
The water courses through an icy delta
like blood along the arteries of a cold-blooded monster,
a monster that is stirring.
And without warning, the water suddenly plunges down an open shaft,
falling a vertical mile into the heart of the ice sheet.
This meltwater has a surprising effect -
it lubricates the junction
between the ice and the rock floor beneath,
so the entire ice sheet is now on the move,
sliding downhill into the ocean.
This, Jakobshavn Isbrae,
is the fastest-flowing glacier on our planet,
moving as much as 40 metres a day.
As it advances, it destroys everything in its path,
even cutting its way through Greenland's great mountain ranges
on its drive downwards towards the sea.
When speeded up,
these solid rivers of ice seem to flow just like liquid rivers.
This is the titanic force
that cuts down mountains and levels the surface of continents.
The ice is now entering the last stage of its descent.
As it gains speed,
huge crevasses open that extend down to its very core.
It's reached the ocean,
and millions of tonnes of ice have lost the support of their rocky bed.
Something must give.
CREAKING
These icefalls are an ominous sign of what is about to happen...
..a rupture deep within the glacier.
A colossal iceberg is born.
This single block of ice,
many hundreds of metres across,
would dwarf the biggest of mankind's buildings.
Every year,
tens of thousands of icebergs are spawned by Greenland's glaciers,
and their number is steadily increasing
as the climate continues to warm.
The break-up of the bergs fills the bays of the Arctic
with exquisite ice sculptures.
It also releases great volumes of cold, fresh water into the sea.
Greenland's meltwater influences the course of the ocean currents,
which, in turn, has an effect on the weather around the world.
The Arctic is closer to home than many of us realise.
It includes the northernmost parts of the three continents
on which most of us live - Europe, Asia and North America.
The first bare land we reach on our journey south
is a bleak treeless wilderness known as tundra.
Each spring, animals travel up from the south,
to be ready for the rich grazing
that will be unveiled by the spring melt.
For the caribou, the timing is critical.
Arrive early and a winter storm could kill you.
Delay too long and you may fail to lay down the fat
needed to survive a polar winter.
Further south still,
and stooped, shrouded figures end the flat monotony of the tundra.
This is the tree line, the first place on our journey
with sufficient warmth and liquid water
to enable a tree to grow.
Surviving here is so crushingly difficult,
that it can take hundreds of years for a seedling
to grow into a stunted shrub.
But even small trees
can provide cover for a predator.
Wolves. These, in northern Canada,
are the largest and most powerful in the world
and they are setting out to hunt.
The pack is 25 strong,
a sign that the prey they are seeking is formidable.
These bison are even bigger than their southern cousins
and the largest land animals in North America.
For generations, wolves and bison here
have been shaped by their battles with each other,
making each the most impressive of its kind.
The bison will not stay long among the trees.
They're not safe here.
The wolves are closing in,
but their chance of ambushing the bison in the woods has passed.
Their prey are now in the open and grouped together for safety.
The wolves will need to work as a team
if they are to make a kill.
They circle the herd, trying to unsettle it
and split it up.
But the bison are armed and dangerous.
They will be safe as long as they stick together.
The wolves up their game, harrying the herd,
a ploy to trigger a stampede
and split away one of the smaller ones.
The bison form a defensive circle around their young,
horns pointing outwards.
The wolves need a bison to break rank.
But the tables are turning and now the wolves have to retreat.
The pack focus their attention on the rear of the herd
and the bison begin to panic.
A young bison falls behind.
Even this yearling dwarfs the wolves.
Running head-down, the herd's only thought is escape.
A stroke of luck for the wolves.
The kill will feed the pack for several days.
But then they will have to resume the chase.
At the frozen ends of our planet,
the struggle for survival never eases.
South of the tree line, the winters are shorter,
so trees grow faster and taller and forests begin to appear.
As the warm, humid air from the south meets the cold, arctic air,
the moisture it carries crystallises and snowflakes fall from the sky.
Each crystal forms around a particle of dust.
All have a six-fold symmetry
but no two have ever been found with exactly the same shape.
Their variety and complexity is breathtaking.
Each snowflake is water waiting to be released in spring.
For this reason,
snow is the lifeblood of these silent forests
and all that live here depend on it in one way or another.
Some, like the great grey owl, appear in spring for the boom times,
then vanish like phantoms.
Others, like their lemming prey,
are here year-round beneath the snow, insulated from the cold air above.
The northern forests are a crossroads
for seasonal visitors and arctic specialists.
But they are so much more than this.
Together, they make up the taiga, an unbroken belt of forest
that stretches 7,000 miles around our planet
and contains one third of all the trees on Earth.
The taiga forest marks the end of our journey through the Arctic,
from the frozen ocean down across the lands that surround it.
The other end of our planet, the Antarctic, is starkly different.
A frozen continent completely surrounded by ocean.
Icebergs here are so large
that they're measured in miles not metres.
They're the only obstacles in the path of giant waves,
which circle around the continent unchecked by other lands.
These seas may be cold and storm-racked
but they're bursting with life.
No bird is more at home in water
and they are masterful surfers.
Penguins are found only in the Southern Hemisphere.
They can't fly, but they don't need to.
There are no polar bears here.
These are Gentoo Penguins.
Each spring, they come ashore to lay their eggs and rear their young.
Their hungry chicks demand so much seafood
that both parents have to go fishing.
And fishing can be dangerous.
A southern sea lion.
It uses the speed of a breaking wave to catch up with the Gentoos.
Sea lions normally eat fish,
so he's used to catching streamlined swimmers,
but the Gentoos seem more than his match out at sea.
He must change tactics.
Perhaps it will be easier in the shallows.
But no! It seems penguins are uncatchable in water.
How about on land?
The penguin's wings, so powerful for swimming,
are of no help when it comes to running.
Now, surely, the sea lion has a chance.
But on the beach, both are like fish out of water.
Rarely do hunter and hunted play their roles with so little skill.
The outcome is anyone's guess.
Every summer,
over 40 million penguins take to the Southern Ocean to feed.
They're joined by thousands of whales.
Minkes are the most numerous.
They all come here to harvest the richest ocean on Earth.
Carrying on south, we get our first glimpse of the frozen continent.
Southern humpbacks, after travelling 4,000 miles from the equator,
are finally arriving in Antarctica.
Humans have long felt the lure of this mysterious world,
yet it was only a hundred years ago
that the first explorers walked inland and were confronted by
the highest, driest and coldest territory on Earth.
Every year, the continent is transformed
as the sea ice that surrounds it begins to disappear.
This melt halves the size of Antarctica.
It's the most spectacular seasonal change occurring
anywhere on our planet.
The remnants of the sea ice are occupied by sunbathing seals
that have been here all winter.
But new arrivals are following the retreating ice edge
and they have come here to hunt.
Killer whales, the ocean's top predator.
Killers are like wolves,
for they will hunt animals far larger than themselves.
But even smaller prey are a problem if you can't reach them.
The solution is teamwork.
Swimming in perfect formation, they flick their tails in unison
and create a wave that cracks the ice.
They regroup and assess the damage. A more powerful wave is needed.
The ice floe is breaking up.
Now they are close enough to get a good look at their target.
The seal is a crabeater, sharp-toothed and feisty.
Not their favourite.
The wolves of the sea move on in search of easier quarry.
A Weddell seal. That's better.
These are more docile and easier to tackle.
The pod stays close together and travels silently.
This time, they unleash a far more powerful wave,
and with astonishing accuracy.
These big waves are not intended to break the ice,
but to knock the prey into the water, and they rarely fail.
The seal is now where the killers want it,
but the hunt is far from over.
They need to grab their prey by the tail
while avoiding its snapping jaws.
Only then will they be able to pull it down and drown it.
Sideswipes create violent underwater turbulence, a new tactic.
Blowing bubbles gives cover for others to lunge at the seal's tail.
Somehow, the seal manages to reach a tiny ice floe.
The killers could easily grab it,
but now this seems to have become a game.
The seal's life hangs on a roll of the ice.
Yet again, the pod joins forces to dislodge the seal.
The seal sees a chance to escape.
Exhausted, it no longer has the energy to pull itself to safety
and the killers are moving in.
Game over.
Although such team hunts are rarely seen, scientists believe
they may be the most complex ever documented in the natural world.
They were first witnessed by Captain Scott and his men
when they came to explore Antarctica 100 years ago.
Journeying further south, the fragmenting ice is replaced
by a permanent sheet that doesn't melt even at the height of summer.
It's a barrier that many creatures find impassable.
It repels even powerful minke whales.
They have to turn back
if they can no longer reach the air they need to breathe.
Under the ice, life has to be extremely specialised to survive.
Few of us will ever experience this strangely-still world,
and, as yet, no-one knows much about it.
The crystalline surface of the ice stalactites
provides a home for ice fish whose bodies are full of anti-freeze.
The ceiling of ice shields those living below it
from the violent polar weather that rages above.
Little here has changed for millions of years.
The cold allows animals to grow very slowly and become giants.
A relative of the woodlouse is the size of a dinner plate.
And this so-called "sea spider" has legs that span half a metre.
Now explorers are revealing other worlds
that lie hidden beneath the ice on land.
These smoking towers are the gateway to a network of caves.
Each contains an extraordinary assembly of ice crystals,
unlike any other on Earth.
Like snowflakes, every crystal is unique.
Some are taller than a man.
Others are thought to harbour life,
seeded by strange bacteria that thrive in these extreme conditions.
The breeze that gently sways these crystals
is responsible for making them.
It's steam from the molten heart of Mount Erebus,
the most southerly volcano on our planet.
It's now thought that the ice caves fringing this crater
may even be a home for hitherto-unknown life forms.
From this oasis of warmth at the edge of the continent,
our journey continues inland towards the South Pole.
The first great hurdle
is the formidable Transantarctic mountain range.
We are following the route taken by Scott and Amundsen
as they struggled to become the first humans to reach the South Pole.
They were travelling on foot
and their first sight of these mountains
must have been daunting indeed.
In front of them stretched one of the world's longest ranges,
spanning 2,000 miles from one side of the continent to the other.
The winds up here are the fastest on Earth.
They reach speeds of 200 miles an hour.
An ice-capped mountain bears the scars of the gales,
bizarre sculptures carved from solid ice.
It's not only the ice that yields.
This sculptured spire is the remnant of a mountain,
eroded from all sides by the ferocious elements.
Beyond, a wholly unexpected landscape - the dry valleys.
Only 1% of Antarctica is free of ice,
and most of that bare rock is here.
The Dry Valleys are more like the surface of Mars
than is any other place on Earth.
The floor is covered with extraordinary natural sculptures,
created by the same winds that help to keep these valleys free of snow.
Over time, entire boulders are weathered from the inside out,
until just a shell remains.
At the head of these valleys, the ice is making a breakthrough.
Millions of tons are tumbling in slow motion into the valley.
These ice blocks are the size of skyscrapers.
And this is the Beardmore Glacier,
which Scott and his men somehow traversed on foot.
It's over 100 miles long
and one of the largest glaciers on Earth.
But nothing could have prepared those early explorers
for what they were about to encounter.
The Antarctic ice cap, the largest expanse of ice on the planet.
It's three miles thick in places
and imprisons 70% of the world's fresh water.
From here to the South Pole 700 miles away,
there is nothing but ice.
I'm at the South Pole at the end of my journey.
Although it's midsummer, the temperature here
is a bone-chilling 35 degrees below freezing.
It's exactly a hundred years almost to the day
that the first human beings stood right here,
Amundsen followed by Scott.
In those days, reaching the poles
was regarded as the ultimate in human endeavour and endurance,
and a source of great national pride.
Today, the polar regions have a rather different significance,
because now we've come to understand that what happens here
and in the north affects every one of us,
no matter where we live on this planet.
The greatest challenge for the team making Frozen Planet
was the extreme remoteness of their locations.
Many of the shoots lasted months at a time
and needed a number of crews to join forces.
One location that would require such siege tactics
was Mount Erebus, Antarctica's most active volcano.
This magical mountain does not give up her secrets easily.
To capture the full story of Mount Erebus from top to bottom
required four different film crews.
The cave team is dropped off at 12,000 feet,
close to the crater.
In howling winds and thin oxygen,
their challenge is to find a way into the volcano itself.
They are venturing into the unknown.
Somewhere below are spectacular ice caves, melted out by volcanic steam.
Getting the team safely underground
is a relief for director Chadden Hunter.
Excellent, it's much warmer down here, it's freezing up there.
Minus 29.
With him is cameraman Gavin Thurston.
You sort of forget being in here, you are actually inside a volcano.
You know, above us and below us, there's bubbling lava
and you've got all these gases seeping up through here,
which is how these caves are made,
so there's also increased carbon dioxide in here.
As the cave team head deeper,
dangerous volcanic gases make breathing difficult.
The clock is ticking.
They will not have long to find the caves of crystals.
Above ground, the aerial team is pushing for the summit of Erebus.
Series producer Vanessa Berlowitz directs from the front seat,
while aerial cameraman Michael Kelem
controls the camera attached to the nose.
We're going to be around 14,000 feet,
on the performance limits of this aircraft.
Any bad weather comes in up there
and you're pretty much screwed, really,
you've got to get off the mountain fast.
Above 10,000 feet, the pilot must breathe oxygen
through a plastic tube in his nostrils.
Approaching the crater, conditions do not look good.
Today, Erebus is belching out steam and gases,
making flying extremely risky.
Up here, the air is so thin, the helicopter can't hover
and must keep moving.
This is aerial filming at its most extreme.
They struggle to get a clear view.
We're just coming up to 14,000 feet,
you can actually look right into the lava lake.
Oh, that's looking really good, Mike, just hold that there.
The cameraman captures a rare shot of the molten lava,
but it's soon obscured again.
The volcano is temperamental.
The team have seized a rare opportunity
to see into its molten heart, but now they must descend to safety.
As the weather closes in above, the cave team are making progress below.
It's Christmas Day and the crew are dressed for the occasion.
Just watch my back on these icicles,
I don't want to snap that top one off.
How strong are these pillars of ice?
It's about... Round about five...
So if I squeeze past, it's not going to snap it?
Gavin is reassured by advice from the scientist.
Oh!
Ohhh! Gavin!
I'm sorry.
That's terrible. Oh, look, it fits perfectly, look. Look at that.
Fortunately, these crystals are made of frozen water
and can grow back in weeks.
You've got these beautiful, clear, glass-like pillars
and right next to it, this really delicate...
Look how thin that filament is there.
As the cave team explore deeper,
each chamber reveals ice crystals
more strange and spectacular than the last.
No-one on the team imagined a single Antarctic mountain
could house so many wonders.
Down at the foot of Mount Erebus, a third crew, the dive team,
plan to explore the volcano's lower slopes,
which extend beneath the frozen sea.
On board is underwater cameraman Hugh Miller.
The problem is, we don't actually know what's under the ice here.
So who knows, it's a bit of an adventure.
Old-fashioned tools still work best.
First, a hand chisel to create an opening,
then a saw to widen the hole.
Ice-diving in the coldest waters on the planet
should be taken extremely seriously.
This dive's going to be a lot of things and warm is not on that list.
Insulated suits will keep them alive under the ice for only 60 minutes.
Once the helicopter departs, there's no margin for error.
The dive team begin to explore the lower slopes of Erebus,
discovering a hidden world rarely seen by humans.
Patrolling the icy shores of the volcano are killer whales,
the most southerly in the world.
Tracking them from above is the orca team.
They need a helicopter to get ahead of the whales
and to land them on the fragile sea ice.
Cameraman Jamie McPherson must pick his spot carefully.
His aim is to get the cameras
as close to the killer whales as possible without disturbing them.
He uses a film camera to capture the action in slow motion.
And the orcas come right by him.
Even in the extreme cold,
a film camera proves to be rugged and reliable...
provided there's enough film in the camera.
End of the run. No!
I've got him coming out, I just didn't get him going back in.
All right!
Below the sea ice, the dive team is setting up an underwater studio.
Using a range of waterproof lights and time-lapse cameras,
they hope to capture the growth of bizarre underwater ice formations.
Over the coming weeks,
the dive team would go below the ice over 100 times
to film the extraordinary secret world
on the lower flanks of Mount Erebus.
On top of the ice, the orca team has repositioned.
Their new goal is to get underwater shots of the whales.
They don't dare to get IN the water with orcas.
Attaching a camera to a pole is a safer option,
provided the whales aren't put off by it.
No-one is prepared for what happens next.
Tell her what you just saw.
HE LAUGHS
The entire pod arrives.
Eyeball to eyeball,
this is about as close to killer whales as it's possible to get.
By using multiple crews and cameras, the Frozen Planet team
have been able to capture the full Erebus story, from the fire
at its crater down to the whales that patrol its frozen shores.
It's quite a privilege to feel whale breath on your face.
Subtitles by Red Bee Media Ltd
E-mail subtitling@bbc.co.uk