Original subtitles

Our planet is a place of constant change.

Each year, the seasons shift and life is transformed.

But there are places where the changes are so epic in scale

they can be seen from space.

In this series,

we reveal three of the most miraculous transformations.

The islands of Svalbard -

within a few weeks, frozen wastelands burst into life.

The African Okavango -

a desert transforms into a magical water-world.

And the mysterious forests of New England

erupting in a blaze of seasonal colour.

Life finds the most ingenious and surprising ways to thrive

in the world's fastest changing landscapes.

Svalbard -

a frozen ice world,

lying far beyond the Northern tip of Norway.

A lonely group of islands,

almost at the top of the world.

For four months, because of the tilt of the Earth,

Svalbard is cloaked in darkness,

hidden from the life-giving light of the sun.

But every year,

a miracle happens here.

As the sun returns,

Svalbard undergoes an extraordinary transformation.

From perpetual darkness to perpetual light.

From frozen ice world to land of vibrant life.

This is the story of how life survives one of the planet's

most extreme changes.

WIND HOWLS

The Svalbard winter.

A night that lasts for months.

Without the sun's light,

nothing can grow...

..and ferocious winds are dragging temperatures to minus 40 and below.

How can anything survive here?

One animal is in its element.

A polar bear has been sleeping peacefully through the storm.

Its unique coat reflects heat back into its body just

like a survival blanket,

so it is quite comfortable, even at minus 40.

And remarkably, for the polar bear,

these are relatively good times.

The sea ice is at its maximum,

connecting the islands of Svalbard to the whole of the Arctic...

..so the bear can stride out over the frozen ocean,

its prey right beneath its feet.

A ringed seal.

Just a metre beneath the bear,

but protected by the ice.

Until it needs to breathe.

The seal scrapes out a network of breathing holes

dotted about the ice.

It can hold its breath for 45 minutes,

but then it must come up for air.

The trick for the polar bear is guessing where it will appear next.

But it only needs to catch one seal a week

and it is very patient.

Bears can wait at a single hole for days.

Only a handful of animals are tough enough to survive the winter here.

The Svalbard reindeer is the world's most Northerly herbivore,

and that's a challenge when the land is locked in ice.

They survive partly off their summer fat reserves,

losing up to half their body weight during winter.

But they do need to eat.

With their sharp hooves, they chisel through the crust of ice

and then literally chew the rocks,

scraping off the coating of frozen moss and lichen.

But after just seven or eight winters

their teeth start to wear out...

..and that's when many struggle to make it.

When winter claims one life,

another is quick to profit.

An Arctic fox.

It scavenges its way through the winter,

visiting frozen carcasses like this,

and following polar bears to feed on their leftovers.

And this is the only bird to over-winter in Svalbard.

The ptarmigan, a relative of the grouse, but tougher.

Like the reindeer, they pack on extra fat in the autumn,

but not for energy -

for insulation.

So they are 50% heavier in the winter.

But now they're too fat to fly any distance.

On feathered feet, they scuttle across the tundra,

seeking out the tiniest shoots of plants

lying dormant in the frozen ground.

For everything but the polar bear,

such conditions are hard to endure.

For the first explorers who came here from Europe 400 years ago,

the Svalbard winter felt like an eternity.

They must have wondered whether the sun would ever return.

For many, it never did.

But there is light here.

When the moon rises,

it can stay up for a week.

And every so often,

the solar wind coming from the other side of the planet

collides with the Earth's magnetic field,

creating magical colours in the Arctic sky.

Aurora Borealis,

the Northern Lights.

It's now mid-February

and after four long months,

the sun finally returns.

At first, the sun is only up for an hour at a time

so it brings little warmth,

but it signals the beginning

of Svalbard's miraculous transformation.

As the sun's light reaches out across the landscape,

the true nature of this

extraordinary wilderness is revealed.

Beautiful but brutal.

Vast glaciers flow from lonely peaks,

pulverising mountains and bulldozing their remains to the frozen sea.

There are no forests or woodlands.

But surprisingly,

the same titanic forces that make this place

so inhospitable have also drawn people here.

Coal,

brought right to the surface by the scouring of Svalbard's glaciers.

A source of great wealth for those

who can survive here long enough to get it.

Svalbard belongs to Norway today,

but in the past, many nations came

to exploit its rich coal deposits,

including Soviet Russia.

But one grand scheme after another succumbed to this frozen land.

This is Pyramiden.

Once home to over 1,000 people,

now a ghost town.

Inside these buildings, Russian workers lived with their families.

But today it all lies abandoned.

The plan was to give the people of Pyramiden everything

they needed to survive here through the long, dark winter.

Including the world's Northernmost piano.

But it couldn't last.

These mines were never profitable.

The cost of survival

here at the frozen ends of the Earth

was just too great.

Today, Arctic foxes roam the streets

where people tried to tame the Svalbard winter.

Mid-March.

The days have been getting dramatically longer.

Only four weeks since the sun's return

and there are already 12 hours of sunlight every day.

Though temperatures are still well below freezing,

the sun's energy is now strong enough to trigger a chain

of events, fundamental to life in Svalbard,

under the sea ice.

These strange colours are caused by ice algae.

It lays dormant all winter,

frozen into the fabric of the ice.

Just like a plant,

it has the power to turn the sun's energy into food.

As the sunlight starts to penetrate the ice,

it energises the algae's green cells.

The switch is flicked.

From the dark depths, tiny creatures are now drawn to the ice.

Copepods,

just a couple of millimetres long.

They may look unimportant,

but they hold a key to life here.

They've been waiting to gorge themselves on ice algae.

Very soon they are chomping away in their millions.

Now they take the sun's energy from the algae

and concentrate it into a clear drop of fatty oil,

which they store in a sack inside their bodies -

bottled Arctic sunshine.

For now, all that energy is locked away beneath the sea ice.

But not for long.

The intensifying sun heats from above.

The warming water melts from below.

CRASHING

It's April and the door to Svalbard's rich waters is opening.

It starts slowly at first,

the silence of winter broken

by the distant calls of seabirds.

But quickly their numbers build.

Guillemots,

little auks,

eider ducks.

Around six million birds return to Svalbard every spring,

travelling many thousands of kilometres

from their winter homes in Europe,

timing their arrival for just this moment.

Right away they start to refuel,

diving into Arctic water to

feast on the oil-rich copepods.

And beneath them,

other life is stirring.

Vast shoals of fish now come for the copepods' bottled sunshine,

and in turn become food for more birds.

The light from the strengthening sun has kick-started spring.

When the birds first reach their nesting cliffs,

they find them covered in ice.

It's still bitterly cold here,

but they need to stake their claim early.

Very soon there will be no more space available.

And they've got less than four months to

raise their chicks before they'll have to be off again.

So immediately they get straight on with the business of breeding.

They don't have the luxury of time.

It's now the middle of April

and Svalbard's transformation is moving into a whole new phase.

As the Earth travels further round the sun,

spinning on its axis once every 24 hours,

Svalbard now moves into permanent day.

Welcome to the land of the midnight sun.

Now that the sun is shining all the time,

it starts to have an impact on the land.

Under the snow,

small plants are already absorbing the sun's light.

As they warm up,

they start to melt themselves out of their icy prison.

The summer is short and it pays to get a head start.

One strange plant has taken this trick to an extreme.

This is the compass plant,

one of the great survivors of the Svalbard tundra.

It can live for over 300 years.

Its success is down to a secret weapon -

a central heating system.

The spongy dome catches the sun around the clock,

absorbing its energy.

Though the air temperature is still hovering around freezing,

the inside of the dome can rise to 30 degrees Celsius.

But it doesn't heat up evenly.

As the sun circles the horizon, its intensity varies.

The south side of the plant gets much more warmth than the north.

So when the flowers come,

they erupt in synch with the sun,

from south to north.

It was the early explorers who first noticed this and

used the strange plant to help find their way,

just like a compass.

As the snow melts further,

it reveals a pile of old mining carts.

For plants that don't have their own central heating,

the carts offer shelter from the biting wind.

A tiny walled garden where spring can really start to take hold.

And as the sun's warmth increases further,

the whole tundra starts to bloom.

By the end of May,

a greener Svalbard is emerging from the ice.

After such a long wait,

for Svalbard's animals, the arrival of spring is miraculous.

The reindeer desperately need the grass that the melt is uncovering,

but at first they seem a little unsure of this new, green world.

They still have their thick winter coats.

As temperatures rise,

it's getting a little hot for them.

So whenever they can,

they take a break from eating

and settle down on the remaining islands of cool snow.

It's the latest arrivals who first really take

advantage of the opportunities here.

Barnacle geese.

They've come all the way from Scotland,

where they spent the winter.

As the tundra is revealed,

it offers an untapped source of rich energy,

worth coming over 2,000km for.

This little bird is a snow bunting.

He too has come far -

all the way from Russia.

And this is the object of his affection.

Together, they have set up home in an abandoned miner's cabin.

In the middle of a whale vertebra,

hanging on the wall, is a cosy nest,

and in that, a ball of soft reindeer fluff, ready to nestle tiny eggs.

Now they are here, they are the Northern-most

songbirds in the world.

And theirs is the song of Svalbard's spring.

As the Arctic fox trots out of winter,

she sheds her coat quickly to avoid overheating.

She has a lot to do.

Foxes are nomadic in the winter,

but now the race is on to establish her summer breeding territory.

She even rolls up a ball of her fur,

adding a dash of urine to help signpost her patch.

And every so often she makes time to meet up with her mate.

They got together in the middle of the winter.

Very soon she'll be giving birth.

And then she will have just 90 days to raise her family.

It's now already June

and off the coast of Svalbard the sea ice is breaking up fast.

The polar bear's world is changing.

Though a polar bear can smell a seal from over a kilometre away,

in this constantly moving landscape, it's much harder to track it down.

It must take to the water to navigate

through the drifting maze of ice.

Bears are excellent swimmers,

but no match for a seal.

Life is getting harder.

As the ice cover falls below a critical 50%,

the bear spends more energy catching seals

than he gets from eating them.

While the breaking ice makes life more difficult for the bear,

it allows Svalbard's heaviest resident to access the land.

Walruses.

At one and a half tonnes,

they can be three times the weight of a polar bear.

After spending the winter at the edge of the sea ice,

they now return to Svalbard's shores.

They haul out on their favourite beaches for the first time

since last autumn.

Both males and females have tusks,

some over a metre long.

The bigger the tusks, the more important you are.

They're also a good defence against polar bears,

and useful props for a heavy head.

THEY GRUNT

It's their handsome whiskers

and extraordinary mouths that are their most important assets.

But they don't come into their own until they go out foraging.

And they're in no hurry.

Walrus siestas can last a week.

When they finally decide to go for a swim,

there are some novel ways of getting all that way down to the water.

Once they're in,

their strange features begin to make sense.

The giant body becomes weightless.

With just its nose on the seabed,

it blasts away the mud with high-pressure jets of water

forced through its nostrils, feeling around with its 500 highly

sensitive whiskers for its favourite food -

clams.

It just loves clams.

When it finds the clams,

it sucks the flesh right out of them

with its unique vacuum mouth.

A walrus can consume over 1,000 clams a day

without eating a single shell.

But these extraordinary animals have

only recently been making a comeback.

Not long ago, they were brought to the brink of extinction.

Just beyond their beach

are strange lumps of what appears to be concrete.

In the middle of these rings were once great

cauldrons in which the blubber from Svalbard's sea creatures was

melted down into precious oil.

Year after year, as the oil spilled over,

it congealed with the surrounding sand and set into stone.

Nearby is the evidence of the scale of this destruction.

The bones of thousands of beluga whales.

Long before it was known for its coal,

Svalbard was one of the places to hunt whales and walruses.

Their oil once lit the lamps

and lubricated the machinery of industrial Europe.

For 300 years, the slaughter continued

until there was almost nothing left to kill.

But it took its toll on humans too.

As the ground repeatedly freezes

then thaws every year,

anything buried is pushed to the surface.

A whaler's grave.

Though the promise of wealth

and adventure drew many to these remote whaling stations,

life expectancy was so short,

you even had to bring your own coffin.

July is the hottest month.

Even the great fjords that cut

right into the mountains are free of sea ice

and the summer heat kick-starts

another chain of events that benefits life here.

For so long, the land and sea were united by ice.

Now open water laps against the faces of Svalbard's great glaciers.

Behind the face, the glacier

stretches into the distant mountains.

Billions of tonnes of ice pushing down towards the coast.

As the sun starts to melt the ice on the glacier's surface,

water funnels downwards and lubricates the junction

between rock and ice under the immense weight of the glacier.

For some glaciers, the pressure gets too much.

They start to accelerate.

Svalbard's glaciers are unusual.

Many remain motionless for years and then suddenly take off.

These surging glaciers are some of the fastest on Earth,

especially when summer melt-water lubricates them.

They can reach speeds of up to 25 metres per day.

At the face, the colossal weight of ice pushes from behind,

while below, the warming sea erodes the base.

Something has to give.

CREAKING

But this is not just a destructive force.

Where the glacier meets the sea,

it enhances life.

In spite of the danger,

kittiwakes and gulls are flocking in their thousands to the ice front.

Right in the impact zone,

they start to feed.

Where the melt water flowing under the glacier reaches the sea,

it billows upwards, right in front of the falling ice.

As this plume of freezing water rises, it stuns tiny plankton

and brings them to the surface.

A microscopic feast,

so rich it's worth risking your life for.

But you've got to keep your wits about you.

It's not only birds that come here.

Beluga whales.

Young calves that don't yet have the white colour of adults.

They swim in their family pods, feeding on fish that in turn

eat the plankton at the foot of the ice cliff.

Though the years of whaling almost wiped them out,

in 1961 they were finally given protection.

Today they are becoming a much more common sight,

especially where the glaciers meet the sea.

By mid-summer,

there is more life on Svalbard than at any other time of the year.

The bird cliffs are now at full capacity.

Every ledge is taken.

The chicks hatched three weeks ago

and the race is now on to feed them fast enough.

In just three more weeks, they must be out of here.

Down below, the tundra too is alive with new life.

The reindeer have finally got their cool summer coats,

and the males are sporting impressive new antlers.

The fox couple are busier than ever.

They've had six pups and the pressure is on to feed them.

They will need to be fully grown in less than a month.

Arctic fox cubs don't like to share food.

When the winter comes they will be completely on their own,

so they need to learn to fend for themselves right from the start.

But for the parents, now is the crunch time.

As they work 24 hours a day,

making many thousands of journeys to the den with food, they become

exhausted, using up more energy than through the whole of the winter.

In the skies above,

aerial traffic has reached fever pitch,

as the birds frantically try

to keep up with the demands of their offspring.

But as they shuttle back and forth,

bringing food from the ocean to the cliffs,

they do much more than feed their chicks.

Some of the ocean's rich nutrients passes straight through the birds.

As all that fertiliser is washed down from the bird cliffs,

it has a profound effect on the land below.

The grass that now fattens up the reindeer for winter.

The soil that nourishes the plants.

The richness of Svalbard's land,

ultimately, comes from the sea.

It's now late July

and the last of Svalbard's summer visitors are only just settling in.

Arctic terns have come all the way

from the other end of the Earth, from Antarctica,

the longest migration of any animal -

over 30,000km.

But in three weeks, they'll have to fly all the way back again

and their chicks have only just hatched.

In only 21 days' time,

this ball of fluff will need to fly 30,000km.

But it's well worth the parents travelling all this way.

Svalbard's super-rich waters contain all the energy required.

All they have to do is transport it from ocean to beak.

As the adults fish nonstop,

sometimes they have to leave a chick on its own,

and because terns nest on the ground,

that can make it vulnerable.

The retreating sea ice has now forced Svalbard's largest

predator onto the land

and it's coming this way.

Now is the toughest time for polar bears.

It loses a kilo of body weight for every day it spends on the land.

The great ice bear turned scavenger -

and he's starving.

Not a good moment to break your cover.

SQUEAKING

But the chick's cries for help have been heard.

Terns may look dainty but they are highly aggressive,

and totally fearless.

Repeated attacks draw blood from the bear's sensitive nose.

The Arctic's top predator,

driven away by one of its smallest birds.

As August arrives,

Svalbard's transformation reaches its maximum extent.

It's only a fleeting transition.

By the end of the month,

the sun will be setting again.

The winter is just around the corner.

But as Svalbard's yearly miracle prepares to come full circle,

the summer sun helps trigger a final dramatic change.

In the far north east of Svalbard

is a place where it always feels like winter.

A massive ice cap.

A frozen monster.

Like a giant fridge, it cools this whole area of Svalbard.

Only now in late summer does the sun start to have any effect here.

On the surface of the ice, melt water pools together

and starts to flow.

Where the ice cap meets the sea

is one of the world's greatest wonders.

The ice cliffs of Austfonna.

For nearly 200km, they rise uninterrupted from the ocean.

But recently, these cliffs have been changing.

Something we can see most clearly from space.

The very latest satellites can make precise measurements of ice

thickness and speed of movement.

What they reveal

is astonishing.

A massive tongue of ice, 50km long,

is on the move,

sliding downwards from the centre of the ice cap out into the ocean.

A wall of ice, advancing half a metre every hour.

4km a year.

It's thought that massive events like this are part

of a natural surge cycle lasting several years,

but no-one knows exactly what sets them off.

The latest research suggests that summer meltwater

penetrating the ice cap may be a trigger.

Svalbard's ice world is incredibly delicately balanced.

Just tiny rises in global temperatures could have profound

effects on the whole seasonal cycle of life here.

Today, as Svalbard heads for the winter once more,

its future lies on a knife-edge of just a few degrees.

It's now the end of August

and Svalbard is returning to the dark time.

Svalbard's summer visitors must now leave.

They've reaped the benefits of the rich summer,

but if they stay here any longer

they'll die.

As parents now force their young to take flight,

some before they're really ready...

..foxes get a last feast before the lean time.

Reindeer just keep on grazing.

What they eat now decides whether they will make it through.

Only one creature here welcomes the coming winter.

As the sun drops below the horizon for the last time

and Svalbard moves back on to the dark side of the Earth,

the big change

comes once more.