Seven Worlds, One Planet

Asia - the largest of all the Earth's continents.

It stretches from the equator to beyond the Arctic Circle.

This is a continent of extremes.

Here, temperatures can drop to below minus 60 degrees Celsius.

0n land, survival is almost impossible.

But for a few weeks in summer,

the ice melts and the coast is transformed.

This is one of the biggest gatherings of mammals

to be found anywhere on Earth.

These are Pacific walrus.

For most of the year they feed out in the Arctic Ocean,

emerging to rest on the sea ice.

But now climate change has melted the ice here,

and the only place within reach of their feeding grounds where they can rest

are a few beaches, such as this one.

100,000 of them, almost the entire world population, are here.

They are gigantic.

A male can weigh over a tonne...

ALL GRU NT

...and many die in the scrum.

On a beach, 250 miles to the west, there's a further danger.

Polar bears.

They, too, have been forced to spend more time ashore by the dwindling ice.

And now they're very hungry.

But adult walrus are tough, well armed and agile in water,

and could fatally injure the bear.

He's failed.

The narrow beaches here are backed by cliffs...

...and some walrus scramble up them, escaping the crowd.

At the top, they are 80 metres above the beach...

...but this is not a place where a walrus should be.

Nor are they the only ones to have found it.

The bears have got up here too.

The walrus's instinct is to find safety in the water.

They can still smell the sea.

And they can hear it.

Just the polar bear's presence is enough to spook the walrus.

Many walrus that climb the cliffs never make it back to the ocean.

Even once the polar bears have moved on,

the walrus need to return to the sea, and some take the nearest way to do so.

As one crashes on the rocks,

those on the beach stampede and more lives are lost.

In the course ofjust a few days, over 200 walrus die.

Now the polar bears can feed on the carcasses.

These events only occur once every few yea rs,

but as the world warms and the ice retreats still further,

they may become more frequent.

Inland, the ground is gripped by winter

for six months of the year.

Two million square miles of northern Russia are locked beneath the ice.

But even so, some creatures have managed to make their homes here.

They leave evidence of their presence in the snow.

These tracks all lead in one direction.

Kamchatka has the highest density of active volcanoes on the planet.

Temperatures underground reach 250 degrees Celsius...

...pushing up cauldrons of boiling mud and clouds of steam...

...but in spite of the dangers,

some creatures travel long distances to visit the area.

A Kamchatka brown bear.

He spent the long winter sleeping in a den below ground

and now he is extremely hungry.

But finding food means getting dangerously close to the scalding fountains.

This is the only place for many miles around

where a bear can reach grass that is snow free, thanks to the hot earth.

Putting a foot wrong here could lead to real trouble,

and bodies have been found of bears

that stumbled into the pools and were scalded to death.

And this bear is not alone.

Brown bears, by and large, are solitary creatures

and this is one of the few times of the year

when they tolerate the presence of others.

And now they are so well fed and relaxed that they even have time to play.

This volcanic spot has become a warm oasis in Asia's frigid north.

Away from Arctic Russia, Asia has the hottest deserts,

highest mountains and tallestjungles on our planet.

This is a continent of incredible variety...

...but it was not always so.

Some 89 million years ago,

India was an island lying away to the south, but it drifted northwards,

pushing up the sediments between it and mainland Asia.

Over millions of years,

the sediments lying between crumpled up and rose to form the Himalayas.

Now these are the tallest mountains on the planet.

They stand over five miles high.

India is still moving northwards, and these mountains are still rising.

Asia's mountains stretch all the way from Afghanistan,

across northern India, to here in central China.

These are the mountains of Shennongjia, among China's highest.

The forests here were, until comparatively recently, the least known in the world.

Few outsiders had any idea of what animals might be living in them.

There were stories of human-like monsters - yetis, abominable snowmen -

who left strange footprints in the snow...

...but little else.

And indeed there are monkeys living in these snowy forests,

and they're very strange.

Meet the blue-faced, golden-coated,

snub-nosed snow monkey.

They are among the heftiest of monkeys.

Big animals keep warm more easily than small ones,

and they survive in colder conditions than any other monkey on Earth.

They all have snub noses.

Perhaps prominent ones would only too easily get frostbitten.

The whole group huddles together at the slightest opportunity to keep warm...

...and who wouldn't?

Even adults, if they get separated from the group, can freeze to death.

Now, in the depths of winter, food is desperately hard to find.

The head of the family leads them to the edge of their territory

in search of something to eat.

The only food here is wretchedly unnourishing -

bark, moss and lichen.

There's hardly enough to sustain one monkey, let alone a family.

But they share it peaceably.

Survival depends on the group keeping together.

In these mountains, any food is precious.

MONKEYS SCREECH

A rival group.

They, too, are searching for food.

The two males go head to head.

MONKEYS SCREECH

SQUEAKS

SQUEAKS

And now the females join the fray.

MONKEYS SCREECH

Outnumbered, the intruders retreat.

Their leader is the last to go.

The fight was over the smallest of meals,

but it was ferocious nonetheless, and the family is now scattered...

...but they muststay together.

The youngest are already badly chilled.

SQUEAKS

She can see her father, but has she the strength to reach him?

SQUEAKING

Back to safety and warmth.

The huddle is the only source of warmth

in these bleak, frozen forests.

To the west of the Himalayas, in Iran, lie some of the hottest deserts on Earth.

This is the Lut Desert...

...and here temperatures can reach 70 degrees Celsius.

The blisteringly hot rocks and baking sands of Iran's deserts

may appear totally lifeless...

...but a few trees manage to grow in the shade of the canyon walls...

...and here at least migrating birds passing through

can stop for a little rest.

A flycatcher.

With luck, there might be a meal of some kind here.

There are spiders in the crevices.

Not much, but worth having.

And there's something moving up there.

The bird was mistaken.

It was a viper with a lethal bite.