Original subtitles

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.

On 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...

...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 of just a few days, over 200 walrus die.

Now the polar bears can feed on the carcasses.

These events only occur once every few years,

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 tallest jungles 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.

A rival group.

They, too, are searching for food.

The two males go head to head.

And now the females join the fray.

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 must stay together.

The youngest are already badly chilled.

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

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.

This species has only recently been discovered

and, so far, it has been found nowhere else but here.

Its camouflage is so effective

that it's almost impossible to see it on these rocks.

And on its tail, moveable scales have been modified to look like a spider's legs...

...and its tip like an abdomen.

Migrating birds only appear in this barren desert during a few weeks of the year.

This is the snake's only chance to eat for months.

A shrike.

It has flown here from Africa and hasn't fed for days.

Better luck next time.

Conditions are almost as harsh on the dry plains of northern India.

A male Sarada lizard does his best to get himself noticed.

It's breeding time.

The wide open spaces are a good place to be seen.

He's only 7cm tall,

but a rock will help to make him conspicuous.

And he's already been noticed by one female.

It's time for him to show off.

The more healthy and virile he is, the brighter his colours are.

And females like bright, flashy colours.

But he, it seems, is not as conspicuous as he might be.

In the neighbouring territory,

there's another male who's found an even bigger rock.

So the newcomer is not making quite such a good impression.

The one on the big rock is attracting all the females.

The newcomer will need a higher platform if he's to be seen by a female,

and he'd better do something about it.

He only lives for a year.

This is his one chance.

He will have to fight, if necessary.

H is rival isn't backing down.

Sarada males can fight to the death.

The newcomer has won.

Now he can claim the high platform and the best territory...

...and the females will choose him for a partner,

as long as he can fight off the other claimants.

As the Himalayas rose over millions of years,

they eventually formed a gigantic barrier

that prevented rain clouds from the south travelling farther north...

...and a completely new weather system developed in Southern Asia.

The monsoon.

These drenching annual rains transformed Southern Asia.

Dense rainforests formed,

in which plants and animals of all kinds were able to proliferate and evolve.

Some of the tallest jungles grow in Indonesia,

the home of the largest of all tree-living animals of any kind...

...the orang-utan.

There is a multitude of things to eat here,

but you have to know where to find them.

Young orangs stay with their mother for years, learning how to do that.

This youngster has only just started.

Termites - an important source of protein.

But perhaps they are an acquired taste.

He's off to search for something he might prefer.

It's hard to know where to look...

...or where it's safe to clamber.

Different levels in the forest contain different foods,

and some of the most delicious are in the very highest parts of the canopy,

50 metres above the ground.

He's a couple of years old and he's already getting adventurous.

H is mother could climb right to the top in ten minutes or so

if she wanted to, but she lingers, to keep an eye on him.

A fall from this height could be fatal.

Where the gaps between the branches are too wide for him,

his mother lets him use her body as a bridge.

Only ten metres to go before the top.

But it's hard going for small hands.

He's had enough.

Time for a rest...

...with mother.

And this is his reward...

...ripe mangos, sweet and juicy.

There's so much he must learn.

He will depend entirely on his mother until he's seven.

It's the longest of all childhoods except ours.

In these dense forests,

it's not easy for animals to see one another at any distance,

but songs carry well through the jungle.

This is the characteristic sound

that echoes through the Sumatran forest at every dawn.

But what can this be?

Of all the sounds in the Indonesian forests,

this is one of the strangest to our ears.

It can be heard nowhere else on Earth.

And this is the singer.

A Sumatran rhinoceros.

She's tiny, only a fifth of the size of her more familiar African relatives.

Her head could rest comfortably on your knee.

She is the gardener of this Eden.

She doesn't just live in it - she helps to create and sustain it.

She eats fruits and then sheds the seeds in her droppings

and so spreads the foods she prefers through the forest.

In this dense tangle, she uses sound to locate a possible mate.

But her calls are unanswered.

She is living behind a fence...

...for her own protection.

In the past, Sumatran rhinos were widespread throughout Southern Asia.

Today, there are fewer than 70.

It may well be that as she approaches the end of her natural life,

she will have become one of the last of her species...

...because, in the last 40 years,

one-third of the forests of Southeast Asia has been destroyed

in order to sell timber and food products around the world.

The forests of Borneo and Sumatra, home to the orang-utan, rhinos

and thousands of other species that have evolved here over millions of years...

...are now in real danger of being lost for ever.

It seems that the animals whose home this once was

are worth less to us than the land they lived on.

Viewed from space, the scale of destruction is only too obvious.

Asia has undergone a faster change in the last 100 years

than at any other time in its history.

Its forests are being annihilated, its cities are expanding,

and as the human population approaches 4.6 billion,

the largest of all continents is no longer able, it seems,

to allow space for its wildlife.

The oceans around Southern Asia are also feeling this pressure.

These seas feed billions of people around the world.

For many fishermen here, their catch is their only source of livelihood.

And there is one fish here that they prize above all others.

The whale shark.

It swims slowly, gently harvesting the plankton.

It's almost 20 metres long -

the largest fish in the world.

They are also under threat.

Like many shark species in Asia,

populations have declined by more than half in recent years.

They are an easy and valuable catch.

But here, there is a respect for the seas and their inhabitants.

Whale shark hunting has now been banned across Indonesia's waters.

This whale shark plays a different part in the lives of these fishermen.

They feed him, and the relationship seems to bring joy to both parties,

and with this new protection has come something truly remarkable.

Whale sharks from far away are seeking out these fishermen,

and in these safe waters, there is a chance for their numbers to increase.

And maybe one day other shark species will be protected too.

The people here have made a simple but extraordinary choice -

fishing in a way that is sustainable for themselves and the animals.

Caring for wildlife is surely our shared responsibility.

Across this vast continent and across the world, it is decisions like these

that are key to protecting the planet's most precious diversity.

Next time... a land of the unexpected.

The richest and most diverse continent on Earth...

...South America.