He hasn't eaten in days.

This may be his last chance.

(theme music plays).

I'm two miles above sea level here,

and it is brutal.

Cold, desolate, hard to breathe.

But, for some, this is home.

Mountains are one of the most hostile environments

on our planet.

Now, with the rise in global temperatures,

life is even tougher.

The relentless search for food.

Intense competition.

Unpredictable weather.

Mountain animals are pushed to the edge of existence.

The Arctic Circle.

Nowhere is the planet warming faster.

Spring has arrived here early.

And that's bad news for the barnacle geese

that breed in these mountains.

Many nests have failed...

but not this one.

Three chicks.

They're lucky to have made it.

Forced by the early spring,

the parents rush to their migration.

They arrived exhausted.

The female sat on the eggs for 25 days.

She's lost 30% of her body weight.

But for this family,

the greatest challenge is still to come.

The parents chose to nest on this 400 foot pinnacle.

It's the only way to evade predators.

Just one problem...

the grass they eat is a mile away,

by the river.

And barnacle geese can't feed their young in the nest.

If the chicks don't feed within 36 hours,

they'll starve.

And these chicks won't be able to fly for another month.

The parents are living proof there is a solution.

Just not an easy one.

Dad leads the way.

But the chicks are instinctively bonded to mum.

Where she goes they follow.

(peeping).

Incredibly, it survived.

But it's stunned.

And now dangerously exposed.

(honking, cawing).

One chick gone.

Now hope rests with the other two.

The back of the spire is a shorter drop.

But it's much harder to avoid the rocks.

For this chick, there will be no escape.

The third and last surviving chick.

♪ ♪

The snow cushions the impact, but offers no grip.

(honking).

Only around 50% of chicks hatched on these cliffs

make it through the first month.

With the seasons increasingly unpredictable,

fewer chicks will survive.

But this chick, at least, has defied the odds.

A changing climate is affecting life in mountains

across the world.

Late winter.

The average temperature here is rising a degree every decade.

Bad news for a snow leopard.

Thick fur enables him to withstand temperatures

of -20 Fahrenheit.

But today, it's 66.

To find enough food, he must patrol a territory

of 80 square miles.

Dry barren slopes don't support much prey.

It can be more than a week between meals.

He must make a kill,

or starve.

BEAR: 16,000 feet up in the Himalayas,

a desperately hungry snow leopard.

His best opportunity in days is within sight.

Blue sheep.

In this heat, he can't run far.

He needs to close the gap.

His camouflage helps.

But with so little cover, it's hard to get close enough.

He ran too early.

And it's too hot to give chase.

Like all who live here,

his fortunes are linked to the mountain climate.

And even small changes can have dramatic consequences.

Here in Africa, rising temperatures

are forcing mountain life ever higher.

An army of Gelada monkeys is gathering.

They're all after one thing.

But to find it, they must climb higher and higher.

Their numbers grow to 1200 strong.

One of the largest gatherings of monkeys on the planet.

At 10,000 feet, this is what they're after.

Grass.

It's almost all they eat.

But so many monkeys in such a small area means trouble.

Especially for this old male.

He needs a lot of energy to defend his family.

Ten females and 12 youngsters.

But you don't get much from grass.

He has to spend ten hours a day feeding.

And today he's gonna need all the energy he can get.

Bachelor males.

Outcasts.

Forced to the edge of society.

Any one of them would be happy to take down the old male and

become the new family leader.

To hold onto power, the old male must prove his strength,

both to the bachelors and his females.

He challenges them to chase him.

(barking, yelling).

But no one dares to attack.

His show of force has worked.

For now.

The old male has little time to refuel

before the herd moves on.

The bachelors are back.

(barking, yelling).

At this high altitude,

each confrontation takes more energy.

A relentless cycle of moving, feeding and fighting.

Moving, feeding, fighting.

By late afternoon, the old male is exhausted.

The strongest bachelor, 45 pounds of muscle,

with energy to burn.

He's the most serious challenger yet,

and the old male knows it.

BEAR: Two male Gelada monkeys fight for supremacy.

A dominant male and a younger bachelor.

One against one the bachelor is stronger.

The old male won't last much longer.

At least not alone.

His females are loyal.

They won't give up on their protector yet.

This united force is overwhelming.

The old male is victorious.

But it's tough at the top.

As the climate warms and the grass they depend on retreats higher,

their battle for survival will only intensify.

In the heat of mid-summer, mountain goats seek out

cooler temperatures on the high ridges.

This female is a natural mountaineer.

She can easily access the best grazing,

even with a kid in tow.

But there's one thing they both need that's

far harder to reach.

Today, they must leave the ridge and descend

into the heat of the valley.

For the little one, this is a dangerous journey.

With the mercury hitting 100 degrees Fahrenheit,

this is the hottest summer on record.

After a winter of heavy snow,

this means more meltwater than ever.

Mum's made this journey before,

but some rivers are at their highest level in 100 years.

♪ ♪

Their goal is in sight.

Just one more river to cross.

But it's the deepest and widest yet.

The current is too strong for little legs.

And this is what they've risked their lives for.

A salt lick.

These goats crave sodium, an essential mineral lacking

in their mountain diet.

Summer in the mountains is short.

Harder times are coming.

Temperatures plummet.

Days shorten.

Winter is here.

But the hunt for food must continue.

Heavy snow on higher ridges has forced these ibex

down into the valley.

A cold winter can be a blessing for

a hungry snow leopard.

He's less likely to overheat.

But against the white, he's visible for miles.

He must rely on stealth.

Not easy in such deep snow.

♪ ♪

The distance was too great.

The ibex too fast.

Now all the animals in the valley know he's here.

And he's burnt precious energy.

These are desperate times.

If he's to see winter through,

he may have to take bigger risks.

Throughout the mountains of the Northern Hemisphere,

winter's grip is tightening.

Animals must make the most of any last opportunity before

conditions drive them to take shelter.

Far above, planetary forces are on a collision course.

A river of air, the jet stream,

flows around the North Pole.

At its center, sits a mass of cold Arctic air.

But now a warming upper atmosphere is slowing the jet stream.

And the cold air can escape.

By the time it hits The Rockies,

it's grown into a mega storm.

Freezing everything in its path.

BEAR: In the depths of winter, extreme storms rage across

Canada and the USA.

Freezing temperatures,

wind speeds of up to 150 miles per hour.

Now, even the toughest animals are at their limit of survival.

(wind whistling).

The storms may have passed, but there is hidden danger

in this landscape.

Winter storms have buried this area of British Columbia

under nearly 40 feet of snow.

But if temperatures rise above freezing,

it can have lethal consequences.

On the high ridges, wind driven snow has created

huge overhangs, some 25 feet thick.

The longer the temperatures stay above freezing,

the more the snow pack weakens.

(crashing).

Soon, tens of thousands of tons of snow are traveling

up to 80 miles an hour.

As weather patterns change, avalanches across the world

are growing bigger.

The more erratic and severe mountain winters become,

the more victims they'll claim.

But some are still succeeding in this harsh world.

Golden eagles live in almost every mountain range in the

Northern Hemisphere.

They endure the alpine winter by using the brutal conditions

to their advantage.

Like all golden eagles, this female has a special sensory

organ that detects change in air pressure,

allowing her to locate air currents rising off ridges.

With her seven foot wingspan, she can climb to over 11,000 feet.

Then, to get to the next peak, she folds her wings and dives.

With a top speed of 150 miles per hour,

she's one of the fastest animals on the planet.

It looks effortless, and it needs to be.

A golden eagle may cover 100 miles a day scouring

the slopes for any opportunity.

A flock of ravens is a good sign.

(cawing).

During winter, golden eagles are forced to scavenge

90% of their food.

If finding food is hard, keeping it is even harder.

A carcass like this attracts a lot of attention.

This male is powerful.

And eagles don't share.

Another brutal storm.

This could be the last chance to feed for days.

Starvation is a serious threat.

Only a quarter of young eagles will survive to reach maturity.

Will it be him or her?

Attacking from the air gives her the advantage.

But her victory is short lived.

Now both eagles may be fighting for their lives.

BEAR: In the peaks of Norway, two golden eagles are fighting

for a chance to feed.

Both are desperate.

The female stands her ground.

But the male is not done.

(screaming).

Each eagle is armed with two inch talons.