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DAVID ATTENBOROUGH: This white wilderness,
this emptiness, is the North Pole.
I'm standing in the middle of a frozen ocean.
Beneath my feet, and for over 500 miles in every direction,
there are several metres of ice.
But something significant is likely to happen here
at the North Pole soon.
Chances are that sometime within the next few decades,
perhaps even as soon as 2020,
there will be open water here
for the first time in human recorded history.
The Arctic and Antarctic are changing.
Enormous masses of ice
that have been frozen for thousands of years
are breaking apart and melting away.
Ice scientists are going to extremes to find out exactly what's going on.
For them, these are exciting times,
but the transformation that's being seen here
will be felt far beyond the polar wilderness.
In this programme, I'll be trying to understand
what these changes mean, not just to the wildlife and people
that live around the Poles, but for the whole planet.
I'm starting my journey in the Arctic, the far north of our planet.
It's still very cold outside by most people's standards,
but the Arctic has been warming fast, twice as fast as the rest of our planet.
My first mission is to find out what effect that's having on the animals.
Although first, we have to find them.
It's April in Svalbard.
We are a thousand miles north of the Arctic Circle
in search of the region's top predator.
We need to travel away from the land and out over the frozen sea.
PILOT: There are some tracks right beneath us.
Over there!
ATTENBOROUGH: I'm with a Norwegian team
which is giving the polar bears of Svalbard their yearly health check.
PILOT: She's under us now. I'll come round for a clean shot.
ATTENBOROUGH: The team works together to give an anaesthetic injection
from a dart gun without hurting the bear.
It takes tremendous skill.
Ah, you got it!
PILOT: I'll just back off until she's asleep.
Nobody likes to see a magnificent animal like a polar bear
lolling about unconscious on the ice,
but it's only by darting them in this way
and keeping check on them year after year,
that we can be sure we know what is happening to them
and the population of polar bears as a whole.
Over the last 30 years, many teams have been seeing
the condition of their local bears deteriorate.
Although not every bear is suffering.
ATTENBOROUGH: How much? MAN: Ninety-six there,
and 102 here, so that's 197, yeah.
-Is that good? -It's not too bad.
It's a bit above average.
So she's a bear in a good condition for Svalbard today.
The trouble is
that if this was underweight, she would be in trouble,
not only from her own point of view but from the point of view of her cubs,
because an underweight female gives birth to underweight cubs,
and underweight cubs have a great problem
of surviving their difficult first year in these circumstances.
It can be -40 degrees centigrade when polar bear cubs emerge
at the start of the Arctic spring from their dens where they were born.
(SQUEALING WEAKLY)
This mother hasn't eaten for half a year.
She and her cubs need to fatten up fast over the next few months
and their chances of survival depend on what's happening beneath their feet.
These polar bears aren't walking on land,
they're roaming across the frozen surface of the sea.
And the bears' food lives under the ice.
Ringed seals are hunted by polar bears.
In fact, in some parts, polar bears eat almost nothing else.
So it's very understandable that this mother ringed seal,
who's looking at me now,
should be a little apprehensive.
That pup of hers is only about three or four days old,
and the pup won't be able to swim for another two or three days.
Seals have good reason to be nervous around their holes.
They need the holes to breathe when the sea is frozen,
but this makes them easy to find.
Polar bears can sniff out seal holes even if they're covered in snow.
Spring is the best hunting season.
This mother's found a food store under the snow
that was probably made by an Arctic fox.
It's a time of plenty now,
but the bear family need to make the best of it
because the good times are about to come to an end.
As the weather warms, the ice beneath the bears' feet
starts to break up and then melt.
And as the ice dwindles,
so do the bears' chances of a successful hunt.
Most of the ice is lost over the shallow coastal waters
where most of the seals live.
It's now summer and these bears have a choice.
Take their chances on the shrinking ice floes
or make for the safety of the land.
It's a case of sink or swim.
Bears have always gone hungry in the summer,
but the length of time when there's enough ice for them to go hunting
is getting shorter and shorter across much of the Arctic.
This is hitting cubs particularly hard
because they can't survive for as long without feeding as their mother.
Cubs that were born underweight are at the greatest risk.
This mother and her cubs may well not get another meal
until the sea freezes again in winter.
There's not much to eat on land,
and the fact is that the longer the cubs have to wait until the ice returns,
the more likely they are to die.
Longer summers with no ice are probably the main reason
why many polar bear populations are dropping.
To help monitor bears into the future,
this female is being fitted with a radio collar
to track her movements.
It's an extraordinary sensation
to be so close to such a powerful animal.
With luck, carrying that collar,
she will have more years to go yet,
and be telling us a great deal about herself
and the rest of the race of polar bears as they face this very uncertain future.
The future of the ice cover on the sea isn't just an issue for the animals.
It's a big concern for the people who live in the Arctic
and travel across the ice every day.
David Iqaqrialu is an Inuit from the village of Clyde River
in the Canadian Far North.
There are very few roads up here,
so David and his community, like most Inuit people,
have always travelled across the frozen sea.
Dog sleds are the safest way to get around
because the dogs feel thin ice underfoot and won't lead travellers into trouble.
(DOGS WHINING)
Old-timers like David know the ice as well as we know the streets
in our local neighbourhood.
Every spring, cracks have always formed in the same places at the same time.
It's going to be big very soon, after two weeks maybe,
it will be more open.
ATTENBOROUGH: But now, cracks are appearing where they never did before,
so David and his friend Laimikie have taken on a new job.
They are using special GPS units
to record the position of new cracks or weak ice.
These findings will be used by locals for their own safety
but they're also being studied by ice scientists
who want to predict how the ice will change
in years to come.
(SPEAKING LOCAL LANGUAGE)
The Inuit are keen to know what the future holds, too,
because they've seen with their own eyes
the changes that the scientists have seen from space.
This satellite photo from 1980
shows the Arctic Ocean at the end of summer
when ice cover is at its minimum.
Since then, there's been a 30% drop in the area covered by ice.
But these images can't tell us about changes to the most important factor,
the thickness of the ice.
Measuring thickness across the whole ocean
was beyond scientists for many years,
until help came from an unexpected source.
The Arctic Ocean is of huge military importance,
as it's the shortest route between North America and Russia.
Since the late 1950s, British, US and Russian submarines
have been patrolling the Arctic Ocean.
But as well as looking out for enemy activity,
they've also been measuring the thickness of the ice,
critical when looking for a place to surface.
When scientists got permission to look at the submarine crews' records,
they discovered that the ice has been thinning fast.
In fact, it's nearly halved in thickness since 1980.
Across most of the Arctic Ocean,
there are now just a couple of metres of ice.
It's so thin that it could melt away almost entirely in the summertime
and that includes the ice at the North Pole.
If current trends continue,
then there will be open ocean here by summer's end
sometime within the next few decades.
So, the days of the Arctic Ocean
being covered by a continuous sheet of ice seem to be past.
Whether or not that's a good or bad thing,
of course, depends on your point of view.
(SHOUTING)
Nobody has had a better view of the changes to the Arctic Ocean
than the people of Barrow, the most northerly town in Alaska.
The people here have always survived by hunting on the frozen sea
and they celebrate this at a festival every year.
The blanket toss was once the best way to spot distant animals to hunt,
as lifelong resident Lewis Brower explains.
When we throw ourselves up into the blanket, you know,
you get that much more of an "Ah!" of seeing further and further out.
So, sometimes you'll jump 15, 20 feet in the air
and hopefully you're being caught right back into the blanket.
I'm okay!
(CROWD LAUGHS)
ATTENBOROUGH: But the old way of life is under threat.
When Lewis was young, the sea stayed frozen to the horizon until July
and some ice remained off-shore all summer,
but now, it's breaking up in June
and melting away completely for two or three months.
I used to go out on the ice all the time this time of the year.
But we can't do that any more because there's no more ice.
ATTENBOROUGH: Lewis can also see that the loss of sea-ice
is affecting the animals he hunts for a living.
Since 2007, something very strange has been happening
on this stretch of coastline close to Barrow.
Mother walruses, confused by the lack of ice,
are crowding onto the land with their pups.
This very tight crowding isn't normal
and it's caused many youngsters to be crushed to death.
Many Arctic animals are threatened by the changing conditions
and that's also bad news for the traditional hunters.
But the ice loss could be good news for some people.
There are trillions of dollars' worth of oil and gas under the Arctic Ocean,
but the only way to get to them until now
has been by building expensive artificial islands like this.
But if the sea ice goes,
it will be much easier to drill for the huge riches below.
So the countries that surround the Arctic
are scrambling to stake their claims.
This daring attempt by the Russians
to claim the disputed seabed at the North Pole in 2007
caused fury among the competing countries
and it's unlikely to be the last such dispute.
The Arctic has never been so important, and not just because of its resources.
The Northwest Passage,
a legendary sea route around the north of Canada and Alaska,
cleared of ice in the summer of 2007 for the first time since records began.
This promises a much faster and cheaper shipping route
between the Atlantic and Pacific Oceans.
And some wildlife could benefit from an ice-free Arctic, too.
Bowhead whales are one of just a few whales
that can live year-round in the Arctic because they have no dorsal fin.
This means they can come up for air in small spaces
and travel easily under the ice.
Their unique body shape used to mean
that the Arctic whales had the seas to themselves for most of the year,
but now, some cousins from down south are moving in.
(WHALES CALLING)
Killer whales are now a much more common sight in the Arctic.
Their tall fins make it difficult for them to travel under ice
but the longer summers mean they can travel much farther north
and make the most of the rich Arctic seas.
For animals and people,
it will be those who can adapt who will thrive in a changing Arctic.
But the loss of sea-ice isn't just an issue for the Arctic,
because the state of the ice affects the climate of the whole planet.
Because it's white, the ice reflects up to 90% of the sun's energy.
This is called the albedo effect,
and it's why we often see heat haze in the Arctic,
even when the air feels cold.
The frozen Arctic Ocean acts as a huge reflector,
bouncing back the sun's heat into space.
Throughout history, that has helped to cool the planet,
but when the ice melts, it's a different story.
Because sea water is dark, it absorbs most of the sun's heat.
In the Arctic, this can trigger a chain reaction
as the warming water melts more ice, exposing more water to the sun's heat.
This cycle of warming,
as huge areas start to absorb rather than reflect heat,
is the main reason why the Arctic, a region the size of North America,
is warming twice as fast as the rest of the Earth.
So, melting sea-ice is a big issue, but there's another kind of ice
that could have an even more dramatic impact on our world,
the ice that is found on land.
This is freshwater ice,
formed from thousands of years of accumulated snowfall.
(ICE RUMBLING)
This is the front of a glacier.
Quite a small one, believe it or not.
Glaciers are like rivers of frozen fresh water
flowing across the surface of the land.
This one, like most polar glaciers,
is flowing down from a vast inland ice sheet,
and it's what happens to those ice sheets
that could radically alter the face of the planet.
The Greenland ice sheet is by far the largest in the Arctic.
It's two miles thick in places
and six times the size of the United Kingdom.
Every summer, some of the surface of the ice sheet melts,
forming sapphire-blue lakes of melt water.
More and more of these lakes have been forming
as Greenland has warmed over the last 20 years.
This lake has grown over several weeks, and now it's overflowing,
carving a deep channel through the ice.
A network of channels criss-crosses the ice sheet,
but many of them come to an abrupt end.
Huge holes like this can open up quite suddenly,
draining the melt water away.
Alun Hubbard is a glaciologist
studying the enormous power of these waterfalls,
which are known as moulins.
We've got this amazing moulin going off here today.
The water's overflowing from the lake, which is beginning to drain.
Tonnes of water cascading down this pipe
that is effectively plummeting to the depths of the ice sheet
through over a kilometre of vertical ice.
ATTENBOROUGH: Alun is here to study where the melt water goes
and what affect it has on the remaining ice.
To do that, he needs to find a moulin that has recently run dry.
Just a week ago, there was a three-mile long, 10-metre deep lake here.
The weight of all that water cracked the ice beneath
and the lake drained in just a few hours with incredible force.
Thousand-tonne ice boulders were tossed about like dice.
Alun's team have found the hole down which the lake disappeared
and they want to have a closer look.
It's not job for anyone with a fear of heights.
As you can see, it's dry up here, but if you listen,
you can hear the thunder of...
There's a lot of water entering it at some depth.
ATTENBOROUGH: Alun wants to place a sensor deep into the moulin
to discover how much water is flowing through the ice.
As they drop, they travel back in time.
Thirty metres down and they reach ice formed from snow
that fell 10,000 years ago, in the last ice age.
When this lake drained and the plug got pulled,
and the whole lot flushed down through here,
this ice sheet, it rose by a metre
as that water accessed the bed and force-jacked up the ice sheet.
So, we know that the water in this whole plumbing cavity system down here,
we know that shoots straight through the ice
and actually hits the bed of the ice sheet.
We've hit the water! I can see the water now.
Great. Nice work!
ATTENBOROUGH: This daring experiment
is measuring how the water flowing under the ice sheet
affects the speed with which the glaciers flow from it down to the sea.
The theory is that the water is acting as a lubricant,
so the more water there is, the faster the glacier flows.
To the naked eye, glaciers don't appear to move at all.
But move they do.
These unique time-lapse images were captured over the last four years.
Through long observations, we now know that Greenland's ice
is flowing down to the sea twice as quickly as it was 20 years ago.
The speed of the glaciers affects our sea levels,
because when they reach the water, they break apart into icebergs.
Occasionally, a real mega-berg is born.
This is the Store Glacier in May 2010.
Seventy-five million tonnes of ice
that had been sitting on land for thousands of years has broken away.
Events like this have become increasingly common
as Greenland's glaciers flow faster into the sea.
Every single one of these icebergs raises the sea level a small amount.
Scientists monitoring the ice sheet
predict that Greenland might add as much as a half metre
to world sea levels by the end of the century,
enough to swamp many of the world's low-lying islands.
99% of the Arctic's freshwater ice is in Greenland.
It's a staggeringly big ice sheet but it's just a drop in the ocean
compared to that at the southern end of our planet.