Original subtitles

NARRATOR: In the extreme, ice-bound regions of the earth,

something unprecedented is happening.

Everywhere, glaciers and ice sheets

have begun breaking apart and accelerating towards the oceans

faster than ever imagined possible.

Can we put the brakes on it at any point?

Do we have that much control over it?

MAN: There are concerns that we get to some point

that the changes become pretty much unstoppable.

NARRATOR: Over the history of the earth,

ice has freqntly advanced and receded,

but now it's changing in ways we don't fully understand.

With the future of the ice in question,

photographer James Balog risks everything

to capture what's happening on film.

BALOG: This is one of the scariest, dumbest things

I've done in my life.

Where I'm laying right now was underwater just six hours ago.

I'm not feeling real comfortable out here.

NARRATOR: His incredible imagery is witness

to one of the earth's most powerful geological forces--

a force that for the first time in modern human history

is radically changing the planet.

"Extreme Ice" revealed, right now

on this NOVA- National Geographic Special.

Captioning sponsored by EXXONMOBIL,

PACIFIC LIFE,

DAVID H. KOCH,

the HOWARD HUGHES MEDICAL INSTITUTE,

the CORPORATION FOR PUBLIC BROADCASTING

and VIEWERS LIKE YOU

NARRATOR: James Balog has a near-fatal attraction to ice.

BALOG: Oh, God, that is intense!

NARRATOR: His fascination is leading him farther and deeper

into the cryosphere, the frozen regions of the earth.

BALOG: I feel like I'm not on planet Earth right now,

like I'm in truly some extraterrestrial environment.

The world isn't supposed to look like this.

NARRATOR: What began as a photographic assignment

has become a mind-blowing odyssey

into an unpredictable world,

where entire landscapes teeter between solid and liquid states.

On the Greenland ice sheet, a crack opens,

and a mile-wide lake pours down a 3,000-foot chasm.

BALOG: This water is just drilling down into the ice sheet.

NARRATOR: One of the world's biggest glaciers sheers off an iceberg

that is nearly a thousand feet thick.

BALOG: You're not supposed to be able to witness things like this.

Human beings don't generally get to see

these massive features of the landscape

changing and vanishing in front of your eyes.

NARRATOR: Changes in the ice are normal.

It is volatile and constantly in flux.

But what Balog is witnessing suggests

something extraordinary is going on.

His passion is to document it

and help scientists understand these monumental changes.

MARK SERREZE: Many of the changes we're seeing

are unfolding faster

than our ability to really understand them.

JAMES WHITE: Our relationship with ice is one

that has very dramatically, if not violently, shifted

from one of, "Ah, don't worry about it" to one of,

"Boy, you knowthis is one of the most important controllers

of the futurenvironment of the planet."

NARRATOR: Balog's work frames

one of the most important scientific questions

humans have ever faced.

How fast will the world's glaciers and ice sheets melt?

And what will all that melting mean for us?

As scientists try to figure it out,

Balog is finding evidence

to help answer some of these questions.

Got it!

NARRATOR: His Extreme Ice Survey

is the largest photographic study of the cryosphere

ever attempted.

He is deploying 26 time-lapse cameras

on glaciers across the Northern Hemisphere

and programming them to shoot a frame

every daylight hour for three years.

It is a massive challenge,

in some of the most hostile regions on earth.

BALOG: So everything we are trying is getting thwarted.

I'm trying not to be frustrated.

NARRATOR: But the pain is starting to pay off,

with thousands of frames revealing unparalleled changes

in the ice.

BALOG: My hope is that it will be powerful and immediate enough

that people will say, "Yeah, I get it, I understand it.

"Okay, this is real.

This is forensic evidence of the reality of what's happening."

NARRATOR: The fact that the ice is changing is nothing new.

Over the millennia,

the expansion and contraction ofce across the continents

has fundamentally altered the planet,

gouging out lakes and valleys

and pushing man around the earth.

RICHARD ALLEY: The waxing and waning of the ice sheets

have been implicated

in who lives where and what they do,

and there are even some people who have suggested

that we're humans now in part because we were responding

to the changes in our environment that were linked

to the growth and shrinkage of the ice.

NARRATOR: In the past, the cycle of ice ages and periods of warming

were caused mainly by shifts

in the earth's orbit around the sun.

But now, humans seem to be driving these changes.

Since the Industrial Revolution, our burning of fossil fuels

has ratcheted up the output of greenhouse gases,

like carbon dioxide, which trap heat in the atmosphere.

Temperatures are climbing,

and the ice is melting faster than ever.

WHITE: I think that if we stay on the path we're on,

we will change the amount of land ice

and, therefore, we will change sea level.

The real questions, the more complicated ones:

How fast are we going to get there?

How much is it going to rise?

Can we put the brakes on it at any point?

NARRATOR: It is the speed of the melt that is most astonishing.

And nowhere is it happening faster than in the glaciers

along the west coast of Alaska.

Glaciers are like massive ice factories.

High in the mountains, snowfall builds up

and is compacted over hundreds of years.

Gravity pulls it down in colossal rivers of ice.

Some glaciers flow all the way to the ocean,

shearing off icebergs in a process called calving.

Over the last 40 years, temperatures here in Alaska

have risen about four degrees Fahrenheit,

twice as fast as the global average.

Now these rivers of ice are flowing faster

and crashing even more spectacularly into the sea.

Some people are taking advantage

of the glacial fireworks while they last.

Surfers towed in by jet skis

are playing a dangerous game of chicken with the ice.

It is rapidly calving glaciers like these

that are the main contributors to rising sea levels.

Alaska's Columbia is one of the biggest ocean-feeding glaciers

in North America.

In the early 1980s, the Columbia started flowing faster

and began calving far more ice into the ocean

than was being replenished by snowfall upstream.

Balog and the Extreme Ice Survey glaciologists are trying

to figure out how much ice the Columbia is losing

and whether or not it can survive.

In the shallow waters of Columbia Bay,

melting icebergs jam up

before being carried away with the tide.

This is the end of the line for the Columbia,

a crystal maze of deteriorating ice that draws Balog in.

BALOG: Basically, we are looking

at a whole landscape full of crystals.

It's a cool spot.

There is a lot of power here.

It seems to be calm, it seems to be still,

but there's this constant energy of the sea coming and going

and carrying this huge glacier away.

Every time you go in here, you are taking a risk,

because these bergs are inherently unstable.

But you get seduced by the beauty of it.

You know, you just get drawn in.

back through the labyrinth.

Okay, Jeff, right about on this line here.

BALOG: The light that really makes these sculptures come alive

is bouncing off the surface of the water,

so the bergs are lit from within.

Oh!

NARRATOR: At the Extreme Ice Survey camp,

glaciologist Tad Pfeffer tracks the flow of the Columbia.

As the glacier moves, it churns up dirt and rocks

that collect on its surface.

The Columbia is so vast, it's hard to imagine it vanishing.

Pfeffer and his colleague, Shad O'Neel,

are taking its vital signs,

measuring the speed of the glacier over several years

to determine whether it's speeding up or slowing down.

To do this, they fire a laser survey gun

at reflective targets that they must deploy

on the surface of the ice.

As the pilot hovers a few inches above the glacier,

O'Neel positions the target onto the ice.

Pfeffer locks onto the target

and shoots a laser that reflects back

to the stationary gun, recording the position.

(high-pitched beep)

I got it. You're good.

Come on back.

Okay, first one down, 1.1 kilometers away.

NARRATOR: The target moves with the ice.

By tracking its movement with the laser over several days,

they will be able to calculate the speed of the Columbia.

Just down the fjord,

Balog and Extreme Ice Survey engineer Adam LeWinter

climb down to one of the time-lapse cameras

they installed a year ago.

Oh, yes! Here it is!

Still all there.

Yeah, the camera's here, but what happened to the glacier?

When I was here a year ago,

the calving face was just right there.

All right, we have pictures!

NARRATOR: The time-lapse brings to life

the dynamic nature of the glacier,

the ebb and flow of the ice as it calves.

BALOG: It's a revelation every time we open up these boxes

and download these images and bring them up on the computer

and play them back.

Your eyes are popping out of your head.

NARRATOR: Although calving is normal,

the Columbia is hemorrhaging ice so quickly

that in the last 30 years,

the glacier has receded ten miles up the fjord.

Balog's time-lapse images capture a rate of retreat

that shows no sign of stopping.

In the last year alone,

the Columbia lost another half-mile of ice.

BALOG: I really never expected

that we were going to see changes

of anything like this kind of magnitude

in the period of time we had to work on this.

NARRATOR: This rapid calving of the Columbia

is a symptom of its decline, but it's poorly understood.

If Pfeffer and O'Neel can figure out

what's causing it to calve more ice,

it may help them predict the glacier's future.

They are taking a curious tack by using earthquake technology

to crack open the mystery of the ice.

They are installing seismometers that pick up the vibrations

of "ice quakes," tremors that reverberate

through the ice as it calves.

From the seismic data, a pattern emerges

that points to one clear culprit, water.

They knew water was melting the ice,

but it appears that it's prying the ice apart

like a powerful lever.

O'NEEL: You can hear meltwater running right now

and it's all getting stuck in the glacier,

and if you have a fracture with high-pressure water in it,

it can ratchet the crack open.

NARRATOR: The seismic record confirms

that the calving events have the unique signatures

of fractures caused by water.

As rising temperatures create more surface melt,

the water pours into the cracks in the glacier

and wedges it apart.

The result is increased calving

and a quicker demise of the glacier.

BALOG: Oh, there's a big one coming up from underneath.

There it is!

NARRATOR: Balog is seeing this powerful fracturing effect firsthand

as the fjord below comes alive.

BALOG: That basal ice has come up

from the very bottom of the glacier,

that dark blue out there.

As the ice and the snow are squeezed together,

the air gets driven out of it,

and so the color becomes more and more pure.

The air bubbles are what make it white.

And so when the base of the glacier breaks up,

you get these fantastic sapphires and turquoises

boiling up out of nowhere, you know,

and that's what these bergs are.

NARRATOR: Meanwhile, after several days of laser tracking,

Tad Pfeffer knows how fast the Columbia is moving--

50 feet per day, eight times faster than it was 30 years ago.

PFEFFER: Go back to 1980.

Here on this bedrock, we had ice above us 1,500 feet.

Look at the trim line over there.

That's where the ice surface was in 1980.

And all of that volume is lost because this calving is so fast,

and snowfall upstream isn't resupplying it.

So in that sense, yeah, it's going too fast,

and the glacier is kind of collapsing.

NARRATOR: Pfeffer suspects that the Columbia

is long past its tipping point

and it's only a matter of time before it withers away entirely.

BALOG: This kind of ice is called "dead ice"--

it's no longer part of the living, active glacier.

It's stranded up on the side of the ice stream,

and it's melting away and collapsing.

And as it does that, all the erosional debris

that's on the top continues to concentrate,

until you have this ice covered in blackness.

I'm really interested in the mortality

of the glacier right here.

There's something very rich and very intense

about the changing landscape.

You know, I feel the end, I feel the death right here.

(shutter clicks)

NARRATOR: The problem is,

it's not just the Columbia that's on its way out.

Glaciers everywhere,

across the Rockies, Andes, Alps and Himalayas,

are in their death throes.

The people that live near the mountains

and watch the glaciers know that the world is changing.

We are heading towards Glacier National Park

without any glaciers.

We're seeing huge changes

in Glacier Bay in Alaska and other places.

If you go, if you look, you see it.

NARRATOR: The consensus is that in the next 50 to 100 years,

mountain glaciers almost everywhere

will simply disappear.

From the loss of mountain glaciers alone,

sea levels will rise by almost a foot,

displacing millions of people around the world.

But the biggest cost will be the loss

of these huge natural reservoirs of fresh water,

water that one-sixth of the world's population depends on.

The hardest hit will be in Asia,

where nearly a billion people get their drinking water

from Himalayan glaciers.

The abrupt collapse of the world's mountain glaciers

raises even more disturbing questions

about the earth's biggest tracts of ice,

the polar ice sheets of Antarctica and Greenland.

SERREZE: The real wild cards are

what the big ice sheets are going to do.

We're already seeing the Greenland ice sheet

start to behave in rather disturbing ways.

WHITE: We're playing with fire, if you will,

when it comes to the ice sheets.

We don't know

whether if we get

these big, massive, freight train-like beasts going,

whether we can stop them.

NARRATOR: The potential for the polar ice sheets

to flood the planet is staggering.

If all of Greenland and Antarctica were to melt,

the oceans would rise 200 feet.

But over geologic time, these ancient bulwarks of ice

have withstood many bouts with climate warming.

Until a few years ago,

scientists thought the ice sheets were simply too big

and too dense to be an immediate risk,

but the latest evidence is making them rethink.

The first wake-up call came from the West Antarctic Peninsula.

In the summer of 2002, a NASA satellite photographed

a Rhode Island-sized slab of ice called Larsen B

as it sheered off the ice shelf.

Other collapses followed, turning the assumption

that it would take thousands of years

for the big ice sheets to melt on its head.

ALLEY: The ice sheets surprised us.

We sort of thought that the little glaciers would melt

when it got warmer, and that the big ice sheets wouldn't do much.

And all of a sudden, the big ice sheets started rumbling faster

and the Larsen B was falling apart,

and we said, whoa, that wasn't supposed to happen.

NARRATOR: On the other side of the globe,

Greenland's cache of ice is also showing signs

that it's starting to feel the heat.

In the last decade, temperatures here have shot up

by about five degrees Fahrenheit.

NASA satellites are already detecting a meltdown

around the edges of the ice sheet.

Global warming is hitting hardest in the Arctic,

and all eyes are now fixed on Greenland's ice.

Its next move could be the game changer for rising sea levels.

In the heart of Greenland, Balog and scientists encounter

an entirely different realm,

a single slab of ice about 1,500 miles long and 500 miles wide.

It's mid-July, and the summer melt on the Greenland ice sheet

is in full swing.

BALOG: It's sort of like a ice version of Kansas out here.

It feels like you're out in the Great Plains,

and it just happens to be white,

and there's this vast dome in the sky overhead.

It's... it's unbelievable.

There's no sound at all, no sound,

except the wind and the water.

It looks quite featureless when you just look horizontally,

but as you walk over it and you look down on it,

there's a tremendous amount of texture and detail in here.

This entire surface is like one gigantic Swiss cheese.

NARRATOR: During the melt season,

the sun's heat transforms the surface of the ice,

creating a landscape that constantly shifts

between solid, liquid and vapor.

The meltwater courses through the ice sheet,

searching for a path down.

Figuring out how this complex plumbing works is essential

for predicting the future of the ice sheet.

Oh, man!

Look at that.

Whoa!

That is intense!

Oh, my God.

I can see, I think, maybe 250 feet down into the dark,

no sign of the bottom.

this great mystery of where does all this water go,

and what does it do to the flowing and the melting

of the ice sheet in sending it out to sea?

Nobody really knows.

NARRATOR: Balog wants to get a shot

that delves deep into the underbelly of the ice.

The only way to secure his ropes

is to thread them through the ice sheet.

BALOG: You know, this ice sheet is cooking down

and melting a lot, so this whole top foot and a half,

where you would normally put an ice screw,

is rotten and loose,

whereas here we are actually using the ice sheet itself

and the strength of the ice to anchor the ropes.

So, here we go.

Yay, how about that?

NARRATOR: These giant holes, called moulins, are thought

to bore thousands of feet through the ice to the bedrock,

but nobody has ever been down there to find out.

BALOG: Oh, God, that's the first time

I've really seen the hole down there.

This whole balcony could go any second.

There it goes!

It's a strange, evil, gorgeous, horrible, fantastic place.

Wow-- I mean, there's hundreds of years of ice here layered in,

and we're looking into the cross section

of this life history of the glacier.

And it's so beautiful, this insane aquamarine,

and all this scalloping and fluting from the water.

What a spot!

NARRATOR: Balog is just scratching below the surface of the ice sheet.

Below him is another half-mile of solid ice.

In these compressed layers of the ice sheet,

there are clues to how fast Greenland could melt.

At the National Ice Core Lab in Lakewood, Colorado,

a giant freezer stores over 45,000 feet of ice

drilled from 34 sites around the cryosphere.

Dating back hundreds of thousands of years,

these ice cores are time capsules that allow scientists

like Jim White to peer deep into the history of ice.

WHITE: This piece of ice is interesting,

because it has a couple of things you can see right away.

One is there are bubbles throughout here.

These bubbles are little packets of air.

It's these bubbles we can take out and measure CO2

and methane and nitrous oxide.

It's the only medium that really collects the atmosphere itself.

The other thing you can see in here quite clearly

is you can see the layers,

and the thickness is going to tell you

how much snow fell that year.

So you get a couple of pieces of climate information

and a dating scale, just out of visually looking

at this ice core.

NARRATOR: Most importantly, scientists have identified

a direct historical link between increases in greenhouse gases,

like carbon dioxide, and steep rises in global temperatures.

At every peak, big rises in sea level followed,

as Greenland's ice sheet shrank.

The ice core records also reveal a particularly telling moment

in Greenland's history.

Roughly 125,000 years ago,

temperatures rose by about seven degrees Fahrenheit.

The entire southern portion of the ice sheet melted,

and global sea levels rose by over ten feet.

It was caused by a change in the earth's orbit around the sun,

which increased temperatures

and released carbon dioxide from the oceans.

The more recent ice core record shows the potential

for a similar meltdown.

Right now, greenhouse gas levels in the atmosphere

are even higher than they were 125,000 years ago,

higher than they've ever been

in the last half-million years.

Temperatures are already following suit.

The only explanation is the burning of fossil fuels.

WHITE: What we see in this ice core

is very solid evidce

that what's happening today in the atmosphere is different.

It's not a normal part of the climate cycle;

it's something caused by human beings.

NARRATOR: Rising temperatures are once again pushing Greenland

towards a major meltdown,

but what the ice cores can't tell us

is how long it will take.

The last time Greenland lost a significant portion of its ice,

White suspects it happened over thousands of years.

But this time, it could happen much faster.

SERREZE: And here we are now,

fiddling with the dials of the climate machine,

not quite knowing what's going to happen,

and we know from these past records

that the climate system can come up and bite us hard.

NARRATOR: So far, global warming is biting hardest

at the fringes of Greenland's ice sheet.

Ringing the island are hundreds of outlet glaciers

that act like pipes, draining the interior ice sheet

out to sea through narrow fjords.

In the late 1990s, many of these spigots began gushing more ice.

One of the largest, Jakobshavn, is now pumping out

over 40 billion tons of icebergs each year,

more than any other glacier in the Northern Hemisphere.

These icebergs reach the open ocean at Disko Bay.

In this deceptively peaceful icescape,

James Balog is on the hunt for giant bergs.

Some of these blocks of ice rise over 300 feet

above the waterline, but 90% of their mass is hidden below.

BALOG: Oh, my God, these things are gigantic.

If they roll over, we'll be swimming with the fishes.

Right in here, there is this line of jewels

as you come around the arc of this berg,

and all the water drops are coming in,

and the sun makes this fantastic necklace-- jewelry

along the edge of this.

Aw, man, let's do it again.

There's something in there.

It's making me crazy, actually,

because there's a picture in here,

there's definitely a picture in here.

Wow! That was amazing.

NARRATOR: 35 miles up the fjord from Disko Bay,

Balog's time-lapse cameras are stationed above the calving face

to capture Jakobshavn's every move.

Balog has teamed up with glaciologist Jason Box,

who has been keeping a close watch on Jakobshavn

and other glaciers along the coast for the past 14 years.

The Jakobshavn glacier is the king of glaciers in Greenland.

It produces by far more icebergs and more ice flow

than any other single glacier.

This is really where the rubber hits the road

in terms of sea level rise.

Glaciers are, of course, very dynamic systems,

but you don't really see that

when you sit there and stare at them.

We're able to observe with the time-lapse cameras

at a much higher frequency, like every hour,

whereas from satellite,

you can only observe the glacier every ten days or so.

NARRATOR: What they are finding is that the ice

is far more sensitive to temperature changes

than they thought.

During the summer melt season, Jakobshavn is now moving

at a clip of 130 feet per day,

almost twice as fast as a decade ago.

The faster it goes, the more pressure builds up

behind the glacier 400-foot-high calving face.

This triggers more frequent and explosive calving events.

In the spring of 2008,

Balog's team was staking out Jakobshavn and got lucky,

capturing the largest calving event ever filmed.

In the space of about an hour,

a section of ice as wide as Manhattan

sheared off the glacier.

BOX: We've underestimated the sensitivity of these systems.

We are approaching

the threshold of viability for the Greenland ice sheet,

and that's when the melting occurs

high enough on the ice sheet

that no matter how much snow accumulates,

there's net loss every year.

NARRATOR: Greenland is already losing

150 billion tons more ice every year

than it gains in snowfall.

As temperatures go up in the coming decades,

even more ice will be lost.

The hard part is figuring out how much and how fast.

There's big questions now

that we didn't think we were going to have to solve.

They're hard questions.

Ultimately, you crank up the temperature in the air,

and the ice sheet notices and it flows faster

and it raises sea level.

But how fast and how much

are questions that really we don't have answers to.

NARRATOR: Some of those answers may be hidden, deep under the ice.

The summer melt season on the Greenland ice sheet

has grown hotter and is now two weeks longer

than it was only a decade ago.

Rivers of meltwater cut deep into the ice,

creating a serpentine canyon that winds for miles.

BALOG: This is one of the most exceptional landscapes

I've ever seen in my life.

You know, this looks so much like those incredible canyons

out in the sandstone country in Utah,

and you have that, except it's sculpted out of ice.

It's like this huge, incredible cake,

sculpted by this river in here,

and it's, like...

the world isn't supposed to look like this.

NARRATOR: As the summers heat up,

features like this ice canyon are becoming more pronounced.

But for all its beauty, it raises perplexing questions

about the effect this water is having

underneath the skin of the ice sheet.

The strangest phenomenon is the mystery of the meltwater lakes.

As the ice sheet cooks down, the meltwater collects

in depressions in the ice, forming thousands of lakes,

some over several miles wide and nearly 50 feet deep.

From satellite images, scientists noticed

that in mid-summer, many of these lakes vanished overnight,

leaving bright circles where the water once stood.

Until recently, it was assumed that the water was absorbed

and re-frozen into the ice sheet.

But Ian Joughin and Sarah Das have a hunch

that the water could be having a deeper impact.

These events are so unpredictable,

nobody has ever observed them,

but Das and Joughin just came close.

A few days ago, a big lake by their camp suddenly drained out.

SARAH DAS: We were in the fog, so we couldn't see the whole lake.

While standing right on the shore of the water,

we started to hear some really loud booms and pops

and it was just extremely spooky.

Cracks would run across the ground beneath your feet.

It was all around you.

It was a strange experience.

NARRATOR: Frightening, but also fortuitous.

They had placed a device that measures water pressure,

called a pressure logger, in the bottom of the lake,

hoping it might drain.

If they can find the logger, their bet might pay off.

DAS: The fish line that we are following,

it's tied at one end to our stations,

and it's tied at the other end to an old plastic bottle

that has a pressure logger attached to it,

and that's sitting in the lake basin.

And so we're following the line out, hoping that at the end,

we'll find it tied off to our loggers.

NARRATOR: The loggers should reveal

exactly when and how fast the lake drained.

ywre, truck-sized blocks of ice litter the lakebed,

evidence of the violent forces uncorked

as the water rushed out.

DAS: I see it!

JOUGHIN: There it is!

In there, under the ice.

Watch your fingers.

NARRATOR: With the loggers in hand,

they can now plot out the minute-by-minute account

of the mass draining of the lake.

So what you see here on the left is early June,

when there's no water in the lake,

and as more water fills the lake, the pressure goes up,

the height of the water column goes up, and up and up,

continues to fill, fill, fill,

until about this point, and then on July 10, boom,

you see the lake drop in a matter of about 40 minutes.

NARRATOR: GPS data reveals that so much water drained out so quickly,

the surrounding ice was pushed up by several feet.

JOUGHIN: Well, as you can see from the blocks all around us,

this was a tremendously violent event.

You have a lake that's two miles wide, 40 feet deep,

and all of a sudden, it drops 3,000 feet through the ice.

It would have basically been one of the tallest waterfalls

in the world.

The flow into these cracks in the lakebed

is greater than the flow over Niagara Falls.

NARRATOR: Instead of being absorbed and refrozen into the surface ice,

they discovered that the water dropped

all the way to the bedrock.

There, it lifts and lubricates the ice sheet

and accelerates its slide.

DAS: And if you have increased warming,

especially in the summertime, over the ice sheet,

you're going to just increase the supply of meltwater

to the bed, and potentially that could escalate the speedup.

NARRATOR: Their breakthrough solves the mystery of the meltwater lakes.

They'd measured it, but because of the fog,

they hadn't seen it happen.

By sheer chance, the very next morning,

Balog and the scientists would witness it firsthand.

About a mile away from his camp, a smaller lake

that was full only hours before suddenly starts to drain.

Balog heads for the water line

to try to find where the water is going.

BALOG: This is the world's most treacherous footing.

These wave cups are hard walking as it is,

and with them just emerged out of the lake,

they're slick as can be.

There's so much water packed in there,

it's just like grease on top of glass.

BALOG: Ah! Oh, my God!

Not being roped up here

is one of the scariest, dumbest things I've done in my life.

Where I'm laying right now was underwater just six hours ago.

And I can see maybe 250, 300 feet down there.

I'm not feeling real comfortable out here.

DAS: This is really the first time

that we've been able to observe these things firsthand,

actually happening, and it's really nice to see

that our theories that we've pulled together

from our instrumental records

match our observations on the ground very nicely.

NARRATOR: Now they know, these billions of gallons of water

are finding a route under the ice and out to sea,

lubricating the outlet glaciers and making them speed up.

Das and Joughin calculate that this lubrication effect

accounts for about 10% of the increase in speed.

So there must be another powerful force

behind the surge of ice from Greenland.

The latest ocean research may have found it.

Around 1997, there was an abrupt three-degree Fahrenheit jump

in coastal water temperatures,

exactly when the outlet glaciers began to speed up.

At the foot of Jakobshavn Glacier, in Disko Bay,

Ian Howat is investigating how the warming ocean

could be eating away at the edges of the ice sheet.

HOWAT: We're trying to get a handle

on how the ocean and the ice interact,

and so by that I mean

how heat is transferred from the ocean,

which is this huge source of heat, up against this ice sheet.

NARRATOR: To figure it out, Howat is using a capsule packed with sensors

that record temperature, salinity and depth,

at intervals going down 1,000 feet to the ocean bed.

The measurements give Howat an immediate picture

of how the meltwater streaming off the glacier

and the denser saltwater below stack up like a layer cake.

HOWAT: So this plot is showing

the increase in temperature with depth.

What we see here is very cold, nearly freezing water

at the surface, and then as we go down,

it increases its temperature as it mixes

with the warmer ocean water below.

So this transition zone, this almost flat line,

shows us that there is a very sharp transition

between that fresh water and the salty ocean water below.

NARRATOR: Howat thinks the rush of cold meltwater

and you increase the force of this conveyor belt

of fresh water going out of the fjord,

you're bringing more heat from the ocean into the fjord

to melt more ice, and that would be a strong feedback

that could actually lead to more glacier melting.

It's a much more dynamic environment

than we thought in the past.

NARRATOR: The story of the mountain glaciers and the ice sheets

shows that abrupt changes in the ice aren't the exception,

they are the rule.

SERREZE: There are concerns that we get to some point

beyond which strong feedbacks in the climate system kick in

and cause changes that we're really unprepared to deal with.

NARRATOR: The ice may have more surprises to come,

but based on the latest research,

the best guess for future sea level rise

comes down to a simple calculation.

In the next hundred years,

the oceans will expand on their own as they warm,

accounting for about a foot of sea level rise.

Another foot will likely come from the loss

of the world's mountain glaciers as they melt away.

The ice sheets of Greenland and Antarctica won't disappear,

but their combined melt is expected

to add about another foot.

The total equals an estimated sea level rise

approaching three feet, or one meter, by about 2100.

It may not sound like much,

but over 100 million people live within three feet of sea level.

Cities around the world will spend trillions

building up coastal defenses.

Low-lying regions such as Florida, Vietnam

and Bangladesh will be devastated.

Many island nations will cease to exist.

The consequences will test our ability to adapt

like never before.

But it doesn't stop there.

ALLEY: If we look beyond 100 years,

the biggest questions might even be what we do.

There's huge things we don't know about the ice sheets.

But our uncertainty about what we decide to do

may be bigger than that.

But if we make it really warm,

I think a whole lot of us get really nervous

about what the ice will do.

WHITE: This is going to be

one of the pivotal moments in human history.

Ice is too important for us in terms of climate of the planet,

in terms of sea level,

in terms of the fundamental operating systems of the planet,

for us to continue to ignore it.

NARRATOR: The final chapter of Balog's story plays out

on the southern coast of Iceland,

where he discovers an unrivaled confrontation

between the ice and the sea.

8,000 years ago, the island was encased in ice.

But now, the last remnant of its ice cap is quickly disappearing.

As the ice seeps down towards the sea,

it discharges into a meltwater lagoon.

Each day, the tide draws the icebergs

out into the North Atlantic.

BALOG: I'm not aware of any other place in the world

where you can see this dynamic

between the ice and the surf in the same way.

What I see in this ice is a unique sculpture by nature.

Each one is a Hope Diamond--

you know, some really perfect, pure manifestation

of form and color and texture.

They come up here on the waves,

they sit here for 12 hours after the tide goes out,

then the tide comes back in, takes them away

and they're gone for good,

and in that transitoriness, I see extinction.

BALOG: Our brains are programmed

to think that geology is something that happened

a long time ago or will happen a long time in the future.

We don't think that that can happen

during these little years that we each live on this planet,

but the reality is that it does.

On NOVA's "Extreme Ice" Web site, see dramatic graphics

that show how the world's coastlines would change

if all of Greenland's ice melted.

Find it on pbs.org.

Captioned by Media Access Group at WGBH access.wgbh.org

This NOVA program is available on DVD.

The companion book, Extreme Ice Now,

is also available.

To order, visit shopPBS.org,

or call us at 1-800-PLAY-PBS.