Original subtitles

(tense music)

- [Narrator] It can be a stone cold killer.

And centuries ago, millions fell victim to its wrath.

- [Kyle] If a hundred mile per hour chunk of ice hits you

in the head, it can very easily kill you.

- [Narrator] How could ice become so violent

and so powerful as to nearly wipe out civilization

while carving out some of America's most natural wonders?

- [Steve] It moved the position of the Mississippi River.

- [Narrator] And has this frozen fury of our ancient past

become the slippery slope towards our future demise?

- As we move into the future,

if the climate state is such that we can have severe storms

and severe weather events coming in every year,

adapting to that kind of extreme is very difficult.

We don't know what to prepare for.

- [Narrator] Earth, air, fire, and water,

essential for human survival,

but in their extreme--

- [Man] Coming down right now, make your turn.

- [Narrator] To everything and everyone in their path.

- [Man] Oh, big power black.

- Wow. - Whoa, whoa!

- [Narrator] These are stories

of Apocalypse Earth.

With every bone chilling winter storm come predictions

of a new Ice Age.

Extended periods of freezing rain,

blinding snow storms, and Arctic air lead many scientists

to predict a return to a frozen earth,

not seen for thousands of years.

A time when our planet was covered in massive ice sheets

with the power to change the shape of continents and oceans.

Evidence from the past could provide key clues to when

and if we return to another Ice Age.

Some scientists predict that the world is entering

a period of extreme climate disturbance.

Freezing temperatures could grip Europe

and the Northeastern Coast of the United States,

while other regions suffer from drought and flood.

It has happened before. (ominous music)

(bell tolling)

Generations had prospered in the stable weather

of pre-Renaissance Europe,

but in the 1300s, without warning,

that predictable world was turned upside down

by the so-called Little Ice Age.

- One of the things that happened was that

you had this whipsaw going to warm, going to cold.

1309 was cold.

1315 was warm.

1317 is cold again.

And creatures and other things respond in different ways.

You get crops rotting in the field if it gets too wet

or germinating too early or never germinating at all.

- [Narrator] The climate rapidly switched back and forth

between cold and warm; wet, and dry.

But this initial erratic climate was only a prelude

to catastrophic changes of epic proportions.

Over the next few centuries, (thunder crackles)

the weather continually fluctuated at temperatures

between 0.5 and three degrees lower than normal.

This small change was enough to awaken an icy killer.

- Throughout the Alps and throughout parts of Europe

and in fact, in North America, and Canada,

the Eastern Canadian Arctic,

we see evidence that during

The Little Ice Age, glaciers advanced.

- [Narrator] The difference of only a few degrees

triggered a self-perpetuating feedback cycle.

- You make a little more ice,

it reflects more of the sun.

By reflecting the sun,

the sun is not warming us up and so it gets colder,

so you make more ice.

- [Narrator] As the glaciers expanded,

the Vikings took the first brunt

of the climate's deadly chill.

- They switched from being a farming economy

to eating a lot from the sea

because they were having troubles raising enough

things on their farms, apparently.

- [Narrator] But as temperatures continue to drop,

storms and freezing winds blasted the settlements,

even the sea held no hope of survival

for the starving Vikings.

- Around Iceland, sea ice expanded,

and the people couldn't get out and go fishing.

And they had open boats, not boats with decks,

so they were particularly vulnerable to bad weather.

- [Narrator] After decades of expansion,

battle ax wielding, pillaging, and plundering Vikings

were defeated by a sudden drop in temperature.

(tense music)

- Well, 10 super cold years,

including one of the coldest years on record ever

in about 1355 AD shut down Western colony

and a hundred years later,

the more Southerly Eastern colonies shut down.

- [Narrator] The Vikings who survived

migrated south, assimilating into populations

living in continental Europe.

Their fearless culture receded into history.

If it hadn't been for The Little Ice Age,

the Vikings may have continued settling in the New World

and today's America would be a very different place.

By the end of the 14th Century,

Europe was buckling under freezing temperatures

all winter long.

In a chain reaction ignited by the cold and stormy weather,

one calamity followed another.

Crops failed and food shortages spread across Europe.

The freezing cold blasted through Asia,

but that was only the beginning.

Relentless storms killed at least 7 million.

The resulting floods produced a horrific and infamous

blowback effect on Europe.

- Everybody's familiar with the Black Death,

but the lesser known story of course

is the role that climate may have played

in unleashing it.

(ominous music)

- [Narrator] The Black Death or The Plague

was a devastating pandemic

that ravaged Europe during the mid 14th Century.

(thunder rumbles)

The drop in temperature changed weather conditions

causing storm patterns to shift and intensify.

In the early 1300s,

Asia had a record breaking series of torrential storms

and subsequent flooding.

Rats carrying the plague thrived to these conditions.

- The animals that react at the first are the ones

that reproduced by the zillions and reproduce very rapidly,

where as the longer lived, slower reproducing animals

tend to lag.

And so weedy species of every sort seem to take advantage

of climate change and flood.

- [Narrator] Rats on ships traveling the trade groups

spread the disease from Asia to Europe.

An already starving and weakened population was no match

for the Black Death.

Within five years, the plague had killed

between 25 and 34 million people in Europe,

one-third of the population.

An estimated 40 million more died in North Africa and Asia.

Generation after generation suffered

the relentless pounding of extreme cold and wet weather,

pushing the starving peasant to his limit.

- Then there intense storms and incessant rain.

Crops are rotting in the field.

There's so little sunlight that you can't make salt

in the summer to preserve anything.

Diseases, molds, blights, and everything else

we're beginning to afflict them.

People fell into robbery, they lost their land, starvation.

They started eating their livestock, dogs, and cats.

And at some point, they even ate each other.

- [Narrator] Sophisticated European societies

quickly crumbled, scratching at the edges of mere survival.

Starving peasants revolted against the aristocracy.

The political unrest and an economic crash in England

were factors in the American Revolution.

And it was the poor of 1789 France

that fueled the French Revolution.

(tense music)

The tragic scope of The Little Ice Age was staggering.

Millions died horrible deaths simply because

the temperature dropped a few degrees.

- You're living on the edge and you get just a little bit

of a cooling, it can push you over the edge.

- Little changes in global temperatures

can have an enormous effect.

A temperature change of five to nine degrees,

which is also within the realm of possibility,

would just be unimaginable.

- [Narrator] The small drop in temperature

that triggered The Little Ice Age

may have been caused by a dimming of solar output

linked to a change in sunspot activity.

(tense music)

Another factor that intensified the cooling

was something else no one could have predicted or prevented.

During the Little Ice Age,

at least three massive volcanoes erupted:

Mt. Vesuvius in 1631,

Mt. Tambora in 1815,

and Krakatoa in 1883.

All spewed particles and gases into the upper atmosphere.

These particulates reflected the sunlight back

into the atmosphere, cooling the earth.

- If you put a lot of volcanic debris

high into the northern hemisphere,

it's going to be everywhere in the northern hemisphere

within just a couple of years.

No matter what part of the earth is facing the sun

day or night, it's still going to get less sunlight.

- [Narrator] After six centuries of death and deprivation,

the weather finally began to warm.

- So, the Little Ice Age likely ends,

because the volcanoes quiet down,

they're not blocking the sun, and the sun brightens

up a little bit.

So, you have warming coming out of 1850 or 1900

into the early part of the 1900s.

- [Narrator] The Little Ice Age may be over,

but some scientists see it as a preview

of what could occur again,

this time with even more devastating consequences.

Coming up.

(speaking in foreign language)

- [Interpreter] How could a snow cloud of that size

not bury whoever was on the face when it hit?

- [Narrator] Some experts believe that global warming

could paradoxically catapult parts

of the Northern Hemisphere into a new Little Ice Age.

(tense music)

rn Seaboard

and Western Europe would be battered

by severe winter blizzards and ice storms.

(wind howling)

Proponents believe this big chill would be triggered

by changes in the Atlantic Ocean.

70% of the earth's surface is ocean.

90% of all rain falls into the seas.

It is a colossal reservoir of water carrying heat

all over the planet.

A huge ocean current system known

as the Thermohaline Circulation,

which includes the Gulf Stream circulates warm water

north from the equator,

giving our Northeastern Seaboard and parts of Europe

relatively temperate climates.

London, England, and Calgary, Canada

are on the same latitude,

yet London is much warmer on average.

The reason: the Thermohaline Circulation,

which brings warm Atlantic water and air North

to the British Isles.

As the heat is absorbed into the atmosphere,

the surface water becomes colder, saltier, and dense.

It sinks deeply, in effect pulling

the current down behind it.

- So in the winter as the water gets really cold,

and colder makes it contract and contracting makes it denser

and then it sinks and then warm water flows up

to replace it.

- [Narrator] In a self perpetuating cycle,

the thermohaline circulation then moves south

where it warms again at the equator

and continues its cycle back up north.

This immense system is dependent upon a delicate balance

between warm and cold water and fresh and salt water.

Some experts believe that global warming

could disrupt this delicate system

and in a worst case scenario create a mini Ice Age

in parts of the Northern Hemisphere.

- The oceans are warming.

Almost all the glaciers on the planet

have gotten smaller over the last hundred years.

You're getting reductions in sea ice in the Arctic.

Things are happening earlier in the spring

and lasting further into the fall

than they did in the past.

And so this is great number of indicators that say,

yes, the planet is warming.

- [Narrator] According to the Big Freeze Theory,

the rise in the ocean temperatures could cause a shutdown

in the thermohaline circulation that brings warmth

to the North Atlantic region.

- The total heat capacity of the ocean is 1,100 times

that of the atmosphere.

So in my mind we really should be trying to understand

what's going on in the ocean

to understand our future climate.

- [Narrator] Researchers from Woods Hole

Oceanographic Institution utilize many tools

to study the changing ocean.

Remote-controlled devices called floaters track changes

in the ocean's condition.

- They're sort of like weather balloons for the ocean

that drift at depths for 10 days

then come to the surface reporting

the temperature and salinity as they rise

and they transmit that data to a satellite.

And we have a program to deploy thousands of these

around the global ocean.

- [Narrator] Using the data transmitted by tools

like floaters, scientists create computer models

that track and then project climate changes.

(beeping)

(crashes)

Researchers continue to find evidence

of a disturbing development:

global warming is melting glaciers and ice sheets

causing an increase in fresh water

flowing into the thermohaline circulation,

a process they call freshening.

This fresh water could throw off the critical balance

between temperature and salinity

that powers the thermohaline circulation.

- What it means is that those warm waters

no longer flow north and they stopped much further south.

And so all that warmth that would otherwise warm

the Northern Hemisphere stays in the south, which means,

for example, there's more energy in the atmosphere.

There are more extreme storms and so on,

but critically much colder in the north.

- [Narrator] Some experts think that if

the thermohaline circulation is disrupted,

temperatures could drop dramatically

in the North Atlantic

leading to a new Little Ice Age

in North America and Europe.

- If the thermohaline circulation was to shut down,

the average temperature changes resulting of that

could be anywhere between eight to 12 degrees possibly,

but that would be on average.

And clearly the extremes that could resolve from an average

temperature change like that could be well beyond that.

- England France, Germany would begin

to resemble Alaska and Canada.

And those parts of the world, particularly Alaska,

might even get colder still.

- [Narrator] In the United States,

the Northeast Coast would be hit the hardest

with extreme temperatures

and more intense blizzards and storms.

- For example, severity of nor'easter storms

could easily increase in a condition where you had

increased storminess, increased wind

velocities impacting the eastern North America.

- [Narrator] Some experts doubt this big chill

would be nearly so dramatic,

that it would in fact be only a side effect

of the real devastation in other parts of the world.

In the Pacific, a warmer ocean will intensify

the El Nino rainstorm cycle that historically batters

the Pacific Coastline.

- Even a two-degree change if we were so lucky,

would be double the intensity or more of the strongest

El Nino we've ever felt.

In 1998, there was a very strong El Nino,

did $100-billion damage around the world and killed

tens of thousands of people.

So, even a very slight variation from the norm

in global weather can cause a lot of damage.

- [Narrator] In the South Atlantic,

warmer oceans will mean intensified hurricanes

and massive storms.

- The fact that we have a great deal of heat built up

in the ocean means that there's plenty of fuel

for more intense hurricanes.

So it seems inevitable that strong hurricanes

are in our future.

- If we get not just one Katrina,

but if we get five Katrinas per year

coming into different regions of the Gulf coast

or in fact shifting to where now these storms

are impacting along the eastern seaboard

and coming into Washington DC and New York City,

then the consequences would be severe.

- [Narrator] And warming oceans and warmer air

could threaten the largest source of frozen fresh water

on the planet, massive ice sheets at the poles.

Melting those could result in floods

never before seen on our planet.

Snow and ice can rapidly become a deadly mix,

especially for hardcore adventure seekers.

(tense music)

The Himalayas.

This mountain range in Nepal is home

to the 14 highest peaks on earth.

It's most treacherous, the one known is Annapurna.

- You have a mountain that's over 26,000 feet

and a canyon right next to it going down

to only three or 4,000 feet,

so the vertical relief is just amazing.

- [Narrator] But it's a hidden danger

that gives Annapurna her deadly reputation: avalanches.

- Over 40% of the climbers who attempt Annapurna

do not come home.

For comparison, Mount Everest,

which is the tallest mountain on the planet only has about

a 9% death rate.

- Looking at Annapurna you can see why the avalanches

are so prevalent.

See those dark rock layers leaning out of the hill,

looking like slides in a playground for the snow

to slide off of and see that U-shaped glacial valley there

acting like a funnel funneling the avalanches down.

And for some reason, the climbers like to go up that,

but that's like playing Russian roulette.

One out of five of them are going to be killed.

- [Narrator] In the fall of 1997,

Annapurna is heavy with a million tons of fresh snow

lying in wait for her next victims.

On a year long quest to scale the world's highest peak,

veteran mountain climbers Jesus and Jose Novas

had been in the Himalayas for months.

To document their triumph over Annapurna,

the brothers hire cameraman Alejandro Rocha.

They brush off forewarnings of the mountain's short temper.

(speaking in foreign langauge)

- [Interpreter] There were conditions

that could be considered favorable

to provoking an avalanche,

but you're always sure that it won't happen.

- [Narrator] As they set up camp at 19,000 feet,

the signs of impending disaster are clear.

(tense music)

- These guys are very well aware

that an avalanches occur.

Avalanches occur on Annapurna all the time.

If you get heavy snow and warming,

you are going to have an avalanche.

- [Narrator] Ignoring the risk,

Jesus and Jose make their ascent.

They're halfway up the cliff face when Annapurna

springs her trap.

(suspenseful music)

A rippling frozen surge, 6,500 feet wide

careens down the mountain at eighty miles per hour.

Alejandro watches in terror as the snow pack

swallows his friends.

(speaks in foreign language)

Then he realizes he could be next.

(speaks in foreign language)

- [Interpreter] The cloud was getting bigger and bigger,

it was like this big white cloud, a huge heap of snow.

- [Narrator] Helpless and terrified,

Alejandro retreats to his only shelter,

waiting for the worst.

[Bleep]

The cameraman braces against Annapurna's fury

as he pummels the tent with snow and ice.

(suspenseful music)

[Bleep]

Remarkably, Alejandro survives the attack.

Immediately, his thoughts turn to the two climbers outside.

He peeks out, not knowing what he'll find.

The entire snow face, all 2,600 feet of it

has plummeted down the mountain

and the Novas brothers are nowhere in sight.

(speaking in foreign language)

If they're still alive, it may be only minutes

before Jesus and Jose suffocate under tons of snow.

(speaking in foreign language)

- [Interpreter] How could a snow cloud of that size

not bury whoever was on the face when it hit?

- [Narrator] He scans the cliffs

desperate for any sign of life.

Finally, his camera catches two tiny figures,

halfway up the slope.

It's Jesus and Jose clinging to the cliff side.

- [Interpreter] I saw them and I screamed at them

asking them if they were okay.

(speaking in foreign language)

Since I only saw two tiny dots, quickly descending.

- [Narrator] Trudging through waist-deep snow,

the climbers returned to camp.

(speaking in foreign language)

(man laughs)

- [Narrator] Astonished that Annapurna

has failed to bury them alive.

- [Interpreter] The avalanche was a total surprise.

All of a sudden we heard a crack like a boom.

It was as if something broke.

It was a dissonant bang, boom!

I said an avalanche, quick, quick, we'll hide over here.

In no time, in just a matter of seconds,

the avalanche was on top of us.

The cliff protected us from everything that was falling

from above, forming something of a shield.

We were under there for about a minute or so.

It was very difficult to breath.

(speaking in foreign language)

- [Interpreter] I got as close to the wall as possible

to avoid being hit by the chunks of ice.

We were only thinking of not falling down,

of holding on with the ice axes.

- You really have to admire the quick thinking

of the two climbers.

To see an avalanche bearing down on them so rapidly

and to be able to take cover that quickly is really amazing.

- They talk about suffocating for not being able to breathe,

but that's a heck of a lot better than being hit

by tons of wet snow.

- [Narrator] All three mountaineers are lucky to survive,

a rare instance of Annapurna missing her targets.

In more recent years,

another disaster on Annapurna would prove the rarity

of their survival.

In January of 2020, several South Korean

school teachers went missing.

Their bodies, not discovered until that spring.

Annapurna with about one in three climbers

failing to survive the ascent

remains the deadliest mountain in the world.

- The fatality rate for Annapurna seems

to be very, very high because

of its great prevalence of avalanches.

Inclined rock layers that are easy for snow to slide off of

and climbers going up glacial valleys funnels

where avalanches are directed into.

Very hard to avoid the avalanches.

Very easy to die on this mountain.

(tense music)

- [Narrator] Each day, several hundred million metric tons

of ice on the polar ice sheet are lost perhaps forever.

This alarms scientists because ice sheets cover nearly

1/10th of the earth's land

and contain about 70% the planet's fresh water.

- The potential melting from the big ice sheets

of Greenland and Antarctica, those are really the gorillas

in the wood shed if you wanna talk about problems.

Far bigger than what we would get

from a few glaciers melting.

That's really a key for civilization in this century,

what's gonna happen to the ice sheets?

- [Narrator] The same ominous phenomenon

is taking place all over the world.

The renowned snows of Mount Kilimanjaro are disappearing.

The frozen current of the Andes are drying up.

And the glaciers in Montana's Glacier National Park

are vanishing.

This full blown retreat of glaciers is the result

of an overall warming trend across the globe.

The world's oceans are heating up.

- The climate system is changing

and it's changing at a rate that compared to previous

decades and centuries is quite rapid.

- [Narrator] And warmer seas mean rising sea levels.

- As water warms, it expands so warmer water actually

takes up more volume and increases the sea level as well.

- [Narrator] Scientists are predicting a rise in sea level

of one to four feet by the end of the century.

But if the significant portion of the polar ice caps melt,

it could be much more.

- It's not totally unrealistic

to think that sea level rise could be maybe up to 10 feet

between now and 2100.

There's a lot of ice in West Antarctica.

It's grounded below sea level and it's inherently unstable.

So, we are concerned it could slip away very rapidly.

And this alone could raise sea level by 15 feet.

- [Narrator] Low lying coastal areas could be devastated.

Entire Island nations in the South Pacific

could be swallowed by the sea.

In Bangladesh, the rice paddies that feed millions of people

could disappear under salt water.

Untold numbers of these people could be displaced

and become climate refugees.

And some of America's great cities:

Miami, Baltimore,

New York, and Boston

may see their most expensive

waterfront properties washed away.

Even worse, warmer oceans will cause more intense

tropical storms and hurricanes.

- A hurricane is a heat engine.

It's a monster that devours heat and it gets it

from the upper layers of the ocean and so the warmer

the ocean the more heat for the hurricane to develop.

- [Narrator] Melting glaciers could be the first sign

of this impending environmental catastrophe.

A glacier is a slow moving river of frozen water,

a tremendous accumulation of snow compacted by the pressure

of its weight and turn to ice.

- It oozes very, very slowly under the weight

of its own gravity and that's the key.

A glacier has to move, in order to be called a glacier.

- [Narrator] Some of these frozen rivers of ice

move as fast as two miles per hour.

During the last Ice Age,

they carved entire landscapes out of rock.

A glacial system may be as large as a continent

or as small as a tiny valley between mountains.

Each year when the snow falls, new ice is added.

- A healthy glacier is one that's getting plenty of winter

snow pack and is not melting too much in the summer,

then it can maintain its mass or it can even grow.

- [Narrator] These mountain glaciers have been here

for more than 10,000 years.

Today, scientists are monitoring their health

on a day-to-day basis.

They predict that every one of these glaciers

will be gone by the year 2050,

but the life span of mountain glaciers is short

compared to the rivers of ice that flow off

the polar ice sheets.

Many of these are more than 500,000 years old.

It is these polar glaciers that are even more crucial

to the future of the planet.

Just in terms of mass, the polar ice caps are astounding.

- Antarctica is not at the human scale.

It's huge.

If you actually wanna count all the individual glaciers

in Antarctica, you're talking about tens

of thousands of glaciers.

- [Narrator] Difficult to get to,

Antarctica, the seventh continent,

was not even discovered until the 18th Century.

Since then, explorers and scientists

have been trying to gather information

about the polar ice sheets.

In particular, they wanna know how quickly the ice caps

are melting, because this information can tell us how fast

and how much the world's sea levels will rise.

But the polar regions have remained elusive.

- You have to realize that maybe 30, 40 years ago,

we didn't even know where all the glaciers were,

the important glaciers.

- [Narrator] For decades, Greenland and Antarctica

proved to be too huge to accurately survey.

- What we relied on was putting together hundreds

or thousands of individual measurements taken

in the field by individual scientists

going and visiting a polar ice cap and taking samples.

- [Narrator] The complete picture of the polar regions

and all their glaciers has remained

an enormous jigsaw puzzle.

- There's no way from fieldwork alone you could say anything

about the entire ice sheet with certainty

and with precision.

- [Narrator] Now scientists say seeing the ice sheets

in their entirety may be a matter of survival

for future generations.

- We really need to look at all of them,

detect the areas where the changes are taking place

and keep an open mind that it may not be just one

or two glaciers that are changing,

but it could be a whole coastal range

of several thousand kilometers

which is changing at the same time.

- [Narrator] These changes in the polar ice sheets

and glaciers could spell disaster.

And what these scientists discovered could have

a life or death impact on millions of people

around the world.

st spectacular

photographic evidence of nature's fury,

it is by far not the only hazard faced by those

sitting below tons of unstable ice and snow.

(tense music)

Namestovo, Slovakia.

It's a thrilling day for a 150 of the country's

junior hockey players.

They get to meet their idol:

13-year NHL veteran Richard Zednik.

The Slovak native survived a brush with death in 2008,

when a player's skate cut his neck.

He never expected that a casual Sunday training session

with his home country's up and coming stars

could also turn deadly.

But just over their heads,

mother nature is putting the finishing touches

on a sinister plot.

- [Narrator] In Northern Europe,

there's a lot of heavy winter weather.

Snow, ice, winter storms,

seemingly everyday weather can lead to big problems.

- Snow might not seem that dangerous when it falls,

but to a very large, very wide flat roof,

it can be very destructive.

- [Narrator] As the young athletes practice their moves

on the ice, ominous noises from above get their attention.

Suddenly, the roof cracks open and buckles,

threatening to kill everyone underneath.

Richard and the other adults try to hustle the children

out of harm's way before they're crushed to death.

They flee the collapsing arena through passageways

along the perimeter that remained free of rubble so far,

but everyone knows the rest of the roof might easily cave in

before they find the exit.

- The ceiling essentially unzipped.

This was a large Quonset hut.

A Quonset hut is a steel arch.

And the one problem we see with arches

is drain drifting snow,

where all the snow will drift to one side of the arch.

And that unbalanced load can cause an arch to buckle.

- These kinds of buildings are always a challenge.

How do you cover a large area with enough strength

to stand up to a stress.

And here they failed the test, the roof collapsed.

- [Narrator] The near fatal disaster is anything

but a triumph homecoming for Richard Zednik.

(speaks in foreign language)

- [Interpreter] It was complete horror

when it started to collapse.

Imagine suddenly a ceiling falling straight on your head.

I looked around and saw people in panic.

In two or three seconds, the ceiling was on the floor.

- Given the number of people that were in this building

and out on the ice at the time the ceiling

began to collapse,

it's remarkable that everybody survived.

And it would have been very deadly

for anybody who had been under it.

- [Narrator] For centuries, America's early geologists

were puzzled by mysterious marks etched into the bedrock

of much of North America,

and by lonely mountain rock

randomly scattered across the land.

(thunder crashing)

Then in 1847, a newly-appointed Harvard university professor

came up with a radical new idea.

Geologist Louis Agassiz

compared North America's landscape and rocks

with the geology of mountain glaciers

in his native Switzerland.

And he built on theories he had developed

in this Swiss Alps a decade earlier to declare that

North America had once been buried deep under ice.

Agassiz's work at Harvard made him world-famous in his day.

But the final proof of his Ice Age theory

had to wait until the 1950s,

when new evidence came from the seabed

of the Atlantic Ocean.

That evidence is still stored to this day

in this refrigerated laboratory at Miami University.

These thousands of plastic tubes offer scientists

a unique window to look back at what the weather was like

on the ancient Earth.

- These records that you see in this room here

basically are the primary information we have now

about the climate changes we have had

over the last two million years.

So these are really starting points

that open people's eyes about changes

which occurred during glacial periods.

- [Narrator] The mud cores were collected

by oceanographer Cesare Emiliani.

The deeper he drilled, the further back in time he went

and the older the sample he pulled to the surface.

- These are cores of deep sea mud.

And within the mud are small organisms,

which record the temperature and the salinity

and the other conditions which were prevalent

when that organism lived.

- Those tiny undersea creatures are called formanifera.

Their chemical makeup varies,

depending on the temperature of the water

in which they grow.

So the sea bugs in different layers of mud

act as tiny thermometers,

recording how hot or cold the Earth was

at different times in its past.

(haunting music)

They reveal that just over two million years ago,

the average annual temperature across the lower 48 states

was around 56 degrees Fahrenheit,

about three degrees warmer than it is today.

Then, the temperature regularly started crashing below zero

and staying there month after month.

(dramatic music)

Huge changes happening in what, in geological terms,

was astonishing speed.

Within 10,000 years,

the year-round average temperature bottomed out

at just 26 degrees Fahrenheit,

about the same as the average winter temperature in Chicago.

Even today, scientists are uncertain

what caused the temperature to drop so quickly.

Variations in the Earth's orbit,

a change and the tilt of its axis,

and even the creation of the Himalayan mountain range

are all prime suspects.

But one thing is certain.

With subzero temperatures all year round,

snow never melted.

A major storm can drop more than 40 million tons of snow.

The ever-increasing weight of snow compacted down

into thick layers of solid ice.

America's Ice Age had begun.

The ice sheets, which built up two million years ago,

began to move, flowing as huge glaciers

across the northern U.S.

- Some of the very large rocks can be literally

frozen on and cut off from the rock that they came from,

and just put it right into glacier and moved that distance.

Hundreds of miles in the glacier,

like a conveyor belt, out to where we finally find it

on the landscape or in an outcrop like this.

- [Narrator] The investigator's next challenge

is finding out just how far the ice flowed,

and for that task, they are taking to the air.

In the early morning light,

Brown spots a mysterious small hill

standing out from the flat Illinois plain.

Stripped of its camouflage layer of trees,

the shape of the hill tells Brown

the secrets of its creation.

- This gently rolling landscape extends for about 400 miles.

We look at the land forms and how they're shaped,

And so we can use that to unravel

the history of the Ice Age.

(lively music)

- [Narrator] The landform Brown is studying

is a mound of rubble that geologists call a moraine.

It is an accumulation of debris that a glacier

has plucked up from the Earth, dragged along,

and dumped at the front edge.

This hill marks the spot where the glacier

finally stopped flowing southward.

Geologists all over the U.S have recorded

the positions of other moraine hills,

helping them map out precisely how far

North America's ice sheets spread.

Nearly 2/3 of the North American continent

was buried under ice,

but the frozen chaos did not stop there.

The challenge now facing geologists is figuring out

how ice created some of modern North America's

most famous features.

Coming up.

- [Man] It's like a fricking war zone.

- It felt like at one point we were under assault.

(dramatic music)

- [Narrator] Two million years ago, temperatures fell,

and massive ice sheets spread out as glaciers

across much of North America.

Geologists set out to discover what the moving ice did

to the underlying land.

Everywhere the ice had flowed,

investigators discovered the same puzzling feature.

Lines of stones, all laid out the same particular way.

- Really good example of pavement of stones,

this concentration of small rocks and cobbles

that are collected here in a line.

It's just one, one stone or two stones thick.

- [Narrator] Scientists realized that the stone pavements

must have been laid down at the base of a glacier.

And even the toughest rocks had scratches and grooves

carved into their surface.

- [Steve] Glacier carries along other fragments of rock.

And as it's doing so it scratches, polishes,

creates grooves in the rock called striations.

- [Narrator] Those scratches offered vital clues

to help uncover the history of

how the Ice Age changed America.

- So by lining my compass parallel to

the striations on this rock,

the compass tells me that the ice is flowing

from about the northeast,

from this direction to this direction.

- [Narrator] But other scratches on rocks

found all over the northern parts of the U.S.

run in puzzlingly different directions.

These ice-scraped rocks in New York's Central Park

show scratches made by a glacier

that arrived from the northwest.

There's only one explanation of the different ways

in which the ice appears to have moved.

The scratches were not all made by a single ice sheet

as first thought, but by many different ones.

- This phenomenon of advance and retreat,

the changing of that landscape, happened many times.

Not just once, but many times.

- [Narrator] Everywhere the ice flowed,

it marked the underlying blocks.

- The ice changed.

The existing conditions on the landscape was changed.

The motion of the glacial debris

changed the whole way these areas look.

- [Narrator] Grinding over the landscape

at speeds of around two feet per day,

the massive glaciers diverted the course of ancient rivers.

Even the mighty Mississippi was no match for the ice.

- It moved the position of the Mississippi River.

The Mississippi River used to flow

through the middle of Illinois.

- [Narrator] A glacier advanced across the state

and created an ice dam across the course of the old river.

A huge lake grew at the edge of the ice,

eventually over-spilled, and cut a new river channel

80 miles to the west.

(stately music)

The same course that it follows to this day.

And when the ice sheets melted away,

their impact on North America was almost as great.

They produced immense floods of water,

which all had to drain away somewhere.

- It formed a completely new landscape,

with a new river mouth, a new channel,

completely rearranging the character

of the existing landscape.

- [Narrator] Where rocks were soft, or weakened by faults,

the glaciers had carved out huge basins in the landscape.

When the floods came,

these depressions rapidly filled up with water.

- Every natural lake here in Indiana, Illinois, Wisconsin,

were all created by glaciers.

- The biggest ice-scoured basins became

what we now call the Great Lakes.

These water-filled craters in the North American landscape

are nearly five and a half thousand cubic miles in size.

The water they hold t could drown the whole

of New York State to a depth of more than 600 feet.

But even that is just a tiny fraction

of the total flood unleashed as retreating ice

poured out nearly 39,000 cubic miles of water.

The flood rushed down Niagara Escarpment,

at the rate of 42 million gallons a minute,

one and a half Olympic-sized swimming pools every second.

And that cut a gorge seven miles long

and 180 feet deep through solid rock.

The Ice Age had created one of

the modern wonders of the world, Niagara Falls.

(haunting music)

The investigators' next challenge was figuring out

why the ice advanced and retreated so often.

It wasn't until the mid 1960s

that the first real clues were discovered.

The U.S. military was building bases

in some of the Earth's most remote locations.

- [Newsreel Narrator] This is an ideal arctic labratory,

permanently frozen under a polar ice cap

which covers all but a few costal areas of the island.

Geologists realized the cores of ice being extracted

by hollow drills held a unique historical record.

(lively music)

Those cores and many others extracted since

are housed in a laboratory in Denver, Colorado.

- We're in the Fort Knox of paleoclimate.

What you see in these tubes is gold

in terms of what we know about climate

and what we've learned about climate over the last 50 years.

- [Narrator] These tubes contain

three-foot-long plugs of ice,

each dug out from layer after layer of compacted snow.

But it is what is trapped inside the ice

that most fascinates the scientists.

As each year's snow falls onto the last,

it builds up and moves packed layers

that trap air between the snowflakes.

- Ice cores are the only archive we have,

really good archive we have, of past atmosphere.

In an ice core, you can see tiny bubbles,

and those bubbles are air, unadulterated air

from as much as a hundred thousand to a million years ago.

- [Narrator] The deeper the bubble, the older the air.

- It contains not only a temperature signal,

but it contains dust signals.

It tells about atmospheric circulation.

It contains a record of the atmosphere,

and specifically the greenhouse gases.

- [Narrator] Each ice layer corresponds with

the precise time in Earth's history

when its snow first fell.

So by analyzing the bubbles from any one layer,

scientists can figure out what Earth's atmosphere was like

at any point in the past.

- Over the last million years or so,

we see fairly regular pacing of major, major glaciations,

roughly one every 100,000 years.

- [Narrator] Some theories suggest those colder spells

coincide with variations in

the Earth's orbit around the sun.

But that's not the only thing the ice cores revealed.

The cores that White has been studying suggest

that the longer the ice age went on, the worse it became.

- Somewhere around 400,000 years ago,

we went from a period that had lesser glaciations,

if you will, to ones that were very, very big.

- [Narrator] But new clues suggests that

the awesome impact of America's Ice Age didn't stop there.

Coming up.

- You've got the snowfall moving down

the side of a steep-sloped mountain

at 60 to 80 miles per hour.

No one can run that fast.

music)

- [Narrator] From the modern day remnants of glaciers past

to their deposits comes the question,

how did they get there?

What forces were in play that could carve great crevices

and deep lines seen across North America?

The answers lie right at our feet,

in some of the most recognizable outdoor spaces on Earth.

The first clue came in New York State, on Bear Mountain.

- No one knows for sure how thick

the ice sheet was that came from the northwest.

But right now, we're standing at the top of Bear Mountain,

about 1,280 feet above sea level.

What we're looking at here are a series of chatter marks.

These are features of glacial erosion,

and they're produced by large blocks of solid rock

embedded in the base of a very thick glacier.

Those boulders were hinged on this bedrock surface,

plucking pieces of rock off as the glacial ice

moved through the area.

- Charles Merguerian's mountaintop discovery

shows how thick the advancing ice must have been.

- Most people think that this glacial ice sheet

was about a mile thick or more.

- [Narrator] The marks are clear evidence that

the New York ice sheet must have towered

about four times higher than the Empire State Building.

(dramatic music)

Figures like this have enabled Merguerian to estimate

the total amount of ice that buried North America.

It's a staggering 17 million cubic miles of ice.

- Imagine this block of ice, it's about six inches thick,

being the ice sheet that covered North America

during the last glaciation.

You would need several billion of these,

maybe a hundred billion.

It's a number almost too big to imagine.

- [Narrator] This block of ice weighs 27 pounds

and is just half a cubic foot in size.

But there were 17 million cubic miles of ice

covering America.

When scientists calculated the total weight of the ice,

it was an almost incomprehensively large figure,

68,000 trillion tons.

Unsurprisingly, such a vast weight of ice

did not just affect America.

It distorted the shape of the planet.

- I've got a beach ball here that has a depiction

of the whole Earth, and every continent on it.

And right here is the outline of North America.

And during the Ice Age,

snow started to accumulate in Canada.

And as that ice thickened,

it started to flow from the centers of snow accumulation

southward into North America,

reaching its maximum extent right here in Illinois.

And when it did that,

this mass of ice depressed the continent.

(energetic music)

- [Narrator] Earth's solid crust sits on top of

a layer that scientists call the mantle,

semi-molten rock which behaves a little

like hot, sticky plastic.

The weight of the vast plains of ice

pushed down inland areas, and simultaneously

made parts of the coastline bulge up from the sea.

But investigators also found that in some other areas,

the ice altered the outline of America's coasts,

the borders of the sea that define

the continent we see today.

A vital clue came in downtown Miami

in the unlikely setting of a municipal courthouse.

- We're here in front of this impressive building

built in the early 1900s because of the materials

used to face its surface.

These stones are constructed of fossilized coral reefs.

And if you know what you're looking at,

it can actually tell you quite a bit about Florida's past

and maybe its future.

(lively music)

- [Narrator] The coral stone is made from

the hard calcium carbon and skeletons

of tiny sea creatures,

animals that only grow in very shallow water.

But this courthouse stone was quarried

out of an ancient coral reef that now lies

a mile from the present-day ocean and way above sea level.

- I'm standing here about five or six feet above sea level

and walking alongside this rock face,

which is about six feet tall.

The interesting thing about this rock face,

it's actually composed of fossilized corals.

And the fact that we're standing here today

amongst these fossil corals tells us that in the past,

we would have been under 10 or 15 feet of water right now.

- [Narrator] The coral stones have been dated

to around 130,000 years ago,

which means the sea level around Miami

must then have been far higher than today.

As experts tried to figure out why the sea level

was so high then, new evidence emerged

about Florida's coral reefs,

and the mystery deepened even further.

(lively music)

Divers off the coast of Miami found a coral reef

now submerged 450 feet under the water.

These corals grew just 25,000 years ago,

and because a reef like this only forms in shallow water,

the scientists realized that the sea level back then

must have been far lower than it is today.

And that means the coastline would have been

in a completely different location.

- Right now we're about two miles offshore Fort Lauderdale,

on the edge of the Gulf Stream.

But 20, 25,000 years ago, at the time of

sea level low stand, we would be sitting

right next to a beach here.

We'd been looking where we see today,

the ocean and the high rises in the back,

we'd be looking towards a sandy beach

in front of a gently rolling hillside.

- [Narrator] Investigators studying the coral records

figured out that the up and down sea levels would repeatly

have altered the entire shape of America.

- If you look at the outline of North America,

the outline that I learned to draw in elementary school,

if we were living years ago,

I would draw Florida differently.

- [Narrator] 25,000 years ago, when sea levels were low,

Florida was triple the size it is today

because more land was out of the water.

Geologists realized that the changes in sea level

around the coast were directly related to

the different levels of ice on land.

That discovery was the key to understanding

what the Ice Age had done.

(dramatic music)

Water evaporated from the oceans

and condensed in the atmosphere to form snow.

But in the colder times,

that snow built up as ice sheets on the land,

and with so much of the world's

total water supply locked up as ice,

the oceans simply ran short of water,

and the sea levels fell.

- When the Earth is cold, there's more ice on the land.

And sea level is lower because of that.

When the Earth is warm,

there's less ice on the land and sea level's higher.

And that makes sense because when that ice,

when it melts off the land, has got to go in the ocean.

- [Narrator] But it's not just enormous

city-sized ice shelves that can rock our world.

Sometimes it's much smaller chunks of ice

that can do the most damage, especially when they're

raining down from above like cannonfire.

(ominous music)

Oklahoma.

Known far and wide as the heartland of the U.S.

But this state has another quality that sets it apart.

And this one can kill.

- Where did the big hailstorms hit?

The epicenter is the state of Oklahoma.

They get more than 25 of these big hailstorms per year.

- Hailstorms tend to happen in locations where you have

hot, moist air colliding with relatively cool, dry air.

It's these forces that cause the warm, moist air to rise up

and start the cycle that leads to a thunderstorm and hail.

And Oklahoma, unfortunately,

is exactly this kind of location.

- These stones can be moving at 100 miles per hour.

If a hundred-mile-per-hour chunk of ice

hits you in the head, it can very easily kill you.

- [Man] No!

- [Narrator] A severe thunderstorm unleashes

a hellish assault on the state capital.

- Oh my god. - That's insane!

- This particular hailstorm was actually

a warm front that was moving through

that caused a lot of instability in the atmosphere.

- [Narrator] Chunks of ice blast the entire city.

- [Man] Holy crap!

- This hailstorm reminded me of a Civil War battlefield

with cannonballs landing all around you.

- [Man] Baseball-size hail.

- When I see baseball and softball-size hail,

that tells me this is an enormously

powerful thunderstorm.

- Softball-sized hail is relatively rare.

'Cause when you think about it,

here's a drop of rain that's frozen into ice.

Ice makes it heavier.

It wants to fall, but that means updrafts of wind

have to pick it up and hold it up.

- Then what happens is the hailstones fall down

and melt slightly and are coated with more water.

Then they're carried up again by more updrafts

to be coated by an additional layer of ice.

At that point, they start to fall.

- [Bonnie] Oh my god!

- [Narrator] College student Bonnie Tibbs

is home visiting family

when their house is suddenly under siege.

- Oh my god, it's hitting the window!

This hail is loud and it's big.

and it's slamming up against our house.

It was like rocks were being pelted at our house.

I literally moved away from the kitchen window

and moments later, large shards of glass were flying out.

So that's when I screamed to get in the closet.

- [Narrator] Across town, Mac Maddox and his fiancee

suddenly find their homes under fire by ice.

It felt like at one point we were under assault.

We hear the skylights getting busted out

and shards of glass going everywhere.

- The house is literally shaking.

It feels like there was an army outside just

taking machine guns through the entire apartment.

I started to worry about even our lives at this point.

- [Narrator] The storm intensifies and Mac realizes

he's under a full-force frozen assault.

Windows were getting busted out.

Blinds were getting ripped off of the windows on the inside.

There were shards of siding that was getting blown off.

It felt like we were in the middle of a war zone.

- [Narrator] 20 minutes later.

- [Narrator] The Tibbs family emerges from hiding.

- [Narrator] The onslaught shatters windows and skylights.

- [Bonnie] Oh my god!

- [Narrator] Allowing pounding ice to destroy

the family's belongings.

- After the skylights are completely gone,

and you've got these six giant holes in your house,

it continued to rain.

It actually came onto the rugs and furniture,

the walls, everything.

- It's crazy to think that your day

could start off absolutely normal.

This is the aftermath.

Windshield's shattered on my car.

And just literally matter of minutes could turn into,

you know, your whole livelihood getting destroyed.

- Hail like this, that destroys car windows,

puts big dents in cars.

If a person happened to be unlucky enough

to be outside and have no shelter,

it could seriously injure or even kill them.

(ominous music)

To see actually literal baseballs

and golf balls flying from the sky

and totally tearing everything apart,

I don't know if I'll ever see anything

like that again in my life.

- Mother nature got us good.

We always thought we could outsmart her,

or she wasn't gonna affect us.

It's in my room!

We know that we can be affected

and that we can't outrun her.

- [Mac] It's Armageddon!

rs melt,

the area of white reflective surface shrinks,

replaced by Earth or ocean,

both dark surfaces that absorb more heat,

which in turn accelerates meltdown.

This is what scientists call a feedback effect.

(energetic music)

In the last four decades,

there's been a significant loss of glaciers

in Montana's Glacier National Park.

- Since the '70s, we've had pretty much a very rapid

and full-scale disappearance of the glaciers.

- [Narrator] Ecologist Dan Fagre

has been monitoring their demise for many years.

- Well, we use several ways of monitoring the glaciers.

The first and most obvious one is that we take pictures,

and these can be pictures from a point in the landscape,

so you're looking at it from the side and

you can just look at the visual changes year by year.

- [Narrator] Sequential photos taken decades apart

show how specific glaciers have shrunk in size.

- I can see with my own eyes

how much that glacier's disappeared.

And it's a little bit of a compelling

and alarming kind of view because you think about glaciers

as being, you know, a steady presence on a landscape.

And to see it disappearing this quickly means

that we are going through some very, very dynamic times.

- [Narrator] Here, Fagre is photographing

Salamander Glacier, which has been losing mass rapidly.

For glaciologists, the surface area is not the only factor

that's important in determining a glacier's health.

- It's also how thick it is or how much total mass.

And for that, we do a lot of ground measurements as well.

And we can go on the glacier with global positioning systems

and get both the area and the height.

- [Narrator] The prognosis for Glacier National Park

is dire.

- Based on the best measurements that we have to date,

it looks like the year 2030 is when most of the glaciers,

if not all the glaciers, will be completely gone.

- [Narrator] A similar fate is predicted

for glaciers all over the world.

- Almost all of the world's alpine,

mountain, or valley glaciers have been receding.

What's happening in Glacier National Park

is basically going on globally.

We're seeing that these mountains

are being transformed by climate changes.

- [Narrator] Melting glaciers have long posed a threat

to local communities.

Like many high mountain areas, the glaciers of Peru

were once feared for the avalanches they unleashed.

Sometimes icy mountains hide their true destructive nature

behind picturesque scenes of winter wonder,

spectacular beauty, secretly poised to destroy whatever

and whomever is in its path.

(ominous music)

Odda, Norway.

Set at the base of the Klungersetskreda Mountain,

Odda is the picturesque home

to approximately 7,000 residents.

- You've got the elevation,

you've got the topography, you've got the mountains.

You've got lots and lots of snowfall.

- [Narrator] These majestic peaks have stood guard over Odda

for hundreds of years,

but locals don't know that the mountains themselves

are poised to attack.

(ominous music)

A loud rumble erupts as an icy juggernaut races downhill.

- This avalanche begins relatively small,

but very rapidly gains force.

- [Narrator] Residents know they're in trouble

when the Earth itself seems to unleash a mighty roar.

(rumbling)

- It's almost like a big jumbo jet

coming down the mountainside.

- [Narrator] Police officer Johnny Helle

is stunned by what he sees out his window.

- I was thinking it will be a big disaster.

- [Narrator] As the mountain shed seven stories

of snow, ice, and rocks,

Eivind Kopperdal videotapes from his home across the fjord.

- This avalanche came like a big waterfall.

There was a rumbling and a very ugly noise.

- This event is triggered because of

an enormous amount of snow leading up to the event.

And then there was a warmup.

- This avalanche was a lot of wet snow,

which means it's heavier and has more mass.

- The snow stored at a high elevation

has tremendous potential energy.

Once it breaks loose and starts moving downslope,

that potential energy is converted to kinetic energy,

which creates tremendous momentum and power.

- It's pushing the air out ahead of it.

So you have gale-force winds coming down this mountain.

- [Narrator] The onslaught wipes out everything in its path,

including trees that have stood for decades.

- One of the reasons why this avalanche is so deadly

is the debris that it's picked up along the way.

A rock or a tree or a boulder has much more momentum

and much more force than snow.

- [Narrator] Seconds later,

the avalanche takes aim at homes,

and now lives are on the line.

- In an avalanche, your chances of survival are very low.

You've got the snowfall moving down the side

of a steep-sloped mountain at 60 to 80 miles per hour.

No one can run that fast.

- The avalanche get bigger and bigger and wider and wider,

and my God, I thought, it's going to the houses.

- I was sure that this would kill a lot of people.

- [Narrator] The snow slide swallows a house

where a family is just sitting down to breakfast.

- Initially it's just knocked off its foundation.

- [Narrator] But the three people inside

don't stand a chance as the 100-year-old structure

topples over.

- The house just disappeared in the snow.

I got a real bad, bad feeling.

- [Narrator] The 70-foot wall of ice

continues down the slope and threatens

another home near the shoreline.

But the house is spared.

- We see two houses attacked by the avalanche.

The one on the left is being hit by brown snow,

that's snow carrying rocks and debris against that house.

The house being hit by the white snow

without the rocks survives.

- [Narrator] Then, after six terrifying minutes,

an eerie silence.

- This was a very special quietness because

I felt like everything stopped, no sound at all.

- [Narrator] Helle fears the worst,

Since the snowpack is like cement.

- I had to go out, see how many people was killed,

because I was 100% certain that houses

had been smashed by this avalanche.

- Unfortunately, rescue in an avalanche

can be very, very difficult.

Even if you survive the crushing power

of the avalanche itself,

it will be very, very difficult to find you.

(ominous music)

- That's where somebody was killed.

There were three people in that house.

Two of them escaped into the basement.

The third person was in a wood-frame portion of the house

above the basement,

and they were killed when the house was crushed.

- [Narrator] Since that fateful morning,

barriers have been built to divert any future avalanches,

but the villagers know that what's up on the mountain

is truly a higher power.

- In the path of an avalanche,

you don't have any really good options.

- You are mostly helpless.

(dramatic music)

- I feel very small compared to what nature can do.

can significantly impact

rising sea levels, but in Iceland,

that meltdown isn't only environmental.

It can be explosive.

In fact, the evidence is mounting that Iceland

has the potential to be

the most lethal island on the planet.

A fearsome volcanic force lies beneath it,

creating powerful volcanoes capable of generating

gigantic lava floes and altering global climates.

(haunting music)

Yet many of Iceland's are covered in glaciers.

Fire and ice are held in a delicate balance.

Scientists fear if this balance were tipped

in the volcanoes' favor, Iceland could become even deadlier.

If the remaining ice were to melt,

what effect would it have

on the activity of Iceland's volcanoes?

The first clue in the investigation

lies in these innocuous-looking piles of rock and rubble.

They're found all over Iceland,

and yet these rocks don't come from a volcano.

They're moraines, the geological term

for rock piles deposited at the mouth of a glacier.

These deposits are evidence the glaciers are shrinking.

Year by year the glacier has melted

and retreated back up the valley,

leaving a moraine like this behind.

Dr. Roberts has studied the Vatnajokull glacier

for many years and has noticed this dramatic trend.

- The glacier has retreated at a remarkable rate.

Since I've been visiting the area

I've seen tremendous changes.

The ice has retreated annually

at a rate of about 200 feet per year.

This lake over here used to be filled with ice.

I've seen the ice progressively melt.

This moraine has formed.

This whole valley has become almost bare.

Maybe in the next 20 years,

this whole glacier will disappear

and a lake will form in the Valley.

- [Narrator] Iceland's glaciers are melting

at an unprecedented rate.

With an increasing amount of Iceland's ice caps

melting in the last 50 years,

the question that scientists are keen to understand

is what effect this rapid melting will have

on volcanoes that lie beneath.

The only other time that glaciers

have melted this quickly

is when Iceland came out of the last Ice Age.

But what can past events tell us about the future?

Geologists professor Bill McGuire

is investigating how volcanic activity changed

at the end of the last Ice Age.

And he's unearthed some surprising results.

- Around about 11 to 12,000 years ago,

you started to see quite rapid melting of glaciers

in Iceland and elsewhere,

and that triggered a recognizable increase

in volcanic activity because you were removing

this large mass of ice very, very quickly.

- [Narrator] The rapid melting of ice

kickstarts volcanic eruptions beneath.

- Volcanic eruptions are triggered by the

gas in the magma,

which expands to form bubbles

and the bubbles drive the eruption.

It's rather like taking the cork out of

a bottle of champagne.

Now, if you have a very heavy weight on top of a volcano,

if there's heavy mass of water or ice,

that can help suppress eruptive activity.

- [Narrator] But when ice melts quickly,

this downward pressure is suddenly released.

And that's when the trouble starts.

- As the ice melts,

so the pressure on the magma underneath is reduced,

the gas in the magma can form bubbles.

They can coalesce and they can eventually drive the magma

upwards towards the surface and trigger either

explosive eruptions or effusions of lava

that can spread out over huge distances.

- [Narrator] Imagining an ice-free Iceland

isn't that far-fetched.

In fact, it's a future Iceland's leaders

are taking very seriously,

not only for its potentially far-reaching economic impact,

but for what is likely explosive geological activity.

- The question is when.

These are things that we have to think about

and try to prepare ourselves to deal with

if they happen in our lifetime.

- [Narrator] Coming up.

- The one major difficulty we have, the flow of glaciers

is mostly caused by what's happening at the bottom.

And the bottom is the part that we don't see.

glaciers serve as vital reservoirs for fresh water,

providing 50% of the water nearby populations need.

- When mountain glaciers disappear,

there can be some real direct consequences for human beings.

Case in point is some of these valleys in the Himalayas

it is the glaciers,

particularly at the end of the dry season,

providing the drinking water for people.

So when those glaciers disappear,

those people will have to find alternate water supplies,

or basically have to move.

- [Narrator] In the Western United States,

our dependence on glacial ice and snow reservoirs

is just as great.

- It's about 87% of the water that Americans

in the West have to use.

So mountains are very, very critical

in providing that water.

- [Narrator] A reduction in drinking water

is only one of the problems caused by melting glaciers.

Equally as troubling is what a meltdown of ice

in the polar regions will do to sea levels worldwide.

And the melting is occurring faster than anyone predicted.

In 2000, scientists were stunned by changes

at Antarctica's Ross Ice Shelf.

The ice shelves act as buttresses for the glaciers,

holding them back from the sea.

Over the course of two weeks, a 4,247-square-mile fragment,

an area the size of the island of Jamaica,

shattered and separated from the continent.

Three trillion tons of ice,

one of the world's largest recorded icebergs,

drifted out to sea.

(ominous music)

- We're talking about several degrees warming,

over the last century, which is a huge number.

The ocean has been very hot and cold, and today,

we just have no idea what's going on with the ocean.

- [Narrator] But it's difficult to determine

how fast the glaciers are melting.

- The one major difficulty we have,

the flow of glaciers is mostly cut short

by what's happening at the bottom.

And the bottom is the part that we don't see.

The changes that we're observing in the ice sheets

are more rapid, and larger than what is predicted by models.

I think in the most extreme case,

a lot of Greenland would be removed,

and a lot of west Antarctica.

Then you could raise sea level 10 times more than that.

30 feet.

- [Narrator] A 30-foot rise means that many low-lying areas,

such as large portions of Florida, would be submerged.

Today satellites are the most important tool

that scientists have for monitoring what's happening

to the oceans and the ice sheets.

- To see the whole ocean,

you have to do it from far away,

and you really have to do it from space.

- Satellites are able to do this for us

because they're observing 24 hours a day,

seven days a week, 365 days a year, for years at a time.

- [Narrator] Scientists estimate about 200 billion

metric tons of ice melt away every year.

For those who study these satellite signals,

it's an alarming picture.

Rising oceans will swallow farmland, towns, and cities.

But unlike floods of the past,

once the waters have been unleashed, they will not recede.

- Most places in the world,

people live within about 100 miles of the ocean.

It doesn't matter where we are.

The population lives close to the sea.

In China and Japan and Europe, America, Africa, everywhere,

and those are the places that are most vulnerable

to climate disruption.

They're the ones that are gonna be hit the hardest.

- [Narrator] One catastrophe slams into another,

like the pinball hitting its target

and ricocheting to the next.

- And so we envision a situation where

you have the West coping with its water problems,

the hurricane zone coping with hurricanes,

the Northeast coping, not just with windstorms,

but with hailstorms and ice storms,

which will also impose a burden.

The Midwest, we're looking for swarms of tornadoes,

which causes an enormous amount of insurable damage.

- [Narrator] So much uncertainty in a world

plagued with an ever-changing climate.

Change is indeed happening,

and more quickly than we might like.

If we fail to act on these things we can change

and prepare for what we can't,

we are doomed to living on a radically different

and hostile planet.

(ominous music)

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