Dallas Campbell delves into the Horizon archive to discover how scientists have tried to predict an impending apocalypse, and asks if science will save us when Armageddon arrives.
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Some say it will end in fire.
Others think there will be a flood.
Some tell of a great plague that will strike down humanity.
Destruction shall come upon this evil generation.
But all point to one thing - the world is going to end.
Armageddon is one of humanity's most powerful and enduring ideas.
Stories of the apocalypse stretch right back
to the dawn of civilization, and they still make blockbuster hits today.
It seems there is nothing we love more than a vision of the apocalypse,
imagining how our world might end
seems a fundamental part of being human, but where
we once might have looked to religion for answers, many now turn to science
both to predict what might happen and to protect us from impending doom.
For nearly 50 years the BBC's Horizon
has been at the forefront of science journalism.
Charting the breakthroughs and discoveries that would change our world.
Science and technology have enabled us to predict earthquakes,
defeat disease, and defend ourselves from the awesome power of nature.
Our understanding of the world around us is better now than ever before.
But are we any closer to knowing how it's all going to end?
And when Armageddon arrives,
will science be able to save us?
For thousands of years people thought the only force powerful enough to end the world was God.
But then in 1945, all that changed.
The horror of two world wars
and the phenomenal power of the Hiroshima and Nagasaki bombs
left little doubt that we were capable of annihilating ourselves.
The creation of atomic energy had been a scientific triumph.
But the sheer scale of death and devastation it had caused
left the scientific community in turmoil.
One of the earliest Horizon programmes
reported on the moral torment that many scientists now faced.
This week, Horizon looks at a dilemma,
the dilemma of the scientist who, try as he might,
cannot reconcile with his conscience
the fear that his discoveries may eventually be used to the detriment of mankind.
Victory over Japan brings a wild ecstasy to the ordinary men and women of the triumphant nations.
At Los Alamos, the place where the winning weapon was created,
most join in the general mood of celebration and relief, but not all the scientists
present at the victory parties there share the popular excitement.
There are some among them for whom the sweets of triumph are soured by
a frightful awareness of the evil forces their genius and efforts have released.
We knew the world would not be the same.
I remembered the line from the Hindu scripture the Bhagavad-Gita
"Now I am become death, the destroyer of worlds."
I suppose we all thought that, one way or another.
But there was no going back. The nuclear arms race had begun.
During the '50s and '60s,
the super powers built increasingly bigger bombs in a bid to defend themselves from each other.
The result was an arsenal of weapons that could wipe humanity off the face of the Earth.
The threat of Armageddon was real
and many people lived each day in fear of nuclear annihilation.
When I was a kid growing up in the 1970's and early '80s
I certainly remember information like this government handbook
about what to do in the event of a nuclear attack
and it's got hints like how to build a bunker in your sitting room,
how to protect your drinking water from fallout
and it's scary stuff because at the time
I remember thinking that Armageddon was just a button push away.
And the terrible responsibility of having to push that button
rested on the shoulders of just a handful of men.
In 1971, Horizon gained unprecedented access to their extraordinary daily lives.
Cherie, would you bring me a cup of coffee, please?
'Bryce Martenson is a missile commander
'with strategic air command.'
Chris, do you know we're going up to Grandma Jean's for Thanksgiving?
'Every four days he leaves his family to go to an underground
'bomb-proof command post to take charge of ten Minuteman missiles.'
'If necessary, he is fully prepared to take part in the destruction
'of whole nations and ultimately his family and himself.'
Once in the heavily guarded compound,
Martenson and his deputy are there for 36 hours of duty.
Both have been checked on by military intelligence and psychiatrists.
Both are armed. If one of them suffers a psychiatric breakdown,
it's the duty of the other to shoot him.
60 feet under the ground, Martenson and his deputy
have to pass through a seven ton steel door
before reaching the entrance to the command capsule itself.
They're now surrounded by thousands of tons of steel and concrete.
Protected from almost anything but a direct nuclear hit.
The red strong box contains the secret orders to be used in case of war.
In the box are two keys.
To fire the missiles, these have to be turned simultaneously
in locks thirty feet apart.
They have been trained to the highest peak of efficiency to carry out
a task which we hope they'll never be asked to perform.
A first strike by the total Russian missile forces would leave
almost all of the American Minuteman missiles undamaged.
If only half of them were used in retaliation,
they could destroy 80% of Russian industry and 100 million people.
They hum menacingly. If you touch them, they feel alive.
# Don't you understand what I'm trying to say
# Can't you feel the fears I'm feeling today
# If the button is pushed There's no running away... #
Thousands took to the streets in protest against the apparent insanity of the arms race.
We will campaign until
all the nuclear bases are cleansed from our soil!
The use of destruction leads to destruction. It solves nothing.
Europe without the bomb can solve its problems.
As far as the people were concerned,
decades of scientific achievement had only brought us closer to
Armageddon than ever before and there was little we could do to prevent it.
Three, two, one, zero.
We have commencement.
But then in 1969, one event transformed public opinion.
I'm at the foot of the ladder.
I'm going to step off now.
It's one small step for man,
one giant leap for mankind.
Around 500 million people watched Neil Armstrong
step out of the Apollo 11 spacecraft onto the surface of the moon.
It was a remarkable achievement.
But seeing the Earth from space brought home
just how vulnerable our planet really was.
The survival of the entire human race depended on this
tiny oasis in the vast emptiness of space.
It would be another two decades before the fall
of the Soviet Union would diminish the threat of nuclear war.
But by the early 1970s, a new branch of science was already emerging,
one based not on destruction, but on protection.
Washington DC, early morning of April 22nd 1970, Earth Day.
Young people, until this time characterised as inward-looking,
and disaffected from public life, had found a cause.
America had discovered ecology.
-Well, ecology is a balance of nature.
-What do you mean by ecology?
Well, to clean it up, not to pollute the atmosphere, the land, the water.
It's the relationship between me
and plants and animals and the world in general.
People talk about it and that's what they do. They say,
"I'm really for ecology," but nobody really does anything for it.
-What is ecology then?
-Going out and doing something!
This enthusiasm for ecology was echoed by many scientists
convinced that if we destroyed our environment,
we would ultimately destroy ourselves.
It's not enough to put bricks in your toilet to save water,
or recycle your tin cans ritually or so on.
The really critical thing, of course, is what you're doing
to the life support systems of the planet because those
are the systems which supply us with all of our food, maintain
the quality of the atmosphere, dispose of all of our waste.
If we get rid of them, we've bought the farm.
CHANTING AND SINGING
The ecology movement was based on working together
to build a better future.
Many scientists echoed this idea, believing that sharing ideas
was the key to becoming the masters of our destiny.
And it was this spirit of co-operation that gave them
the confidence and the courage to tackle one of humanity's biggest killers.
There are probably two diseases that have caused more fear
in the population of the world than any other,
and that is plague and smallpox.
Smallpox is probably one of the most frightening,
ugly diseases that one can imagine.
I had seen worms in wounds, I had seen all kinds of rashes,
and people amputated, but smallpox, it's the worst I've ever seen.
Half of them were dying and there's nothing we could do.
In the post-war era, the scourge of smallpox was still killing
15 million people a year.
So members of the World Health Organisation met to lay out
the plans of an extraordinary global challenge - to end smallpox forever.
I felt overawed by the task ahead, recognising we had
so many languages to deal with
that we had so many different countries to deal with, that we were
dealing with countries where there was famine, where there was war.
There were many scientists who said
that this was just not possible to do.
And in fact, at the time, even the Director General of WHO said
it just can't be done.
The task was immense.
No disease had ever been eradicated from the world before
and smallpox was endemic on every continent.
The challenge was to vaccinate every one at risk,
all one billion of them.
Doctors, nurses and health workers joined forces across the globe.
This was war and the troops worked around the clock.
People were dying like flies and if I sleep,
that means there is nobody else who is going to do the work.
The best that I ever did was in a prison,
I did 600 people in 20 minutes.
The best I ever did in a day was something over 11,000.
Oh, it was a real battle.
Hundreds of thousands of people were working - health workers,
volunteers, so many different people.
But no matter how hard they tried, it was just too big a task.
Vaccinating everyone at risk was impossible.
The team needed a new strategy.
And so we asked the question, what would we do if we were smallpox viruses?
What would we do if we were bent on immortality?
What we would do is, we would find another susceptible person to move to.
Using that idea, we got on the radio to missionaries in the area
to tell us where are the cases of smallpox.
We used our vaccine precisely around those cases and then what was left,
we used where we predicted the smallpox virus would go next.
By finding every case of smallpox and vaccinating
everyone in contact with them, they broke the chain of transmission.
We had out-thought the smallpox virus.
Having vanquished the disease in North America,
South America, Europe and Asia,
the team were finally on the trail of the very last strain in Somalia.
They tracked the virus to this village.
And then to this woman.
They traced all her contacts and that's when they found him.
Ali Maalin - the last person on the planet with smallpox.
A disease that had plagued humanity for thousands of years
was finally under our control.
It was a fantastic achievement.
In 1979, smallpox was officially eradicated
as a threat to human life.
Science had shown that it could put us one step ahead of Armageddon.
Perhaps we could be masters of our destiny.
But then in 1981, Horizon reported on a controversial new theory
that suggested the fate of humanity was beyond our control.
It had long been known that 65 million years ago, Earth had
suffered a catastrophe that had wiped out nearly all living things,
including the dinosaurs.
No-one had managed to pinpoint what caused this mass extinction
until a father/son team proposed a radical new idea.
My son Walt brought along this little sample of rock,
which he has put together in Lucite to keep it from crumbling.
He said, "Dad, do you see this clay layer here,
"it's about a half inch thick."
He said, "That's when the dinosaurs went out," and I said,
"Do tell me more about that," and so he said that not only the dinosaurs
but 65 or 75% of all species alive on the Earth then
suddenly disappeared. And I said, "Gee, Walt,
"that's about the most exciting thing I've ever seen in my life."
And he had to confess ignorance to some things, he said,
"We really don't know how long it took, why it's there,"
and so I said, "Maybe some of the tricks that I know as a physicist might help unravel that story,"
and then we talked about it for the next couple of weeks
and finally decided to look for iridium
as a measure of the deposition rate.
Iridium along with all the other elements
was present in the cloud of dust that was to form the solar system.
What little there is comes from the slow drizzle of the stuff
that's still falling on the Earth at a known rate.
Alvarez decided to measure how much iridium there was in the clay
and so calculate how long it had taken to fall.
The results surprised everyone.
Iridium was found in large amounts,
much more than a slow drizzle from space could explain.
Now, there was no way that we knew of that we could explain
such an increase by conventional,
terrestrial chemistry or geo-chemistry.
Luiz realised they had stumbled upon something important,
but what did it mean?
And I went through a lot of scenarios.
Some of them were so wild I wouldn't even dare mention what they were,
but I remember thinking at the time, each of them looked pretty good.
One idea was that the iridium was showered on the Earth
from a nearby exploding star, a supernova.
The idea was that if the iridium had come from a super nova,
it would have carried with it a rare type of plutonium
that no longer exists in the solar system, plutonium 244.
-He went on churning out the ideas.
-He would come up with them.
These would be evaluated and discarded.
After about a month and a half, he came up with one that none of us
could knock down and that's the one that we're working on now.
What they're working on now also comes from space.
The vast majority of iridium-bearing meteorites
started life as asteroids.
Most of them in an orbit between Mars
and Jupiter never come anywhere near the Earth.
But the theory goes that a few are occasionally
swung out of line by the enormous gravitational pull of Jupiter.
A very few of these finish up in an orbit which crosses the Earth's.
Alvarez' theory is that 65 million years ago, a huge asteroid,
six miles wide, smashed into the Earth with devastating effects.
It was this collision, he believes, that covered the Earth
with iridium and wiped out the dinosaurs.
Ten years later, Alvarez' theory became widely accepted
when a 200 kilometre-wide impact crater the asteroid left behind
was identified in the jungles of Mexico.
When it became clear that a rock falling from the heavens
had exterminated nearly all life on Earth,
we realised just how vulnerable we were.
The mass extinction of the dinosaurs was proof that Armageddon was real.
If it had happened before, it could happen again.
Against the awesome might of nature,
our science and our technology seemed powerless,
but if we couldn't prevent the devastation,
we needed to get really good at something else,
the science of prediction.
Astronomers began scouring the heavens for killer asteroids
that might be heading our way.
And then radio telescopes captured the image everyone was dreading.
A one kilometre-wide asteroid with our name on it.
It's known as 1950 DA.
An interesting question is, is 1950 DA the most dangerous rock in space?
And at the moment, one could say it's the most dangerous
known rock in space.
Astronomers have tracked 1950 DA more closely than almost
any other asteroid in the solar system,
and all the indications are it is cosmic enemy number one,
expected to collide with or come perilously close to the Earth in 2880.
Its impact could kill hundreds of millions of people.
If 1950 DA hit the Earth, the energy released would be
roughly 100,000 megatons.
Ten megatons is a very powerful hydrogen bomb.
So this would not be a pleasant event for the Earth.
It seems that in the mere blink of a cosmic eye
we have a date with Armageddon.
The world of science now faced an awesome task.
What could it do to save the Earth?
Jay Melosh was part of an elite group of scientists
summoned by the US Government to tackle this new threat to humanity.
The solution they confidently proposed would be
to turn our weapons of mass destruction into weapons
of mass salvation -
attack an incoming asteroid with nuclear missiles.
It would seem that a big nuclear weapon detonated
either on the surface or drilled inside an asteroid
would be the answer to this problem.
We've been trained from watching movies like Star Wars that
if we were to do that,
the asteroid would disappear in a cloud of vapour.
But then Melosh and his fellow scientists
pointed to one very obvious snag.
Those movies ignore the really gigantic scale of these objects.
Even a nuclear weapon of the normal yield, 20 megatons,
would not disperse it.
Firing even our most powerful missiles,
20 megaton warheads would be useless.
In fact, it could just make matters worse.
Scientists calculated that the explosion could simply
shatter the asteroid, causing huge pieces of rock
to rain down across continents and oceans.
One huge killer would be turned into something every bit as deadly -
a cluster bomb.
Even if we could break it up into fragments, it's not clear that
that would help things unless all of the fragments missed the Earth.
Because if they didn't,
gigantic fires could be ignited by those fragments hitting land.
Large fragments that hit the sea could raise tidal waves
up to four kilometres high.
It would be utterly devastating.
It seemed no existing nuclear weapon could save the Earth.
What was needed was something much bigger, something that
wouldn't just fragment an incoming asteroid, but completely vaporise it.
Nothing that we have in our arsenals can release that much energy.
Nevertheless, the nuclear weapons designers assure us that there
is no theoretical limit to how big you can build a nuclear weapon
and many were eager to try.
So they set to calculating just how big a weapon they would need.
The answer was staggering.
The biggest bomb ever made would have to be
placed on the biggest rocket ever made.
And the whole contraption fired out of the Earth's atmosphere
at 40,000 kilometres per hour.
We're talking something on the order of a thousand megatons.
Such weapons constitute a bigger threat to us
than the asteroids themselves do.
This weapon, if mishandled or misused, would itself be
capable of causing a global catastrophe.
The idea was dismissed as insane.
Nuclear weapons, it seemed, were not the answer.
Science had to find a better way.
So Melosh put forward an extraordinary idea.
He suggested building a device
that would act like a giant magnifying glass.
We imagine this is the asteroid.
We get it lined up, focus it
and we can start to vaporise the surface of the asteroid.
If we focus the solar energy in a narrow spot on the surface
we can actually vaporise rock, generate a jet,
kind of like a little rocket motor, a solar-powered rocket motor,
that will then gently push the asteroid away.
His name for this device was a solar collector.
This solar collector would focus
an intense beam of the sun's energy onto the asteroid.
The heat would burn away the surface of the asteroid, releasing energy
which would gradually push the asteroid off course.
It might sound like science fiction
but it offered hope that science could save the Earth.
But there was a problem.
It would take at least ten years to build and deploy the solar collector
and many asteroid hunters believed that we might not have that long.
They estimated there could be up to 600 kilometre-wide asteroids
still undiscovered near Earth.
And any one of them could be heading straight for us.
While astronomers trained their telescopes on the skies,
other scientists were fine-tuning their instruments to find out
what might be lurking here on Earth.
And they discovered that nature was far more dangerous
than they'd ever imagined.
Increasingly sophisticated seismological research
found that a single earthquake
could trigger a chain reaction of devastating quakes
capable of bringing entire nations to their knees.
And in the Canary Islands
an unstable volcano could cause a massive landslide,
creating a huge tidal wave far higher than any normal tsunami.
It would race across oceans, killing millions.
And then, hidden beneath Yellowstone Park in Wyoming,
geologists found an even bigger threat.
We realised that Yellowstone had been an ancient volcanic system.
We suspected that it had been a caldera volcano
but we didn't know where the caldera was or how large it was.
It wasn't until photographs were taken from the air
that the true scale of the caldera was revealed.
It was a monster.
70 kilometres across, 30 kilometres wide.
Beneath it lay a vast magma chamber
that encompassed almost the entire park.
The question was, when would it erupt?
To find out, geologists needed to work out
when it had erupted in the past,
so they examined the ancient sheets of hardened ash
and they discovered something unexpected -
three different layers from three different eruptions.
Quite amazingly, we realised that there was a cycle of caldera-forming eruptions,
these huge volcanic eruptions, about every 600,000 years.
Yellowstone was on a 600,000-year cycle
and the last eruption was 600,000 years ago.
And there were worrying signs that the volcano was once again beginning to stir.
Professor Bob Smith has been working in the park for most of his career.
I was working at the south end of this lake in a place called Peale Island.
I was standing on the island one day and I noticed a couple of unusual things.
The boat dock that we would normally use at this place seemed to be under water.
That evening, as I was looking over the expanse of the south end
of the lake, I could see trees that were being inundated by water.
I took a look at these trees and they were being
inundated with water a few inches, maybe a foot deep.
What does it mean? We did not know.
Bob commissioned a survey to measure the elevation of the park
above sea level.
He compared these figures to those of a survey carried out in the 1920s.
The results were surprising.
They seemed to show that the ground was heaving upwards.
The surveyor said, "There's something wrong."
And he said, "It's not me. It's got to be something else."
So we went through all the measurements again,
trying to be very careful
and the conclusion kind of hit me in the face. It said this caldera has uplifted, at that time,
740 millimetres in the middle of the caldera.
The ground beneath the north of Yellowstone was bulging up,
tilting the rest of the park downwards.
This was tipping out the south end of the lake,
saturating the shore-side trees with water.
The scientists realised there was only one thing that could
make the earth rise up in this way -
a vast, living magma chamber.
The Yellowstone super-volcano was alive.
And if the calculations were correct, the next eruption was already overdue.
They predicted that when this super-volcano erupts again
it will have a devastating impact across the whole world.
Gigantic plumes of ash and debris will be thrown into the atmosphere,
blotting out the sun.
Global temperatures will plummet, devastating agriculture
and pushing humanity to the brink of extinction.
It seemed the more scientists scrutinised nature
the more terrifying threats they found.
Increasingly sophisticated scientific techniques might have
brought us greater knowledge but we were scaring ourselves stupid.
And as the millennium approached we were gripped by Armageddon fever.
We even convinced ourselves that the turn of the new year itself
would spell our doom.
Patients' lives could be at risk because the Health Service
may not be ready to deal with the so-called Millennium Bug.
At the stroke of midnight, the Millennium Bug would cause computers to crash,
power grids to seize
and planes to fall from the skies.
Three, two, one.
When the New Year arrived uneventfully,
hysteria turned to apocalypse fatigue.
We'd believed all the hype and now started to wonder
if the scientists were crying wolf.
But then, just when we thought we were safe, an event witnessed by millions changed everything.
Nearly 3,000 people died in the terrorist attacks of September 11th 2001.
It was a stark reminder that there were some things we could never predict
and that Armageddon could yet be a man-made catastrophe.
These shocking acts of violence put the world on red alert.
And then on Boxing Day, 2004...
..the Indian Ocean Tsunami,
one of the most devastating natural disasters in living memory,
claimed over 200,000 lives in a single day.
Dire warnings of the apocalypse can sometimes feel dramatic
But these events were a chilling reminder that our lives
could be snuffed out in an instant.
Science was powerless to prevent these tragedies,
but one year later,
when devastation looked set to strike again,
scientists made sure they were ready.
Good evening, European governments have been told to take urgent action
to prepare for a possible flu pandemic.
The virus found is H5N1 - highly pathogenic virus.
Any bird flu could cause a pandemic.
But hidden inside H5N1, is something that makes it a more dangerous virus
than any we've seen before.
This particular H5N1 virus
falls into the category of what we call a highly pathogenic virus.
Um, much, much more deadly
than your run-of-the-mill avian influenza viruses.
When we analysed it, we found a tiny extra piece
of genetic material
that's in one of the genes of the virus.
The tiny genetic anomaly turns H5N1 into a particularly nasty killer.
What is different about the H5N1 virus
is that this very small change
allows the virus to spread throughout the body
infecting various organs and tissues around the respiratory tract.
And of course, we've seen the result quite clearly,
many of these people who have become infected with H5N1
are dying from multi-organ failure.
The idea that a killer bird-flu virus could
take hold in the human population isn't scientific theory -
it's historical fact.
Medical archives reveal a pattern of flu pandemics
stretching back through the centuries.
The most devastating outbreak of all occurred in 1918,
shortly after the end of the First World War.
A deadly strain of avian flu spread rapidly across the globe,
carried in the lungs of soldiers returning home to their families.
The death toll was terrifying.
Within 14 months, the virus had taken 15 million lives.
'The biggest shock, I guess, about 1918 was
'the way the virus turned its face and attacked
'young people between the ages of 25 and 35.'
They are not the sort of young people who were normally killed
by an influenza virus, but in 1918 they were.
'The virus spared the elderly -
'they're usually the most vulnerable - and attacked the young group.
'Whenever you think about 1918, you think,'
"Oh, my goodness, I hope that's not going to happen again."
The flu strain responsible for the 1918 pandemic was H1N1.
Not the same virus that is threatening us today,
but the similarities between the two are striking.
'At the moment, with H1N1,
'140 people have died, in a population of six billion.
'People come to me and they say, "That's not many."'
But my answer to that is, go back to the year before 1918.
There, you had 140 people dead, 140 soldiers dead.
'There you had a virus that didn't seem to spread at all,'
but within a year it had exploded, and killed 50 million people.
So, there's a warning there.
We cannot ignore a virus that's done that in the past. We really can't.
The predictions surrounding avian flu were truly apocalyptic.
Virologists warned that millions could become infected and die,
plunging society into chaos.
But in the end, the pandemic never came.
Scientists are keen to warn us when they spot a looming disaster,
but when their predictions don't come true,
they're often accused of scaremongering.
Yet their most persistent warning, the one they've been shouting about
for decades now, is still something that many people don't want to hear.
It's a story Horizon has been following since the '80s.
Our world is getting hotter.
The atmosphere is changing, trapping more heat from the Sun.
Changing with it may be climate, agriculture and the level of the sea.
The cause is odourless, colourless and non-toxic, and it's man-made.
Some of the trouble comes from this power station at Vesteros in Sweden.
The emissions should be harmless - water vapour
and carbon dioxide, or CO2 - but carbon dioxide is the problem.
Burning coal, or any fossil fuel such as oil or gas, makes CO2.
We put 18 billion tonnes of it out into the atmosphere each year.
CO2 traps heat like a giant greenhouse,
and it may be changing the climate of the Earth.
'20 years ago, when this matter was discussed among scientists,
'the response was one of dismissing it -
'"This is fiction, we don't believe it."
'Today, many are concerned, and that's a major difference.'
It's been an evolutionary process in people's mind
as well as with regard to our knowledge about the phenomenon.
What is happening is that we as human beings are
bringing about a climatic change.
We are emitting things into the atmosphere now with a rate
that will change the climate more rapidly
than it has changed naturally during the last hundred thousands of years.
# I've got the brains
# You've got the looks
# Let's make lots of money
# You've got the brawn... #
But the apocalyptic warnings fell on deaf ears.
The 1980s were the boom years of optimism and progress,
and consumerism was running wild.
The idea that our success and progress could be harming
the planet wasn't something that people really wanted to hear.
After all, if global warming was making Britain
a few degrees warmer, what was there to worry about?
But as the years passed,
the complexities of climate change started to unfold.
Scientists began to think that a few degrees of warming
in some parts of the world could trigger global chaos.
This is the cleanest place on Earth,
the Clean Air Facility at the South Pole,
where the impact of human civilisation is measured -
the Earth's environmental oracle.
It was in Antarctica that the hole in the ozone layer was first spotted.
It is here the increase in carbon dioxide levels is measured,
and it is here that scientists are prophesying doomsday...
..global warming at the end of the Earth.
For it has been predicted that, if temperatures rise,
part of the vast ice sheet that covers Antarctica
might suddenly collapse.
And Antarctica is warming up.
# We're all going on a summer holiday... #
We're heading for Leonie Island over there.
It's a small island about four kilometres square
with a thin ribbon of vegetation along one side of it.
Head of terrestrial life sciences for British Antarctic Survey,
David Walton has been measuring climate change,
and on Leonie Island the evidence is irrefutable.
The desert that is Antarctica is blooming.
There's a tremendous amount of Colobanthus up here,
growing amongst the mosses.
It looks really good, lots of vegetation.
Lots of grass all along here, colonising all the bare ground,
and in the cracks up amongst the rocks.
'We've been mapping these plants for some time.'
Over 25 years, we've noticed a tremendous increase
in their spread, into areas they'd previously never colonised,
and this paralleled measurements that we were making which showed
that the mean temperature was going up year on year.
The records show that, in the last 50 years,
the Antarctic Peninsula has warmed by an unprecedented 2 degrees Celsius.
The Antarctica team feared this increase in temperature might
cause the ice sheet to collapse.
And if that happened,
they predicted global sea levels could
rise by as much as three metres,
swamping coastal towns and cities across the world.
And there was evidence it was already beginning to happen.
..have discovered that an ice shelf which used to be
the size of East Anglia has completely collapsed...
Since that programme was made, a further 2,500 cubic kilometres
of the polar ice sheets have melted into the sea.
That's more fresh water than could flow over Niagara Falls in 40 years.
But scientists realised that rising sea levels might only be
half the problem.
Fresh meltwater flooding into the oceans could also disrupt
a natural cycle we all depend upon...
..the Gulf Stream.
Britain bathes in its heat.
It begins south of the Equator, absorbs heat from the tropics
and delivers it to our shores.
It means we can swim in the sea at the same latitude
that Canada has polar bears.
But the most important thing about it happens further north.
This sinking is caused by the salt in the water.
The dense salty water plunges to the bottom and is pushed back south,
where it warms and rises, and the whole cycle begins again.
For thousands of years, the current has circulated without interruption.
But then a fisheries researcher working off the coast of Scotland
discovered something alarming.
This graph shows the salinity, or saltiness, of the bottom water.
It's the saltiness from 1900 to the present day.
Until the 1970s, the salinity had been almost constant,
but then it began to fall.
After the late '70s, we began to see a freshening of the bottom water,
so much so that we began to doubt our own results.
We took further samples,
we checked with other countries who were sampling the same water,
until eventually we became convinced that
this change was actually happening.
Fresh water flooding down from the melting Arctic ice caps was
threatening to disrupt the Gulf Stream's cycle.
And scientists warned that if the Gulf Stream shuts down...
..global weather patterns would be thrown into turmoil.
Europe would be plunged into a bitter winter
that could last 100 years.
The lush forest of the Amazon would wither and die.
The life-giving monsoon rains would fail,
leaving hundreds of millions of people
to face drought and starvation.
It could be the end of the world as we know it.
Right now, many scientists regard climate change
as the single greatest threat to our survival.
It's not as dramatic as a supervolcano
or as immediate as a killer virus,
but the consequences of climate change could be just as apocalyptic.
Life on Earth has been wiped out in the past,
so we know it could happen again.
All we can do is hope that, this time, we'll have enough warning.
Over the last 50 years, science has done everything it can to try
and keep one step ahead of Armageddon -
to predict, to prevent or simply to dispel every likely threat.
But the facts still remain.
However advanced our science, however hard we try and prophesise,
we can never be sure what might be lurking around the corner.
# It's the end of the world as we know it
# It's the end of the world as we know it
# And I feel fine
# It's the end of the world as we know it
# It's the end of the world as we know it
# It's the end of the world as we know it
# I feel fine... #
Subtitles by Red Bee Media Ltd
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Our understanding of the world around us is better now than ever before. But are we any closer to knowing how it is all going to end?
Dallas Campbell delves into the Horizon archive to discover how scientists have tried to predict an impending apocalypse - from natural disaster to killer disease to asteroid impact - and to ask: when Armageddon arrives, will science be able to save us?