(plaintive music) (ominous roaring) (taut mellow music) - [Narrator] In 535 AD,
scientific evidence suggests that a massive volcano
erupted in the tropics. It threw up so much ash that
it turned summer to winter. Crops failed for years, drought and famine gripped the land, millions died. (taut mellow music) For the last five years, David Keys, a writer on history and archeology, has immersed himself in this
worldwide climatic catastrophe. By consulting historians, scientists, and in particular, volcanologists, Keys has concluded that
the most likely culprit was the notorious volcano, Krakatoa. An expedition to Krakatoa, which lies off the coast of Indonesia, further supported his theory. But Keys believes that the eruption, the biggest in the last 1,500 years, was only the beginning. What followed was over
100 years of upheaval that would change the course
of human history forever. (violent burbling) (mellow music) So what would the volcanic eruption of one and a half thousand
years ago have been like? - The amount of power
generated by this eruption would have been equivalent to around 2,000 million Hiroshima-sized nuclear bombs. (volcano bursting) - The eruption of this ancient Krakatoa is something mankind has never witnessed, perhaps tens, hundreds of times larger than any volcano that's
ever been witnessed. (electronic beeping) - [Narrator] David Keys
asked volcanologist, Dr. Ken Wohletz, an expert on Krakatoa, to feed all the available data about 6th century climate
change into a supercomputer to simulate how the
explosion began to unfold. - I will start the simulation. It will show several
phases of the eruption. - [Narrator] Wohletz
has located the eruption in the Sunda Straits
between Java and Sumatra. By combining tree ring and ice core data with eyewitness accounts
of the dimming of the sun, it's possible to estimate
how much material might have been thrown up
into the Earth's atmosphere. With that figure, it's
possible to calculate the scale and power of the explosion and associated aftereffects. (distant roaring) Using Wohletz's model,
we have reconstructed the Krakatoa 535 AD Big Bang. (volcano explodes) A giant red hot fountain of molten rock and a vast cloud of ash
towered over the countryside. Then a second crack would
have let seawater in. (volcano explodes) This caused an absolutely vast explosion, creating a 30-mile high fountain
of magma, dust, and ash. Up to a thousand away, ash rained down on forests and fields. (magma burbling) - The towering clouds
of steam and gas and ash pierced and shot upwards, and at times when it seemed
like could go no higher, it would continue to go
high, eventually to the point where it started to block out
the sun in all directions. And this gray, white cloud would then see to sort of move laterally across the sky, like a mushroom cloud. (tense music) - [Narrator] The fallout from the eruption would have been the natural
equivalent of nuclear winter. (ominous music) So how did Krakatoa affect the world? Ken Wohletz has studied Krakatoa in detail and he can see similarities between it a huge dormant volcano near his laboratory high in the hills of New Mexico. (taut electronic beeping) The 15-mile-wide volcanic
crater, or caldera, at Valley Grande, New Mexico last exploded a million years ago. Ash from here landed as
far away as Louisiana. Using the remains of Valley Grande, Ken shows how high-flying
volcanic ash blocks out the sun. - This is ultra-fine volcanic ash formed by phreato-plinian eruption, similar to what we think happened in the 6th century at Krakatoa. It's so fine, (wind blowing) that even just a baby's breath of air will keep it suspended
by minute turbulence. It will never fall to the earth as long as the air is moving, which of course, it always does high up in the atmosphere. (ominous music) - [Narrator] In 535 AD, similar microscopic particles of ash and sulfur dioxide from Krakatoa would have shrouded the whole sky, turning it endlessly gray. Temperatures dropped. Without the full strength of
the sun to heat the oceans, less water would have evaporated, and the atmosphere became drier and drier. (ominous music) - As a result, there would have been progressively less rainfall. As a result, there were
droughts and famines. Very often at the end of major droughts, you do get massive floods. And that seems to have been what occurred. (somber music) - [Narrator] But what
fascinated David Keys most was not the climatic catastrophe itself, but the possible effects
on human civilization. (fire crackling)
(suspenseful music) - I began to think to myself, well, disruption as severe as this has got to have political consequences. It's really the long-term consequences that I was interested in isolating, to see whether one big event can actually have a knock-on effect
throughout history, worldwide. (mellow music) - [Narrator] Keys decided to examine a series of historical
puzzles of the 6th century AD. He looked at events which
from contemporary writings and archeological evidence
were known to have taken place, but whose cause has never
been properly explained, The first puzzle was the
spread of a terrible disease, which brought the greatest
superpower of the time, the Roman Empire, to its knees. (suspenseful music) In 535 AD, under the Emperor Justinian, the late Roman Empire
based in Constantinople was flourishing. (suspenseful music) But in 542 AD, something
awful struck at the heart of Justinian's glittering empire. The horrors were described
by a contemporary writer, a monk called Evagrius. (somber music) - [Evagrius] With some
people, it began in the head, made the eyes bloody,
and the face swollen, descended to the throat, and then removed them from mankind. With others, there was
a flowing of the bowels. (somber music) - [Narrator] Evagrius was describing a massive outbreak of bubonic plague, the first time it was recorded in history. But how could the plague
have anything to do with the climatic catastrophe
unleashed seven years before? Plague is a bacteria,
a bacillus transmitted from infected rats to humans. The carrier is the humble flea,
which feeds on rats' blood. - This is a flea, which
has had a blood meal and has a known plague
organisms in its gut. And you can see that it's
quite, stomach's quite full, and everything's fine. If we contrast this with a flea, which has taken up some of the bacillus, we can see that there's a blockage here. And this is brought about by a reaction between the bacillus and the flea's gut. Now, the result of this is, of course, the flea can't feed properly. - They become so ravenously hungry, because they begin to starve,
in effect, the more they eat. Well, they can eat and eat and eat, and they don't satisfy their hunger because their gut is blocked. And so they will jump
onto absolutely anything in the chance of getting a free meal. - [Narrator] As the rats
themselves die from the plague, the flea has an obvious new target to bite for blood: humans. And then, as Evagrius
describes, the agony begins. - [Evagrius] Some came out in sores, which gave rise to great fevers, and they would die two or three days later with their minds in the same state as those who had suffered nothing, and with their bodies still robust. Others lost their senses before dying. (ominous music) - [Narrator] What Keys
found out is that scientists now know that outbreaks of plague are strongly related
to changes in climate. (ominous music) The sort of changes that followed 535, in particular, cooling, could have had a huge impact on the
spread of the disease. Temperature directly affects
how the plague bacteria form in the flea's gut. - Well, plague epidemics
are temperature-related. What happens is that
in the gut of the flea, the fibrin clot only forms at temperatures below 25 degrees centigrade. Above 25 degrees centigrade,
the clot doesn't form and any bacillus is simply passed out of the flea with the feces. - [Narrator] If cooler
conditions bring about the onset of the disease,
did that happen in 535 AD? And if so, where? - Well, according to one of
our contemporary sources, the church historian, Evagrius, the plague originated in Ethiopia. What we know, both
scientifically and historically, is that the Great Lakes
area, Central Africa, is one of the oldest foci of
plague activities in the world, and that it would appear that the assertion of Evagrius is correct. - [Narrator] Because
Africa is normally hot, the disease is kept at bay, but if Africa was affected by the global
cooling of 535 and 536, it would have been a lethal
breeding ground for plague. From Africa via the trade
route, ships, rats, and sailors could easily bring the
plague up the coast, first hitting the major
port of Alexandria in Egypt and on into the heart of the Roman Empire. And Roman greed for one precious commodity from African elephants would only accelerate that process. In the 6th century, there was an enormous
trade in African ivory. (suspenseful music) - Hundreds of tons of
ivory are being brought into the empire every
year, and being processed for luxury furniture, for luxury objects, which important magistrates
would give out as gifts, processed for diplomatic
gifts that the empire could then use to impress his neighbors farther to the north
and farther to the west. People who would never have
seen an elephant in their lives. - And it was essentially the European and Mediterranean greed for
ivory that brought the roof in. - [Narrator] Only seven years after the climatic catastrophe in 542 AD, on the back of the ivory trade, the plague surged into Constantinople. - Its impact was devastating. We had to dispose of
over 10,000 bodies a day, week after week after week, throwing them into the
sea off special boats, sticking them in the
towers of the city wall, filling up systems, digging up orchards. - Soldiers were forced to dig mass graves in which to cast the bodies
of those who had died. The impression is one of
chaos and pandemonium. - Constantinople, Europe's
biggest city stank for month after month after month. - [Narrator] One
contemporary writer recorded that when the number of dead
reached a quarter of a million, city officials simply stopped counting. As people left the stricken city, they took the plague to towns, villages, and farms throughout the empire. Untold millions died. (ominous music) And unknown to the empire,
a second mortal threat was brewing 3,000 miles to the east. (horseman yelling) The climatic catastrophe was also having an extraordinary effect on
an extraordinary people. They, too, would play their part in the decline of the Roman Empire. And the simple reason for this new threat was the difference between
the digestive systems of horses and cows. (volcano exploding) (ominous music) In the isolated planes of Mongolia, hundreds of miles north of China, something strange was about to happen. Before 535 AD, the overlords of the region were a tribe of violent
barbarian horsemen, the Avars. Chinese writers recorded
their uncivilized way of life. - These are foul-smelling barbarians, from their point of view, with outrageous habits. The Avars never bathed,
never washed their clothing. They cleaned their dishes by
having the women lick them dry, all of which was simply
horrifying to the Chinese. - [Narrator] But in one respect, as both Chinese chronicles
and archeological finds show, the Avars were years
ahead of the competition. (electronic beeping) Finds from archeological digs all over Avar territories suggest that they were the most
advanced horsemen in the world. Their style of riding,
saddles, and mouth bits are still in use by
Hungarian plainsmen today. And many believe that the Avars almost certainly invented the stirrup. - It was this large
concentration of horses that gave them a military edge, the latest in the military
technology of that era. (pensive music) (indistinct chattering) The horses also provided
food and sustenance. The Avars drank fermented mare's milk, an alcoholic beverage. (indistinct chattering) So, horses were central
to their existence. (horsemen yelling) - [Narrator] But then in 535 and 536, the years of the catastrophe, Chinese records and tree
ring evidence from Siberia suggest that the Mongolian Steppe was crippled by cold and dry conditions. The knock-on effect would
have been long-term, lasting decades. (suspenseful music) By 552 AD, the Avars
were attacked by people who lived in the surrounding
highlands, the Turks. They had previously
been ruled by the Avars. Mysteriously, the once
invincible Avar horsemen were crushed. Up until now, the cause of
this sudden reversal of power has never been explained, but
then David Keys had an idea. (taut music) - So I was very puzzled by this and decided to try and find out what the mechanism was. I thought, well, maybe
it's something to do with their economy. Well, the Avar economy
was a horse-based one. The Turk economy was
a much more mixed one, involving considerable numbers of cattle. The question came to my mind, well, was there something about the way that a cattle economy works
and a horse economy works? The difference between those
that might shed some light on the political events,
on the demise of the Avars. (electronic beeping) - [Narrator] Keys contacted John Milne at Macaulay Land Use Center in Aberdeen. Milne has made a detailed study of how different animals feed and survive. - Yes, these horses here are
actually highland colonies, but in terms of the sort of size, they're very similar to what I believe the Avar horses would have been like. They're quite similar to some of the, at least in terms of size,
in terms of the Mongolian and Kazakh horses that you see now. - [Narrator] Milne had
done intriguing research into the difference between
horse dung and cow dung. - Here, you can see some horse dung, and you can see that it's very
fibrous, which demonstrates, and it's made up up of
very large pieces of fiber, which demonstrates that this has not been well digested by the horse. Now, if you compared some cattle feces, you would see that it was
much more finally ground up, and in fact, much better
digested than horse manure. - [Narrator] Could the contrast in horses' and cows' digestive systems have made a vital strategic difference
on the Mongolian Steppes when after the catastrophe,
grass and vegetation were in a terrible state? - Cows have a greater
efficiency to digest food. They also have the ability
to eat a wider range of different herbage types
so that they can eat, for example, very rank vegetation. In contrast, the horses are
less capable of eating rank, really poor quality
vegetation, than cattle. And in a drought situation, you would get eventually to the state where the horse was not
able to eat enough food. And because it was not able
to digest it successfully, then it would not be able to survive. And so in those circumstances, then the Avars would be very vulnerable. (dramatic music) - I was absolutely amazed when I found that in fact, it was
merely the differences between a cow's and a
horse's stomach design that had probably had such a major effect on subsequent history. (wind howling) - [Narrator] Chinese chronicles record how in the defeat by the once subject Turks, thousands of Avars were
slaughtered or enslaved. Their leader committed suicide. Most of the surviving Avars began a 4,000-mile trek westwards. Their journey triggered,
according to David Keys, by the catastrophe, was about to have a huge effect on history. The Avar refugee caravan cut across what is now Northern Kazakhstan, skirting the northern
shores of the Caspian Sea, and on into the fertile grasslands to the south of the Carpathian Mountains, an area which is now the Balkans. (taut mellow music) And as they traveled, the Avars recovered. Their horse technology was still superior to anything they found on their route. Once again, the Avars
became a conquering people, driving all others before them, until finally, Roman writers recall how they reached the
fringes of the Roman Empire. (suspenseful music) - They arrive in the
late 550s as refugees. Within a decade, their
ruthless horsemanship, ruthless military ability,
has come to dominate all the tribes, all the groups
of Slavs, Huns, Germans, living north of the Danube
on the empire's frontiers, and having imposed their
control over these groups, the Avars can then turn their
attention against the empire. (horseman yelling) - [Narrator] The Roman Empire, already weakened by the plague, was constantly harassed
by Avar incursions. At one point, Constantinople
was besieged by the barbarians. Rather than take over, the
Avars opted for blackmail and extracted vast amounts
of gold from the empire in return for not fighting. Some of it can be seen today in museums. Much of it is still believed to lie buried in the plains of Hungary. (horsemen yelling)
(taut music) It's reckoned that over 50 years, the Avars netted in today's terms, seven billion pounds worth of
gold from the Roman Empire. (taut music) (mellow music) - The Avar impact,
combined with the plague, and the economic problems that ensued, destabilized the empire. And at the end of the day,
it can all be traced back to this climatic destabilization
of the 6th century, which was triggered by
the volcanic eruption. (magma swooshing) - [Narrator] David Keys
believed a pattern was emerging, which showed huge political consequences stemming from the catastrophe. He had already found evidence
of the catastrophe's effects throughout Europe and the East. Now he turned to the
Americas, where he found another extraordinary
coincidence of timing, and another historical puzzle where a great city had been destroyed, but no one had ever known why. (electronic beeping) In the early 6th century, 125,000 people lived in Teotihuacan in the Central Mexican plain. - In 500 AD, when the
city reached its peak, it really was what is
called the primate city. By that, I mean the
second next largest city is so far below it in
size that there really, you could almost say
there are no other cities. I mean, that's an overstatement obviously, but there were cities of
10,000 people, 20,000, but compared to the 125,000
here, there was nothing. So it was the only huge, large city in the entire Central Mexican plateau. - [Narrator] Then, midway
through the 6th century, shortly after the 535 AD catastrophe, things began to go wrong in Teotihuacan. (suspenseful music) For the past 20 years, Rebecca Storey has been painstakingly
studying skeletons of people who lived in one of the city's
suburbs called Tlajinga. The bones provide a remarkable history of the population's health. (suspenseful music) - Well, the Tlajinga
population has adults. It also has quite a few children
and an awful lot of babies. - [Narrator] Rebecca
Storey began to notice that it in Teotihuacan's later period, the population, in particular, the babies suffered a severe decline in health. (somber music) - These kinds of infections
that show up on the bone are long-lasting bacterial infections. And they're very common on the children. Now, babies shouldn't
have infections like this. Normally, they should be
born with relatively good immunological protection from
their parents, their mother, but in the case of Tlajinga,
we find lots of babies with already infectious reactions, indicating that the health
of the mothers was so poor that the children are
getting sick as well. The problem with the very
late population there around the 6th century
is that overwhelmingly, it is babies, children, and
individuals under the age of 25. They should not be dying
at that proportion. So they start to become 70% of my sample, rather than the much lower 40 or 45% that they were in the earlier period. It is a population that
is in great trouble and is probably collapsing. - [Narrator] New scientific
evidence suggests that the city's decline occurred around the middle to late 6th century, 150 years earlier than previously thought. For David Keys, this
re-dating was a breakthrough. (somber music) - Now, in fact, one can
see that Teotihuacan's fall really comes straight on the
heels of the climatic disaster. And I think that there's
a very, very high chance the two are connected. (somber music) - [Narrator] There are
no existing tree rings or other evidence from Mexico itself to show whether there was a
significant climate change. However, lake deposits in
the nearby Yucatan Peninsula show a 30-year long drought
starting the mid 6th century. Tree ring evidence from
Chile and California shows a dramatic reduction in tree growth from the late 530s onwards. (somber music) And a study of river levels in Colombia shows that the mid to late 6th century was the driest period
in the last 3,000 years. The evidence throughout the Americas, combined with Rebecca Storey's
findings of malnutrition, suggest that Teotihuacan was gripped by a long-lasting
drought, a drought which, according to David Keys' theory, was directly linked to
the climatic catastrophe and had a devastating effect
on the city's supply of food. (pensive flute music) - When something happens
to the food supply, well, that makes people
more subject to getting ill because they're not getting enough food. Then, this is a very dry environment. Water had to always have
been a very important thing. And without water, you have (indistinct) sanitation problems. Sanitation would then
lead to lots of diseases circulating through the people and causing mortality in your health. And that affects the productivity of city. City's not productive
when its people are sick. And that becomes one of the
things that then to say, "Well, no, we don't wanna
go to Teotihuacan anymore because it's not a good place to be." - [Narrator] According
to the latest research, Teotihuacan was finally destroyed when the people rose up
against their leader, smashing their palaces and setting light to the city's biggest temple. (pensive flute music) - Somebody went in there and set fire to all the roof (indistinct), and caused the ceiling
and roof to collapse, bring down the upper walls and
formed a big mound of debris. And that's what happened all up and down the main street of the city. Maybe they decided that elite class that was making demands on
them was asking too much, that the priests who were
supposedly bringing the rain and making the springs flow
were no longer successful, because the spring flow was dropping and the rains were diminishing. Then they lost confidence maybe in the priestly class as well. - What appears to happen is that you've got a destabilization, perhaps some religious
and political changes, followed by a revolution of some sort, and the collapse of the city, in a way similar to events in Europe, indeed in the way that Constantinople, Roman Empire was affected. (plaintive flute music) (mellow music) 535 disturbs the status quo and allows history to reform itself all over the world. It really is the interface
between the ancient world and the world we live in today. (taut upbeat music) - [Narrator] In Central
Mexico, it took 300 years for a new civilization
to establish itself. Throughout the 6th century, a similar story was unfolding
all over the planet: ancient civilizations crumbling, others just beginning. And according to David Keys, one example of an emerging
nation was England itself. (taut mellow music) (suspenseful music) Britain in the mid 6th
century, the Dark Ages. The Romans had left 100 years earlier. In the west of the island,
native British tribes, the Celts, fought to stem the tide of Anglo Saxon invasion
from Northern Europe. According to legend, it was the time of the
death of King Arthur. His country turned into a wasteland. - [Man] As he rode dust through the land, he found trees down and grain destroyed and all things laid waste as if lightning had struck in each place. He found half the people
in the villages dead. (ominous roaring) The earth no longer
produced when cultivated. From that time on, no wheat
or other grain grew there, and no tree bore fruit and very few fish were found in the sea. For this reason, the two kingdoms
were called the wasteland. - [Narrator] But could
the wasteland of legend be a distant memory of
a climatic catastrophe that really did hit the native British as a result of 535? (ominous roaring) What is certain from
British and Irish annals is that the bubonic plague, which had devastated Roman Empire finally reached Britain by around 547 AD. It entered mainly through
ports on the Cornish coast, from which the British still
traded with the Roman Empire. - This was a significant
event in the history of Western Britain and Ireland. Certainly, as one goes through the annals, one can find many references to plagues. One of them is referred to as the Mortalitas Magna, the Great Mortality. Another one is the Mortalitas Prima, the first plague, like this. This does suggest something special. - They'd never experienced
the plague before. It was completely new horror
that they knew nothing about. They wouldn't have understood
even what was happening. Suddenly people began to
develop these terrible pustules underneath their
armpits, in their groins, and they would've died in
the most terrible agony. - [Narrator] According to
Keys, the plague changed the political shape of Britain. At this time, Britain was divided in two. In the west lived the
native Celtic Britons. The east was occupied
by invaders from Europe, the Angles and Saxons. East and west had very little
contact with each other. The Celtic Britons traded
with the Roman world. The Anglo Saxon peoples traded mainly with their former homelands
of Germany and Scandinavia. It meant that the Celts,
the native Britons, were far more exposed to the plague arriving from the Roman Empire. - So, by the time you come into the latter part of the century, the Celtic west and center have experienced a huge
population reduction. There's a population vacuum. And so Anglo Saxon peoples are
able to move from the east. They're able to move west
into partially empty lands. And England was born. - [Narrator] Keys' theory
is that England came about because the Anglo Saxons
were able to defeat the plague-stricken Britons. A 6th century poem tells of the defeat of one group of Celts, the man of Gododdin and
their leader, Madawg. (dramatic percussive music) (speaks in foreign language) - [Translator] He did
not retreat from battle until blood flowed. Like rushes, he cut down
men who did not flee. The man of Gododdin relate
from the floor of the hall, but before Madawg's tent when he returned, there would come but
one who from a hundred. (tense percussive music) - One can see 535 as a watershed where you see the forces coming into play, which create such countries as England, Spain, France, Japan, the United China. (volcano exploding) - [Narrator] Now came the final and boldest turn in his theory. Could it be that the
catastrophe was linked, not just to the emergence of new nations, but also to the birth of a
new world religion, Islam? (taut energetic music)
(religious chanting) This is all that is left today
of the Marib Dam in Yemen at the southern tip of Arabia. But at the beginning of the 6th century, Yemen was the region's greatest power. It depended on the Marib Dam, its greatest piece of engineering. The Marib was huge, 2,000 feet long, feeding into hundreds of miles of canals. But within a few years
of the 535 catastrophe, climatic chaos hit Yemen, first, drought, and then a succession of
storms and flash floods, which weakened the dam. The constant attempts to repair the dam are recorded on contemporary inscriptions. - What we're looking at is
one of the great inscriptions that was put up on the facade of the dam, really commemorating the
rebuilding of the dam, repair of the dam, in this
case, in the year 542, and it's a long inscription describing all the various people who
came and contributed to this. And we can pick out
right in the center here, the cartouche, the symbol of the ruler of the kingdom at that stage, one Abrahah. And there are a whole
series of these inscriptions for about two or 300
years, and then they stop, which is very indicative of exactly what the Arabic sources are telling us that there was a period
when this dam was broken and was not repaired again. - [Narrator] The Marib Dam was abandoned. Its ruin was also the ruin of Yemen. Its population migrated to
a new regional power base, which emerged in its place,
around Medina and Mecca. (mellow music) In 570 AD, the prophet
Muhammad was born in Mecca. - It's in precisely
that Mecca Medina area, that Muhammad was based. And so it's really the growth of Medina as a important political center that is so crucial in the
early development of Islam. - [Narrator] The climatic chaos had not only smashed the Marib Dam and shifted power to Medina. It also brought Muhammad's
own family to prominence. - The prophet's family or
the prophet's ancestors had taken it upon themselves
really to provide food, to import food into this area and provide food for the population. And this was one of their
claims to fame and to status. - [Narrator] Muhammad's
family's reputation for social concern helped
his ministry take root in a time of drought,
famine, and the plague which had spread from the Roman Empire. (man chanting) (men chanting) - I think Muhammad's
message was attractive because this was a period
of upheaval and disturbance. - One's got this whole
apocalyptic atmosphere in the ancient world at that time. There's been war, there's
been a revolution, the Roman Empire, which
had really dominated the political scene for about 800 years appeared to be tottering. - There is a lot of apocalyptic
literature from this period. There are a lot of people saying, "This is terrible, the
world's coming to an end. How do we interpret these disasters? What are they a sign of," and so on. - The political certainties of the world were collapsing around everybody's ears. Nobody seemed sure of the future. It was a very, very
unsettled time to live. All these things can be
traced back, to an extent, to the climatic chaos caused
by the eruption of 535. And they all feed into the
early evolution of Islam. (mysterious music)
(religious chanting) (soft serene music) Now, if a volcanic eruption, 535, could wreak all this havoc and draw the ancient to a final close and really help lay the foundations of the world we live in today, what would happen if there
was another massive eruption? - [Narrator] This is not
fantasy or wild speculation. While nothing may happen
in the next hundred years, there are a handful of
underground volcanic monsters whose arrival date is long overdue. - The granddaddy of them all is believed to be Yellowstone
Caldera in Wyoming. This caldera is maybe twice the size of any known modern caldera, and its eruptions, which have occurred not once, not twice, but three times over the last two million years, indicate that it has devastated
Northern America several times. Besides Long Valley Caldera, there's a caldera in California, which is also heating up. The ground is shaking there. There's been a die-off of
the forest by noxious gases, carbon dioxide coming out of the earth. Public is very concerned
about that volcano. (pensive music) Closer to home for some people would be the area around Naples, Italy. Sure, it's famous for Vesuvius, which has erupted many times in the past and potentially will again in the future. There is also a caldera just
on the north side of Naples, underlying a metropolitan area of Campi Flegrei and Pozzuoli, where thousands of people live and have lived for a long time. - [Narrator] The last eruption in the Campi Flegrei complex was in 1538. At that time, 3,000 people were killed by the immediate explosion. Now, 400,000 people live
within the same area. The whole complex is still active and capable of major eruptions. - That would be a total
disaster for Italy, a major disaster for Europe, and would no doubt have
worldwide climatic repercussions, which would have huge
implications for agriculture, huge implications from a
disease point of view worldwide, and would no doubt have
the effect of destabilizing all sorts of potentially
unstable countries all over the world. (mellow music) - It would change our climate. It would produce change in the pattern of wet and dry cycles for vast portions of the earth. We're familiar with the El
Nino and La Nina effects. This would be even a much
greater perturbation, perhaps lowering the temperature, the global average temperature
several degrees and more. - The biggest effect for people anywhere is that it's going to
disrupt the food supply. And it's going to take years for the climate to
either go back to normal, or for people to change
the crops that they use and the way that they plant them. (ominous music) - There may not be food to
import from other countries because they'll need it every bit as much or more than we will. And if our agriculture
has failed in some way, then there just wouldn't be enough to eat. I mean, that to me seems to
be the logic of the situation. Now, in times past, you're
right subsistence economies, if they had low population densities, they could go to the seashore
and live on shellfish. And indeed people sometimes did that under real stressful conditions, but you can't do that nowadays. There aren't enough
shellfish to go around. If we are confronted with a global event at any time in the future, it's not quite clear how we would cope. (soft pensive music) - The whole infrastructure of civilization will collapse around us due to the huge environmental
catastrophe that would happen because of the failing of crop production, the darkening of the skies. (ominous music) - Communications would be taken out, satellite communication, aircraft, transport would be interrupted very severely for a long period. That type of event will
occur in the future. - Well, people start to
struggle for resources. I mean, basically that means warfare, and the modern world is not quite clear exactly what would happen. You either sit and starve
or you get out there and try and acquire food. And there's not much alternative in a really stressful situation. (volcano exploding) - One of the big lessons
from 535, I think, is that we're not talking about a Big Bang and then the world changes. We're talking about a Big Bang, and then it takes 100 to 150 years for the new reality to actually emerge. (suspenseful music) What will happen in the future? Of course, one doesn't know, but I think that historians,
economists, politicians should really pay rather
more attention perhaps to the ability of natural
forces to change history than they do at the moment.
Interesting program. Gives some insight into how bad things were in the past. It's amazing that humans were not entirely wiped out by the plague
One of those years with no summer and the years after that affected too - famine brings disease and war and of course death