NARRATOR
535AD has come and gone- the world has been hit by a catastrophe.

Now comes bizarre weather - the sun is darkened, skies are turbulent, rain is red and snow falls yellow.

There is frost and famine.

Seasons are blurred.

In some places great drought destroys the land. In others floods bring chaos.

The world will never be the same.

The theory belongs to David Keys. With dogged detective work he has pieced together the story of an ancient catastrophe.

By bringing together evidence from contemporary eye witness accounts and tree rings- he has developed a picture of a lethal climate change that began in the year 535AD and affected most of the world for the next ten to twenty years.

He found three possible causes for the huge amounts of dust, ash and water vapour that must have been hurled into the atmosphere to block out the sun-a comet, an asteroid or a volcano.

The presence of sulphuric acid in arctic and Antarctic ice cores from that period has pointed the finger at a massive volcanic eruption. But where did it occur?

From Chinese and Javanese records, Keys has deduced that the culprit could have been the world's most notorious volcano - Krakatoa.

Volcanologist Prof. Haraldur Siggurdson, took up the chase. He already knew that at some point in the distant past there had been a massive eruption at Krakatoa that had left a huge deposit of dust and ash.

The goal of this trip was to dig up charcoal to carbon date the eruption, but he was only able to find samples from the levels above and below the major eruption layer.

The samples, while not as accurate as Keys would have liked, did indicate that the gigantic eruption could have occurred during the first millenium AD.

But for Krakatoa to have been the cause of the climatic catastrophe, it must have been a spectacular event.


DAVID KEYS
The amount of power generated by this eruption would have been equivalent to around 2,000 million Hiroshima sized nuclear bombs.


KEN WOHLETZ
The eruption of this ancient Krakatoa is something that mankind has never witnessed perhaps tens, hundreds of times larger than any manmade explosion, any volcano that's ever been witnessed.'


NARRATOR
David Keys asked Ken Wohletz, an expert on Krakatoa, to feed all the available data about the 6th century climate change into a super computer to simulate how the explosion began to unfold.


KEN WOHLETZ
I will start the simulation and show several phases of the eruption.


NARRATOR
Wohletz placed 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 is possible to estimate how much material might have been thrown up into the earth's atmosphere. With that figure it is possible to calculate the scale and power of the explosion and its associated after effects.

NARRATOR
Wohletz's simulation was used to model Krakatoa's 535 AD big bang.


DAVID KEYS
A giant red hot fountain of molten rock and a vast cloud of ash would have towered over the countryside. A second crack let seawater in creating a thirty-mile high fountain of magma. Up to a thousand miles away ash would have rained down on forests and fields.


KEN WOHLETZ
The towering clouds of steam and gas and ash pierced and shot upwards and at times when it seemed it 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 grey white cloud would then seem to sort of move laterally across the sky like a mushroom cloud.


DAVID KEYS
In a way it would have been a sort of natural equivalent of a nuclear winter.


NARRATOR
The effects would have been global and devastating.


NARRATOR
Wohletz has seen evidence of similar major eruptions farther back in history. One remnant is a dormant volcano near his lab, high in the hills of New Mexico.


NARRATOR
The 22 km wide caldera at Valle Grande, New Mexico last exploded a million years ago. Ash from here landed as far away as Louisiana. Using the remains of Valle Grande, Wohletz shows how high-flying volcanic emissions can travel great distances.


KEN WOHLETZ
This is ultrafine volcanic ash formed by phreato-plinian eruption similar to what we think happened in the 6th century at Krakatoa.
It's so fine 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 in the atmosphere.


NARRATOR
Keys believes that in 535AD similar microscopic particles of ash and sulphur dioxide from Krakatoa would have shrouded the sky in endless grey.

Temperatures would have dropped. Without the full strength of the sun to heat and evaporate the oceans' surfaces, there would have been less moisture released into the atmosphere.


DAVID KEYS
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.


NARRATOR
Confident he understands the natural course of events, Keys now delves into the catastrophe's effects on human civilization.


DAVID KEYS
I began to think to myself, well disruption as severe as this has got to have political consequences, it was 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 world-wide.


NARRATOR
The idea that nature and climatic change can alter history is winning increasing respect from academics. In fact, evidence of the huge impact a volcanic eruption can have already exists from more recent times.

Less than two hundred years ago another Indonesian volcano, Tambora, exploded.


HARALDUR SIGURDSSON
The Tambora eruption of 1815 produced a tremendous amount of sulphur dioxide that went up into the stratosphere ...in New England there was a frost recorded every month during the summer, crop killing frosts, there was starvation in parts of Europe, social unrest. This triggered both the migrations out of Germany into Russia and triggered migration out of New England into the Ohio valley and western United States, so it was a true social upheaval and it's been referred to as the last great subsistence crisis in the western world and that was caused by a volcanic eruption.


NARRATOR
David Keys wanted to prove that a more massive and longer lasting eruption in 535 would have had an even greater effect on world history. He decided to examine a series of historical puzzles from the 6th century AD.


He looked at events that, from contemporary writings and archaeological evidence, were known to have taken place - but whose causes had never been fully explained.

The first was the spread of a terrible disease that brought the mighty Roman Empire to its knees.

By 535, under the emperor Justinian, the Empire, now based in Constantinople, was flourishing. It had recovered from the assaults of the Huns and Goths and had recaptured much of its former territory, and glory.

But in 542 AD, something awful struck at the heart of Roman civilisation.

The horrors were documented by the monk Evagrius.


ACTOR 1
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.


NARRATOR
Evagrius was describing the first recorded outbreak of Bubonic Plague. Could the plague have been tied to the climatic catastrophe?

The Plague is a bacillus bacterium transmitted from infected rats to humans.

The carrier is the humble flea that feeds on rat's blood.


FRANK CLARK
This is a flea which has had a blood meal and there's no plague organisms in its gut and you can see that it's stomach is quite full and everything's fine. If we look at, if we contrast this with a flea which has taken up some of the plague bacillus you 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 course is that the flea can't feed properly.


DAVID KEYS
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 fleas jump to other animals-including humans-for blood. And then, as Evagrius describes, the agony begins.


ACTOR1
Some came out in buboes 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.


NARRATOR
Keys found out from scientists that outbreaks of the plague are strongly related to changes in climate.

And the sort of changes that followed 535, in particular cooling and unpredictable rainfall, have a huge impact on the spread of the disease. Temperatures affect how the plague bacteria form in the flea's gut.


FRANK CLARK
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 faeces.


NARRATOR
So cooler temperatures allow the bacteria to flourish, and, there is new scientific evidence that cooler temperatures also increase rat populations.


NARRATOR
In Colorado, scientists are detailing the climate/plague connection. They examined thirty years of climate records and plague infections in the American southwest. Their work shows that cool weather and additional rainfall significantly increase the prevalence of the plague.


KEN GAGE
Now this model only talks about the American southwest but the general principles we believe are involved here would be that once that cycle begins you're likely to see a dramatic increase in rodent populations and when that occurs then you have a greatly increased likelihood that you'll see these plague outbreaks in the animal populations and that's the time when it can spill over to the human population.


NARRATOR
That is exactly what happened in the southwest in the early 1980's. Cooler conditions swelled rat populations. Could a similar increase have occurred in 535 AD?

And if so, where? In ancient times the plague could have come from only two sources.


PETER SARRIS
Well according to one of our contemporary sources, the church historian Evagrius, the plague originated in Ethiopia people have attempted to argue the plague may have come from China from the Orient but if that were the case one would have expected it to reach Persia before it reached the Roman Empire. What we know both scientifically and historically is that the great lakes area of 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 Central Africa tends to be hot, the disease is kept at bay. But if the region was affected by the global cooling of 535 and 536, it may have become a lethal breeding ground for the plague.

From Africa, via the trade routes, ships' rats and sailors could easily bring the plague up the coast, first hitting the port of Alexandria in Egypt - then north into the heart of the Roman Empire.

And Roman greed for one precious commodity would only accelerate that process. In the sixth century there was an enormous trade in African Ivory.


MIKE WHITBY
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 emperor could then use to impress the neighbors further to the north and further to the west, people who would never have seen an elephant in their lives.


DAVID KEYS
It was essentially the European and Mediterranean greed for ivory that brought the roof in.


NARRATOR
Only seven years after the 535 climatic catastrophe - the ivory trade allowed the plague to surge into Constantinople.


MIKE WHITBY
Its impact was devastating. They 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 cisterns, digging up orchards.


PETER SARRIS
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.


MIKE WHITBY
Constantinople, Europe's biggest city, stank for months after month after months.


NARRATOR
One writer recorded that when the number of dead reached a quarter of a million, Constantinople officials simply stopped counting.

As people left the stricken city they took the plague to towns, villages and farms throughout the empire. Untold millions perished.

And Mike Whitby believes the long term implications were disastrous for the Romans.


MIKE WHITBY
The plague struck a mortal blow at the health of the empire, it also struck a mortal blow at the military vitality of the empire, partly by killing off potential recruits, it also effect the armies indirectly, less tax from farming, from agriculture, less money into imperial coffers, less money to pay troops, less money to hire mercenaries to supplement the armies.


DAVID KEYS
The plague delivered a heavy punch from the south to the Roman empire, it caused mayhem in the empire, massively reduced population, they have all sorts of economic, military, social implications, but there was another
punch that hit the empire really from the east.


NARRATOR
This second threat was brewing some three thousand miles away.

The climatic catastrophe was having an extraordinary effect on an extraordinary people and their livestock.

In the isolated plains 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.


PETER GOLDEN
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 archaeological finds show, the Avars were years ahead of other cultures.

NARRATOR
Finds from archaeological digs all over Avar territories suggest 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.


PETER GOLDEN
It was this large concentration of horses that gave them a military edge,
the latest in the military technology of that era, the horses also provided food and sustenance, the Avars drank fermented mare's milk, an alcoholic beverage. So horses were central to their existence


NARRATOR
But then, following 535 AD, Chinese records, and tree ring evidence from Mongolia and Siberia suggest that the Mongolian steppe was crippled by cold and drought. These conditions may have lasted for more than a decade and may have severely weakened the Avar nation.

By 552 AD the Avars were attacked by the Turks, a people who lived in the surrounding highlands. They had previously been the Avars' subjects, but mysteriously the once invincible Avar horsemen were crushed.

Up until now the cause of this sudden reversal of power has never been identified.

But David Keys had an idea.


DAVID KEYS
I was very puzzled by this and decided to try and find out what the mechanism was so I thought well maybe it's something to do with their economy well the Avar economy was a horse based one, the Turkic economy was a much more mixed one involving considerable numbers of cattle. The question came to my mind well was there something about perhaps the way that a cattle economy works and a horse economy works that might shed some light on the political events, on the demise of the Avars.


NARRATOR
Keys contacted John Milne at the Macauley Land Use Centre in Aberdeen, Scotland. Milne has made a detailed study of how different animals feed and survive.


JOHN MILNE
These horses here are actually highland ponies 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 Kazac horses that you see now.


NARRATOR
To understand the differences between horse-based and cattle-based economies, Milne picks up some unexpected evidence.


JOHN MILNE
Here you can see some horse dung and you can see that it's very fibrous which demonstrates... and it's made up of fairly large pieces of fibre which demonstrates that this has not been well digested by the horse, now if you compared some cattle faeces you would see that it was much more finely ground up and in fact much better digested than horse manure.


NARRATOR
After the catastrophe, when the climate deteriorated and the vegetation grew sparse on the Mongolian Steppe, could the contrast in horses' and cows' digestive systems have made a vital difference and put the Avars at risk?


JOHN MILNE
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.


DAVID KEYS
I was absolutely amazed when I found out 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.


NARRATOR
Chinese chronicles record how in the defeat at the hands of the Turks, thousands of Avars were slaughtered or enslaved. Their leader committed suicide.

Most of the surviving Avars began a four thousand mile trek westwards. Their journey was about to play a huge part in history.

The Avar refugee caravan cut across what is now northern Kazakshstan, skirted the northern shore of the Caspian Sea, and into the fertile grasslands to the south of the Carpathian mountains, the area that is now the Balkans.

And as they travelled, the Avars recovered. Their horse technology was still superior to anything they found on their route. Once again they became a conquering people, driving all others before them. Eventually they reached the fringes of the Roman Empire.


MIKE WHITBY
... 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.
The impact of the Avars was particularly devastating because when they captured fortified cities the fate of the

inhabitants was not pleasant, people would be impaled,

if they were lucky they could be taken off into captivity and exploited as Avar serfs or as cannon fodder in Avar armies.


NARRATOR
The Empire, already weakened by the plague, was constantly harassed by Avar incursions. At one point even Constantinople was besieged.

Rather than take over, the Avars opted for blackmail and extracted vast amounts of gold from the Empire in return for peace. Some of it can be seen today in museums - much of it is rumored to lie buried under the plains of Hungary.

Historians believe that over a 50-year period the Avars netted gold from the Roman Empire that would be worth 11 billion dollars today.


DAVID KEYS
The Avar impact combined with the plague and the economic problems that ensued destabilised the empire. And at the end of the day it can all be traced back to the climatic destabilisation of the mid-6th century which was triggered by the volcanic eruption.


NARRATOR
David Keys believed a pattern was emerging that showed huge political consequences stemming from the catastrophe. By now he had found fallout in Europe and the East.

He next turned to the Americas to investigate an extraordinary coincidence of timing - and another historical puzzle where a great city had fallen without explanation.


NARRATOR
In the early sixth century 125 thousand people lived in Teotihuacan in the Central Mexican Plain.


BILL SANDERS
In 500 AD when this city reached its peak it really was what is called a primate city and by that I mean the second next largest city is so far below it in size that really you could almost say there are no other cities - that's an overstatement obviously there were other cities 10,000 people, 20,000 - but compared to the 125,000 here that was nothing, so it was the only huge, large city in the entire Central Mexican plateau.


NARRATOR
Then midway through the sixth century, shortly after 535 AD, things began to go terribly wrong in Teotihuacan.

For the past 12 years Rebecca Storey has been painstakingly studying skeletons of people who once lived in one of the city's suburbs, called Clahinga. The bones provide a remarkable history of the population's health.


REBECCA STOREY
Well the Clahinga population has adults, it also has quite a few children and an awful lot of babies.


NARRATOR
Storey began to notice that in Teotihuacan's later period, the population, and in particular the babies, suffered a severe decline in health.


REBECCA STOREY
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 Clahinga 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.


REBECCA STOREY
... the problem with the very late population 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 per cent of my sample rather than the much lower 40, 45 per cent 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 sixth century, a hundred and fifty years earlier than previously thought. For David Keys, this re-dating is a breakthrough.


DAVID KEYS
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 that the two are connected.


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 possible 30 year long drought starting in the mid 6th century.

Tree ring evidence from California shows a dramatic reduction in tree growth from the late 530s onwards. And Chilean ring samples show 540 as the coldest year of the first millennium.

A study of river levels in Colombia shows that the mid to late 6th century seemed to be the driest period in the last three thousand years.

The indications throughout the Americas, combined with Rebecca Storey's findings of malnutrition, suggest to David Keys that Teotihuacan was gripped by a long lasting drought that devastated the city's food supply. - A drought Keys believes was directly linked to the climatic catastrophe.


REBECCA STOREY:
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 to have been a very important thing and without water you have great sanitation problems, sanitation would then lead to lots of diseases circulating through the people and causing mortality and ill health and that affects the productivity of a city, a city's not productive when its people are sick and that becomes one of the things that then they say well no, we don't want to go to Teotihuacan any more 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 the palaces and setting the city's biggest temple ablaze.


BILL SANDERS
Somebody went in there and set fire to all the roof beams and caused the ceiling and roof to collapse, bringing 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 rains were diminishing, they lost confidence maybe in the priestly class as well.

DAVID KEYS
What appears to happen is that you've got a destabilization, perhaps some religious and political changes followed by revolution of some sort and the collapse of the city in a way similar to events in Europe, indeed in the way that Constantinople, the Roman Empire was affected.


DAVID KEYS
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.


NARRATOR
In Central Mexico it took 300 years for a new civilisation to establish itself. Throughout the 6th century, similar stories were unfolding. Ancient civilisations crumbled - others were just beginning. And according to David Keys the emergence of the new-- including the birth of England-can also be linked to the catastrophe.


NARRATOR
Britain in the mid-6th century - The Dark Ages. The Romans had left a hundred years earlier. In the west of the island, native British tribes - the Celts - fought to stem the tide of Anglo-Saxon invasion. According to legend it was the time of the death of King Arthur, when his country turned to a wasteland.


ACTOR 2
As he rode thus through the lands, he found trees down and grain destroyed and all things laid to waste, as if lightning had struck in each place. He found half the people in the villages dead.


ACTOR 3
... the earth no longer produced when cultivated, from that time on no wheat or other grain grew there, no tree gave 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 the 535 catastrophe?


What is certain from British and Irish annals is that the Bubonic plague that had devastated the Roman Empire finally reached Britain around 547 AD. It arrived on Roman ships that were still trading with Britain.


JOHN HINES
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.


DAVID KEYS
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 have died in the most terrible agony.'

NARRATOR
According to Keys the plague changed the political shape of Britain. At that 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 the Saxons.

East and West had very little contact with each other.

The Anglo Saxon peoples traded mainly with their former homelands of Germany and Scandanavia. The Celtic Britons still traded with the Roman world.

This meant that the Celts were at far greater risk of catching the plague as it arrived on Roman ships.


DAVID KEYS
So by the time you come into the latter part of the century, the Celtic West and centre have been .. 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's theory is that England was formed because the healthy Anglo-Saxons were able to defeat the plague-stricken Britons.


DAVID KEYS
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.


NARRATOR
Now came the final and most controversial turn in David Key's theory. Could the catastrophe have been linked not just to the emergence of new nations - but also to the birth of a new world religion - Islam?


NARRATOR
This is what is left today of the Marib Dam in Yemen, at the southern tip of Arabia.

But at the beginning of the sixth century Yemen was the region's greatest power and it depended on the Marib Dam - its greatest engineering feat.

The Marib was huge - 2,000 feet long, feeding into hundreds of miles of canals. But within a few years of the 535 event, climatic chaos hit the region - first drought and then a succession of storms and flash floods that weakened the dam.

The constant attempts to repair the dam are recorded on contemporary inscriptions.


HUGH KENNEDY
What we're looking at here is one of the great inscriptions that was put on the facade of the dam, really commemorating the rebuilding of the dam, the 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 centre here the cartouche the symbol the ruler of the kingdom at this stage, one Abraha. And there are a whole series of these inscriptions for about 2 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 ultimately abandoned and its ruin was the downfall of Yemen. Her people migrated to a new regional power base that had emerged around Medina, and Mecca-where back in 570 AD, the prophet Mohammed had been born.


DAVID KEYS
It's in precisely that Mecca, Medina area that Mohammed was based and so it's really the growth of Medina as an important political centre that is crucial in the early development of Islam.


NARRATOR
Keys contends that the climatic chaos weakened the Marib and began the shift of power to Medina, where Mohammed's family was already well established.


HUGH KENNEDY
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
Mohammed's family's reputation for social concern helped his ministry take root in a time of drought, famine and the plague-which had by now made its way to Arabia.

By the end of the 6th century, the people were crying out for an end to their suffering.


HUGH KENNEDY
I think Mohammed's message was attractive because this was a period of upheaval and disturbance.


DAVID KEYS
One's got this whole apocalyptic atmosphere in the ancient world at that time, there's been war, there's been revolution, the Roman Empire which had really dominated the political scene for, what, 800 years appeared to be tottering.


HUGH KENNEDY
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?


DAVID KEYS
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.


NARRATOR
While some scientists remain sceptical about the cause and effects of the 535 event, Key's deductions provide a stern warning about the global repercussions that could arise from a future climate-altering occurrence.


DAVID KEYS
Now if a volcanic eruption in 535 could wreak all this havoc and draw the ancient world 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
Keys' concern is more than just idle speculation. While no one can predict exactly when a major eruption will happen, there are a handful of volcanic monsters lurking underground.


KEN WOHLETZ
...the granddaddy of 'em 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, the public is very concerned about that volcano.

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's 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 Flegri Complex was in 1538. At that time 3,000 people were killed by the immediate explosion. Today, 400,000 people live within the same area. The whole complex is still active and capable of a major eruption.


DAVID KEYS
... that would be a total disaster for Italy, a major disaster for Europe and would no doubt have world-wide climatic repercussions which would have huge implications for agriculture, huge implications from a disease point of view world-wide and would no doubt have the effect of destabilising all sorts of potentially unstable countries all over the world.


KEN WOHLTEZ
...it would change our climate, it would produce a 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 or more.


ERIC JONES
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.


MIKE BAILLIE:
There may not be food to import from other countries because they'll need 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 really stressful conditions but you can't do that nowadays, there aren't enough shellfish to go round. If we were confronted with a global event at any time in the future it's not quite clear how we would cope.


ALAN FITZSIMMONS
The whole infrastructure of civilization would collapse around us due to the huge environmental catastrophe that would happen because of the failing of crop production, the darkening of the skies.


HARALDUR SIGURDSSON
Communications would be taken out, satellite communication, aircraft transport would be interrupted severely for a long period. That type of event will occur in the future.


MIKE BAILLIE
Well people start to struggle for resources and basically that means warfare, in the modern world it's not quite clear exactly what would happen. You either sit and starve or you get out there and try and acquire food, there's not much alternative in a really stressful situation.

DAVID KEYS .
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, ...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.