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new internationalist
issue 319 - December 1999

The case for the links between global warming and extreme weather grows ever stronger. Events like this year’s unprecedented floods in China, to cite just one example, show how extreme weather impacts on the world economy and how climate change can even trigger epidemics. Indeed, late this summer helicopters were busy spraying New York to counter an outbreak of St Louis Encephalitis triggered by global warming. Climate change won’t just make sea levels rise in a few unfortunate locations or make life miserable for El Niño victims. It has the capacity to change the economic, political and demographic shape of the world.

According to historian David Keys, the last time global climate change transformed our planet was back in the sixth century AD, the heart of the Dark Ages. Today climate change is at least partially driven by human agency. But 1,500 years ago it was triggered by a massive volcanic eruption (535 AD) in Southeast Asia (Krakatoa being the likeliest culprit), setting in motion a chain of events which included plague, barbarian migrations and revolution.

‘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. Some came out in buboes [pus-filled swellings] 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. Malignant pustules erupted and did away with them. Sometimes people were afflicted once or twice and then recovered, only to fall victim a third time and then succumb.’

Thus wrote the sixth-century church historian Evagrius, describing the gruesome symptoms of the bubonic plague which devastated the Roman Empire and much of the wider world in the sixth and seventh centuries, the so-called Dark Ages.

By decimating populations and wrecking economies, the plague transformed the history of the eastern Mediterranean, Western Europe, the Middle East and Africa. In a sense, it was the final nail in the coffin of the Classical World and helped give birth to a string of modern European nations – England, Ireland, France and Spain. But the plague wasn’t simply a disaster which erupted out of nowhere. Research which I’ve carried out over the past four years shows that it was almost certainly triggered by the climatic chaos of the mid-sixth century AD.

It seems that the disease had long been endemic among wild rodent populations in East Africa – but it was the climatic disaster following 535 AD which enabled the disease to spread outside its normal territory.

The climatic situation (probably cooler, drier weather followed by floods) helped the plague bacillus in three key ways. Cooler weather increased the population of the fleas which carried the bacillus in their gut. It also forced the fleas to bite more rodents and other mammals because cooler temperatures prevented the bacillus releasing a natural anti-coagulant in the flea’s gut, a failure which resulted in the flea becoming ravenously hungry as its gut was blocked by blood clots. Third the climatic chaos destabilized the relationship between predators and their rodent prey – a destabilization which led to a breeding explosion by the flea’s rodent hosts.

Once the disease had broken out of its normal territory, it appears to have spread throughout much of Africa – and northwards into the Mediterranean world. Its journey to Europe and the Middle East was by way of the Red Sea and the Roman equivalent of the Suez Canal – and was almost certainly transmitted courtesy of Roman greed for African elephant ivory. It was probably the ivory-trade vessels which introduced bubonic plague into the Mediterranean world.

I believe that in Africa it killed off the continent’s major ancient ports. Indeed to this day their precise locations are a complete mystery to archaeologists. The plague also fundamentally changed the nature of the culture and the economy across vast swathes of eastern and southern Africa. Agriculture declined in many areas and pastoralism took over – almost certainly because plague-carrying rodents were more attracted to agricultural settlements and their stores of grain than they were to milk and meat on the hoof.

‘They are treacherous, foul, untrustworthy and possessed by an insatiable desire for riches.’ These ‘scoundrels’ are ‘very experienced in military matters’ and ‘prefer to prevail over their enemies not so much by force as by deceit, surprise attacks and the cutting of supply lines.’

The Roman Emperor Maurice was writing, in the late sixth century, about the hordes of Mongolian Avars who had migrated across Asia and had begun to cause major problems for his Empire.

Originating in far-off Mongolia, the Avars had been forced to migrate westwards by the self-same climatic catastrophe which had scattered plague across the continents.

Tree-ring analysis and historical evidence from Siberia to the north of Mongolia, and from China to the south, suggest that the region was hit particularly badly by drought. And, as in so many other parts of the world, it was the fact that the disaster affected different peoples with different economies in quite different ways that led to political change.

In Mongolia, the event seems to have humbled the Avars and, in net terms, benefited their vassals, the Turks. Indeed, it enabled the Turks to overthrow their Avar masters and to launch their own empire. The Avar fall from grace was bad news for the Romans – but, in the long term, definitely good news for the Turks and, indirectly, good news also for the Arabs and for Islam, who were to benefit from Roman weakness.

Yet the spectacular geopolitical change which the 535 catastrophe wrought in Mongolia happened not simply because the weather was bad – but because the Avar and Turk economies reacted differently to the event.

Mundanely, in Mongolia it was the difference in the designs of cows’ and horses’ stomachs which was probably responsible. The Avar economy – and military strength – was utterly dependent on the horse, whereas the Turks had a more mixed economy, including cattle. To the Avars, the horse was everything – a source of meat, milk, cheese, yoghurt and even alcohol (the sweet fermented mares’ milk called koumis). But horses often find it much more difficult to survive drought than cattle. Horses fail to digest – and therefore excrete – up to 75 per cent of the protein they eat. By contrast, cattle excrete as little as 25 per cent. Thus, when all there was to eat was dried-out, low-protein grass, cattle had a marked advantage over horses.

As hard winters and drought continued into the second and third years of the catastrophe, families would have begun to starve to death. Unable to find food, unable to barter food from others (horses had been their wealth), unable to raid effectively, unable to defend themselves adequately without healthy horses, the Avars must have known that time had run out. Fleeing the Turkic uprising, thousands of Avars fled into exile and began their 3,000-mile trek towards Europe.

The climatic chaos of the mid-sixth century also re-synchronized history in Southeast Asia, China, Japan, Korea and South America – but nowhere more dramatically than in Mexico.

There, I believe, the catastrophe was responsible for killing off the greatest ancient civilization of the Americas – the spectacular pyramid-building empire of Teotihuacan, the ‘Place of the Gods’ in the Mexican language Nahuatl. Recent redating of the collapse of the Teotihuacano civilization shows that it followed directly on the heels of the climatic disaster.

Archaeological and skeletal evidence strongly suggests that in its final phases the population suffered from malnutrition and disease – and that the Empire’s government and its religion were finally overthrown in a bloody revolution.

Infectious disease was common in Teotihuacan at all times. However, when the agricultural system failed, nutritional deficiency seems to have massively reduced the population’s ability to counteract infection. Infection would then have manifested itself in several major ways, often including severe diarrhoea and a tremendous lowering of the digestive system’s ability to absorb nutrients. Nutrient starvation, rather than the total non-availability of food, would then have resulted in death.

High death rates in the city – creating demand for migrants – coupled with economic collapse due to agricultural failure in the countryside, would have led to substantial migration into the metropolis. But research suggests that most of these migrants, with lower immunity to urban disease, died within a few years of their arrival. In the final period of Teotihuacan, deaths in the prime migrant age group (15 to 24) trebled from 8.3 per cent to 27 per cent of total deaths.

The end almost certainly came in the form of an extraordinarily violent popular insurrection. Nearly every major building in the city associated with the ruling élite was ransacked, torn apart and put to the torch. Archaeological excavations have yielded evidence that palaces and temples were burnt to the ground in an orgy of systematic hate-filled destruction. Religious buildings and the city-centre palaces were the main targets, probably because all the major deities were associated with the rains that had failed. Relatively few apartment compounds were attacked, and those that were probably belonged to extended families that were somehow associated with the Government or with the failed religious system.

All the evidence shows how ancient America’s most extraordinary civilization was finally humbled by the horrors of climate change. As in Africa, the Mediter-ranean world, Central Asia and many parts of the globe, the sixth-century climatic catastrophe quite literally re-synchronized history.

David Keys, archaeology correspondent with the London-based Independent newspaper, has explored well over a thousand archaeological sites in over sixty countries. He has recently published a groundbreaking study of past global climate change and its political consequences – Catastrophe: An Investigation into the Origins of the Modern World (Century, ISBN 0 7126 8069 1) – which covers in greater detail the events mentioned in this article and much else besides.

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