Climate change 3000 years

Climate Change and the Fall of the Late Roman Empire

Compiled by Lewis Loflin

The extreme weather events of 535-536 were the most severe and protracted short-term episodes of cooling in the Northern Hemisphere in the last 2,000 years. The event is thought to have been caused by an extensive atmospheric dust veil, possibly resulting from a large volcanic eruption in the tropics, or debris from space impacting the earth. Its effects were widespread, causing unseasonal weather, crop failures and famines worldwide. (Wiki)

This came at a time Emperor Justinian was reclaiming the Western Empire from various barbarian tribes that overrun the area. Yet in history class when I read this the whole subject was dropped without explanation. The next thing we read was the Muslims were halted in France at the Battle of Tours (also called the Battle of Poitiers) in 732.

In fact what was it that really caused so much chaos in the Western Roman Empire from the end of the rule of Marcus Aurelius (180 AD also called end of the Pax Romana) to the "Fall" of the West around 480 AD? Better yet, what was it that drove the Germanic tribes of Northern and Central Europe into the Roman West? The answer it seems was climate change.

Looking at the climate chart above a general cooling trend lasting five centuries would have reaped havoc on agriculture in much of Europe. There were also a number of plagues that swept the Empire as a weakened and sick population would be far more vulnerable. Add political corruption and war it was a recipe for ruin.

Another massive but short and severe cold snap, probably caused by a volcanic eruption (535-536), opened the door to the bubonic plague. The plague and famine devastated the Roman and Persian Empires, but spared Arabia. Beginning in Egypt, the plague would be carried on grain ships from Britain to the Black Sea and along the vast and still surviving system of Roman roads. The plague would kill millions and continue to erupt in waves for years. By 632 Islam would begin its sweep out of Arabia and destroy Persia and much of the Byzantine Empire. See Chronology: Early Islam

Only during the Medieval Warming Period would Christian Europe begin the counter-attack against Islam commonly called the Crusades. The better climate enabled Europe to recover when farming expanded. The Vikings also would be able settle in Iceland and Greenland. The early victories of the Crusaders halted and turned back Muslim aggression for nearly 200 years between 1095 and 1291.

Temperatures suddenly dropped again around 1300 and within 40 years the Black Death would sweep in from Asia. The Vikings would survive in Greenland until about 1600 when a very severe cold period set in. At the same time severe drought and cold ravaged Eastern North America and killed many of the early English colonists.

Byzantine or Eastern Roman Empire circa 540 AD
Byzantine or Eastern Roman Empire circa 540 AD

The following are extracts of answers given by William Rosen author of Justinian's Flea Plague, Empire, and the Birth of Europe His website and ordering information are at

Q: What were the consequences of the plague of Justinian?

The best way I know to answer that is this: Between the end of the 4th century and the beginning of the 6th, the Roman Empire had lost Britain, Spain, France, and Italy to a series of barbarian invasions. Between the years 532 and 540, the empire had reconquered North Africa, southern France, Italy, and Spain, and was a good bet to reestablish itself over almost the entire territory ruled by Augustus. Similarly, in the middle of the fourth century, the Sassanid Persian Empire was at its absolute apex of power and wealth, ruling from Pakistan to the shores of the Black Sea.

Then Yersinia pestis arrived.

Before the 6th century was over, it had killed somewhere around 25 million people, and nearly killed the emperor Justinian himself. Within decades, Rome and Persia were so plague-weakened that the armies of Islam, formed in one of the only parts of either empire to remain plague free, could conquer Mesopotamia, the Middle East, North Africa, Spain, and most of Asia Minor

So, while it would be wrong to say that we know that something as complex as the fall of the Roman Empire was caused by a flea, it is even more wrong to say that we know it wasn't. Or, put another way, hard as it is to say precisely how the pandemic changed the course of history, it is just plain wrong to suggest that subsequent events would have been the same had it not appeared.

Q: We've heard a lot recently about the way in which global warming/climate change may result in future epidemics; was there any relation between climate and the Plague of Justinian?

A National Academy of Sciences study last year actually showed a relationship between warming and the percentage of rodents that become infected with the plague bacterium, predicting up to a 50% increase in prevalence in places like Central Asia. However, something that depends on as many factors as a plague epidemic is more complicated. The same weather that makes Y. pestis more infective may limit the travel of the fleas that carry them.

Case in point: One of the best guesses for the origin of the disease is East Africa; some pretty persuasive research indicates that one of the events that preceded its arrival at the mouth of the Nile in Ad540 was a several years-long worldwide drop in temperature, probably caused either by a comet, or by a massive volcanic eruption...and the change may have caused the flea-carrying rats to migrate north.

The lesson of the Plague of Justinian, partly because it depends on such an extraordinarily unlikely - and extraordinarily unhappy - alignment of rats, fleas, and humans moving them around fast enough that they can spread infection before they die themselves, is that small disruptions in ecological equilibrium (what we used to call the balance of nature) can have big consequences. So, while it's too much to say that overall global warming is likely to be the cause of a new outbreak of bubonic plague, it is not something we ought to be sanguine about.

Q: What about Islam and Persia?

A lot of modern-day Iranians obviously take a great deal of pride in their Persian imperial much so that the movie 300 generated quite a lot of anger on behalf of folks who thought the movie defamed the Persians of Xerxes.

In some ways, they are the successors of those empires, but it's also true that when the armies of Islam conquered the Sassanid Persians, as a direct consequence of the events described in Justinian's Flea, they did their level best to destroy everything about all those Persian empires that preceded them; they leveled the Persian's capital city, built Baghdad on the opposite side of the Tigris, remade the language, the calendar, pretty much everything. I suppose it's a testimony to the size of the shadow that the Persian empire cast that it's still visible fifteen centuries after it was destroyed.

References below taken from Plague and the End of Antiquity: The Pandemic of 541-750 Edited by Lester K. Little

A number of plagues are noted in the Roman Empire from the late 1st to 4th Centuries according to Little. This corresponds to a cold wet period:

What came before were lethal epidemics to be sure, but of diseases that still lack generally agreed-upon diagnoses. The most notable of these were the 'plague' at Athens in 430 BC described by Thucydides, in which Pericles died, the Antonine Plague in Galen's time that stretched over much of the Roman Empire between 169 and 194, in which Marcus Aurelius died, and that of a century later, between 250 and 270, in which another emperor, Claudius Gothicus, died. Smallpox, typhus, and measles were most likely the diseases involved in those epidemics...

Due to climate change in 535-536 and massive crop failures in Europe, Egypt the ancient bread basket of the Middle East was once again called on. The plague started there and got exported everywhere. Once the pestilence gained a foothold, it came again and again. To quote Little:

The principal Greek source is the work of the historian Procopius of Caesarea, who was present at the court of Justinian in Constantinople in the early 540s. In his Persian War, Procopius says with reference to this time, "there was a pestilence by which the whole human race came near to being annihilated...

It started among the Egyptians. Then it moved to Palestine and from there spread over the whole world...In the second year it reached Byzantium in the middle of the spring."

He says that for the majority of those stricken the onset of fever was the first sign, and then there developed after a few days a bubonic swelling, either in the groin, in the armpit, or beside the ears. He reports that the mortality rose alarmingly, eventually reaching more than ten thousand each day.

Procopius also mentions that the emperor himself was taken ill, but only in his Secret History did he go on to reveal that there were rumors at court that Justinian had died and that speculation about the succession flourished. Justinian, however, recovered and reigned for two more decades.

The lawyer Agathias undertook to continue the history of Procopius. He says that after 544 when plague ceased in Constantinople, it had never really stopped but simply moved on from place to place, until it returned to the city almost as though it had been cheated on the first occasion into a needlessly hasty departure.

This was the spring of 558, when "a second outbreak of plague swept the capital, destroying a vast number of people." The form the epidemic took was not unlike that of the earlier outbreak.

A swelling in the glands in the groin was accompanied by a high fever that raged night and day with unabated intensity and never left its victim until the moment of death.

This seemed to be carried by ships:

The port of entry for the disease into Gaul in the first place, we can assume, was Marseilles, since the earliest report we have of it in Gaul was in the Rhone Valley.

While Gregory did not mention Marseilles in his passage on the outbreak of 543, he has an astonishing tale to tell of the one there in 588, astonishing for the bits of etiological insights it contains.

"A ship from Spain put into port with the usual kind of cargo, unfortunately also with it the source of this infection.

Quite a few of the townsfolk purchased objects from the cargo and in less than no time a house in which eight people lived was completely deserted, all the inhabitants having caught the disease.

The infection did not spread through the residential quarter immediately. Some time passed and then, like a wheat field set on fire, the entire town was suddenly ablaze with the pestilence...

At the end of two months the plague burned itself out. The population returned to Marseilles, thinking to be safe. Then the disease started again and all who had come back died. On several occasions later on Marseilles suffered from an epidemic of this sort."

The Black Death was one of the deadliest pandemics in human history, peaking in Europe between 1348 and 1350. It is widely thought to have been an outbreak of bubonic plague caused by the bacterium Yersinia pestis. Usually thought to have started in Central Asia, it had reached the Crimea by 1346 and from there, probably on merchant ships, it spread throughout the Mediterranean and Europe.

The Black Death is estimated to have killed 30% to 60% of Europe's population, reducing the world's population from an estimated 450 million to between 350 and 375 million in 1400. This has been seen as creating a series of religious, social and economic upheavals which had profound effects on the course of European history. The plague returned at various times, resulting in a larger number of deaths, until it left Europe in the 19th century. (wiki)

After the cooling of the Medieval Warming Period and a severe cold snap in the early 1300s, the plague reappeared. Unlike the earlier pandemic that spared Arabia:

The second pandemic, well known to all readers of history as the "Black Death," erupted in Central Asia in the 1330s, reached the Crimea by 1346, and then moved on the following year to Constantinople and thence to ports all around the Mediterranean.

It spread more widely and moved further inland than it had eight hundred years before, for example, by reaching Scandinavia and also far into the Arabian peninsula for the first time. For more than a century and a half it continued to recur with notable regularity, but then became sporadic, though still deadly, vanishing from Europe in 1772, but lingering in the Near East until the 1830s.

This plague too was carried on ships and emerged from seaports that now covered even larger areas.


Posted September 6, 2009 by Lewis Loflin