January 20, 2011

Climate and the demise of the Western Roman Empire

This paper got a lot of attention, deservedly, in my opinion. Here is a high-level description of the research from the BBC:

A team of researchers based their findings on data from 9,000 wooden artifacts from the past 2,500 years.

They found that periods of warm, wet summers coincided with prosperity, while political turmoil occurred during times of climate instability.
There are theories a-plenty about the Western Roman Empire's demise, and prima facie this seems as good as any. It has a desirable property that, unlike more "historical process" explanations, there is no indeterminedness of whether something that occurred was a symptom of the decline, or its cause: tree rings are presumably oblivious to human societal organization.

I was recently reading a book on the subject, I believe it was the Grand Strategy of the Byzantine Empire but correct me if I'm wrong, which made the point that the eastern Empire should have been a better candidate for failure for several reasons, including the fact that it was partitioned across three continents, and faced more formidable foes. Did climate do the Western Romans in?

A good test of the theory would be to identify other instances (in space or time) where climate can be linked to social organization; obviously there are not that many candidates with a continuously recorded history that long, and the fact that climate may have unstabilized the Western Empire does not mean that every "collapse" can be traced to climate.

Science DOI: 10.1126/science.1197175

2500 Years of European Climate Variability and Human Susceptibility

Ulf Büntgen et al.


Climate variations have influenced the agricultural productivity, health risk, and conflict level of preindustrial societies. Discrimination between environmental and anthropogenic impacts on past civilizations, however, remains difficult because of the paucity of high-resolution palaeoclimatic evidence. Here, we present tree ring–based reconstructions of Central European summer precipitation and temperature variability over the past 2500 years. Recent warming is unprecedented, but modern hydroclimatic variations may have at times been exceeded in magnitude and duration. Wet and warm summers occurred during periods of Roman and medieval prosperity. Increased climate variability from ~AD 250 to 600 coincided with the demise of the Western Roman Empire and the turmoil of the Migration Period. Historical circumstances may challenge recent political and fiscal reluctance to mitigate projected climate change.


pconroy said...

IIRC, there is pretty good evidence linking the demise of the following groups to climate instability:
1. Lowland Maya in Central America
2. Anasazi in SW USA
3. Vikings in Greenland

Luke Lea said...

"Historical circumstances may challenge recent political and fiscal reluctance to mitigate projected climate change."

A stretch.

AK said...

I've never read the book you mentioned, although I've read his earlier volume on the Roman Empire (isbn=978-0801821585). Anyway, I'm pretty sure I don't agree (pending reading it): both empires relied primarily on ocean (Mediterranean/Euxine) transport for troop and supply movement, and IMO the Huns and Persians were no more formidable than the Parthians. (In fact, the Huns got their start as mercenaries for the Romans, fighting other steppe tribes.)

I don't recall where I first read it, but one of the big differences between the western empire and the eastern was that in the west the territory extended too far north for olives, thus deprecating the ancient Mediterranean triumvirate of olive, wheat, and vine to a twosome, with no traditional source of oil. (Of course, there was always rape seed (turnips), evidently a traditional Teutonic crop, but the Romans were never very good at adopting alternative economies, their tax structure tended to make them unprofitable.)

This would fit with the climate explanation, although it's not as simple as the abstract makes it sound: the period of maximum political instability (AFAIK) centered around 250CE, with the reign of Diocletian coinciding with a recovery. Note that Diocletian was the emperor who split the fisc into eastern and western (pretty much coinciding with the later Empires) which put the western territories on their own financially, probably (IMO) leading to the later collapse, as various emperors taxed the inferior economies to death.

Unlike the Western Empire, the Eastern Empire didn't have to defend huge territories without a suitable tax base, as almost everywhere the Eastern Empire covered was suitable for olives, wheat, and vine. (AFAIK.)

Anonymous said...

This is how to find justifications after the event. It is possible to link the collapse to a number of statistical factors, if you wanted.
I think a year of drought is not enough to bring down an empire and the reasons for the fall of the Roman Empire are many and complex.
Until a few decades before it was to the east seems weak and destined to perish.
Many have a traditional view of the Empire which is not realistic, it was still prosperous enough to put together substantial forces, as for the shipment of the Emperor Maggioriano , the wrong policy choices have been to cause the fall.

El Lurker said...

The western roman empire fell because it was poor, apart from North Africa and Betica in Spain.

They had nothing to offer, and that situation remained unchanged (western europe having nothing of value to export to the rest of the world) until the people of what is now Benelux begun mass producing wool clothes in the middle ages.

dderinoss said...

The Virginia Company's Jamestown colony, the first English settlement to (narrowly) survive in N America (preceding the Plymouth Colony by some 14 years) nearly failed due to a climate catastrophe. Tree ring studies now demonstrate that the "starving time" their journals describe was due to the most prolonged and severe drought of the century. Because of this, the Virginian Powhatan Indian population, reluctant to trade their survival reserve of corn, were subjected to corn raids, generating enmity.