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When Civilizations Collapse

Posted by Richard Conniff on June 18, 2012

For the past 30 years, midway through the drive from his expedition living quarters in Qahtaniyah to his archeological excavation at Tell Leilan in northeastern Syria, Harvey Weiss has contemplated the enigma of a railroad station. French colonial authorities built the modest two-story structure, along with a railroad to the Mediterranean Sea, shortly after World War I, and everything about it belongs in rural France—the hipped roof, the multipaned casement windows, the interior post-and-beam timbers. It is the architecture of empire, writ small.

For Weiss, though, the train station has come to tell a larger story about climate change and human adaptation to it (or failure to adapt)over thousands of years. The French built it, he explained recently, to pull out the cereal harvest of the Khabur Plains, the most fertile rain-fed agricultural area in northern Mesopotamia, and it still serves that function. At harvest time, the 100-kilo sacks of wheat are piled high there, awaiting shipment to market.

But why was the Khabur region barren and largely abandoned for hundreds of years before the French arrived? “Why do all the 18th- and 19th-century travel accounts indicate that the region was empty?” asked Weiss. “And what is the meaning of that abandonment for the Ottoman economy and the historical problem of Ottoman decline?” Other scholars have argued for the past 50 or more years that provincial administrators in the declining centuries of the empire were corrupt, inefficient and unable to maintain law and order, allowing the region to be abandoned despite its high productivity and its tax value for the central government. “The argument being,” Weiss added, “that there were no environmental and certainly no climate reasons for the abandonment.”

The alternative answer, in the title of a paper just published by Weiss and his French co-authors in Proceedings of the National Academy of Sciences, may seem unsurprising: “Drought is a recurring challenge in the Middle East.” But it has been the subject of bloody academic combat ever since Weiss first proposed 20 years ago that long-term shifts in climate are a key factor in understanding the tumultuous history of the Middle East. Before then, archaeologists working in the region took it for granted that the climate had been essentially stable and benign over the long-term, and that social, political, military and economic forces were the key determinants in the rise and fall of civilizations.

The new study suggests merely that climate change caused the late Ottoman abandonment of the Khabur River Plains, not collapse of the entire Ottoman Empire. But it also makes the case that archaeologists and historians ignore climate change at their peril. “There is an environment in which history occurs,” said Weiss. “There are reasons for regional abandonments that are definable, observable and testable,” even when ancient peoples have left no written record of climate changes.

For the new study, Weiss and co-authors David Kaniewski and Elise Van Campo from the Université de Toulouse, France, used pollen to reconstruct 10,000 years of climate history in the region. Their technique was to take a column of stratified sediment from the side of a dry river channel near Tell Leilan and identify the mix of plant types in different layers. The percentage of pollen in a sample from dry climate plants (like dryland wormwood and tamarisk) or humid climate plants (like flowering sedges and buttercups) provided a measure for estimating rainfall and agricultural productivity at that period. To construct a chronology, the researchers determined radiocarbon ages on plant remains in different layers, using mass spectrometry.

The pollen record showed a pattern of climate fluctuations, with periods of relatively moist climate vegetation alternating with periods of arid climate vegetation. One such dry spell began suddenly around 1400 and lasted until the beginning of the 20th century, the same bleak era when Weiss’s regional archaeological surveys showed villages on the Khabur Plains being emptied. Because this part of Syria is semi-arid to start with and most farmers depend on a single crop of wheat or barley grown in the moist winter months, people then, as now, were highly vulnerable to climate fluctuations. In the absence of irrigation or other technological means of adapting, they practiced what Weiss characterizes as “habitat-tracking,” or moving to areas that could still sustain agriculture.

The evidence suggests, in other words, that incompetent Ottoman bureaucrats were not solely to blame for the demise of agriculture on the Khabur Plains, nor do ingenious French bureaucrats deserve much credit for its 20th-century revival. An intervening force was climate change. And those two words, together with the idea of collapsing civilizations, may explain the intensity of the reaction and the abundance of research Weiss’s work has provoked.  (To be continued.)

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