When Civilizations Collapse: Conclusion
Posted by Richard Conniff on June 19, 2012
The Khabur River rises in Turkey and then flows south through eastern Syria, parallel to its border with Iraq, before joining the Euphrates. Harvey Weiss first arrived there in 1978 as a young archaeologist at Yale. He recalls being impressed by the harvested wheat stacked in “huge mounds” at the train station—“You don’t see that sort of thing growing up in Queens”—and it immediately struck him how productive unirrigated, rain-fed “dry farming” could be.
His focus was on the site now called Tell Leilan. Even before the height of the Akkadian empire almost 5,000 years ago, it grew from a rural village into one of the most important cities in northern Mesopotamia. The city walls from that era still rise above the Khabur Plains, enclosing almost a square kilometer of the ancient metropolis. The excavations Weiss directed revealed construction during the same period of grain storage and administrative facilities for collecting and shipping barley and wheat. Agriculture was being “commodified” and “imperialized” to support a central government or a distant imperial force. It was the ancient equivalent of the French train station.
But around 2200 B.C., both the major Khabur Plains settlements and the Akkadian Empire suddenly collapsed. The next 300 years have left their mark on Tell Leilan in the form of a thick deposit of wind-blown sand, with no architecture and hardly any trace of human habitation. Those centuries also survive in a desolate contemporary poem long thought to be a fictional account of the divine wrath that ended the empire:
For the first time since cities were built and founded,
The great agricultural tracts produced no grain,
The inundated tracts produced no fish,
The irrigated orchards produced neither wine nor syrup,
The gathered clouds did not rain…
In a 1993 article in Science, Weiss proposed, in effect, that the poem was nonfiction. The gods were, of course, no more to blame than were Ottoman bureaucrats in more recent centuries. But the ancient agricultural collapse was real, and the cause was an abrupt climate change. Co-author Marie-Agnes Courty, a soil scientist at the National Center for Scientific Research in Paris, documented the process of sudden drying that produced wind-blown pellets and dust. Other researchers later confirmed an abrupt region-wide dust-spike. Weiss also linked what happened in Mesopotamia to the simultaneous failure of agricultural civilizations from the Aegean to India. This suggested that abrupt climate change had reduced rainfall and agricultural production across the region, reduced imperial revenues, and thereby caused the collapse of the Akkadian Empire. More recently, cores taken by other researchers from ocean and lake floors, cave stalagmites, and glaciers have indicated that this abrupt climate change was probably global.
Why the climate changed abruptly then remains a mystery. The researchers at Tell Leilan found evidence of a distant volcanic eruption, in the form of rare and microscopic volcanic tephra, but regarded that as insufficient to explain a drought that lasted 300 years. Abrupt climate changes of the past were different from modern climate change, says Weiss, in at least two regards: The cause was natural, not the result of human behavior. And where we now have technological means to track and model climate change, society then “had no prior knowledge and no understanding of the alteration in environmental conditions.”
The 1993 Science paper was one of the first to link an abrupt climate change to the collapse of a thriving ancient civilization. But in the 20 years since then, other researchers have followed with studies implicating abrupt droughts lasting decades or centuries in a variety of other collapses, among them the ancient Cambodian Khmer civilization at Angkor, the pre-Inca Tiwanaku around Lake Titicaca, the great urban center of Tenochtitlan in ancient central Mexico,and the Anasazi in the American Southwest. Early this year, yet another article in Science reported that the collapse of the Mayan civilization coincided with prolonged episodes of reduced rainfall. Researchers have been careful not to say that climate change directly caused the collapse of civilizations, merely that drought slashed agricultural productivity and likely aggravated social and political unrest, ultimately leading people to abandon the area.
But many archaeologists have been skeptical of any connection between climate change and the collapse of civilizations.And,at times,the response has displayed all the loopy vehemence of the modern climate change debate, taking denial back 5,000 years. Critics have characterized such research as “environmental determinism” and dismissed the proliferation of evidence as merely a “bandwagon” product of an intellectual zeitgeist that is, as one 2005 a1rticle in a scholarly journal put it, “suddenly sympathetic to the idea of environmentally triggered catastrophes.” That article even seemed to categorize the idea of climate-induced collapse with “Nazi-tainted eugenic theories” about Darwinian determinism. The authors acknowledged that the Akkadian and some other collapses “were of a scale and a rapidity that seemed impossible to explain by purely cultural means.”But they complained that paleoclimate researchers fail to take account of “the inseparable nature of environmental and cultural influences.”In place of farms drying up and people going hungry, the authors preferred to explain it all in terms of cascading collapses in self-organizing systems, “as easily triggered by a pebble as by a boulder.” But not, apparently, by a loaf of bread.
“There’s a book a year,” Weiss said, incredulously, “that claims to point out the errors, lapses, gaps in data and misinterpretations” in the relationship between abrupt climate change and regional collapse. “It’s almost like, ‘Do you believe in evolution?’ They don’t ‘believe in’ the paleoclimate data and they don’t understand that the settlements that remained on the Khabur Plains after the abrupt climate change were few, tiny and short-lived.”
But paleoclimatologists have perhaps been too quick “to couple climatic and human events,” said co-author David Kaniewski. This encouraged traditional archeologists to treat the climate data “as simplistic, just because it failed, in their minds, to adequately consider and make enough room for the social and political context.” Paleoclimatologists and archaeologists could work together more closely “to study coupled natural and social systems.”
The PNAS paper notes that drought periods have become more intense and disruptive in the Middle East just in the past decade and are likely to become more common in the near future. “Interacting with other social, economic and political variables, they act as a ‘threat multiplier’” in a region that has plenty of threats to start with and that has also long exceeded the water needs of its population. One drought that lasted from 2007 to 2010 displaced hundreds of thousands of people in the Tigris and Euphrates basin, suggesting that Syria faces “the same environmental vulnerability as in antiquity.”
Nationwide, that drought drove 1.5 million people from the countryside to the cities, with no jobs or other means of support. Such underlying environmental causes rarely get much attention in reporting on the protests and violent crackdown in Syria. But they are liable to be a recurring challenge even if political and human rights issues get resolved. (Weiss has suspended his research at Tell Leilan because of the continuing crisis. But he has a research permit to drill a pollen core in a swamp alongside the nearby Iraqi border. Asked if he will be able to do the work before the permit expires, he shrugs and says, “I always go back. Let us hope the present tragedy ends quickly.”)
“In spite of technological changes,” Weiss has written elsewhere, “most of the world’s people will continue to be subsistence or small-scale market agriculturalists,” who are just as vulnerable to climate fluctuations as they were in past societies. In the past, people could go elsewhere.
“Collapse is adaptive,” says Weiss. “You don’t have to stay in place and suffer through the famine effects of drought. You can leave. And that’s what the population of the Khabur Plains did. They left for refugia, that is, places where agriculture was still sustainable. In Mesopotamia, they moved to riverine communities.” But climate change is now global, not regional, and with a world population projected to exceed 9 billion people by midcentury, habitat-tracking will inevitably bring future environmental refugees into conflict with neighbors who are also struggling to get by.
One of the most important differences between modern climate change and what he is describing at Tell Leilan, said Weiss, is that we can now anticipate and plan for climate change. Or we can do nothing. The danger is that, when there’s no longer any grain to stack up at the train station, the strategy of collapse-and-abandon may be streamlined to a simpler form: Collapse.