Not everyone agrees on what can be extrapolated from correlations spotted in archaeological and environmental records. But some ideas have come to light. “Societies have to be viewed as complex adaptive systems,” says Tim Kohler, regents professor of archaeology at Washington State University. If they stretch themselves too thin, “they become susceptible to external disruptions of almost any sort” – environmental, political, or economic.

Researchers are cautious about over-attribution of environmental factors, and are taking a more nuanced view of how climate change may have influenced societies throughout history. That approach may yield insights into what makes a civilization resilient or vulnerable to environmental changes.

You never know what you are going to find when you start digging through an ancient pile of trash. Researchers studying an ancient garbage dump in Israel’s Negev Desert uncovered evidence that shifts in climate may have contributed to the demise of the once bustling Byzantine settlement of Elusa.

Dumpster diving archaeologists in Israel may have uncovered a connection between climate change and the decline of a once bustling Byzantine settlement.

Researchers studying an ancient garbage dump in Israel’s Negev Desert found evidence that shifts in climate in the mid-sixth century may have played a role in the downfall of the urban settlement of Elusa.

Scholars have long pondered the role of climate change in the rise and fall of empires. Such research has taken on renewed significance as modern day societies grapple with climatic shifts.

Over the years researchers’ perspectives on how closely to link environmental factors to societal outcomes have shifted. Scientists today are cautious about overattribution, and are taking a more nuanced view of how climate change may have influenced societies throughout history. That approach may yield insights into what makes a civilization resilient or vulnerable to environmental changes.

“You can’t say that climate changed civilization, full-stop,” says Brian Fagan, a professor emeritus of anthropology at the University of California, Santa Barbara.

“The way you have to look at this is to think of throwing a pebble into a calm pond, and there’s a plop, and there are radiating circles that come from the impact, which then vanish,” says Professor Fagan. “It is very much those sort of social and economic changes which really make a difference.”

That’s just the kind of evidence that researchers studying Elusa reported finding this week in the journal Proceedings of the National Academy of Sciences.

When Guy Bar-Oz, lead author of the new study and a professor of archaeology at Israel’s University of Haifa, first began surveying the archaeological record of Elusa, evidence of the so-called Late Antique Little Ice Age following three volcanic explosions was just coming to light. So he hadn’t considered that climate change could have been a factor in the demise of the settlement.

As the team examined the artifacts remaining in ancient trash mounds around the city, they found that right around the mid-sixth century, Elusa’s landfills went from containing immense amounts of trash and a broad variety of items from deep inside the city to practically nothing.

Courtesy of Guy Bar-Oz A study of ancient urban trash mounds suggests a correlation between climate change and societal collapse in the Byzantine Empire. Researchers posit that a change in the disposal of trash in the settlement of Elusa in the Negev Desert could be linked to a sudden climactic shift.

It’s possible that the city transitioned to a different waste management system around that time. But it also could indicate a more profound shift in Elusa that may have marked the beginning of the city’s downfall, the authors say. Historians generally think that the Byzantine Elusa declined in the mid-seventh century, as the early Islamic period rose in the region.

There’s no environmental evidence that Elusa experienced the Late Antique Little Ice Age, further complicating that possible link. But, Dr. Bar-Oz says, climate change in Europe, where there is evidence of that cooling, could have had an economic impact on societies linked through trade. Perhaps a dramatic downturn in demand for Elusa’s products prompted residents in the city to move elsewhere or at least change how they did things. But at this point, the researchers caution, there is only a time correlation between Elusa’s trash transition and climate change. More research has to be done to see if the cooling period did indeed play a role.

That’s the tricky part of connecting climatic shifts with civilization changes, says Tim Kohler, regents professor of archaeology at Washington State University in Pullman, Washington. Often the evidence is simply that both things happened at the same time. And climate change is not always a direct causal relationship or the only factor involved. So, he says, making an argument for a relationship takes seeing as much of the whole picture as possible.

Nineteenth-century scholars saw environmental factors as one of the main drivers of societal changes. More recently, that perspective, known as environmental determinism or climate determinism, has been thought to have over-attributed the role of these external factors. But a few decades ago, social scientists began looking anew at the role of climate, this time taking a more nuanced view of environmental factors as just one influence among many that societies respond to in myriad ways, both directly and indirectly.

Scholars today are also looking for hints as to what makes a civilization either resilient or vulnerable to climatic changes, particularly in light of current environmental challenges. Not everyone agrees on what can be extrapolated from correlations spotted in archaeological and environmental records. But some ideas have come to light.

Professor Kohler, for example, points to how societies expand as a potential vulnerability. “Societies have to be viewed as complex adaptive systems,” he says. If they stretch themselves too thin, “they become susceptible to external disruptions of almost any sort” – environmental, political, or economic.

Empires that reached across regions and were reliant on long-distance trade networks, like the Byzantine, theoretically should be buffered by those many relationships, says Professor Kohler.

“Nevertheless,” he says, “there is also a sense in which all those connections also make them vulnerable because it means that if any portion of that complex network of relationships that sustains an area collapses, then it puts other portions of that network at risk, and you can have cascading failures.”

To Professor Fagan, “By far the most important characteristic, I think, is societies that are governed by people with very rigid views. If you have a society with rigid views, ruled by authoritarian rulers who have done things for generations a certain way, they are very resistant to change. And you get this happening with all kinds of societies. The Maya are a good example,” he says, pointing to evidence that a series of droughts shook the civilization sufficiently to lead to its demise.

It goes beyond a society’s resistance to change, though, Professor Fagan says. In a society based around divine rulers, if the rains don’t come, the people may begin to question the power of their leaders.

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One lesson is clear today, says Professor Kohler. “I would guess that many of these societies were quite confident in their own abilities to weather climate downturns because they could say things like, ‘Oh we plant maize in many different places. Oh, we have these long-term, long-distance trade relationships with other societies,’ and so forth,” he says. “But then they get to a point where there will be a downturn to which those things are no longer adequate buffers.”

“As we continue to grow, you know, as we go from 7 to 9 billion people in the next couple decades, we should worry that ... there will be something that can disrupt the elaborate global system that we have put together that we cannot envision,” he says.