What Ancient Civilizations Can Teach Us about Drought

It’s time we pay more attention to past episodes of ‘great warming.’

With some climate scientists and media outlets increasingly attributing severe weather events in part to global warming, a big challenge going forward is about proportionality. In other words, to what extent can we connect hurricanes, heat waves, and droughts to greenhouse gases? Scientists are working to clarify any linkages, but it’s unlikely there will be clear-cut answers for at least a few years.

The odd thing about this endeavor and the larger severe weather/global warming debate is that we have yet to appreciate what science has already learned about climate change in the distant past, specifically (tree ring) evidence of devastating, prolonged droughts.

Analysis

“The dry spells of a thousand years ago spanned not years, but generations, anthropologist Brian Fagan writes in his 2008 book, The Great Warming: Climate Change and the Rise and Fall of Civilizations. “The medieval droughts in California’s Sierra Nevada lasted decades, far longer than those of modern times.” Fagan’s book examines other nasty ancient droughts and how they laid waste to some of the world’s great empires, from the Maya in Central America to the Khmer in Cambodia.

But just as the contemporary question of drought and its global warming signal is a complicated one, so too is the question of drought and its impact on prehistoric societies.

For example, new research published in PNAS, as reported by Live Science, postulates that the Khmer’s ancient city of Angkor “might have collapsed” while battling an extended drought.

Researchers have been trying to puzzle-out this story for years. Live Science provides some context:

Suggested causes for the fall of the Khmer Empire in the late 14th to early 15th centuries have included war and land overexploitation. However, recent evidence suggests that prolonged droughts might have been linked to the decline of Angkor — for instance, tree rings from Vietnam suggest the region experienced long spans of drought interspersed with unusually heavy rainfall.

In fact, previous studies (which Live Science might have mentioned and linked to in its dispatch) have found that extended droughts and other climate forces played a major role in Angkor’s collapse. Columbia University’s Brendan Buckley, for instance, led a study published in PNAS in 2010, which declared:

The Angkor droughts were of a duration and severity that would have impacted the sprawling city’s water supply and agricultural productivity, while high-magnitude monsoon years damaged its water control infrastructure.

Science writer Ed Yong, in a post at his Discover magazine blog, provides a detailed perspective on the Buckley study and on the larger question of what ultimately led to Angkor’s demise. As Yong noted, “By the time the droughts kicked in, the city was already weakened by social, economic and political strife.”

What’s interesting about Ankgor’s story is how similar it may be to other famous “collapse” stories in prehistory, like the Maya and Anasazi, which Jared Diamond chronicled in his best-selling book, Collapse: How societies choose to fail or succeed. Additionally, in an article for Science several years ago, I explored the complex mix of social and environmental factors that led to the unraveling of prehistoric southwestern societies, such as the Fremont and Anasazi, a millennium ago.

The general theme that runs through all these cases, according to archaeologists, is this: In boom times, when the environment was good, cultures flourished and populations expanded; when the climate went bad, hard times set in, along with societal conflict. But when ecosystems got stretched beyond their capacity, as a result of multiple stresses, including a series of extended droughts, the cultures eventually broke under the strain. For example, that Science article cited one study published in Quaternary Science Reviews, whose authors wrote that, “In some sense, the 13th century drought may have simply ‘finished off’ some cultures that were already in decline.”

But as many scholars will also attest, these were cultures that had withstood previous ferocious episodes of climate instability and had built a good bit of resilience into their systems and institutions. Why would one bad drought knock them out when previous ones didn’t? Kevin Anchukaitis, a Columbia University paleoclimatologist and co-author with Buckley on the 2010 PNAS Angkor paper, offered some insight into this question in a recent e-mail exchange:

So, were the crops of the Maya or the [Angkor] Khmer withering in the field during megadroughts? Perhaps, probably. But I tend to subscribe to the theory — elegantly described by University of Illinois anthropologist Lisa Lucero — that it wasn’t drought per se that tipped these civilizations into collapse, but rather the failure of “elites” and the infrastructure that was part of their power, effectiveness, and control. There may have been direct consequences of drought — crop failure, famine, malnutrition — that played a role, but before those aspects would have become lethal in and of themselves, there likely would have been a crisis of confidence and elite control. Add to that enemies at the gates — like the Siamese of Ayutthaya for the Khmer at Angkor — and it may have become too much for complex societies to withstand.

Lessons as We Anticipate Projected Droughts?

While such a nuanced picture that emerges from accumulated scholarship is fascinating, are there lessons for us here in the 21st century, as we stare down the barrel of projected, long-lasting droughts that are likely to be worsened by the build-up of greenhouse gases? After all, writes Fagan in his book, the U.S. has “experienced droughts, but none of them have endured like that descended on the Sierra Nevada a millennium ago.”

Referring to the same history that Fagan documents in The Great Warming, Anchukaitis, again in an e-mail, wrote:

We know the climate system is capable of producing longer and more severe drought than we’ve seen in the instrumental record even without the influence of anthropogenic climate change, and we’ve constructed massive infrastructure and have large sedentary populations in hydrologically-marginal environments. But at least in the [U.S.] Southwest (and, I think, southeast Asia) perhaps more so than the direct consequences of drought will be the institutional and infrastructural consequences: People aren’t going to die of thirst or famine this time in the modern and future southwestern United States, but you have to wonder what the social and political consequences of a Puebloan-style [Anasazi] Great Drought would be today for the infrastructure and institutions that make it possible to sustain large populations in the region.

Fagan, in his book, discusses this possibility and says that, in terms of water, “if the lengthy droughts of a millennium ago were to return, much of the western United States is living on borrowed time.” He also suggests that the contemporary public debate, with its singular focus on climate change, extreme weather, and sea level rise, may be shortsighted: “The melting of ice caps and the increased danger of flooding are no trivial matter.” But the experience of the civilizations he surveys in his book is that “the silent and oft-ignored killer is drought, even during a period of mild warming.”

Lest one think Fagan has misread the dynamics of the public discourse, consider what Kate Galbraith wrote last year, when a severe dry spell was starting to bake Texas: “The drought has become a touchstone for climate scientists and journalists in the debate over global warming.”

But there is also evidence that local Texas authorities and populations most affected by the persistent drought are managing it well, and that this story of resilience, as Albuquerque Journal science reporter John Fleck suggests, is not getting enough attention.

Still, Columbia University’s Anchukaitis cautions: “What I think we don’t know yet is what combination of drought characteristics and societal response to them would strain that resilience. To what extent are we immune from the type of drought-civilization synergies that brought about the demise of past complex civilizations?”

That’s a good question, one deserving a lot more serious consideration.

Keith Kloor

Keith Kloor is a New York City-based freelance journalist who writes often about the environment and climate change.
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7 Responses to What Ancient Civilizations Can Teach Us about Drought

  1. Graham Daly says:

    Thank you for this engaging article that ties into current issues and ends with the possibilty of solutions and success. I am currently exploring the impacts of bottled water with my senior students and was delighted to see Texas mentioned as a case study of reslience in response to the current and continued drought. I talk often with my students about the projected increase in population and current use of water in our state. I appreciate that the articles ends with more questions on the possible adaptations to the future of water use on our planet.

  2. Menth says:

    To what extent are we immune from the type of drought-civilization synergies that brought about the demise of past complex civilizations?

    Probably one of the greatest insulators against the type of civilization crushing droughts you describe is the globalization of food production. Cheap transport has made the surplus of one land available to the deficit of another. Historically even a culture “a couple valleys over” could be stricken with poor growing conditions while another flourishes. The ability to benefit from the produce of a variety of different climates has not only led to healthier, more diverse diets but vital protection from inevitable local climate variability. While an isolated country such as North Korea would be harshly affected(and has been) by periods of poor climate, a country benefiting from effective trade policies and cheap transport would be much better off.

    I’m not trying to a give a big [hooray!] to the fossil fuel industry here, just pointing out what I think is the case: whether you like it or not fossil fuels have been a tremendous boon for humanity. Of course, I believe it would be beneficial to find an even more efficient, cleaner form of energy and hope that we do.

  3. Erl Happ says:

    Apart from the apparently obligatory reference to the supposed linkage between extreme weather and ‘global warming’, whatever that currently means in a globe that has not warmed as predicted, this article is timely, responsible and refreshing.

    The first two comments are in the same vein.

    What we need is an acknowledgement that there is no correlation between planetary surface temperature and carbon dioxide levels. Plainly there is no correlation and we need to look at other modes of causation. That would be truly refreshing.

    Droughts in many parts of the globe are plainly associated with the ENSO phenomenon, which is in itself just a description of a state of affairs in the Pacific. We must acknowledge that there is a good correlation between ENSO and planetary surface temperature and set out to discover what causes the phenomenon. It is plainly not ‘an internal oscillation of the climate system’ that is temperature neutral. We have no ability to predict it. We don’t know what causes it. However, we do know that it is associated with a weakening and strengthening of the trade winds associated with shifts in atmospheric pressure between Tahiti and Darwin.

    The prime driver of shifts in atmospheric pressure globally is the coupling of the stratosphere and the troposphere over Antarctica. This is studied as the Southern Annular Mode. Let’s not ignore what is patently obvious.

  4. EdG says:

    My doubts about the AGW story were initially based on my knowledge of climate history. So, needless to say, I choked on the hockey schtick and it just got worse from there. The more we look back at real climate history the better. Context is vital.

    But given the hysterical talk about ‘unprecedented’ and ‘permanent’ droughts in Texas of late, there’s no need to delve into ancient history to understand how dubious those claims are. The link below leads to a composite video of the monthly Palmer Drought Index in the US for the past century plus. A rather amazing moving picture of climate change as expressed by drought, or lack of it, that is well worth the two or so minutes it takes to watch it.

    http://www.real-science.com/droughts-happen

    Note the 1930s. One can only imagine what some of today’s AGW promoters would be claiming about that when it was happening.

  5. EdG says:

    ““What I think we don’t know yet is what combination of drought characteristics and societal response to them would strain that resilience. To what extent are we immune from the type of drought-civilization synergies that brought about the demise of past complex civilizations?”

    That’s a good question, one deserving a lot more serious consideration.”

    Not only a good question but also a large one. In fact two or three large ones.

    Drought characteristics? Who knows? Unanswerable. Will there be another drought as severe as the 1930s in the next future? Probably, but we do not know. Will there be an Altithermal level drought anytime soon? I hope not.

    Where? Where droughts happen will determine whether any given society can cope with them. The US can cope with droughts better than Somalia. And no, there is no such thing as a global drought.

    Can we cope? Again, depends on who and where ‘we’ are. But for the US, I see a rather ironic twist. We have a cushion because we waste so much water. As was demonstrated in recent events, letting lawns go brown is hardly the end of the world. And beyond the conservation savings, we have the resources and the technology to address many problems which earlier societies or poorer countries or regions do. For example, they didn’t have water desalinization plants in the Middle Ages.

    That said, the climate always changes so there are bound to be more droughts, including some severe ones. Best to prepare before they happen. A far wiser investment than squandering any more of our limited resources on the giant sucking AGW project and its many bankrupt concepts.

    But good luck building any more water storage reservoirs, thanks to our friends in the ‘environmental’ movement.

  6. Dean says:

    There is a big difference between a drought hitting the US Southwest, and one hitting a prominent agricultural area. Above, Menth mentions that global food trade will help to insulate against that. But we have very little surplus if a major food producing region has a long-term drought that lasts a decade or longer. A drought in an already dry area would cause a migration. A drought in a major food-producing area would not only drive the global price of food up, but would probably undermine food trade as food exporters would shut off the exports if prices went up for a long time.

    The other issue you discuss deals with governance. Any culture that has good governance will adapt to challenges better than one with bad governance. Same for an area that is already stressed.

    By the way, the fact that the focus of this articles – civilizations that collapsed during what some call the Medieval Warm Period – demonstrates that such periods are by no means beneficial. That one was beneficial to Europe, and harmful in many other areas. I’ve also read that a drought in Central Asia may have motivated the Mongols to head out and cause their widespread mayhem. It was at the same time.