Sunday, February 14, 2016

The collapse of the Western Roman Empire: was it caused by climate change?

Image from the recent paper by Buentgen et al., published on "Nature Geoscience" on February 8, 2016. The red curves are temperature changes reconstructed from tree rings in the Russian Altai (upper curve) and the European Alps (lower curve). Note the remarkable dip in temperatures that took place starting with the 6th century AD. But, by then, the Western Roman Empire was past and gone. Its collapse was NOT caused by climate change. 

The relationship of climate and civilization collapse is a much debated subject. From the recent collapse of the Syrian state to the much older one of the Bronze Age civilization, climate changes have been seen as the culprit of various disasters befalling on human societies. However, an alternative view of societal collapse sees it as the natural ("systemic") result of the declining returns that a society obtains from the resources it exploits. It is the concept termed "diminishing returns of complexity" by Joseph A. Tainter.

On this point, there may well exist several causes for societal collapse. Either climate change or resource depletion may sufficiently weaken the control structures of any civilization to cause it to fold over and disappear. In the case of the Western Roman Empire, however, the data published by Buentgen et al. completely vindicate Tainter's interpretation of the collapse of the Roman Empire: it was a systemic collapse, it was NOT caused by climate change. 

From the data, we can see that there was a cooling episode that probably affected the whole of Eurasia and that started with the beginning of the 6th century AD.  This period is called LALIA (Late Antiquity Little Ice Age) and it seems to have been stronger than the better known LIA (Little Ice Age) that took place during the 18th and 19th centuries. Apparently, the LALIA was mainly caused by a series of volcanic eruptions that injected large amounts of particulate in the atmosphere; cooling it by reflecting sunlight. Overall, temperatures went down by a couple of degrees in comparison to the time that we call the "Roman Warm Period."

A brutal cooling, yes, and it surely had effects on human life, as discussed at length in the paper by Buentgen et al. But it had nothing to do with the fall of the Western Roman Empire whose decline had started at least two centuries before. The Empire started its final disintegration phase with the beginning of the 5th century; when it ceased to be able to garrison the fortifications at the borders. Then, Rome was sacked one first time in 410 AD; and finally destroyed by the Vandals in 455 AD. That was the true end of the Western Empire, even though, for some decades, there were still individuals who claimed the title of Emperors. But all that took place in a period of relatively stable climate, at least from what we can say about the available data. So, the collapse was systemic, related to factors other than climate and, in my opinion, mainly related to the collapse of the Roman financial system, in turn caused by mineral depletion.

But could it be that, after all, there is a correlation between the Roman collapse and climate change? Just it would be the reverse of what it had been sometimes proposed: could the Roman collapse have caused the LALIA cooling (or, at least, contributed to it)? The idea is not farfetched: the population collapse that took place with the fall of the Empire could have led to a considerable level of reforestation of Western Europe, and that would have absorbed CO2 from the atmosphere. That would have been an added factor to volcanic cooling. It is an idea already expressed some time ago by William Ruddiman. It seems to be out of fashion, nowadays, but I think that it should be explored more.

In the end, this story can teach us a lot: first of all, how fragile climate is. In the interpretation by Buentgen et al., just three volcanic eruptions - relatively large ones, but not truly gigantic - were sufficient to cause a two-degree cooling extending all over Eurasia. Think of what could be the effect if something similar were to happen in our times! Then, it shows also how the situation, today, has completely changed. Temperatures have taken a completely different trend with the start of large scale emissions of greenhouse gases in the atmosphere. Incidentally, these data also confirm the "Hockey Stick" data by Michael Mann and others. Global warming is real, the earth's climate is fragile, and we are in big troubles.

Additional note: The data published in "Nature" generated a truly awful article in the "Daily Express" titled "Mini-ice age 1,500 years ago contributed to fall of Roman Empire". There, they put together an incredible mix of unrelated things, showing for instance gladiator games that had ceased to exist at least one century before the LALIA. Then, they say that the 6th century cooling "contributed to the collapse of the Eastern Roman Empire." Which is an interesting extrapolation, since the Eastern Empire didn't collapse until about a thousand years after the LALIA!!  At least, they should go back to junior high school but, on the other hand, think of how they report about climate change: what would you expect from them when they discuss about the Roman Empire?

(h/t Graham Readfearn)


  1. Sir, I found this a fascinating post and the references to Tainter and his proposition of their beinga complexity boundry. Tainters proposition is not a new idea but one put forward in the 19th Century by the English economist W S Jevons observed and correctly elucidated. Having studied the History of the Romans and Greeks when you stop and look at or hypothesise on the nature of the ecological capacity and technology available as to the sustainability and viability of very large city states Rome plus later Constantinople and the aggregation of a large portion of the Mediterranean and European land and waterways and its various inhabitants and societies. Specifically the reliance on humans for labour for every possible activity and despite significant civil engineering and scientific advances(medical) meant that they reached the limits of any economic endeavour posited by W S Jevons. Despite the view that the profligacy of various rulers and or civil strife had an inevitable destruction is misplaced, simply Rome required increasing inputs of military activity, men on the ground and those costs increasingly outweighed the inputs by way of resources. Rome itself required a huge effort to keep supplied in the staples of life. Fuel was plentiful but had to be brought in as did water etc. For some reason most historians ignore the input costs if you like to maintaining complexity and cheap resources or energy and especially a militarised state across a very dispersed geographical area. War and civil wars sent Rome broke and for the boundaries of its environment it had to collapse but as we know collapse for Rome is a matter of degree, Rome as a city may have nearly disappeared by the States and countries it once controlled did not they in fact continued on in a lot of case thrived in their own way. As to environmental causes if you wish to look for examples and proof that civilisations collapse once they overgrow their resources, Rome is not it, yes, it is a form of financial collapse but war breaks everyone eventually.

    I think the markers for signifcant climate change events destroying or so damaging societies that they seemed to have vanished then it seems clear that in period after the last age when people began recolonising the planet and domestic agriculture and towns or cities developed at about 6000 years to about 2500 years ago. The Bactrian or high Indus civilisation, the Old Persians, Egyptians and even those that once lived in is now what is the Saharah Desert, flourished for long long periods, centuries yet it is clear when you look at the geography of where they are today, then it is clear that significant climatic change has occurred. When the keepers of Jason and the Argonauts retold the stories of the exploration to the west, in sometimes quite imaginary mythical ways, the core of the story is that once people of Dorian descent possibly took a boat from the Greek Islands all the way to Bactria. That river system has gone and it collapsed or vanished some time ago, possibly as a result of seismic activity changing landscape flows in a way detrimental to agriculture with it went the Bactrian Empire even though their religion has somehow managed to survive. Look at Persepolis, can you imagine the Persian King Cyrus the Great or Xerxes having made these capitals their basically so arid now they are desertified.

    South America has similar examples, we know that, so there is no real dispute that societies and civilisations dissipate and shrink as a result of significant shifts in climate or water resources that is catastrophic.

  2. Thanks for a thought-provoking post again, Ugo. However, James Tainter should be Joseph A. Tainter.

  3. "From the recent collapse of the Syrian state...(to much older examples)....climate changes have been seen as the culprit of various disasters befalliIng human societies" . A carefully constructed statement to be sure.

    Let's deconstruct it. And let's take one disaster at a time to try to specify and attempt to render more concrete and verifiable or falsifiable the general "argument". (Which may or may not be true depending on the presence or absence of logically and flawlessly linked evidence in various specific concrete situations, and not assertions or carefully crafted insinuations)

    Has the Syrian state indeed collapsed? Well not exactly, though of course it may eventually. But this could be an honest mistake confusing the Syrian "state" (which recently has been scoring significant victories against its opponents) (mostly terrorists armed and financed by Western governments and their regional friends and proxies) with Syrian society which has not "collapsed" but has indeed been systematically destroyed by the many warring factions. Have these warring factions started and continued and sustained their warring because of climate changes? This is a completely unproven assumption.

    But it is certainly true that it has been "seen" that way by some. By whom, and is it true, and how has it been proven or demonstrated rather than insinuated? The "whom" is fairly simple to specify. On the one hand it has been "seen" this way by Prince Philip and several other New World Order proponents. This is well documented and easily can be googled. Naturally the NWO is also "seen" by many as being a "conspiracy theory" without merit. But not by everyone so it is at best or at worst a contested matter. The other group which "sees it" that way is the primarily anthropogenic climate change believers or alarmists (or "true scientists" as they tend to see themselves perhaps joined in this belief too by "the 97 % of the scientific community" which "has been counted accurately " to agree with them) (about what?).

    But maybe these folks "see it that way" because they already have in their possession the incontrovertible logically and flawlessly linked evidence " that I (as a heretic) dared to refer to above? In which case why keep it a secret, let's see it so the rest of us can more easily "see things" their way too.

    The other stuff about Michael Mann and the hockey stick at the end is beyond rational evidence based debate in a blog like this or other similar blogs As a quick perusal of the link to the other post about the hockey stick demonstrates there are hermetically sealed arguments within other hermetically sealed arguments justifying simply JUST NOT TALKING ABOUT IT ANYMORE. Only a fair bit of time will allow starting to pry open some of the sealed mental spaces to allow honest scientific debate. In the meantime skeptics (heretics) will continue to see some of these same arguments used against them. So who is right? Only real scientific discussion and real evidence can determine that. But probably no need to discuss with stubborn fools or unscientific ignoramuses anymore. THe Science is WITH US ! But if that were true how come many eminent climate scientists disagree? I know. That is simply Not True. And why isn't it ? Because we "the real scientific and scientific community" say so that's why and either by direct simple assertions or-typically- by far more clever insinuations. End of story and the Syrian people have been devasted by climate change. Time to get with program if you don't want Syrian blood on your hands too.

  4. Max
    Good to see you back you old heretic!

    BTW, in American, appellations like 'Prince', 'Duke', 'Lord' or 'Lady' are usually affectionate tributes to character or are just pet names. This is not the case for Brits. I would go as far as suggesting as a rule to beware Brits bearing those titles! ;-)

    I agree with you about Syria. The Post-Cold War Cold War continues hot in less fortunate places. I remember that ‘Go on - Get Syria’ appeared to be (?) an argument among influential US circles at the time of the American jihad in 2003. (But how should I have verified this history and maybe I am hijacking and misusing a legitimate faith-term because I prefer it to ‘Crusade’? I am not sure what is reasonable.)

    But climate change progresses (nice word – some would rather assume an undulating plateau tilting with the sun and stars) as far as I can see ‘on schedule’. I admit to having stood on the edge peering at published studies for more than 30 years. To me ‘the reality’, if that is a reasonable term, seems a bit like the kind of ‘progress’ we see in the ‘progressive’ chronic diseases, or indeed the progress we see in old age and generational succession, but not so benign or reliable. The carbon cycle and the linked hydrological cycle are indeed cyclical and with some period oscillations beyond our species let alone our familial lifespan, but very suddenly we got into an awful hurry. When were we born? Perhaps we were born in the Eemian? Should I mourn for my remote mother from the long lost tribes of the ice from before the Eemian? What is reasonable?

    NB I used the ‘progressive disease’ metaphor for industrial civilisation before when Ugo proposed (wished) ‘we’ should ban plastics.


    1. Hi Phil, many thanks for the nice comment. "The old heretic" was AWOL for a while because a) busy planting lots of bananas in Thailand (during one of the COLDEST winters in memory BTW) and b) collecting his thoughts and doing more and better research on the tremendous CO2 causes global warming going on including during the Roman and Medieval periods WARMING which happened all over the world and not just in Europe. (But in China they had already invented solar powered efficient air conditio eres). And also cheering for Michael Mann to be allowed to play defense for the Toronto Maple Leafs. Those two things and much more have allowed me to emerge from my POLAR BEAR hibernation without finding myself drowned in a pool of warm water in my lair but instead with a much better grounded and invigorated sense of HERESY. Naturally as an APOSTATE I hope to get off light with maybe just a couple of hundred lashes of the whip. And how have you been keeping up there in the SUNNY British Isles? Enjoying your life or planning your own private BREXIT maybe? Take good care and Keep the Faith ! Max

  5. I just wanted to express my biggest thank you for all you have done! I have found one more intriguing post, which is published at! Wishing you a happy reading!

  6. It's the inverse correlation. Southern regions gain population relative to northern regions during warm periods. Global warming helped the romans, global cooling ended them.



Ugo Bardi is a member of the Club of Rome and the author of "Extracted: how the quest for mineral resources is plundering the Planet" (Chelsea Green 2014)