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Tuesday, 18 January 2011

There is Unrest in the Forest, there is Trouble with the Trees (or 'Climate change brought down the Roman Empire, scientists *don't* find')

[Research on Tree-Rings has recently grabbed the headlines as showing that 'Climate change may be responsible for the rise and fall of the Roman empire'.  This is unlikely.  The problem lies principally in the scientists trying to explain phenomena which are not now thought to have existed in the form the scientists believe.  Furthermore, there are all sorts of logical problems in arguing that climatic features explain the multifarious, divergent features of a 300-year long period of European history!]


The chance to use the opening lines of a Prog classic as the title for some writing on late antiquity comes but rarely in a career, so when it does it should be seized with both hands. 

My texts today are taken from The Daily Telegraph and from the BBC's news website:

http://www.telegraph.co.uk/earth/environment/climatechange/8262919/Climate-change-may-be-responsible-for-the-rise-and-fall-of-Roman-empire-scientists-find.html
http://www.bbc.co.uk/news/science-environment-12186245
The abstract of the research in question can be found here:
http://www.sciencemag.org/content/early/2011/01/12/science.1197175

Reduced to a couple of headline-grabbing paragraphs, what the research is claimed to show is that:
"Wet and warm summers occurred during periods of Roman and medieval prosperity. Increased climate variability from 250-600 AD coincided with the demise of the western Roman empire and the turmoil of the migration period," the team reported.
"Distinct drying in the 3rd Century paralleled a period of serious crisis in the western Roman empire marked by barbarian invasion, political turmoil and economic dislocation in several provinces of Gaul"

The first thing that needs to be said is that this approach is not new.  Back in the mists of time, when I was preparing to go to university, I read Geoffrey Parker's Europe in Crisis (recently a second edition has appeared, which I have not read [http://www.amazon.co.uk/Europe-1598-1648-Blackwell-Classic-Histories/dp/0631220275] - these comments may well not apply to the new version, though a quick skim on Amazon suggests they do).  This began with a discussion of climate history and how tree-ring research suggests that the seventeenth century was a period when bad weather might have helped to produce the turmoil of the era.  At the time this fired my imagination (if I hadn't turned out to be an early medievalist I would almost certainly have specialised in the sixteenth or seventeenth century) as a real New History.  Over time, of course, my faith in this sort of environmental determinism (as in all other sorts of determinism) waned.  I ceased to be convinced by this kind of explanation, parodied by a friend and colleague as 'there was an unusually heavy frost, so the Thirty Years War broke out.'

As with my comments on DNA, my gripe is not (it cannot be) with the science itself, with the reality of the observations.  Similarly, if the aim of the researchers is to use these findings to try and spur governments on to act further and faster on climate change, then I can cut them quite a lot of slack.  But we do need to show a considerable degree of caution about their historical conclusions, at least as far as the Roman Empire is concerned.  Here are some points which you might like to bear in mind:

As with the DNA research, the scientists have not critically probed the reality of the historical phenomena they claim their research explains.  First, recent research has poured considerable doubt on the idea that the third century was an economic crisis in the sense that used to be understood, that is as a period of economic decline.  It might have been a crisis in terms of a weakening of the economic unity that had characterised the Empire in its very early phase but in large parts of the Empire (such as Britain) there is no trace of any decline at all: quite the opposite.  And the fourth century in Britain and elsewhere was an era of prosperity.

Second, the turmoil of the migrations.  Again, one needs to think much harder about what these migrations were like.  No one sane denies that people migrated in the last century of the western Empire's existence, but people have always migrated.  We do not know whether more people migrated in the fifth and sixth centuries than did in the third or fourth, or the first or second.  There were, allegedly, tribal movements on a considerable scale in the Roman Republican period too.  Large numbers of people migrated from the heart of the Empire out to the peripheries during the centuries of Roman expansion.  It is a curious view that sees the Roman invasions as a period of 'prosperity' and the probably far less dramatic migration of barbarians in the fifth century (as stated, the continuation of a set of relationships that had lasted for centuries) as one of turmoil.  More curious still that one movement might be explained by one climatic set of conditions and the other by another. 

So, again, this science is bolted on to explain a historical 'problem' whose outlines have been entirely changed as the result of serious historical enquiry.  Sometimes they have changed so far as to make it no longer a problem at all, or at least no longer a problem that can be explained in those terms.  How to explain this by analogy?  This is the best I can do.  It is 'a bit like' a situation where 'scientists' claim that the kind of wheat grown in later ninth-century England would produce a flour that, if used in cakes, could suddenly and unpredictably burn.  'Scientists show Alfred unfairly blamed for burning cakes!' then gets plastered across every news site in the land.  But we now know that the story of Alfred burning the cakes at all is a twelfth-century invention...

That is the main flaw in these sorts of explanation.  But there are myriad other issues.  The collapse of Roman civilisation in Britain was the affair of a couple of generations around 400, after a century of prosperity.  Difficult to explain that through climatic variations over the longue durée, but socio-political explanations do perfectly well.  Migration is a constant of human existence.  Barbarians had been moving into the Empire for centuries, from Caesar's time (and indeed before) right through to the fifth century, and the factors and processes behind their movement remained demonstrably analogous throughout.  Whether any more (or fewer) moved in the fifth century than the third is impossible to know, but the migrations of the third century did not spell doom for an Empire in the thoes of all sorts of other political problems, whereas those of the fifth century did become a focus for political developments that ended up in the fragmentation of the western Empire.  Climate seems incapable of explaining this difference.

Equally, the fourth century was a period of strong imperial rule and remarkable coherence for the Roman Empire, in spite of its situation in the heart of the period where climatic features are supposed to be causing crisis.  The economic revival of the West during the seventh century could be said to fit with the findings of this research but again problems soon arise.  It seems clear (to me, at the moment, at least) that this revival began in the late sixth century and has perfectly adequate socio-political explanations.  More importantly, this does not explain the fact that, although the north-west may have revived, the Mediterranean world experienced a comparative economic decline at this time.  What about the Arab invasions of the seventh century?  Is this sort of 'turmoil' not explained by climate (people used to think it was but - as far as I am aware - this is an explanation in desuetude)?  If it is explained by climatic optimum, then the opposite climatic conditions cannot in themselves explain migration, can they?  Not without considerable modification to the thesis.  And if the Arab expansion is to be explained by politics, society or ideological/religious factors, then why can the northern barbarian migrations not be explained in those terms?

And so on, and so forth.  Let us be clear that this research is valuable and interesting and that it doubtless adds important and interesting details to the picture we have of these centuries.  But we need to think much more carefully about how and why they are important and interesting.  That means asking new and better historical questions that these data can go some way towards answering, not in bolting them on to explain problems which they can't explain and which, in some cases, are no longer problems in any case.

The article concludes with the researchers in question saying "We are very interested in understanding past civilisations and making our research more dense."  More dense.  Ah, that'll be because of the 'less favourable growing conditions' then: the funding 'drought'.  That, at least, is one conclusion that all of us in British academia will currently find it hard to disagree with!