Historians have long known that the middle of the sixth century was a dark hour in what used to be called the Dark Ages, but the source of the mysterious clouds has long been a puzzle. Now, an ultraprecise analysis of ice from a Swiss glacier by a team led by McCormick and glaciologist Paul Mayewski at the Climate Change Institute of The University of Maine (UM) in Orono has fingered a culprit. At a workshop at Harvard this week, the team reported that a cataclysmic volcanic eruption in Iceland spewed ash across the Northern Hemisphere early in 536. Two other massive eruptions followed, in 540 and 547. The repeated blows, followed by plague, plunged Europe into economic stagnation that lasted until 640, when another signal in the ice—a spike in airborne lead—marks a resurgence of silver mining, as the team reports in Antiquity this week.
Kyle Harper, author of the excellent The Fate of Rome: Climate, Disease, and the End of an Empire, is quoted in the piece. It’s curious to me to observe the stochastic and correlated events in this particular story.
I assume that volcanic mega-eruptions occur in a pattern defined by a Poisson distribution. That is, they are rare and random events. One thing about the Poisson distribution is that the events tend to cluster together more than human intuition would predict based on what we think might occur when we hear “random events.” Those with more paleoclimate knowledge that I can evaluate this, but it seems that massive eruptions that occurring so close in time are going to be rare indeed, but, they will happen now and then.
That’s the random part. The outbreak of plague is probably less random. In Europe, the plague faded in the early modern period. Though people disagree about the reasons, modern developed societies where people are more well-fed are probably less susceptible to it (as well as low-density hunter-gatherer or pastoralist populations). As Peter Turchin has pointed out only one sitting European monarch died during the Black Death of the bubonic plague, even as 30-60% of the local population succumbed. It seems likely that extremely difficult conditions for agriculture, and the consequent malnutrition, made the spread of plague through vulnerable populations much more likely.
A major consequence of the calamities of the mid-6th century is the reconquest of the West Roman Empire under the push from Justinian and his heirs lost steam. Unlike in China, the Roman system was never recreated in full. Many explanations have to do with the violence of the Gothic Wars, or the inability of East Roman power to expand west while dealing with a more vigorous Persia to the east. We can’t rerun the experiment, but the above volcanic eruptions suggest that the likelihood of total reconquest took a major hit because of an event that was not inevitable.
Remember that the Roman state recovered by near total unwinding in the middle of the 3rd century.
Though we will never resolve the issue of whether the fall and collapse of the Roman Empire was inevitable and its reassembly impossible, by looking in totality at volcanic events and seeing how it correlates with state-formation or collapse, and social complexity, we may get a sense of the nature of the balance of endogenous cyclical forces and exogenous random shocks in the rise and fall of polities. By endogenous cyclical forces, I’m referring here to social cohesion and elite unity, which over time degrades and decays. As states and societies fracture and a new cycle of integration begins anew. I suspect that the exogenous shocks occur periodically, but that if they slam a society at its peak, then the social structure may be able to absorb the shock. In contrast, societies under stress collapse due to unexpected perturbations.