This piece is part of HWO’s feature on ‘Apocalypse Then and Now’. The feature brings together radical reflections and historic perspectives on catastrophe and calamity. How have crises (both real and imagined), and responses to them, shaped our world?

Some years stand out in the historical record as especially momentous: 2020 will almost certainly be one of them, politically, economically, climatically and, above all, biologically. Within the space of months, a virus invisible to the naked eye has threatened the health, lives and livelihoods of millions. It has placed healthcare systems everywhere under immense and, in some instances, impossible strain; thrown all political plans into disarray; and precipitated a massive global downturn in both economic output and carbon emissions. The shock has been seismic and clearly its reverberations will be felt for a long time to come. By general consensus, there can be no return to the pre-pandemic status quo. Conceivably, even historians may begin to pay more attention to the role of natural agencies as tiny as microbes and as vast as global climate systems in shaping the course of history; and the fledgling subject of environmental history may win new converts among the Covid-19 generation of students.

There are plenty of precedents within the Old World for the crossover of infection from mammals to humans and the progression of disease from a panzootic, to an epidemic and, finally, a pandemic. This, after all, was the course taken by the Second Plague Pandemic, popularly known as the Black Death. The Black Death originated from the crossover of the potentially deadly bacterium Yersinia pestis from ground-burrowing wild marmots and gerbils either directly to humans or indirectly via commensal rats to humans. Its mechanism of transmission was more cumbersome than that of the virus Covid-19, since it typically involved insect vectors, notably fleas. Within its natural reservoirs, the bacterium, its ground-burrowing rodent hosts, their food supply, and the flea vectors that transmit the infection are all powerfully influenced by prevailing temperatures and levels of humidity. This makes plague one of the most intrinsically ecological of diseases.

“The people of Tournai bury victims of the Black Death”. Miniature by Pierart dou Tielt illustrating the Tractatus quartus bu Gilles li Muisit (Tournai, c. 1353). Wikimedia Commons.

Over the course of seven deadly years – between its first recorded European outbreak in 1346 at the besieged Crimean port of Kaffa and almost its last in the spring of 1352 at Pskov in Russia – the Black Death killed at least 25 million Europeans and claimed countless more victims in Central Asia, the Near East and North Africa. Few communities escaped unscathed from this first tsunami of infection. In a devout age, those in the front line were not health service staff but the clergy, who – as a result of ministering the last rites to the dying – themselves contracted plague and perished in great numbers. The human and environmental consequences of this catastrophic surge in mortality were immediate and profound. They were rendered all the more enduring by return visitations of the disease over the next 50 years, which decimated both the survivors and the children born to them. Populations shrank, the area required for food production contracted, woodland regeneration became widespread, and people became preoccupied with the fear of death and impermanence of life. For the next three centuries in Europe, plague periodically subsided but always returned. It was not until the end of the seventeenth century that plague, seemingly of its own volition, finally retreated and at last left the bulk of the continent plague free. In its Asian reservoirs, however, it remained endemic, with the potential always to re-emerge and inflict further suffering upon vulnerable human populations, as would occur when the Third Plague Pandemic ignited in 1855 in the Yunnan Province of China and thence was spread to seaports throughout the world.

In 1346, as in 2019, Europeans had little inkling of the fate that was in store for so many of them. They had other more pressing anxieties to preoccupy them than the as yet unknown disease spreading stealthily towards them along the highways and seaways that led west from Asia. Jobs, wage rates and living standards in the leading European economies were all under pressure from worsening economic conditions as international commerce succumbed to a deepening recession. War had already blocked the vital trans-Syrian caravan routes that linked the Persian Gulf with the Mediterranean. Those that terminated at the Black Sea either from the Persian Gulf or overland from China were now under threat, as the once mighty Mongol Empire fragmented. Banking failures added to these woes. In Florence in 1344 the last of the great merchant banks — the Bardi and Peruzzi companies — had collapsed into bankruptcy, brought down by changing market conditions, narrowing profit margins and accumulating bad debts. At that time the Italian economy was the richest and most advanced in Europe. As overseas markets were lost and its banking sector contracted, Italian GDP per head declined, dragging down the earnings and employment of the poorest with potentially destabilising political consequences in such crowded artisanal cities as Florence. Across Christendom, popular support for the peace and order — the Pax Christiana — promulgated by the church, that had underpinned centuries of European economic expansion, was also weakening, as the papacy became a political pawn and dynastic wars broke out on many fronts. Among the most costly and destructive was the claim to the French crown by Edward III of England. In 1346, to uphold that claim, an English army invaded France and in August shocked Europe with the unconventional defensive tactics used to score a great military victory against a far larger French army at Crécy. This victory would consign both kingdoms to over one hundred years of ultimately futile and ruinous conflict.

At Crécy, the wet weather responsible for the soft ground – which so encumbered the heavy and over-confident French cavalry – was simultaneously ruining grain harvests across Europe. Food scarcity became widespread; driving up prices, putting further downward pressure on living standards, and provoking grain riots. Explosive eruption of an unidentified equatorial volcano in or around 1344 (known from the ejected sulphate aerosols that settled over both poles where they have been preserved in datable layers of Greenland and Antarctic ice) may have been partly to blame. From a combination of historical and environmental evidence, however, it is plain that already in 1341/2 the weather was turning extreme. There were damaging storm surges in the southern North Sea and record-breaking floods in the Main and Danube drainage basins of central Europe; a sudden increase in the discharge of the Blue Nile fed by a revived Ethiopian monsoon; and, in China, onset of prolonged drought brought about by corresponding failure of the East Asian monsoon. No one at the time could have known this, but global patterns of atmospheric circulation were de-stabilising and shifting. One climate era, now known as the Medieval Climate Anomaly, was ending and the transition was well under way to the more unsettled and periodically colder conditions of the Little Ice Age. Within this transition the 1340s stand out as a pronounced short-term climate anomaly marked by depressed growing conditions and reduced tree growth almost everywhere.

Economic, political and environmental stress levels were therefore already high when, seemingly out of the blue, plague erupted with devastating and transformative effect. Both individually and collectively these burgeoning problems shaped plague’s emergence, spread and impact and greatly complicate the historical task of disentangling what difference the Black Death made to the changes that were already afoot. Help is nevertheless to hand from biologists, geneticists and palaeoclimatologists, whose breakthrough research is casting many aspects of this long-familiar episode in a fresh new light. Their work was already rekindling interest in, and reinvigorating debate about, the Black Death before the outbreak of Covid-19 made pandemics a hot topic.

Until a little over a decade ago historians had become bogged down in an increasingly arid and historically ultimately irresolvable debate about exactly what disease the Black Death was. This was a question to which written sources could never give a definitive answer. Instead, it was Michel Drancourt’s team of biologists at Marseille who realised that it might be possible to locate and identify the DNA of the killer pathogen within the dental pulp of known plague victims. Their early results, affirming that Y. pestis was indeed the culprit, were received with scepticism by both the scientific and historical communities. In 2010, however, they were confirmed using the most scrupulous methods by Barbara Bramanti’s Mainz-based team of researchers. Here at last, from analysis of Black Death burials in France, England, the Netherlands and Germany, was the scientifically conclusive forensic proof that had for so long been sought.

Excavation of a mass burial of bodies, known to be victims of the Black Death, at the site of a 14th-century monastery hospital at Thornton Abbey, Lincolnshire. University of Sheffield.

Further crucial insights followed. With little delay, the full Y. pestis genome sequence was reconstructed and published, against which all future DNA results could be matched. From this it became clear that, as the bacterium spread and mutated, specific strains became associated with particular countries. As a Chinese team of researchers led by Yujun Cui pointed out, this incriminated a plague reservoir in the semi-arid Qinghai-Tibetan plateau in western China as the most likely origin of the Second Pandemic. It is from a variant of the genome specific to this region that that most subsequent strains of plague have evolved. Earlier outbreaks, in contrast, notably the sixth-century First Pandemic often known as the Justinianic Plague, have recently been shown to have originated from a quite separate crossover of the bacterium from animals to humans. The quest is now on to use this genetic information to reconstruct plague’s pattern of diffusion, both before it reached Europe and after it reached Africa north and south of the Sahara. Meanwhile, debate continues as to whether the Black Death might have been spread directly between humans by the human flea and louse. Opinion is also divided as to whether Y. pestis was repeatedly reintroduced to Europe or a separate European reservoir of infection became established.

Little of this purely biological research paid much attention to the ecological circumstances prevailing when and where plague re-activated from a dormant enzootic state and then escalated to become a panzootic of rodents and zoonotic of humans. Nevertheless, knowledge of past climates and, therefore, ecological conditions was advancing equally rapidly, funded out of the political desire to know more about the back history of the scale, novelty and rapidity of the climate changes currently threatening the world. Before the availability of instrumental recordings palaeoclimatologists have to rely upon proxy climatic measures derived from such natural archives as the chemical content of stratified layers within polar ice cores; the annually-dated growth rings of living and fossil trees and timbers; the incremental growth within caves of speleothems (i.e. stalagmites and stalagtites); and the thickness and contents of sediment deposits in lakes and on the ocean shelf. This information is often expensive, difficult and even arduous to obtain but much of it is chronologically precise and often spans significantly longer periods than even the longest continuous historical records.

Although the palaeoclimatologists were as little interested in plague as the biologists were in past climates, Nils Chr. Stenseth of the University of Oslo saw the potential of combining both approaches and types of evidence. Towards that end he assembled an interdisciplinary team of biologists, ecologists, zoologists and dendro-chronologists to investigate the interactions between climate and plague within the long-established plague reservoir of Kazakhstan, for which an exceptional Soviet-era dataset was available. From this research emerged the critical insight that a clear connection existed between Central Asian climate fluctuations and regional human plague frequency in the first part of the twentieth century and ‘probably over the past 1,500 years’. Here was the missing link that explained the causal connection between the increasingly unsettled and often extreme climatic conditions of the first half of the fourteenth century and the outbreak of the Black Death. Their concurrence was no coincidence.

Thus, it was under conditions of extreme ecological stress in or near Qinghai in western China, sometime between the 1270s and 1340s, that what had begun as a panzootic of wild rodents crossed over to become a zoonotic that infected humans. The genie was then out of the lamp. In the absence of scientific knowledge and effective quarantine measures, the zoonotic swiftly escalated to become an epidemic and then a fast-spreading pandemic that engulfed the greater part of the known world (antibiotics, of course, would have stopped the disease in its tracks). The timing of all this proved crucial. After centuries of commercial and urban growth, the human preconditions for rapid diffusion of a deadly pathogen happened to be almost optimal. Once the plague-carrying caravans across the vast and thinly peopled spaces of Central Asia reached the crowded and busy commercial ports of the Black Sea, with their maritime connections throughout the Mediterranean trading world and beyond, the disease’s spread accelerated and became unstoppable.

The realisation that climate change, extreme climatic events, ecological stress, and the re-activation of a deadly pathogen were all intimately interconnected has proved both revelatory and transformative. A seismic historical event previously viewed from an almost exclusively western perspective has been revealed as a complex and multi-faceted phenomenon, with an Asian origin but known-world reach. The climate forcing which appears to have set the Black Death in motion was global, while far-reaching and long-established human interconnections ensured that the disease eventually infected three continents: Asia, Africa and Europe. Documentary sources and historical methods alone could not have yielded these insights, refocused perceptions of this event, or generated so much debate and research across such an array of academic disciplines. Nor, indispensable though they are, can written records by themselves provide answers to the many outstanding questions still posed by the Second Pandemic. Progress will come from combining the approaches and evidence of historians with those of natural and environmental scientists, including bioarchaeologists. Direct collaboration between historians and scientists may prove particularly productive.

With the post-pandemic future still so unclear, curiosity about the lessons to be learned from past interactions between climate, disease and society has never been greater. This presents both a challenge and an opportunity to historians in the new post-Covid-19 world. For those prepared to move outside their traditional humanities comfort zone, there are exciting opportunities for fruitful interdisciplinary engagement to be seized, with all the valuable academic insights that are likely to flow from them. Re-examining the past from this broader perspective is also likely to resonate with many and affirm why knowledge of an event as remote from us as the Black Death is so relevant to making sense of the comparable crisis of public health unfolding across the world today.

Bruce Campbell is Professor Emeritus of Medieval Economic History at The Queen’s University of Belfast, a Member of the Royal Irish Academy and Fellow of the British Academy. He is the author of The Great Transition: Climate, Disease and Society in the Late-Medieval World (CUP, 2016), awarded the 2017 biennial Gyorgy Ranki Prize by the Economic History Association for an outstanding book in European economic history. You can listen to podcasts of his 2013 Ellen McArthur Lectures, 2008 Tawney Memorial Lecture, ‘Nature as historical protagonist’, and 2016 lecture, ‘The environmental origins of the Black Death’. He is currently working on the economic and environmental history of late-medieval Ireland.

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