CityReads | The Environmental Origins of the Black Death

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The Environmental Origins of the Black Death

The black death is a clear case of the teleconnections that existed between environment and society

Bruce M.S. Campbell，evening lecture, 25 February 2016, International Conference “The Crisis of the 14th Century. ‘Teleconnections’ between Environmental and Societal Change?”, German Historical Institute, 24-26 February 2016.

Bruce M. S. Campbell. 2016. The Great Transition: Climate, Disease and Society in the Late-Medieval World, Cambridge University Press.

Sources：https://mittelalter.hypotheses.org/7868

https://www.bilibili.com/video/BV1Mz411b7Vt/

The other day, I watched a lecture by Bruce M. S. Campbell, titled The Environmental Origins of the Black Death. It is very informative, insightful, and enlightening. His thread of analysis offers implications for understanding the origin of the novel coronavirus.

Bruce Campbell is Emeritus Professor of Medieval Economic History at the School of Geography, Archaeology and Palaeoecology, Queen's University Belfast. He gave this talk as an evening lecture in an international conference “The Crisis of the 14th Century. ‘Teleconnections’ between Environmental and Societal Change?”hosted by German Historical Institute on 25 February 2016.  His talk is largely based on his book, The Great Transition: Climate, Disease and Society in the Late-Medieval World.

Even back in the medieval era, human being lived in a world where disease spread globally. It took 80 years for the plague to spread from Central Asia to Europe with devastating consequences. Now virus travels much faster. Within months, the novel coronavirus has spread to 1810 countries/regions and infected over a million people.

There is a close connection between the emergence of new virus and environmental change. Climate change and global warming probably paly an important part.

It was not until 2010 that scientists have reached a clear understanding of the plagues. I guess it will take much longer time than we expect to understand the novel coronavirus.

1 Teleconnections between climate, environment, plague and society

The 14^th witnessed profound changes in established patterns of atmospheric circulation.

Along with the decrease of precipitations, Europe in the 14^th century witnessed subsequent famines, panzootic, and harvest failure.

The century also witnessed dramatic changes in population levels and trends.

The contraction in population brought about a corresponding contraction in economic output.

In terms of GDP per head, loss of numbers proved to be beneficial for England and Holland, a mixed blessing for Italy, and a significant setback for Spain.

If plague was material to the reduction in population, and, thus, economic output

Was climate change material to the re-emergence of plague?

David Zhang and others stated,“climate change was the ultimate cause, and climate-driven economic downturn was the direct cause, of large-scale human crises in preindustrial Europe and the northern hemisphere”.

This claim patently fails to do justice to the complexity of human actions and reactions, let alone the autonomy of biological agents. In the case of the large-scale human crisis of the 1340s, climate's impact upon society was mediated through the intervening influence of ecology, disease, microbes and many aspects of human behavior.

The Black Death constituted a massive and enduring biological shock, the outcome of a unique conjunction of climatic, ecological, biological and human circumstances. Collectively, these transformed a long-dormant enzootic infection of sylvatic rodents, largely confined to Arid Central Asia, into a fast-spreading ‘global’pandemic of humans.

Plague, whatever its origin, constituted a massive and recurrent biological shock. It killed producers and consumers in equal measure.

By 1400, c.50 million Europeans had succumbed to the Plague.

Epidemiologically, genetically, demographically, economically and in many other ways the Black Death cast a very long shadow.

2 Plague: the identity of a killer

Not until October 2010 were clinching results from aDNA analysis published which established beyond reasonable doubt that the Black Death was indeed, vector-borne Yersinia pestis.

Yersinia pestis has now been identified in dental remains from datable 14^th-century plague burials in 5 Western European countries: France, Italy, Southern Germany, The Netherland, and England.

Yersinia pestis is a bacterial infection.

Wild rodents are its maintenance hosts and commensal(i.e. domestic)rodents its amplifying hosts.

Bites by insect vectors, primarily fleas, are its most common form of transmission, although it can be contracted in a variety of other ways.

Occasionally its crosses over and infects human and, on occasion, can ignite and spread as a devastating pandemic.

Plague has existed in the wild for millennia as a sporadic enzootic disease of ground-burrowing rodents, responsible for only the occasional human fatality. Yet in the sixth century, the fourteenth century and the nineteenth century it crossed over and became a devastating pan-continental human pandemic.

Historically, there have been three great human pandemics beginning respectively in the 540s, 1340s and 1850s.

Genetic reconstruction has yielded the following key conclusions:

1)Y. pestis evolves clonally; small mutations differentiate plague’s different branches (polytomies) and strains.

2)Fresh polytomies are prone to emerge during major epizootics/ panzootics.

3)Almost all strains are capable of infecting and killing humans.

4)There is nothing to suggest that the genomes responsible for the Black Death were more dangerous than any others.

5)The first and second Pandemics arose from different crossovers of the pathogen from animals to humans

6)The plague genome embodies its own evolutionary history and pattern of spread.

7)Individual strains tend to be country-specific.

8) Regions where plague has existed longest tend to exhibit the greatest genomic diversity and the presence of the earliest genotypes.

9)Geographically, the semi-arid Qinghai-Tibet Plateau of Western China appears to have been the ultimate origin of the Black Death，where plague had long persisted as an enzootic infection of the region's ground-burrowing gerbils and marmots.

10)Temporally, the Black Death genome emerged during a biological “big bang”shortly after 1268 or 1282.

11)Environmental conditions in Arid Central Asia between the mid-13^th and mid-14^th centuries were therefore fundamental to plague’s re-emergence and spread.

A sequential ‘plague cycle’ comprises five main stages: enzootic, epizootic, panzootic, zoonotic and pandemic.

Historically, climatic conditions in Arid Central Asia have exercised a powerful influence upon the incidence of plague, either lowering or raising the risks of enzootic plague becoming amplified into epizootic and then panzootic plague etc.

3 Climatic conditions influence plague’s behavior in 5 main ways:

Plague is a vector-borne disease and, as such, especially susceptible to changes in climatic and therefore environmental conditions, since the pathogen and its hosts and vectors are all directly and indirectly responsive to ecological influences.

1) Ecologically via the supply of food to sylvatic rodent hosts and hence the density and survival of host populations.

2) Via the host-dependent growth of vector (i.e.flea) population.

3) Via the effects of temperature and humidity upon the bacterium itself.

4) Via the effects of temperature and humidity upon flea activity.

5) Interactions between factors 1-4.

Ecological stress in Arid Central Asia, generated by increased climate instability, appears to have ignited the epizootic that led to the Black Death.

As, from c.1310, aridity eased, plague spread westwards from its source in Qinghai along the caravan routes that traversed desert and mountains to reach Issyk-Kul in Kirgizia by 1338.

The chronology of plague’s spread

Over a period of approximately 80 years, with gathering momentum, plague spread westwards from the Tibetan-Qinghai Plateau of western China to Europe’s Atlantic seaboard.

4 Conclusions

The black death is a clear case of the teleconnections that existed between environment and society as change cascaded through the Old World socio-ecological system in complex and unpredictable ways and with transformative results.

Plague’s biological re-activation from a dormant enzootic state to a more virulent epizootic state occurred in ACA during the late-13^th and early-14^th centuries under conditions of mounting ecological stress generated by the alternation of drought and pluvial events, as global atmospheric circulation de-stabilized and changed.

Plague’s subsequent crossover from sylvatic-rodent maintenance hosts to amplifying commensal-rodent hosts and its wholesale transmission to humans as a zoonotic or fast-spreading pandemic with soaring fatalities then occurred during the marked climate and environmental anomaly of the 1340s.

The fate of late-medieval European populations, in fact, was intimately bound up with environmental developments taking place more than six thousand kilometres to the east in the semi-arid and sparsely populated interior of central Asia, for without the ecologically triggered eruption of the Black Death the trajectory of socio-ecological trends would undoubtedly have followed a different course. Microbial-scale developments in this case had macro-scale consequences.

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