Between 1347 and 1353, the Black Death spread across Europe, killing up to 60% of the population, leading to long-lasting demographic, economic, political, cultural, and religious changes which changed the continent, and eventually the world, beyond recognition. Recent palaeogenetic studies have now confirmed the long held belief that the pandemic was caused by the Plague Bacterium, Yersinia pestis, a zoonotic disease with wild reserves in a number of Rodent species. Despite the presence of a wild reserve, outbreaks of Yersinia pestis in Human and Domestic Animal populations are quite rare, with only three documented pandemics of the disease. The first of these, the Plague of Justinian, began around 541 AD, and persisted into the eighth century. The second, the Black Death, began around 1338 in Central Asia, and persisted in places into the early nineteenth century. The third began in China in the 1770s, and spread around the world; arguably this third Plague pandemic is still ongoing, with all wild reserves and outbreaks outside Asia apparently derived from this source.
Studies of the archaeological, historical and ancient genomic records have suggested that the Black Death was a genetically distinct strain of the Yersinia pestis Bacterium which probably originated in arid foothills of the Tien Shan mountains west of Lake Issyk-Kul in modern-day Kyrgyzstan. This spread along the trade routes of Central Asia, entering Europe via the northern Black Sea region in the 1340s. Notably, the Black Death abruptly entered Venice and other Mediterranean ports in 1347, presumably through the importation of infected Fleas from the Black Sea reason.
From this time, there were repeated outbreaks of Plague across Europe until the early nineteenth century, although it is unclear if these represent a series of re-introductions, or the presence of a wild-reserve within Europe. Nor is it entirely clear why the Plague appeared in multiple Mediterranean ports at the same time, having been established in the Black Sea region for some time prior to this, without previously making the jump, though it has been suggested by several people that some socio-economic challenge led to a change in Human behaviour at this time, giving the disease an opportunity to spread.
Bauche and Büntgen note that there has been extensive previous research into potential links between a volcanically induced climate crisis at the start of the Late Antique Little Ice Age and the onset of the Plague of Justinian, but little previous investigation into such a link to the onset of the Black Death. They also note that ice cores from Greenland and Antarctica have revealed a spike in sulphur concentrations in 1345 considerably larger than the one caused by the Mount Pinatubo eruption of 1991, which probably represents an injection of about 14 megatons of sulphur into the atmosphere. Furthermore, there were also major spikes in 1329, 1336 and 1341, representing eruptions which would have injected roughly 3.7, 0.7, and 1.2 megatons of sulphur into the atmosphere, respectively.
Weather records from Japan, China, Germany, France, and Italy, all record the years from 1345 to 1349 as being exceptionally cloudy. A lunar eclipse in 1345 is recorded as having been exceptionally dark by witnesses in both Bohemia and China; something which can be another sign of a high volcanic dust level within the atmosphere.
Studies of tree rings have shown that trees in the Spanish Pyrenees produced 'blue rings' in 1345 and 1346, which are interpreted as signs severe cold spells during the growing seasons affected growth. The production of blue rings in consecutive years is considered exceptionally rare. Studies of wood density across the Northern Hemisphere have suggested a progressive cooling from 1345 to 1347, with 1347 being the coolest year since 1257, when a cold spell was linked to an eruption on Mount Samalas on Lombok Island, Indonesia.
May–September (MJJAS) temperature anomalies from 1119–2020 AD (uncertainties are expressed by grey shading), based on 534 maximum latewood density (MXD) measurement series from living and relict samples from Mountain Pine, Pinus uncinata, trees from undisturbed upper treeline ecotones in the Spanish central Pyrenees. The pre-Black Death cold phase is indicated by the vertical blue shading. The right-side double-stained thin section shows two consecutive Blue Rings that were formed in 1345 and 1346 AD in a Mountain Pine, Pinus uncinata, from the upper treeline in the central Spanish Pyrenees. Bauche & Büntgen (2025).
While it is harder to assess rainfall in past than temperature, tree-ring data suggests that the cool period from 1345 to 1347 was accompanied by a prolonged west-east dipole in Europe, with wetter conditions around the eastern Mediterranean and dryer conditions around the western Mediterranean. Morocco, the British Isles, northern France, the Low Countries, Germany and southern Scandinavia, all appear to have suffered dry conditions, while the Iberian Peninsula, Italy, and the Balkans, had high spring and summer rainfall in those years.
Bauche and Büntgen also examined historical records from across Europe and beyond, which show a declining agricultural output from across Europe from 1345, and in particular a failure of (environmentally sensitive) Grape crops from northwestern Italy. Severe flooding was also recorded in Italy in the autumn of 1345 and the springs of 1346 and 1347, along with accompanying problems such as soil erosion. The winter of 1344/45 was exceptionally cold and snowy in the Middle East, with the winters of 1345/46 and 1347/48 being marked by drought and Locust invasions.
Late medieval Italy had a highly urbanised population, with a complex grain supply system in place to support this population. Many city states, including major centres such as Bologna, Florence, Genoa, Siena, and Venice, had limited farmland and large urban populations, consequently importing grain over long distances to redress this imbalance. Only Rome and Milan were largely self-sufficient. Cities developed communal granaries run by officials with the power to manage these granaries, source supplies of grain from elsewhere, and prevent the export of grain from cities troubled by poor harvests or military conflicts. Typically, managing grain supplies was the second-largest source of expenditure for any late medieval Italian city-state, behind only military spending. Maritime powers such as Venice, Genoa, and Pisa, negotiated treaties with grain-producing areas such as Apulia, Sicily, Sardinia, North Africa, the Aegean and the Black Sea region.
In 1346/7 severe famines were recorded across parts of Spain, southern France, northern and central Italy, Egypt, and the Levant. This led to spikes in the price of grain in Spain, Italy, Egypt, and even the Arabian Peninsula. Strict grain regulations were implemented in many Italian cities from 1346, at least in part to grain-shortage induced civil unrest.
Northern Italy suffered a series of famines during this interval, which appear unrelated to any political crisis, supporting a climate-related problem as the cause. Initially, this shortfall was met by increased imports from southern Italy, but it quickly became clear that this would not be sufficient to alleviate the crisis, and that more imports would be needed from further afield.
At this time, Venice and Genoa were in a state of conflict with the Mongols of the Golden Horde, who had been trying to eliminate Italian power in the Black Sea region. This had led to the Italian cities blockading the ports of the Black Sea, preventing the Mongols from trading with the Mediterranean. However, the onset of famine in Italy led to a re-appraisal of this situation, with a ceasefire and renegotiation of trading arrangements leading to a restoration of grain trading, saving Venice from starvation.
The Plague Bacterium, Yersinia pestis, had been present in the Black Sea region for some time, and it is likely that it would eventually have reached the Mediterranean at some point. However, Bauche and Büntgen contest that the lifting of the trade embargo against the Golden Horde in response to the volcanically-induced famine affecting northern Italy was the immediate cause of the Black Death reaching multiple Mediterranean ports in a short interval.
The trade embargo was lifted in 1347, and shortly thereafter, Venetian and Genoan trading vessels began entering the trading ports of the northern Black Sea and the Sea of Azov, returning to Italy laden with grain. The Plague appeared in Venice less than two months after the first such trading vessel. In March 1348 Venice lifted an embargo on the export of grain to Padua, with the first Plague outbreak there coming shortly after. Records of the grain trade to Florence and Sienna are less clear, but again the first Plague outbreaks in these cities were associated with the abating of the famine. Notably, this first wave of Plague outbreaks did not affect cities such as Rome, Milan,Verona, Ferrara, Ravenna, and Bari, which controlled larger grain producing areas, and were not involved in grain imports from the Black Sea region. Elsewhere around the Mediterranean, Marseille, Palma de Mallorca, and many other important port cities had Plague outbreaks before the end of 1347, probably as a result of grain shipments from Genoa. Smaller cities such as Savona, Ventimiglia, and Tunis, began to suffer outbreaks in April 1348, again probably linked to Genoan grain shipments. The reached Trento along with grain shipments from Venice, and from their spread across the Alps into northern Europe.
Grain trade and plague dispersal. Main aspects of the Venetian, Genoese, and Pisan grain trade network that prevented much of Italy from starvation in 1347 AD but also brought the Plague Bacterium, Yersinia pestis, to Venice and other Mediterranean harbours during the second half of 1347 AD, from where it spread rapidly. Location of the tree ring-based climate reconstructions is indicated (with two sites in Scandinavia not shown). Map is an equal-area, pseudo-cylindrical Mollweide projection with greyscale referring to elevations above sea level. Bauche & Büntgen (2025).
In 1344, a decade-long papal embargo on trade with the Mameluke Sultanate was lifted, enabling Italian merchants to resume trade with the Middle East. Following the resumption of trade with the Black Sea region, Venetian ships began carrying grain to Alexandria, and the ports of the Levant, while Mameluke traders began visiting the ports of the Crimea. While individual shipments are harder to trace for these ports than those of Italy, these ships are probably responsible for the arrival of the Black Death in North Africa and the Middle East.
Thus the resumption of trade with the Black Sea region appears to have resolved the immediate problem of a widespread famine, but also led to the simultaneous import of the Black Death to ports around the Mediterranean. The subsequent rapid spread and high fatality rate for the disease may also have been a result of a population weakened by famine. The sophisticated trade system developed by the Italian city states to ensure against famine appears to have made those states, and their allies around the Mediterranean and Europe, particularly vulnerable to the spread of the Plague. Bauche and Büntgen conclude that the Black was not just a singular event, but rather the culmination of a prolonged crisis which began with a climate crisis and then a famine.
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