Almost everything is known about the Black Death. Which was the worst pandemic in history (some put the 1918 influenza before it). Which reached Europe first in coastal cities on the Mediterranean Sea. This came in ships loaded with grain, but also with rats and fleas, vectors of the causative bacteria, Yersinia pestis. The ships came from ports in the Black Sea and the Sea of Azov, which are gateways to the steppes of Central Asia. Genetics suggests that the deadly strain originated in wild rodents on the slopes of the Tien Shan Mountains, in modern-day Kyrgyzstan. But why did it erupt in 1347? Why not in 1348, 1350, or 10 years later? The answer is written on some pine trees in the Pyrenees.
Researchers from the University of Cambridge (UK) and the Leibniz Institute of Eastern European History and Culture (GWZO) believe they have found not the origin of the bubonic plague, which emerged in Central Asia, but why it punished Europe so severely and why they did so when it did. The epidemic peaked between 1347 and 1353, seven years in which between 80 and 200 million people died and changed European history forever. In the Iberian Peninsula, for example, the disease killed up to 65% of the population. In a work published in the scientific journal Earth and Environment Communications It details the sequence of events that led to the disaster.
They found the beginning of everything in many pine trees in the Central Pyrenees. They grow only in summer and strong or scanty growth appears in the rings of their trunks. What they discovered is that it has stopped for at least three consecutive summers since 1345. Raul Sanchez, from the Pablo de Olavide University, specializes in dendroclimatology. “As summer progresses, trees produce lignin, a polymer, to thicken their cell walls, so they don’t have a stroke,” explains Sanchez, who is not connected to the study. “When there is a cold thermal anomaly, its density decreases.” This is what the authors saw in trees sampled in northern Europe, the Alps, or Greece. “But when it gets too extreme, they stop producing lignin.” They have only seen this in the pines of the Pyrenees.
What is the reason for this cooling? By delving into historical records, they found references in Japanese, Chinese, German or English writings indicating the darkness of the sky for a very long time. After ruling out a solar anomaly, they saw in the ice cores a sign that several volcanic eruptions had occurred in the years before the start of the epidemic, a sign that coincided with the atrophy of tree rings. Specifically, an unknown volcano erupted in the summer of 1345. This eruption released 14 million tons of sulfides into the atmosphere. In comparison, the Pinatubo (Philippines) disaster in 1991 released six million gases and caused average global temperatures to drop by 1.5°C. In the years immediately before and after the main eruption, three other eruptions occurred in the Northern Hemisphere, although they were smaller in size.
European agriculture could not withstand three such cold years. There are records showing the loss of wine grape production in most of southern Europe. The worst was the failure of the grain harvest, and without wheat or barley, hunger came, especially in the cities. At that time, northern Italy was among the most urbanized regions. It was in these cities, the real powers of the time, such as Genoa or Venice, that the first plague outbreaks occurred. because?
“A city like Florence could be self-sufficient on its own production for only five months a year, and had to import grain even in good years,” recalls Martin Bausch, a medieval historian at the GWZO and co-author of the study. “Other small towns, such as Siena, were self-sufficient from their surrounding areas, but in case of poor harvests, imports were necessary,” Bauch adds. However, there were also large cities such as Milan or Rome that controlled territories so large that they never had to import grain. “It is important that these are cities where the Black Death did not spread,” he adds.
Faced with shortages and the threat of uprisings, Europeans looked east, to the steppes that had been, yesterday as today, a major grain producer. The problem is that at that time the Golden Horde was ruling and the two Italian powers, Genoa and Venice, were at war with the Mongols. “In the second quarter of 1347 both city councils pressed for a quick peace,” Bauch recalls. Already in the third quarter, ships laden with grain began to arrive at the ports of Mediterranean Europe. And with them the plague. Dates are appropriate. The first outbreaks all occurred in coastal cities. In Genoa, the nightmare began in November. In Palma de Mallorca and Marseille in December and already in January 48 in Venice. The opening of trade to the east prevented death from starvation, but brought about the Black Death.
Hannah Parker is a historian at Arizona State University. Parker, an expert on trade relations between medieval Europe and Central Asia, agrees with the authors: “In the period leading up to the Black Death, from the fall of 1343 to the spring of 1347, there was a struggle between Italian merchants (Genoese and Venice) and the Mongol ruler of the Golden Horde (Janibek Khan) over who should control the Black Sea ports,” says Parker, who was not involved in the study. He concludes that “the conflict ended in the spring of 1347 due to a combination of famine (pressuring the Italians to reopen the grain trade at all costs) and plague (pressuring the Mongols to stop fighting and focus on other priorities). The important contribution of this new article is to explain why the pressure of famine on the Italians was so strong in 1347, unlike any other year.”
A few years ago, Norwegian Niels Stenseth led work that showed how plague arrived in Europe in waves from Asia, driven by climate throughout history. Regarding the Black Death, he says, “Drought in Central Asia could have caused plague bacteria to spread from wild rodents to humans.” In contrast to the new study, he believes that “increased grain transport from Central Asia to Europe may have played a major role.” From the coastal cities it only took a little time to spread across the entire continent inhabited by people already suffering from cold and hunger.