Nutrition is a basic requirement for a healthy bio-terrain. During acute food shortages consequently, mass sickness leading to death occur.
Dramatic climatic fluctuations in the early 14th century were responsible for Europe's Great Famine of (1315-1321) and the Black Plague Black Death (1346-1353).
""The 14th century is one of the most dynamic centuries of the Middle Ages," said Seung Hun Baek, an earth and environmental sciences graduate student at Columbia University who presented the new findings this week at AGU's Fall Meeting 2019 in San Francisco. "This is when the [Black Death] happened, it's when the Hundred Years' War for the French throne was happening, it's also when the Irish independence movement was going on."
The Hundred Years' War, which began in 1337, and Black Death, which reached Europe in 1347, were as devastating as they were, in part, because they happened in the context of a Europe already weakened by years of hunger from the Great Famine. This was a "whopper of an event in a whopper of a century," Smerdon said."
"Europe's Great Famine of 1315–1317 is considered one of the worst population collapses in the continent's history. Historical records tell of unrelenting rain accompanied by mass crop failure, skyrocketing food prices, and even instances of cannibalism."
""When we think about extreme hydroclimate events, we talk a lot about drought," said Jason Smerdon, a paleoclimatologist with Lamont-Doherty Earth Observatory and lead author of the study. "But this was a deluge. And both of those things are going to be more frequent as a consequence of climate change."
https://phys.org/news/2019-12-europe-worst-famines-devastating.html"The transition from the Medieval Warm Period to the Little Ice Age was apparently accompanied by severe droughts between 1302 and 1307 in Europe; this preceded the wet and cold phase of the 1310s and the resulting great famine of 1315-21. In the journal Climate of the Past, researchers from the Leibniz Institutes for the History and Culture of Eastern Europe (GWZO) and Tropospheric Research (TROPOS) write that the 1302-07 weather patterns display similarities to the 2018 weather anomaly, in which continental Europe experienced exceptional heat and drought. Both the medieval and recent weather patterns resemble the stable weather patterns that have occurred more frequently since the 1980s due to the increased warming of the Arctic."
"According to the Leibniz researchers' hypothesis based on their comparison of the 1302-07 and 2018 droughts, transitional phases in the climate are always characterized by periods of low variability, in which weather patterns remain stable for a long time."
"The Great Famine (1315-1321) is considered the largest pan-European famine of the past millennium. It was followed a number of years later by the Black Death (1346-1353), the most devastating pandemic known, which wiped out about a third of the population. At least partially responsible for both of these crises was a phase of rapid climate change after 1310, called the 'Dantean Anomaly' after the contemporary Italian poet and philosopher Dante Alighieri. The 1310s represent a transitional phase from the High Medieval Climate Anomaly, a period of relatively high temperatures, to the Little Ice Age, a long climatic period characterized by lower temperatures and advancing glaciers."
"Based on the recorded effects, the team reconstructed the historical weather conditions between the summer of 1302 and 1307. Through evaluations of the 2018 drought and similar extreme events, it is now known that, in such cases, a so-called 'precipitation seesaw' usually prevails. This is the meteorological term for a sharp contrast between extremely high precipitation in one part of Europe and extremely low precipitation in another. "This is usually caused by stable high and low pressure areas that remain in one region for an unusually long time. In 2018, for example, very stable lows lay over the North Atlantic and southern Europe for a long time, which led to heavy precipitation there and an extreme drought in between in central Europe," explains meteorologist Dr. Patric Seifert from TROPOS"
https://phys.org/news/2021-01-drought-century-middle-ageswith-parallels.html?fbclid=IwAR05jJiBCLbP-p1_iOPKX2_0AgUB3Q-2r1lpIPciO7OzVZVTq5vxKPJTGAQOf course there is an assumption that a flea carrying a bacteria riding on a rat made its way to Europe along the Silk Road from, you guessed it, China.
https://simple.wikipedia.org/wiki/Black_Death"Ancient septicemic plague epidemics were reported to have killed millions of people for 2 millenniums. However, confident diagnosis of ancient septicemia solely on the basis of historical clinical observations is not possible. The lack of suitable infected material has prevented direct demonstration of ancient septicemia; thus, the history of most infections such as plague remains hypothetical. "
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC22883/"Because of the limits inherent in historical sources on ancient plague epidemics, many questions concerning their etiology and epidemiology remain unanswered. Molecular biology tools and the use of dental pulp as a preserved source of bacterial DNA enabled us to demonstrate that Yersinia pestis was the etiologic agent of the 1347 European Black Death and of two additional epidemics in 1590 and 1722 in southern France."
https://www.sciencedirect.com/science/article/abs/pii/S1286457901015155?via%3DihubBut for dramatic climate change, millions would not have died in the first half of the 14th century.