Explaining Extreme Weather in the Middle Ages

What was causing extreme weather in the Middle Ages? A medieval historian is starting to examine how chroniclers and writers from this period were turning to the night sky to better understand and perhaps prevent natural disasters.

Halleys comet 1456

In his paper, ‘Managing Meteorological Hazards in the Early and High Middle Ages, 5th-11th Centuries’, Thomas Wozniak explained how he is looking at how medieval communities often used weather to explain unusual circumstances. The paper was given earlier this week at the International Medieval Congress at the University of Leeds.


Wozniak, who is currently doing a Post-Doctoral program at Philipps University Marburg, noted that it is important to understand the difference between weather and climate. Weather is the current state of the atmosphere and climate is the weather over a longer period of time; weeks, months, seasons or even years. Wozniak asserted that his paper was not about climate change because these weather and climate models are not useful at the micro scale level. “Weather is just one possible part of the framework in which politics and change occur,” he explained.

Wozniak’s research has involved compiling over 120 sources, such chronicles, annals and letter collections, that examined several specific weather related situations. At this point, he has decided not to use other types of sources, such as charters – which he notes rarely mention weather data, and are often forged so they are unreliable as accurate sources of information – or hagiographic material.


However, the sources he did use were not without their own set of problems. Annals could be written by different authors, and newer writers completing older annals. Writers from different regions might determine certain weather as colder than it really was if they came from a warmer climate, like Ibn Fadlan, the traveller who visited Bulgaria in the winter of 921/922. It was also important to consider the writer’s intent. Narratives that provide actual dates and times, are more likely eye witness accounts.

He also categorised his sources by region: Byzantine sources, Irish sources, etc. Wozniak noticed that the Byzantine descriptions were much wider and contained more information.

Wozniak gave examples of some how medieval writers looked for answers:

Locust Invasion of 873/874 AD

The hot summer of 872 created the perfect conditions for an excess of locusts. That year, there was a massive famine in parts of Europe and the locusts appeared in the words of one chronicler, “Like snow they covered the entire surface of the country. They were able to gnaw through the roughest tree bark.” The reactions to locusts were between scientific interpretation and prayer but oddly enough, no one likened it to the Egyptian plague of locusts from the Bible.

A Comet in Constantinople in 975 AD

In the History of Leo the Deacon, the author tells of how a comet that could be seen in the night sky for 80 days, “a marvelous and novel sight exceeding human understanding; for nothing of the sort had been seen in our time, nor had one shone previously for so many days.”


Leo goes on to explain:

When the emperor saw the unusual portent, he asked scholars of astronomy for their opinion on the significance of such phenomenon. And they interpreted the appearance of the comet, not as their technical knowledge would lead them to conclude, but in accordance with the wishes of the emperor, and declared that he would be victorious over his enemies and live a long life…But the appearance of the comet did not foretell these events, which the men told the emperor to please him, but bitter revolts, and invasions of foreign peoples, and civil wars, and migrations from cities and the countryside, famines and plagues and terrible earthquakes, indeed almost the total destruction of the Roman Empire, all of which I witnessed as the events unfolded.

You can learn more Thomas Wozniak, from his webpage at Philipps University Marburg