Climatic evolution in the Early Middle Ages

The climate of each region on earth is the result of the interaction of large-scale systems with local physical features, especially topography and hydrography, which in the Mediterranean Basin, were very complex. To fully understand the consequences of climate change in the past, it should be noted that food production in the ancient world was the basis of economy, as well as the creation and distribution of wealth. In a context of limited storage and interregional transport, severe climatic anomalies could disrupt the production chain and food supply, creating serious famines, followed by plagues, human and animal mortality.

Up until the second century, the Roman Empire enjoyed an extraordinarily optimal climate that scientists called Roman Climate Optimum, with warm temperatures documented by the growth rings of Alpine trees, which also shows the sharp regression of glaciers. This relatively stable, warm and humid climate with conditions that kept the variability of Mediterranean weather to a minimum, was quite favorable to intensive farming. In fact, many historians associate this specific climate to the economic growth and consolidation of military and political power, that defined the Roman world and its territorial expansion.

In the mid to late fourth century, multiple indicators suggest increasing warming that peaked with a drought between 338 and 377, which was one of the longest in the late Holocene, perhaps due to the El Nino phenomenon. Some believe that the drought in the late fourth century would have prompted nomadic groups known under the name of Huns to seek out new lands west and south of the River Don. They crossed that river in 375, forcing the Goths into the land of the Roman Empire. Three years later, at the Battle of Adrianople, which is present day Edirne in Turkey, they defeated the Romans in one of the biggest military disasters in history.

This marks the start of the displacement of other groups, effectively leading to the disappearance of the Western Empire within a few decades. Another long phase of instability, which lasted 30 years from 536 to 660, was probably caused by one or more volcanic eruptions dated from glacier sediments in Greenland. Those eruptions shot enormous quantities of sulfates in the stratosphere, causing particularly low solar radiation. In fact, contemporaries of that period called 536-37 “the year without summer”, reflecting the drop in temperature. The phenomenon is confirmed by tree rings in the Alps and Russia’s Altai mountains, especially by the unusual evolution of glaciers in the Swiss Alps. This phenomenon has led scholars to define this period as the Late Antique Little Ice Age.

The worsening of the climate is described by contemporary writers such as Cassiodorus and Procopius of Caesarea, who mentioned how colder weather had provoked serious food shortages for people and animals. Consequently, the army went without its rations of wine, foxtail millet, and bread, usually taking from the districts of Concordia, Aquileia and Cividale. In addition, the increase in rainfall and the resulting episodic floods created serious environmental disasters. Albeit very cautiously, scholars have associated this dramatic change in climate and the resulting malnutrition with the Plague of the Justinian era that caused many deaths between 541 and 750.

The same climate event may have also caused the migration of some populations, such as the Avars and the Slavs, who moved westward in search of new opportunities after the collapse of the Western Roman administrative structure by the end of the fifth century. The arrival of the Avars to Pannonia, which is present-day Hungary, in 550, pushed the Lombards towards Italy, which they invaded in 568. In Greece, the raids of the Slavic populations provoked migrations towards Southern Italy.

Even in Northern Europe, in the Baltic area north of the Oder river, which is the border between Germany and Poland, multidisciplinary studies point to climate change as the motivator for southern migrations that produced numerous abandonments and the gradual depopulation of that area between the fifth and twelfth centuries. Starting in the late seventh century, a better climate returned with a period known as the Medieval Warm Period, which ended around the middle of the thirteenth century. Atmospheric circulation in the North Atlantic would have favored the prevalence of dry, warm air, with temperatures similar to the present day and subsequently, an increase in agriculture in marginal areas or high elevations.

It was also the period in which the Vikings began settling in Iceland and Greenland, when grapes could once again be grown in England, Norway, and on the Baltic Coast. In the Alps, the tree line extended up to 2000 meters above sea level, much higher than today. It is inevitable to then associate climate stability with the positive demographic trends that occurred in many parts of Europe, starting in the eighth century.