The present is not the first period in which it rained too little in Central Europe: At the transition from the Medieval Warm Age to the Little Ice Age between 1302 and 1307, there were also periods of extreme drought. Researchers have reconstructed this on the basis of historical documents. The climatic situation at that time shows parallels to today’s weather events, such as the very warm, dry summer of 2018. The reasons for this could have been particularly stable high and low pressure areas as well as decreasing temperature differences between the Arctic and mid-latitudes.
From 1315 to 1321 Europe experienced the greatest famine of the millennium. It had been preceded by a few cold, damp years with poor harvests. This is well documented from climate archives such as tree rings. So far, there has been a lesser scientific focus on the previous years. They mark the beginning of a phase of rapid climate change, which is known as the “Dante anomaly” after the Italian poet Dante Alighieri. The following 1310s are considered to be a transition phase from the high medieval climate anomaly, which was characterized by relatively high temperatures, to the Little Ice Age, which brought a cool and humid climate.
Historical documents as sources
A team led by Martin Bauch from the Leibniz Institute for the History and Culture of Eastern Europe (GWZO) has now taken a closer look at the “Dante anomaly”. To do this, they consulted numerous historical sources: regional chronicles, city books and administrative documents from today’s France, Italy, Germany, Poland and the Czech Republic. Among other things, they found information on crop yields and city fires – important indicators for climatic factors such as temperature and precipitation.
“We want to show that historical climate change can be reconstructed much better if not only climate archives such as tree rings or sediment cores are used, but also historical sources,” explains Bauch. “The inclusion of research in the humanities makes a significant contribution to better understanding the social consequences of climate change in the past and to drawing conclusions for the future.”
Extreme droughts in Europe
According to the analyzes, there was severe drought south of the Alps from 1302 to 1304, while at least 1302 north of the Alps was still quite rainy. This changed between 1304 and 1306, however, and the regions north of the Alps were also particularly hot and dry, combined with crop failures and city fires. “Sources from the Middle East also report severe drought. For example, the Nile carried unusually little water. We therefore think that the 1304-06 drought was not just a regional phenomenon, but probably had transcontinental dimensions, ”reports Bauch’s colleague Thomas Labbé.
Based on the historically documented effects, the team reconstructed the weather conditions in the summer of 1302 to 1307. By evaluating the drought of 2018 and similar extreme events, it is now known that in such cases a so-called “precipitation swing” often prevails: extremely high rainfall in part of Europe and extremely low rainfall in another. “The reason for this is usually in stable high and low pressure areas that remain in one region for an unusually long time. In 2018, for example, very stable lows were long over the North Atlantic and Southern Europe, which led to heavy rainfall there and an extreme drought in between in Central Europe, ”explains co-author Patric Seifert from the Leibniz Institute for Tropospheric Research (TROPOS).
Transitional period with parallels to today
According to the study, a stable high over Central Europe could also have been between 1303 and 1307, accompanied by a severe drought. According to current knowledge, such stable extreme weather conditions can arise from the fact that the temperature differences between the Arctic and mid-latitudes decrease and so the atmospheric dynamics decrease. This topic is currently particularly relevant, as the Arctic has warmed more than twice as much as other regions in the past few decades. “Even if it was a phase of cooling in the Middle Ages and we are now living in a phase of man-made warming, there could be parallels: The transition period between two climatic phases could be characterized by lower temperature differences between the latitudes and cause longer-lasting general weather conditions, what could explain an increase in extreme events, ”said Seifert.
Despite the possible parallels between medieval and today’s climate change, the researchers point out that the study hardly allows conclusions to be drawn about the future development of our climate: “While natural fluctuations in the climate still dominated in the 14th century, today it is the influence of the People on the climate, ”says Bauch.
Source: Martin Bauch (Leibniz Institute for the History and Culture of Eastern Europe) et al., Climate of the Past, doi: 10.5194 / cp-16-2343-2020)