By Thomas E. Lambert
The Byzantine Empire was affected by climate change. New research reveals how warming and cooling trends correspond to economic upswings and declines that took place in Byzantium.
Modern-day climate change has generated quite a bit of debate and concern among scientists, politicians, business people, economists, and people of all backgrounds. To better understand the effects that climate change will have upon us, it is useful to look at how it changed past societies.
Some researchers have analyzed how past climate changes could have affected and caused the decline of Imperial Rome, and others have shown the results of archaeological and geological findings that indicate the eastern part of the remaining half of the Roman Empire, the Byzantine Empire, probably was affected by climate changes such as the Late Antique Ice Age from around the 6th and 7th centuries AD; the Medieval Climate Anomaly (aka the Medieval Warm Period) from around the time of the 10th to the 13th centuries; and the Little Ice Age from around the 14th to 18th centuries. The findings mostly point to decreasing crop output thanks weather that was too cold or too warm, and these in turn have often been offered as to why the Byzantine Empire undertook conquest in order to get more land for more/better agricultural production for some foods, or why the empire was the victim of others attacking it in order to get more land and food production for their nations.
In a paper I wrote for the journal Human Ecology, I developed from historical accounts some estimates of the Byzantine Empire’s real Gross Domestic Product (GDP) per person in nomismata and an agricultural land output index of 0 to 1 (wheat production, a major staple) over the time of the empire’s life. Although approximations, the trend in Figure 1 shows that declines and upswings in Byzantine real GDP per capita roughly correspond to the three periods of climate change. During the Late Antique Ice Age, the empire suffered declines in economic output as noted by the downward trend in real GDP per capita shown in Figure 1. Some of this was due to declining agricultural productivity in the 6th century perhaps due to colder climate conditions then (see Figure 2) and losses in territory during the 7th century (see Figure 3) due mostly to setbacks on the battlefield. Perhaps the wars occurring during the 7th century in the region are due to rival nations looking for new territory to conquer in order to make up for failing crop production and better lands.
During the Medieval Climate Anomaly Period of the 10th to 13th centuries, Figures 1 and 3 show the fortunes of the empire at first improving and then declining. Real output or GDP per person climbs during most of this time period as the empire adds new lands with beneficial natural resources in the 10th and 11th centuries through conquest under the leadership of emperors such as Nikephoros II Phokas, John Tzmiskes, and Basil II. Yet these lands are later lost in subsequent decades. Estimated wheat productivity does well during the 9th century but then falls afterward and through the 13th century (see Figure 2). Too hot weather and too little rain harm wheat production and the yield of other types of crops, yet according to some historical accounts, the empire has enough of a warm weather assortment of crops to make up for lost wheat production. Since wheat is a staple of many other food items, the decline in wheat productivity, however, could have been a catalyst for the empire to undertake conquest opportunities, and if rivals were suffering from low agricultural output at this time, their food shortages could have made them easier to defeat on the battlefield.
The remaining centuries of the empire correspond to the first two centuries of what climate scientists call the Little Ice Age. Real output per capita continues to fall as the empire shrinks in size (see figures 1 and 3), and despite estimates of wheat output rising during the 13th and 14th centuries, it falls during the 15th century as the empire comes to the end of its existence in 1453 (figure 2).
As the empire gained and lost regions with vast natural resources, its real GDP per capita fluctuated correspondingly. At the same time, these fluctuations in territory and output also corresponded to past climate changes which could have either prompted territorial conquests by the empire or led to the empire losing land and other assets that were needed for continued economic growth. In the statistical models developed for my paper, conjectures by scientists for past climate variables such as temperature, solar irradiance, greenhouse gas emissions, tree ring growth data (for rainfall estimates), and volcanic ash are useful and statistically significant in predicting real GDP per capita trends when controlling for empire territorial size. These variables are also usually good predictors of the occurrence of Byzantine weather cataclysms (floods, droughts, etc.) that some historians have chronicled. Climate change seems to have mattered in the economic fortunes of the empire as others have shown through archeological findings, and the conjectures of real GDP per capita appear to support these.
Historians and other social scientists have often looked to events in the past in order to try to understand current events or to anticipate future events. In recent decades, estimates of economic data for different nations going back to ancient and/or medieval times have been created by various economic historians so as to help understand how societies transitioned from slavery to feudalism to capitalism. In studying the Byzantine Empire, we possibly can find clues as to how current climate change can affect the economies of societies throughout the globe. More likely than not, current and future global economic output will be affected by predicted rising temperatures due to global warming.
Thomas E. Lambert is Assistant Professor of Practice, Economics at the University of Louisville. Click here to visit his university webpage. His paper, “Byzantine Empire Economic Growth: Did Past Climate Change Play a Role?” is published in Human Ecology. Click here to read it.