Historians and climatologists have suspected for some time that there could be a link between outbreaks of plague, the fall of the Roman Empire and the climate of the time: the Roman Empire is said to have experienced its heyday during a period of unusually hot weather. This Roman Period optimum, also known as the Roman Warm Period, is dated to around 200 BC to 150 AD.
Cold climatic conditions from 540 AD – referred to as the Little Ice Age of Late Antiquity – are said to have played a key role in the fall of the Roman Empire. A research team led by Karin Zonneveld from the University of Bremen in Germany has now examined these assumptions – using deep-sea deposits in southern Italy. This is possible using paleoclimatological methods.
Climate archives provide data
Climate measurements using measuring instruments go back around 250 years in Europe. However, previous climate history, paleoclimate, can be reconstructed indirectly, namely through climate archives. These could be fossils, stalactites, and tree rings – anything that contains information about past climate conditions. For example, air bubbles trapped in Antarctic ice can be used to examine air from thousands of years ago.
The data provided by climate files is called proxy data. As a climate archive for the present study, now published in the journal “Science Advances”, the research team used marine sediments from the Gulf of Taranto, namely fossilized remains of plankton. The proxy data comes from the cysts that this type of plankton – dinoflagellates – form.
Henrie – stock.adobe.com The research team used sediments from the Gulf of Taranto as a climate archive
“If you take a sediment core and cut it into small slices, you can deduce from the composition of the cyst types what conditions existed in the sunlit upper waters at the time the sediments were deposited,” Zonneveld told science.ORF. at. From the proxy data obtained, temperature and precipitation records from the period 200 BC to 600 AD could be reconstructed. And with a temporal resolution of three years. In paleoclimatology, the interval between two data points that provide information about climate is specified.
“We were able to cut the core into such small slices that each slice represents approximately three years of sedimentary deposits. “If we analyze the composition of the cysts, we can reconstruct the average temperature conditions in southern Italy in the late summer and autumn of these three years,” says Zonneveld.
Three plague outbreaks in one cold spell
Using this data, researchers were able to observe how the climate in the Roman Empire developed over a period of 800 years: from around 130 AD, temperatures and precipitation became increasingly variable. Cold periods mark the end of the Roman Warm Period and coincide with historical pandemics: the Antonine Plague (circa 165 to 180 AD) and the Cyprian Plague (circa 251 to 266 AD).
The most devastating, however, was the Plague of Justinian, which broke out around 540 AD. Using the proxy data, the research team found that there was a sharp drop in temperature between 537 and 590 – it was about three degrees cooler than the warmest intervals of the Roman Warm Period.
“The first pandemic broke out when the climate became colder and began to fluctuate outside the range of relatively small climate variations that had occurred in previous centuries. The second and third pandemics each coincide with a new shift to a colder period with even colder temperatures,” said Zonneveld.
Did the cold lead to the fall of the Roman Empire?
But why do pandemics break out during cold spells? “We know that ancient Rome was an agricultural society: in Italy, wheat, wine and olive oil formed the basis of the economy. Along with the Nile Valley, Italy was also the most densely populated part of the Roman Empire. We also know that climate is an important factor that influences fundamental aspects that affect human well-being, such as agriculture, biodiversity, geographic distribution and species migration”, says the geoscientist.
Which of these factors or which combinations of factors caused or intensified the pandemics cannot be determined from the current study, but more research is needed. However, the results highlight the link between climate fluctuations and the occurrence of pandemics.
According to Zonneveld in the interview, it is “very difficult” to answer whether the cold periods from 130 AD were really decisive for the fall of the Roman Empire: “But we see that the times in which the Roman Empire expanded correspond to these times, where our records show relatively stable climate conditions. However, times of social instability and turmoil coincide with times when the climate has become very unstable.”
Learn from historical examples
But the research team was not only interested in the effects of natural climate change on people in the Roman Empire, but also – in light of the coronavirus pandemic – in the general links between climate and the dynamics of infectious diseases. Modern societies have completely different resources than people of ancient times, such as productive agriculture, global trade networks, and medical and scientific resources, but the coronavirus pandemic has shown the risks that still accompany infectious diseases, according to the authors of the study.
Then, as now, climate is “an important factor affecting fundamental aspects that affect our well-being: agriculture, access to clean water, biodiversity, geographic distribution and migration of species, including pathogens,” Zonneveld said. Examples from history can help you better understand these complex relationships.