“Unraveling the Threads of Time: Ancient Climate Shifts and Infectious Disease Outbreaks in the Roman Empire”
For those fascinated by the ebb and flow of the Roman Empire, a connection between ancient climate shifts and the outbreaks of infectious diseases is worth considering. According to historian Kyle Harper and colleagues, who reported their findings on January 26 in Science Advances, periods of cooler temperatures and reduced rainfall coincided with three pandemics that affected the Roman Empire.
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Roman Empire
The study, based on climate reconstructions spanning from 200 B.C. to A.D. 600, suggests a strong link between cold, dry phases and the severity of disease outbreaks. Harper, from the University of Oklahoma in Norman, notes that these findings help illuminate the role of climate stress in contributing to the spread and severity of mortality due to diseases.
Harper has previously proposed that the First Plague Pandemic, also known as the Justinianic Plague, in combination with declining global temperatures, played a role in weakening the Roman Empire. The recent findings support the idea that climate shifts can influence the origin and spread of infectious diseases, according to Princeton University historian John Haldon. However, uncertainties persist about various factors in the ancient Roman realm, such as long-distance trade networks and densely populated settlements, which may have heightened vulnerability to disease outbreaks.
To reconstruct the ancient climate, marine palynologist Karin Zonneveld and her colleagues analyzed fossilized dinoflagellates from sediment cores in southern Italy’s Gulf of Taranto. Different species of these single-celled algae, which live in the upper part of the sea, exhibit distinct shapes in late summer and autumn. By tracking changes in the composition of dinoflagellate species, the researchers estimated late summer/autumn temperatures and changes in rainfall during the Roman Empire.
The analysis revealed that warm, stable temperatures and regular rainfall characterized the Roman Warm Period from around 200 B.C. to A.D. 100, corresponding to a time of political and social stability for the Roman Empire. Subsequently, periods of colder and drier conditions preceded or occurred during three pandemics: the Antonine Plague, the Plague of Cyprian, and the Justinianic Plague.
Despite the correlation, it remains unclear how high death rates rose during these disease outbreaks and their role in the empire’s decline. The study points out that the Roman Empire experienced a significant decrease in power and influence around the time of the Justinianic Plague, with the eastern half lasting until the fall of Constantinople in 1453.
While the study provides valuable climate information from ancient Roman times, there is no certainty about how temperature and rainfall shifts may have facilitated the spread of infectious diseases, according to classical archaeologist Brandon McDonald of the University of Basel in Switzerland. The specific disease-causing agents for the Antonine Plague and the Plague of Cyprian also remain unknown, complicating efforts to explain the influence of climate on these events.
Economic and social historian Colin Elliott suggests in his new book, “Pox Romana,” that many infectious microbes thrive under cold, dry conditions. He argues that during cold years, grain production in Italy and other parts of the Roman Empire may have suffered, leading to hungry people migrating to cities where imported grain was available, potentially increasing pandemic virulence.
The study also raises the intriguing possibility that cooler and drier autumns reduced malaria cases, according to Ohio State University historian Kristina Sessa. The milder climate may have affected or killed temperature-sensitive mosquitoes that transmitted the disease regularly in southern Italy.
