Roman Plagues Struck During Cool, Dry Periods – GWC Mag

Major disease outbreaks periodically struck southern Italy during the Roman Republic and Roman Empire. Researchers have now confirmed that at least three of those pandemics took hold when climate conditions in the region were cooler and drier than normal, suggesting that climate may have played a role in the spread of disease.

In a recent study published in Science Advances, paleoceanographer Karin Zonneveld of the University of Bremen in Germany and her colleagues concluded that a periodic 1°C–3°C air temperature change between 100 CE and 600 CE contributed to significant stress on Roman societies.

Their discovery does not explain how or why diseases thrived when the climate cooled, however.

The researchers used a sediment core from the Gulf of Taranto, which lies between the heel and foot of Italy’s boot and collects material flushed from the Adriatic and Ionian seas.

Thanks to well-documented volcanic eruptions that deposited layers of ash in the region, the sediment core has clear time stamps, explained coauthor Gerard Versteegh, an organic geochemist also at the University of Bremen. In addition, the sediments accumulated rapidly and were not stirred up much by plants or insects over time, so the layers are preserved in relatively pristine conditions.

“That is a kind of ideal combination,” Versteegh said.

The team analyzed precipitation and temperature histories hidden in the sediment using more than half a dozen different paleoclimate markers, including dinoflagellate cysts and pollen.

Combining their analyses with existing tree ring and speleothem records from nearby locations, the researchers created a 3-year-resolution climate reconstruction for southern Italy from roughly 200 BCE to 600 CE.

They showed that during this period, the Antonine Plague (onset ~165 CE), the Plague of Cyprian (onset ~251 CE), and the Plague of Justinian (onset ~541 CE) coincided with periods of cool, dry climate conditions.

For 20 years, Zonneveld had been intrigued by possible overlap of the outbreaks with discrete climate conditions. Once she and her colleagues developed a reliable model, she contacted Kyle Harper, a historian at the University of Oklahoma, to understand more about the human conditions at the time.

“I can do climate reconstructions,” Zonneveld said, “but I’m not a historian.”

No Cause and Effect

Harper helped the geologists develop hypotheses about the impacts people might face amid climate change, such as new germ spillovers from animals to humans, or diminished agricultural output, in turn leading to food shortages and heightening vulnerability to infection.

Looking at the timeline, it appears climate could have contributed to the pandemics, Zonneveld said, but there are no data yet to support that hypothesis.

“Can this happen again? What can we learn? You start to think differently about the causes.”

“We just can’t yet identify cooling as contributing, in a major or minor way, to the spillover or the spread of disease in [the] second, third or sixth centuries,” wrote Timothy Newfield, a historical epidemiologist at Georgetown University, in an email. He was not involved in the study.

But, Newfield added, “our knowledge of Roman climate remains very limited, so this new reconstruction is most welcome.”

Studying long-ago outbreaks while living through the COVID-19 pandemic added another dimension to the work, Zonneveld said. “Can this happen again? What can we learn? You start to think differently about the causes.” Evaluations of future risks to global public health should include climate, according to the researchers.

—Amy Mayer (@amyhmayer), Science Writer

Citation: Mayer, A. (2024), Roman plagues struck during cool, dry periods, Eos, 105, https://doi.org/10.1029/2024EO240086. Published on 28 February 2024.

Text © 2024. The authors. CC BY-NC-ND 3.0
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