Cold snaps may have started devastating plague pandemics for ancient Romans that killed countless people, new research finds.
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The new study links periods of climate variation with major pandemics and finds that the three largest pandemics of the Roman period occurred during some of the most abrupt and deep cold snaps ever recorded.
There could be a number of reasons to explain this overlap, study co-leader said. Kyle HarperRoman historian at the University of Oklahoma and the Santa Fe Institute.
“When you shake up the climate system, it really impacts pathogens, ecosystems and, most of all, human societies,” Harper told LiveScience.
The research focuses on a long core of sediments excavated from the Gulf of Taranto, the wide gulf under the “sole” of the Italian “boot”. This area captures sediment washed from the Po River and other rivers that drain the Apennine Mountains — essentially the heart of the Roman Empire, Harper said.
Study co-leader Karin Zonneveld, a paleoceanographer at the University of Bremen in Germany, used several clues within the sediment cores to match sediment layers to specific years. The key data came from volcanic glass in the sediments, which can be chemically traced to known eruptions.
“Several of these eruptions are world famous, such as the eruption of Vesuvius in AD 79 that destroyed Pompeii,” Zonneveld told LiveScience in an email.
The clues revealed that the sediments stretched from 200 BC to 600 AD, starting in the late Roman Republic and recording all the way to the final days of the Roman Empire. “You get a complete picture of what we think of as ancient Roman history, starting with the later Republic,” Harper said.
To reconstruct temperature and precipitation, the team turned to small organisms called dinoflagellates preserved in the sediment. The life cycle of these organisms is very sensitive to temperature and precipitation. In late and early autumn, dinoflagellates transform into a resting state known as a cyst, which can be preserved in the fossil record. Because different species have different preferences, scientists can count the types of dinoflagellates that thrived in a given year. In colder years, species that like the cold will be more abundant, for example. In times of high rainfall, when river water overflows into the sea carrying additional nutrients, species that prefer high nutrient conditions will be more common.
The results showed a stable climate period between 200 and 100 BC, followed by a series of short cold pulses. Between 160 and 180 AD, there was a strong cold period. This coincided with the Antonine Plague or the Plague of Galen, a pandemic brought to the empire when Roman armies returned from Western Asia. The disease was caused by an unknown pathogen that caused symptoms such as fever, diarrhea and skin pustules. (Experts think it may have been smallpox or measles.)
Another period of cold occurred between 245 and 275 AD, which again coincided with a pandemic, known as the Plague of Cyprian. Historical records reveal that this disease caused vomiting, diarrhea and sometimes putrefaction of the limbs. Again, historians don’t know what caused the illness, but they speculate that it could have been measles, smallpox, or some type of hemorrhagic fever.
Finally, the environmental record suggests another cold snap after 500 AD, coinciding with the Little Ice Age of Late Antiquity, a period of cooling known from other climate records. In 541 AD, the first outbreak of bubonic plague reached western Eurasia. The Plague of Justinian, as it is known, was the precursor to the Black Death that would devastate Europe in the 13th century.
“The correlation between the times when Europe suffered from large infectious disease outbreaks corresponding to phases of cold weather was striking,” Zonneveld said.
There are many reasons why disease outbreaks and climate may be linked, Harper said, from ecological changes that may make it more likely for animal diseases to spread to humans, to changes in human resilience. In an agricultural society like ancient Rome, he said, farmers may have had difficulty producing sufficient crops during cold periods, leading to malnutrition that left people susceptible to disease.
The topic is interesting, said Ulf Büntgen, professor of environmental systems analysis at the University of Cambridge who was not involved in the study. However, there are doubts about the certainty of climate reconstruction, he told Live Science.
The next step for scientists is to make a deeper comparison of the sediment core data with other climate records and archaeological studies from the Roman heartland, Harper said.
“Researching the resilience of ancient societies to past climate change… can give us better insight into these relationships and the climate change-induced challenges we face today,” Zonneveld said.
The research was published in the journal Science Advances and the article published in LiveScience