Plagues in Roman Italy Linked to Climate Change, Scientists Say

A plague that ravaged through Roman Italy has been linked to extreme temperature drops in the region, scientists say.

The Justinian Plague—the first recorded wave of bubonic plague to spread through Europe—is thought to have begun in the year 541 CE in Lower Egypt. Within months, it had spread across the Mediterranean in ships to the center of the empire in Constantinople, or modern-day Istanbul. From there, the plague raged on until 590 CE, killing as many as 10,000 people a day at its peak.

By the time the plague had run its course, nearly half of the population of Constantinople had died, as well as about a third of the population of Europe.

Now, this was not the first plague during the Roman period. Indeed, the Antonine Plague of 165 to 180 CE and the Plague of Cyprian from 251 to 266 CE also devastated the Roman population. And, according to new research from the universities of Bremen and Oklahoma, these plagues all had one thing in common: they were linked to a changing climate.

During the Roman period, temperatures in Europe were different to how they are today. "We could reconstruct that the climate (at least the late summer autumn temperature in middle/south Italy) was relatively to today somewhat warmer," Karin Zonneveld, a professor of micropaleontology at the University of Bremen and the study's first author, told Newsweek. "We see in our record that a cooling trend started at about 100 CE but it was not before about 130 CE that the climate changed such that it moved out of the range that was occurring in the previous centuries.

"From this time on, temperatures varied largely with a continuation of the first cooling trend to about the year 215 followed by a several centuries with an unstable climate."

Then, in the 530s and 540s, Europe experienced what the researchers describe as "extreme cooling," roughly in line with the early origins of the Justinian Plague.

In their study, published in the journal Science Advances, Zonneveld and colleagues used marine sediments to reconstruct the changes in temperature and precipitation between 200 BCE to 600 CE. Their study marks the first high-resolution (within three years) climate record from the heartland of the Roman Empire during this period. And this allowed the team to match the changing climate to key events in the ancient Roman timeline.

"I was completely baffled by the good timely correlation between climatic change and major events in Roman history," Zonneveld said. "The expansion of the Roman empire at times of relatively stable conditions and periods of turmoil and crisis after climate started to vary strongly, as well as the times when Europe was suffering under major outbreaks of infectious diseases corresponding to phases of cold climate.

"This was one of the moments that we as scientific team thought....wauw....can this be true?.... we have to verify this double, two double, three double check...... but yeh, it is clearly there in the data."

While this correlation does not prove that the colder weather was causing disease outbreaks, it is well know that changes in climate can affect disease dynamics.

"In short, climate affects the biology of the pathogen, ecosystems (including animal hosts and insect vectors), and human societies (causing migration, war, social crisis, and above all food shortages that make populations vulnerable to infection," co-author Kyle Harper, a professor of classics and letters at the University of Oklahoma, told Newsweek.

"In general [these societies were] very poorly equipped [for these outbreaks.] Ancient societies lacked modern biomedicine, vaccines, antibiotics, public health, and so on."

While modern medicine has advanced considerably since the time of the Romans, this data offers insights into how diseases might change in our own changing climate. "Within the scope of the current climate change it is of major importance to understand the links between climate and human health and we unfortunately do not understand these links as well as we would like," Zonneveld said. "Investigating the resilience of ancient societies to past climate change and relationships between past climate change and the occurrence of infectious disease might give us better insight into these relationships and the climate change induced challenges we are facing today.

"As in Roman times, climate is still a major factor affecting basic aspects that are influencing our well being such as agriculture, accessibility to clean water, biodiversity, geographic distribution and migration of organisms etc."

Harper added: "Our study underscores the need to study in more detail the mechanistic links between climate change and infectious disease dynamics."