Julius Caesar, leader of the Roman Republic, was stabbed 23 times in 44 BCE. Clearly, his republic was left in a politically unstable state. But his death was soon followed by famine, disease, and unusually cold and inclement weather. Soon after, the Roman Republic collapsed followed by the fall of the Ptolemaic Kingdom after its leader Cleopatra was defeated in 30 BCE. The extremely cold climate, and the problems that it creates, likely fanned the flames of political turmoil across the region. And a team of researchers have found the likely cause of that extreme cold: the eruption of an Alaskan volcano on the opposite side of the world. The findings were published recently in the Proceedings of the National Academy of Sciences.

Scientists can often figure out what the past environment was like by looking at the air from that time period. But where can you find well-preserved ancient air? By examining Arctic ice cores. Ice sheets encase air from the past as the annual snowfall compacts into ice with little air bubbles trapped within. An ice core is a cylinder of ice pulled out from an ice sheet, where the cylinder contains older air as you go deeper into the ice sheet. Led by Joseph McConnell who is a Hydrology Professor at the Desert Research Institute in Nevada, the study determined that ice-trapped air from around 43 BCE contained a bunch of volcanic ash. This coincides with separate climate records that indicate 43 and 42 BCE were exceptionally cold years in many parts of the world.

Okay, they confirmed there was a volcanic eruption somewhere on Earth . But how did they figure out what volcano erupted? They examined the volcanic ash they found within the ice core and determined what elements it is made of. Rock from different volcanoes are each made of a slightly different blend of elements (such as varying amounts of sulfur or chlorine). In that sense, the elemental make-up of volcanic ash is kind of like a volcano’s fingerprint. And they matched that fingerprint to the Okmok Volcano, which resides on the Umnak Island in Alaska, USA.

As a final flourish to the study, McConnell and his colleagues also ran a climate model to simulate the effect of the historic Okmok eruption they discovered. According to their models, a massive eruption like the one evidenced by the ice cores would have caused a 7-degree-Celsius (13 degree Fahrenheit) drop in the region. Historical accounts corroborate this, with many records showing people at the time lamenting the particularly brutal winters.

Lining up historical events with abrupt environmental change is always a tricky game. The Mediterranean region was also suffering social unrest just before Okmok’s eruption (as most clearly evidenced by the brutal killing of Caesar). Still, the massive eruption probably caused the intense cold that led to crop failure, famine, and disease that plagued ancient Rome and Egypt. These exacerbated regional instability and likely further pushed the region towards the drastic political realignments that occurred shortly after. Taken more broadly, the study’s findings may serve as a reminder of how impactful an abruptly-changing climate can be on civilizations – including the ones we live in today.

Joseph McConnell is a professor of Hydrology at the Desert Research Institute in Nevada, as well as a Sir Nicholas Shackleton Visiting Fellow at the University of Cambridge.

Managing Correspondent: Jordan Wilkerson

Original article: Extreme climate after massive eruption of Alaska’s Okmok volcano in 43 BCE and effects on the late Roman Republic and Ptolemaic Kingdom

Image Credit: U.S. Geological Survey