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.

Map of Alaska, with Okmok Volcano’s location shown as the red cross (image created by Jordan Wilkerson in MATLAB).

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

2 thoughts on “Et tu, Okmok? Alaska’s Okmok Volcano Contributed to Fall of Roman Republic and the Ptolemaic Kingdom

  1. The first century BCE fall of the Roman Republic and Ptolemaic Kingdom and subsequent rise of the Roman Empire were among the most important political transitions in the history of Western civilization. Volcanic fallout in well-dated Arctic ice core records, climate proxies, and Earth system modeling show that this transition occurred during an extreme cold period resulting from a massive eruption of Alaska’s Okmok volcano early in 43 BCE. Written sources describe unusual climate, crop failures, famine, disease, and unrest in the Mediterranean immediately following the eruption—suggesting significant vulnerability to hydroclimatic shocks in otherwise sophisticated and powerful ancient states. Such shocks must be seen as having played a role in the historical developments for which the period is famed.
    The assassination of Julius Caesar in 44 BCE triggered a power struggle that ultimately ended the Roman Republic and, eventually, the Ptolemaic Kingdom, leading to the rise of the Roman Empire. Climate proxies and written documents indicate that this struggle occurred during a period of unusually inclement weather, famine, and disease in the Mediterranean region; historians have previously speculated that a large volcanic eruption of unknown origin was the most likely cause. Here we show using well-dated volcanic fallout records in six Arctic ice cores that one of the largest volcanic eruptions of the past 2,500 y occurred in early 43 BCE, with distinct geochemistry of tephra deposited during the event identifying the Okmok volcano in Alaska as the source. Climate proxy records show that 43 and 42 BCE were among the coldest years of recent millennia in the Northern Hemisphere at the start of one of the coldest decades. Earth system modeling suggests that radiative forcing from this massive, high-latitude eruption led to pronounced changes in hydroclimate, including seasonal temperatures in specific Mediterranean regions as much as 7 °C below normal during the 2 y period following the eruption and unusually wet conditions. While it is difficult to establish direct causal linkages to thinly documented historical events, the wet and very cold conditions from this massive eruption on the opposite side of Earth probably resulted in crop failures, famine, and disease, exacerbating social unrest and contributing to political realignments throughout the Mediterranean region at this critical juncture of Western civilization.
    We find that people revise their beliefs about climate change upward when experiencing warmer than usual temperatures in their area. Using international data, we show that attention to climate change, as proxied by Google search volume, increases when the local temperature is abnormally high. In financial markets, stocks of carbon-intensive firms underperform firms with low carbon emissions in abnormally warm weather. Retail investors (not institutional investors) sell carbon-intensive firms in such weather, and return patterns are unlikely to be driven by changes in fundamentals. Our study sheds light on peoples’ collective beliefs and actions about global warming.

  2. why all winters of ww2 was so cold? was it an small ice age? but what was the trigger? for climate researchers is easy to answer just a quarter of century before there was other war the ww1 and it was extremly polluting there was all kind of chemicals send into atmosphere as gas or biologic weaponry that precipited back to earth bottom in form of poison that alter the climate behaviours so that from 1939-45 every winter was colder than former being prosecuted until 1956 -7 and changing our actual climate situation what the responsable of these crime used to say it is just a natural cycle instead a criminal fact

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