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

Abstract

<jats:p>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.</jats:p>

Past pandemics and climate variability across the Mediterranean

“…There was, evidently, no simple relationship between summer cooling and ancient Mediterranean pandemic disease, as several pronounced cooling periods do not correspond to known large-scale disease outbreaks, including the cooling associated with the massive eruption of 43 BCE (McConnell et al 2020 ). Weary as we should be of drawing macro-level climate-pandemic linkages on the basis of current evidence, that significant summer cooling contributed to pandemic emergence beyond the Mediterranean region, whether in Africa, Asia or Europe, and facilitated Mediterranean disease diffusion, indirectly through a combination of mechanisms, remains a possibility, as plague-cooling concurrences visualised in Fig.…”

The importance of “year zero” in interdisciplinary studies of climate and history

“…Interdisciplinary projects and international networks applying combinations of geographically diverse tree-ring and ice core records, radiocarbon measurements, and documentary and archaeological sources for climate reconstructions and historical studies before the Common Era (e.g., refs. 9 – 13 ) raise the stakes of misassociations. At the very least, mixing different data and timescales, in tandem with a lack of clarity or consistency in the use of astronomical and historical calendars, can lead to confusion.…”

Cryptotephra from the Icelandic Veiðivötn 1477 CE eruption in a Greenland ice core: confirming the dating of 1450s CE volcanic events and assessing the eruption's climatic impact

“…While the particle measurements are not a direct proxy or solely controlled by the presence of tephra shards, this approach has been used successfully to identify tephra horizons in both Greenland and Antarctic ice cores (e.g. Jensen et al, 2014;Dunbar et al, 2017;McConnell et al, 2017McConnell et al, , 2020Plunkett et al, 2020).…”