The sun of Rome is set! Volcanic dust veils and their political fallout

Abstract

Within a year of the slaying of Julius Caesar, Okmok volcano in the Aleutian Islands (Fig. 1) begat one of the greatest eruptions of the past 2,500 y, according to research in PNAS (1). The study explores the repercussions of climatic change induced by the eruption for the unstable Roman Republic. Fig. 1. The 10-km-diameter caldera of Okmok volcano dominates the northeastern end of Umnak Island in the Aleutian archipelago. It was formed partly by a paroxysmal eruption now dated to early 43 BCE. Okmok’s last eruption was an explosive affair in 2008. Image credit: NASA Earth Observatory/Joshua Stevens, using Landsat data from the US Geological Survey. Since the 1991 eruption of Mt. Pinatubo, large eruptions have been widely recognized as a leading driver of natural climate variability (2⇓–4). Their study has also revealed many insights into the nature of magmatic processes of the Earth’s interior. However, lately, a renewed research focus on major volcanic episodes has been motivated by passion for world history. One of the first scientists to delve deep into this topic was the British meteorologist Hubert Lamb. In a landmark paper published in 1970, he formulated the dust veil index (DVI) to characterize the climate-forcing potential of volcanic eruptions, and compared his multicentennial time series of DVI values against climate proxies (5). What particularly interested Lamb were the influences of climatic change on societal trajectories, and his research laid the modern foundations of historical climatology (6). The importance of his work was quickly recognized by climate scientists, such as Stephen Schneider, who used the DVI in models to investigate the scale of climatic influence due to volcanism (7). In 1977, the economic historian John Post combined these themes of volcanism changing climate, and climatic change impacting society, in a compelling book with the provocative … [↵][1]1Email: co200{at}cam.ac.uk. [1]: #xref-corresp-1-1