Climatic and societal impacts of volcanic eruptions in the Western Han Dynasty (206 BCE-8 CE): A comparative study.

Abstract

The Western Han Dynasty (206 BCE-8 CE) experienced periods of extreme climate, accompanied by the evolving concept of the "mandate of heaven"that shaped societal responses to disasters. While recent studies suggest that certain Han-era climate anomalies followed explosive volcanic eruptions, we employ quantitative and qualitative methods to establish these associations more systematically. We categorize and quantify documented climatic stressors and selected societal events and apply superposed epoch analysis to examine their temporal associations with ice-core-based dates of explosive eruptions. Several climate and related disasters, including drought, cold and locust outbreaks, but not flooding, are repeatedly associated with explosive eruptions. We observe a more complex association with societal stressors, including a potentially delayed increase in vagrancy and a suppression of warfare that may reflect resource constraints and revised priorities following disasters. We then select two periods with notable volcanic climate forcing, 180-150 and 60-30 BCE, respectively, and offer a comparative analysis of their climatic and societal stresses and responses. Hydroclimatic extremes following the 168-158 BCE "volcanic quartet", and the cold and atmospheric optical anomalies of 43 BCE, are consistent with expectations given the scale of volcanic forcing. Poor harvests from 163 to the mid-150s BCE and the 40s BCE, plus subsequent grain price spikes and famines are also plausible consequences. Such impacts are nonetheless mediated by other factors (e.g., economy, politics, and perceptions of the environment) that contribute to a society's resilience and vulnerability, and which require further research focusing on extended historical periods to more fully understand.