Climate as a Contributor to the Rise and Decline of the Roman Empire

Contributor(s): 
April 15, 2015

Michael McCormick and colleagues examine the climatic backdrop to the rise and fall of the Roman Empire, adding an essential environmental context to one of the most-debated topics in history. Their paper also represents an important advance in the Journal of Interdisciplinary History’s promotion of climate history, which began with a special issue on the topic in 1980. As McCormick et al. note, the questions arising in that special issue quickly outstripped contemporary science and history. Since then, there has been a proliferation of paleoclimate reconstructions, covering more regions, more seasons, and with greater dating precision and accuracy, yet no consensus on the role of climate in the fortunes of the Roman Empire has emerged.

Given widespread scientific concern over present and projected climatic change, natural scientists have understandably sought to learn lessons from the past by examining how societies responded to the often-dramatic changes discerned in their reconstructions. But as McCormick et al. remark, ‘the natural-scientific literature… draws sweeping historical inferences from slender evidence…’. This is often reminiscent of the simplistic determinism of the twentieth century, wherein the environment is endowed with direct and dominant powers of causality over the course of human history, and the role of culture, politics, economics and individual agency is marginalized. At the same time, McCormick et al. note that ‘alarmed historians and archaeologists understandably struggle with evaluating highly technical scientific analyses and methods, sometimes failing to understand them at an elementary level.’ As a solution, McCormick and colleagues advocate concerted collaborative interdisciplinary research.

While previous studies have focused on particular regions or periods of Roman rule, and/or on particular palaeoclimatic proxies, McCormick et al. attempt a first synthesis of multiple climate records relevant to the greater area of Roman rule, 100 BCE to 800 CE. This is a considerable challenge given differences in the seasonality of available proxies, their varying dating accuracy and resolution (e.g., where proxies such as tree-rings reflect climate at an annual resolution, while others such as speleothems reflect climate at decadal and greater resolutions). Several insights emerge from this effort, not least that the sheer size of the Empire, spanning three continents, requires historians, archaeologists and palaeoclimatogists to grapple with complex counter-intuitive aspects of large-scale atmospheric circulation. These include anti-phase relationships wherein anomalies of different sign (e.g., cooling vs. warming) may exist simultaneously in different parts of the empire as a response to the same climatic forcing (e.g., volcanic, solar).

The authors also stress that the societal impact of any given climatic anomaly does not simply depend upon its magnitude, but also upon the pre-existing robustness of society and the underlying marginality of its subsistence base, which may itself be the product of longer-term social and environmental processes interacting in complex ways. In sum, McCormick and colleagues see the period of the Roman Empire’s maximum expansion occurring in the context of a relatively stable climate, lacking in many major climatic shocks such as those induced by volcanic eruptions, while the deleterious episodes of the Empire’s later history occurred in the very different context of rapid ongoing climatic fluctuations.

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Michael McCormick, Ulf Büntgen, Mark A. Cane, Edward R. Cook, Kyle Harper, Peter Huybers, Thomas Litt, Sturt W. Manning, Paul Andrew Mayewski, Alexander F. M. More, Kurt Nicolussi, Willy Tegel (2012) Climate Change during and after the Roman Empire: Reconstructing the Past from Scientific and Historical Evidence, Journal of Interdisciplinary History, XLIII (2), 169-220. http://www.mitpressjournals.org/doi/suppl/10.1162/JINH_a_00379.