Examining the Direct and Indirect Effects of Climatic Variables on Plague Dynamics

Abstract

Climate change can influence infectious disease dynamics both directly, by affecting the disease ecology, and indirectly, through altering economic systems. However, despite that climate-driven human plague dynamics have been extensively studied in recent years, little is known about the relative importance of the direct and indirect effects of climate change on plague outbreak. By using Structural Equation Modeling, we estimated the direct influence of climate change on human plague dynamics and the impact of climate-driven economic change on human plague outbreak. After studying human plague outbreak in Europe during AD1347-1760, we detected no direct climatic effect on plague dynamics; instead, all of the climatic impacts on plague dynamics were indirect, and were operationalized via economic changes. Through a series of sensitivity checks, we further proved that temperature-induced economic changes drove plague dynamics during cold and wet periods, while precipitation-induced economic changes drove plague dynamics during the cold periods. Our results suggest that we should not dismiss the role of economic systems when examining how climate change altered plague dynamics in human history.

Did Hydro-climatic Extremes, Positive Checks, and Economic Fluctuations Modulate the Epidemics Outbreaks in Late Imperial China?

“…The key findings from multiple regression and wavelet coherence analyses are: In China in 1841–1911, with the climate-related factors, economic well-being, and Malthusian checks were taken into account simultaneously, I found that economic fluctuations drove the waves of epidemics outbreaks at the inter-annual and decadal time-scales. My findings are consistent with previous research findings that economic factors are critical catalysts in triggering epidemics outbreaks in the past, whether in historical China (Pei et al ., 2015 ) or pre-industrial Europe (Yue & Lee, 2020b ). On the other hand, epidemics could also deteriorate the agrarian economy’s stability (Voigtländer & Voth, 2013 ).…”

“…Given that a large portion of the Chinese population was still living at the subsistence level during the time, those economic fluctuations might have engendered severe hardship and malnourishment across societies (Lee, 2014 ; Ma & de Jong, 2019 ). Such a situation further increased the underprivileged social groups’ susceptibility to epidemics (Yue & Lee, 2020b ).…”

“…However, I found that the hydro-climatic extremes did not significantly affect the epidemic outbreak when other factors’ influence was controlled (Table 6 ). The disparity of findings may be attributed to the fact that the climatic effects on epidemics have been indirect and sporadic and have been materialized through economic changes (Pei et al ., 2015 ; Yue & Lee, 2020b ; Zhang et al ., 2011 ). Also, the different time-spans of the study between this and the previous studies matter because the ranges of ecological and social responses to climate change are subject to the length of the study periods (Tian et al ., 2017 ) and its associated temporal scales (Orlove, 2005 ; Pei et al ., 2020 ).…”

“…First, climate-related factors, such as temperature cooling (Lee, 2014 ; Lee et al ., 2017 ; Tian et al ., 2017 ) and hydro-climatic extremes (Lee et al ., 2016 ; Schmid et al ., 2015 ; Xu et al ., 2011 , 2014 ; Yue & Lee, 2020a ), disrupted agricultural practices and the ecological environment, and then triggered the migration of people and rodents in the affected regions and facilitated the transmission of the epidemics. Second, the downturn in economic well-being due to changes in grain prices, which affected the supply of subsistence resources to humans, reduced the nutritional level of the human population and subsequently increased their susceptibility to the epidemics (Duncan et al ., 1997 ; Pei et al ., 2015 ; Yue & Lee, 2020b ). Third, there was a mutual reinforcement between positive checks such as famines, wars, and epidemics during overpopulated periods (Lee, 2018 , 2019 ; Malthus, 1798 ).…”

Climate Change, Climatic Extremes, and Human Societies in the Past

“…Yue and Lee [5] examine the relative impact of the direct and indirect impacts of climate change on plague outbreaks in Europe between 1347-1760 using Structural Equation Models. They found that all of the climatic impacts on plague outbreaks were indirect and were materialized through economic changes.…”