**5. Conclusions**

The identification of the direct and indirect relationship between climate change and human plague dynamics is a topic of high interest in the context of surging researches over the potential elevating risk of plague outbreak under climate change. Although many studies have revealed the possible linkages in the climate-plague nexus and have highlighted the concern of scale-dependent variability in climate-driven plague dynamics in the spatio-temporal dimension [45], they seldom explicitly consider the possibility that the relationship is an indirect one. In this study, we applied SEM to quantitatively justify that the casual pathway from climate change to plague dynamics in historical Europe was not a direct one but was mediated by climate-driven economic changes. In a nutshell, the influence of temperature was only significant in the cool and wet periods, corresponding to the total e ffect and indirect e ffect of temperature in SEM; whilst the influence of precipitation on human plague dynamics seemed to be indirect in nature and was significant only in cold climate. The study evidenced that climate-driven economic changes, rather than climate change alone, were the direct cause of human plague outbreak. The investigation on such indirect influence of climate change on human plague dynamics should receive more attention in the future.

**Author Contributions:** R.P.H.Y. and H.F.L. designed research; R.P.H.Y. and H.F.L. performed research; R.P.H.Y. and H.F.L. analyzed data; and R.P.H.Y. and H.F.L. wrote the paper. Both authors read and approved the final manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study is supported by the Improvement on Competitiveness in Hiring New Faculties Funding Scheme (4930900) and Direct Grant for Research 2018/19 (4052199) of the Chinese University of Hong Kong.

**Conflicts of Interest:** The authors declare no conflict of interest.
