Climate Change, War and Population Decline in Human History

* Article: Global climate change, war, and population decline in recent human history. By David D. Zhang , Peter Brecke, et al. PNAS, December 2007

URL = https://www.pnas.org/doi/10.1073/pnas.0703073104

"We show that long-term fluctuations of war frequency and population changes followed the cycles of temperature change."

Description

"Although scientists have warned of possible social perils resulting from climate change, the impacts of long-term climate change on social unrest and population collapse have not been quantitatively investigated. In this study, high-resolution paleo-climatic data have been used to explore at a macroscale the effects of climate change on the outbreak of war and population decline in the preindustrial era. We show that long-term fluctuations of war frequency and population changes followed the cycles of temperature change."

Excerpt

By David D. Zhang et al. :

"The hypothesis we propose posits that long-term climate change has significant direct effects on land-carrying capacity (as measured by agricultural production). Fluctuation of the carrying capacity in turn affects the food supply per capita. A shortage of food resources in populated areas increases the likelihood of armed conflicts, famines, and epidemics, events that thus reduce population size. As a feedback mechanism, population decline has a dominant tendency to increase the food supply per capita (seen in decreasing food prices), which results in relative peace and fast population growth. The interactions among these components in a social system create an important rhythm of macrohistory in agricultural societies."