In “The Causality Analysis of Climate Change and Large-Scale Human Crisis,” published in last month’s Proceedings of the National Academy of Sciences, authors David Zhang et al. write that changes in food supply are key indicators for the likelihood of climate change-induced conflict. Adding to the debate on the links between climate and conflict, the authors write that their purpose was to discover the specific causal mechanisms behind the relationship by analyzing various climate- and crisis-related variables across several periods of peace and conflict in pre-industrial Europe. They found that “climate-induced agricultural decline,” as opposed to resource scarcity caused by rapid population growth, was the clearest indicator of impending crises. “Malthusian theory emphasizes increasing demand for food as the cause,” write the authors, “whereas we found the cause to be shrinking food supply” – a distinction with “important implications for industrial and postindustrial societies.”