In recent years, scholarly interest in the nexus between climate change and human societies has risen dramatically, and many researchers from different disciplines have begun studying the possible effects of climate change and climate anomalies on past and present societies. In this article, we join this lively debate, seeking to extend it by raising, and providing possible answers to, two fundamental questions: what type of climatic anomalies can undermine social stability? What duration and intensity are necessary to instigate structural change? When attempting to answer these questions, researchers tend to view short-term climatic events, such as storms or mudslides, as "unusual" events that instigate an "unusual" reality for temporary, and measurable, time periods. We argue, instead, that gradual and more "usual" climatic events, such as prolonged droughts or extended periods of untimely rains, impact societies in a more profound and "extraordinary" manner, and it is here that our paper meets the theme of the extraordinary and the usual, the axes of the current collection of essays. Based on qualitative examination of collapse periods in western Asia and northern China during the eleventh and early twelfth centuries, and a high-resolution re-examination of the crisis in Mali at the beginning of 2010, we argue that extended climate anomalies that cause decreases in the amount of available food are the anomalies that most affect the fate of human civilizations. While people can cope with short-term climate anomalies that cause periodical food crises, lasting a year or two, extended climate anomalies that affect the availability of food, like droughts, cold spells or untimely rains, can have disastrous, long-term effects: they accelerate decisive processes, push people to migrate outside their regions of residence, increase violence and religious extremism, and, ultimately, lead to structural changes in the societies that are affected by the crises.
