How long and how strong must a climatic anomaly be in order to evoke a social transformation? Historical and contemporaneous case studies

The paper engages the debate on how climate anomalies affect social and political transformations, questioning which anomalies destabilize societies and what durations/intensities trigger structural change. While proxy-based historical studies often link singular events (e.g., volcanism) to societal outcomes, their dating and spatial limitations constrain reconstruction of human processes; contemporary studies often emphasize institutions over climate. The authors propose refocusing on gradual anomalies that reduce food availability, arguing these have the most profound societal effects. They outline case studies—Liao dynasty collapse in northern China, crises in western Asia/Egypt in the 11th century, and Mali (2012–2013)—with shared placement in a "Fragility Zone" (annual precipitation ~400–600 mm) and initially efficient administrations that nonetheless rapidly deteriorated, suggesting climate-driven food shortages as a key driver.

The paper situates its approach within resilience theory and historical methodology. Building on Holling’s concepts of resilience (single vs multiple equilibria) and later social applications (adaptation, transformation, transition), the authors focus on disturbances (climate events) themselves—their duration and intensity—as triggers of structural change. They contrast short-term hazards (hurricanes, floods, earthquakes, eruptions) that garner attention and immediate response with gradual, long-term events (droughts, heat waves, sea-level rise) whose onset and end are hard to define and whose impacts can be cumulative and severe. Citing Smith (2011), they emphasize evaluating both the climatic driver (statistical extremeness) and the response (ecosystem/societal impact). The National Research Council (2013) highlighted how gradual forcings can push systems past thresholds to abrupt change, producing new states lasting decades. Historical perspectives from the Annales school (Braudel) remind that meaningful structural changes must be analyzed over timescales relevant to human lives (years to decades), not only the longue durée. Empirical literature indicates gradual heat stress influences migration and economic downturns (Pakistan studies), while short-term disasters dominate discourse and aid flows despite smaller long-run migration effects. The authors argue that durations of a few years to a decade, when anomalies reduce food availability, are critical for social transformations.

The authors apply a historical-climatological methodology emphasizing duration and intensity of anomalies and their effects on food systems. For northern China (Liao dynasty), they conducted a systematic reading of dynastic histories (Liao Shi, Jin Shi), encoding indicators of climatic-environmental stress (climatic disasters, food price spikes, food riots, large-scale migrations) to chart temporal clusters (per Li et al., 2019). For Egypt/western Asia, they used precisely dated Genizah documents and annual records of the Nile’s rise to reconstruct sequences of droughts and governmental responses (grain market regulation, granary releases). For Mali (2012–2013), they built a decade-long database (2005–2019) combining quantitative observations (temperature anomalies, drought indices, precipitation) with qualitative contemporary reports (2008–2014) on social impacts and political events, enabling high-resolution temporal alignment of climate conditions, food availability/price signals, and conflict dynamics. Across cases, they trace how cumulative anomalies over consecutive years undermine food security, constrain state response capacities, and precede social unrest, migration, and political upheaval.

- Extended climatic anomalies that reduce food availability—droughts, cold spells, untimely rains—are most likely to trigger deep social change; short-term, single events, while damaging, rarely produce lasting structural transformations. - Northern China (Liao dynasty, 11th–12th c.): Two phases emerged. c.980–1030 saw manageable droughts/floods mitigated by Liao relief (granaries, tax reductions, infrastructure repairs). From 1066–1130, stronger, longer anomalies required intense intervention. Ten of sixteen recorded extraordinary cold anomalies (901–1130) occurred 1109–1127, with additional droughts (1109, 1113, 1119/20, 1123). Combined droughts, floods, and cold constrained agricultural production in southern/eastern circuits, causing dearth and frequent relief efforts. Repeated severe cold (dzud) disrupted Jurchen pastoral systems, driving unification and southward push, contributing to rapid Liao collapse (1125) and broader regional political shifts. - Egypt/western Asia (10th–11th c., Fatimid era): Nile rise records and Genizah documents show unprecedented clustering of drought years. Between 383–950 CE: 11 drought years (~1 every 60 years). Between 950–1072 CE: 27 drought years (~1 every 4 years), including sequences of 4, 6, and 7 consecutive years (e.g., 963–969 six years; 1065–1072 seven years). Despite efficient management (grain imports, market oversight, opening 150 granaries, fixed prices, ship confiscations), sustained sequences overwhelmed capacity, leading to famine, plague, army indiscipline/raiding, and regional instability. The cumulative nature—short intervals between crises—prevented replenishment and preparation. - Mali (2012–2013): Droughts in 2009–2010, exceptional spring 2011 heat, and 2012 heavy rains/floods interacted to degrade food availability for northern nomadic/pastoralist groups. By spring 2012, diminished reserves heightened vulnerability; floods damaged roads and crops, disrupting supply chains and aid from the south. Food prices (millet, sorghum, local rice) reached record highs in summer 2012. Rising food insecurity intensified unrest, coinciding with demonstrations (Feb 2012), a coup (Mar 21–22, 2012), Islamist advances (May 2012), and broader displacement/migration. Climate-driven food stress is implicated in escalating a localized Tuareg revolt into a wider conflict with international ramifications. - Threshold: Continuous anomalies lasting two or more consecutive years can push societies beyond resilience thresholds via food insecurity, triggering migration, violence, and structural political change within timescales of several years to a decade.

Findings support a refined concept of “extreme climatic events” where extremeness is judged not only by statistical rarity but by cumulative, prolonged impacts on food systems and social stability. Seemingly usual events (recurrent droughts, untimely rains, cold winters) can, when clustered over short intervals, become extraordinary catalysts for civil conflict, mass migration, and regime change. Compared with single rapid-onset disasters (hurricanes, earthquakes), multi-year anomalies more profoundly alter economic and social structures by persistently undermining food security, especially in marginal “Fragility Zones.” The analysis highlights a 2+ consecutive-year duration as a critical threshold beyond which societies face rising fragility, scapegoating, extremism, and political upheaval. Emphasizing the food variable clarifies mechanisms linking climate to societal outcomes and helps explain why short-term disasters attract attention yet have less transformative long-run effects than cumulative anomalies.

Irregular climatic anomalies lasting from several years up to one or two decades can precipitate enduring social crises that outlast the climatic trigger. Across China, Egypt, and Mali, food availability emerged as the pivotal variable linking climate anomalies to political, economic, and social transformations: prolonged droughts, cold spells, and untimely or excessive rains abruptly reduced food supplies and raised prices, eroding resilience and fostering unrest, migration, and structural change. The cumulative impact of consecutive-year anomalies exerts a more substantial and extraordinary societal effect than single, powerful short-term events. Framing extreme climatic events through their effects on food reserves and security offers a practical lens for identifying when climate anomalies are likely to become socially transformative.

- Proxy-based reconstructions for historical periods have dating and spatial limitations, with measurement uncertainties often exceeding a decade, complicating resolution of short, multi-year crises. - The Mali case, despite high-resolution data, cannot conclusively prove causality between climate conditions and conflict; multiple interacting political and regional factors co-occurred. - Reliance on historical textual sources (dynastic histories, Genizah documents) may introduce reporting biases and uneven coverage. - Data availability: The compiled datasets are not publicly available (accessible upon reasonable request), limiting external replication. - Geographic focus centers on regions within a defined “Fragility Zone,” which may limit generalizability to other agro-environmental contexts.