Can climate affect societies? This question, of both past and present importance, is encapsulated by the major socioeconomic crisis that affected the Mediterranean 3200 yr ago. The demise of the core civilizations of the Aegean and eastern Mediterranean during the Late Bronze Age and the early Iron Age (Dark Ages) is still controversial because it raises the question of climate-change impacts on ancient societies. Although evidence for this climate shift has gradually gained currency, recent attempts to quantify its magnitude remain equivocal. Here we focus on the northern Levant (coastal Syria) where the economic, political, and cultural changes were particularly acute. We quantify past climate changes and find that mean annual temperatures attained anomalies of − 2.3 ± 0.3 °C to − 4.8 ± 0.4 °C compared to present-day conditions. Rainfall regimes displayed an important shift in seasonality, with a 40% decrease in winter precipitation. A 300 yr period of dry and cool climate started ∼3200 yr ago and was coeval with deep social changes in the eastern Mediterranean. These “Little Ice Age”–type conditions affected harvests, leading to severe food shortages that probably aggravated the sociopolitical tensions. This crisis highlights the fragility of societies, both past and present, to major climate-change episodes and their broader consequences.