Introduction. Global patterns of climate change produce mental and behavioral health consequences. These include stress, psychological distress, diagnosable psychopathology, and harmful behaviors that are observable at individual and population levels. Multiple causal pathways are implicated, with some involving complex cascades of stressors. Methods. The relationship between planetary climate change and societal mental health is receiving increasing attention. This review integrates the vantage points of public health and complexity science to examine possible causal pathways by which climate change dynamics may influence individual and collective mental health status and associated human behaviors. Complex systems thinking is useful for understanding how climate-related risk factors for mental health consequences are globally networked and create unanticipated, “emergent” outcomes. Frequently these climate risks co-occur, cascade, and compound. Results. First, climate change, including global warming and sea level rise, is directly implicated in increases in the frequency and intensity of such phenomena as El Niño and attendant disaster events, including tropical cyclones, heat waves, droughts, and floods. Second, climate change is modifying the geographic distribution of infectious diseases, in part by shifting the range of vector populations. Third, climate change affects agricultural production leading to distress associated with hunger and sometimes, starvation. Fourth, climate-induced forced migration leads to myriad stressors associated with the relocation of entire communities. Fifth, climate-change associated drought and famine are triggering armed conflicts that may evolve to the scale of humanitarian emergencies. Sixth, these events co-occur in complex permutations. Disasters, pandemic outbreaks, food insecurity, water scarcity, forced migration, and humanitarian crises produce psychological distress with high risk for progression to psychopathology (posttraumatic stress disorder, major depressive disorder, generalized anxiety disorder, psychosomatic complaints, increases in substance abuse). Conclusions. A review of the expanding research literature clarifies the layered richness and complexity of interrelated mechanisms that convert climate change dynamics into mental health consequences.