Indian summer monsoon (ISM) rainfall is the major prerequisite of agricultural productivity in the region and its variability severely affects the livelihoods of a large share of the world’s population. While average ISM rainfall has been relatively stable during the past century, rising trends have been observed in the annual number of extreme rain events. This study shows severe failure of ISM rainfall is possible but unlikely under present climatic conditions, according to a comprehensive climate model. However, monsoon failure is projected to become much more frequent over the next 200 years as a result of global warming. The climate model presented in the paper provides a simple dynamical explanation for future changes in the frequency distribution of seasonal mean all-Indian rainfall. The approach offers an alternative perspective on large-scale monsoon variability as the result of internal instabilities modulated by pre-seasonal ambient climate conditions.