Global monsoon variability in a 1.5 °C warming climate: Observational changes and end-century projections

Monsoon systems underpin the water, food, and economic security of over two-thirds of the global population, yet they are entering a state of instability as global temperatures have now surpassed +1.5 °C above pre-industrial levels. This crossing of the 1.5 °C threshold raises a critical problem: Are monsoon onset, duration, and extreme rainfall already shifting in detectable, regionally differentiated ways? Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 framework, we screened 784 peer-reviewed studies (2000–2024) and synthesized 72 high-quality articles. A complementary global diagnostic using Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS; 1981–2024) ensured uniform comparison across monsoon regions. Results reveal onset shifts of ±15 days, rainfall-intensity increases of +10–60%, and duration changes of ±15 days, with the strongest signals in South Asia, East Asia, the Western North Pacific, and Southeast Asia. Attribution using CMIP5/CMIP6, ERA5, TRMM, GPM, and IMERG identifies El Niño–Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), sea-surface temperature anomalies, and greenhouse-gas (GHG)–aerosol interactions as dominant drivers. Although seasonal totals often change modestly, clustering of extremes and lengthening dry spells markedly elevate compound flood–drought risk. This review establishes the first harmonized global baseline of observed monsoon change and highlights urgent needs for convection-permitting regional models, improved subseasonal prediction, expanded observational networks, and increased representation of African and South American monsoon systems.