Résumé
We analyze projected tropical sea surface salinity (SSS) changes in 32 CMIP6 models' historical and SSP5‐8.5 scenario simulations, examining both the multi‐model mean (MMM) and inter‐model diversity. By 2100, MMM inter‐basin contrasts strengthen, with freshening in the tropical Indian Ocean (TIO) and equatorial‐northern Pacific (ENPO), and saltening in the southern Pacific (SPO) and tropical Atlantic (TAO). Basin‐scale future SSS changes are primarily driven by surface freshwater fluxes, with lateral advection redistributing anomalies within each basin. Precipitation dominates the freshwater flux changes, except in the tropical Atlantic where evaporation plays a key role. Two uncorrelated indices, contrasting SPO versus TIO and TAO versus ENPO, explain 76% of the variance across models. Physically, stronger relative warming of the Northern Hemisphere enhances rainfall over the TIO monsoon region (freshening) while suppressing rainfall along the South Pacific Convergence Zone (saltening). The increasing TAO–ENPO contrast arises from two distinct mechanisms: in the Pacific, an enhanced El Niño–like warming pattern reduces atmospheric stability, intensifying rainfall and freshening ENPO; in the Atlantic, saltening reflects stronger evaporation under warmer conditions, though at a weaker rate than predicted by Clausius–Clapeyron scaling (∼ ${\sim} $4.2 vs. ∼ ${\sim} $7% K−1 ${\mathrm{K}}^{-1}$). Previous studies linked strengthening of inter‐basin salinity gradients to a thermodynamically intensified hydrological cycle. Our analysis highlights a more nuanced picture: Atlantic saltening reflects this thermodynamic control, while SSS changes elsewhere are mainly driven by atmospheric circulation and rainfall changes tied to uneven SST warming. The CMIP6 statistical analyses highlight dynamical mechanisms that motivate further testing through targeted ocean simulations.