The Pacific Decadal Oscillation (PDO) is the most prominent form of decadal variability over the North Pacific, characterized by its horseshoe-like sea surface temperature (SST) anomaly pattern. The PDO exerts a substantial influence on marine ecosystems, fisheries, and agriculture. Through modulating global mean temperature, the phase shift of the PDO at the end of the 20th century is suggested to be an influential factor in the recent surface warming hiatus. Therefore, determining the predictability of the PDO in a warming climate is of great importance. By analyzing future climate under different emission scenarios simulated by the Coupled Model Intercomparison Project phase 5 (CMIP5), we show that the prediction lead time and the associated amplitude of the PDO decreases sharply under greenhouse warming conditions. This decrease is largely attributable to a warming-induced intensification of oceanic stratification, which accelerates propagation of Rossby waves, shortening the PDO lifespan and suppressing its amplitude by limiting its growth time. Our results suggest that greenhouse warming will make prediction of the PDO more challenging, with far-reaching ramifications.