Observational studies indicate that the characteristics of El Ni¿o-Southern Oscillation (ENSO) during the 1980s are noticeably different from those during the 1960s and 1970s. Here, we provide modeling evidence that stochastic processes can not only produce a shift in the persistence of sea-surface temperature (SST) but also causes changes in the predictability of ENSO. Based on this result, we suggest that climate shifts of ENSO, such as that occurred around 1976, could be induced by stochastic processes. Therefore, the stochastic mechanism should be taken as a null hypothesis for climate shifts against which competing mechanisms must be compared. ¿ 1999 American Geophysical Union