El Niño and Its Predictability: 1856-2003

Recent studies suggest that the predictability of the El Niño-Southern Oscillation (ENSO) is limited by the effects of atmospheric “noise” such as the westerly wind bursts in the western equatorial Pacific. Here retrospective forecasts of the interannual climate fluctuations in the tropical Pacific for the period from 1856 to 2003 were carried out using an improved ocean-atmosphere coupled model. The predictability of ENSO was evaluated based on the skill of actual predictions over an unprecedented number of events. The model successfully predicted all of the prominent El Niños, including those occurred in the late 19 century, at lead times up to two years. Our results suggest that the evolution of El Niño is more controlled by self-sustained internal dynamics than driven by stochastic forcing, and as such it depends more on initial conditions than on unpredictable atmospheric noises. Because of the simplicity of our model and data assimilation procedure, the predictive skill demonstrated here is a lower bound on the predictability of ENSO. Throughout the past century, El Niño has been more predictable than previously envisioned.