ENSO cycles mostly after extreme El Niño events

The El Niño–Southern Oscillation (ENSO) arises from ocean–atmosphere interactions in the tropical Pacific and is a major source of global seasonal climate predictability. Canonical theories describe ENSO as a cyclic phenomenon, with ocean dynamics favouring transitions between warm (El Niño) and cold (La Niña) phases, and atmospheric noise introducing irregularities. Here, we show that ocean dynamics rarely favour such transitions. Following La Niña and moderate El Niño events, opposing wave signals from the central and western Pacific weaken the ocean’s memory, inhibiting consistent phase reversals. In contrast, extreme El Niño events—such as those in 1982, 1997, and 2015—trigger strong, nonlinear atmospheric responses that generate distinctive ocean heat content anomalies and set up a robust transition to a two-year La Niña. We propose revising the canonical recharge oscillator framework to account for this behaviour and explain ENSO’s dominant 3–7 year timescale as emerging from transitions between extreme El Niño and multi-year La Niña events. Overall, these results indicate that extreme El Niño events uniquely provide two-year ENSO predictability, while in other cases, predictability stems from external forcing that generate imbalances between heat content anomalies in the central and western Pacific.