Changes in El Niño–Southern Oscillation and global frequency entrainment

The El Niño–Southern Oscillation (ENSO) periodicity governs the recurrence of its warm and cold phases, shaping the climate variability and the frequency of extremes, yet remains poorly constrained in climate model projections. Here we assess, using coordinated multi-model large-ensemble simulations, the forced modulation of ENSO periodicity from the last millennium to the future and its global imprint. ENSO periodicity tends to shorten under future warming, and this periodicity shift extends to tropical climate modes and propagates globally through teleconnections, a phenomenon we refer to as ENSO frequency entrainment. The frequency entrainment appears to be ubiquitous, evident in forced responses in last-millennium simulations and under nonstationary, nonmonotonic CO2 forcing, as well as in periodicity modulation driven by internal multi-decadal variability. Changes in future ENSO periodicity may alter the frequency of local climatic events globally, potentially favoring more frequent extreme events. Multi-model large-ensemble simulations agree that El Niño cycles may become shorter under future warming, shifting climate rhythms around the world through teleconnections and potentially increasing the frequency of regional extreme events.