Unraveling non-monotonic responses of the El Niño–Southern Oscillation to post-2100 global warming

The El Niño–Southern Oscillation (ENSO) shapes global climate extremes. Although most climate models project its intensification through the 21st century, its behavior beyond 2100 remains unclear. Here, we conducted multi-scenario simulations extending to 2500 with an Earth System Model to assess ENSO responses across different warming levels and analyzed a multi-model ensemble. We find that ENSO amplitude, asymmetry, periodicity, and diversity change non-monotonically: under moderate global warming, ENSO strengthens with persistent positive skewness and ~4-year periodicity. Under extreme global warming, ENSO amplitude and skewness decline, and its period shortens to 2–3 years, favoring Central Pacific events. These non-monotonic changes arise from a shift in the eastern Pacific background from equatorial surface wind divergence to convergence, which promotes ocean heat discharge and efficiently terminates ENSO. Our findings indicate a shift toward more frequent but less intense ENSO variability in a high-warming world, posing challenges for climate projection and adaptation.