Understanding ENSO Weakening in Warmer Climates

Abstract El Niño and La Niña events control much of Earth's interannual variability, impacting surface temperatures and precipitation worldwide. Despite their importance, how these events will change as the climate warms is not fully understood. Here, we use idealized atmosphere‐ocean simulations to study the El Niño/Southern Oscillation (ENSO) under equilibrated greenhouse warming. In warmer climates, the atmosphere transports energy more efficiently, smoothing the Pacific zonal temperature gradient and weakening the Walker Circulation. Since these zonal asymmetries are the source of ENSO instability, ENSO growth rates decrease in warmer climates, leading to less extreme ENSO events. Additionally, the weakening of ENSO leads to less ENSO asymmetry so the strengths of El Niño and La Niña events become more similar in warmer climates. We interpret these results with an energy budget of the Central‐Eastern Equatorial Pacific.