ENSO skewness hysteresis and associated changes in strong El Niño under a CO2 removal scenario
Chao Liu, Soon‐Il An, Fei‐Fei Jin, Malte F. Stuecker, Wenjun Zhang, Jong‐Seong Kug, Xinyi Yuan, Jongsoo Shin, Aoyun Xue, Xin Geng, Soong‐Ki Kim
Abstract
Abstract El Niño-Southern Oscillation (ENSO) sea surface temperature (SST) anomaly skewness encapsulates the nonlinear processes of strong ENSO events and affects future climate projections. Yet, its response to CO 2 forcing remains not well understood. Here, we find ENSO skewness hysteresis in a large ensemble CO 2 removal simulation. The positive SST skewness in the central-to-eastern tropical Pacific gradually weakens (most pronounced near the dateline) in response to increasing CO 2 , but weakens even further once CO 2 is ramped down. Further analyses reveal that hysteresis of the Intertropical Convergence Zone migration leads to more active and farther eastward-located strong eastern Pacific El Niño events, thus decreasing central Pacific ENSO skewness by reducing the amplitude of the central Pacific positive SST anomalies and increasing the scaling effect of the eastern Pacific skewness denominator, i.e., ENSO intensity, respectively. The reduction of eastern Pacific El Niño maximum intensity, which is constrained by the SST zonal gradient of the projected background El Niño-like warming pattern, also contributes to a reduction of eastern Pacific SST skewness around the CO 2 peak phase. This study highlights the divergent responses of different strong El Niño regimes in response to climate change.