Mean State Change‐Induced Differential Responses Between Strong Positive and Negative Events Reduce Indian Ocean Dipole Asymmetry Under Greenhouse Warming

Abstract Climate models robustly project a reduction in the skewness of Indian Ocean Dipole (IOD)‐related sea surface temperature anomalies (SSTAs) under future greenhouse warming. However, it remains unclear how strong positive IOD (spIOD) and negative IOD (nIOD) events respectively contribute to the projected skewness changes. Here, using multiple CMIP6 models and large ensemble (LE) simulations that are skillful in simulating nonlinear IOD dynamics, we show that the weakened IOD skewness reflects differential responses of spIOD and nIOD to greenhouse warming induced by mean‐state changes. SpIOD events, although occurring more often in the warming 21st century, are projected to weaken in event‐average intensity. The opposing changes between the frequency and amplitude of spIODs induce a compensatory effect on the skewness change, with the net contribution depending on model internal variability. In contrast, nIOD events not only occur more frequently but also strengthen in amplitude, both conducive to the weakening of IOD skewness and thus determining the forced skewness response. These differential responses between spIOD and nIOD stem from a pIOD‐like mean state change, which induces asymmetric changes in associated air–sea feedbacks under global warming. A drier eastern Indian Ocean (EIO) inhibits atmospheric convection feedback, thereby limiting the nonlinear growth of cold SSTAs, while an elevated EIO thermocline promotes oceanic thermocline feedback favoring the development of warm SSTAs. Collectively, these diverse changes in spIODs and nIODs weaken IOD asymmetry in a warming climate, with nIODs playing an indispensable role.