Resolving the Paradox of Changing ENSO-Monsoon Relation through Global-ENSO

Recent debates over the changing correlation between Indian summer monsoon rainfall (ISMR) and the El Nino-Southern Oscillation (ENSO) have raised inconclusive claims about the stability of the ENSO-Monsoon relationship (EMR) and ISMR predictability. Here we show that this apparent instability arises because traditional Pacific-based ENSO indices incompletely represent ENSO's global influence and are affected by climate noise, making their correlation with ISMR unreliable. We introduce a Global-ENSO framework using the depth of the 20-degree Celsius isotherm (Dp), a subsurface predictor integrating contributions from all three tropical ocean basins and maximizing ISMR teleconnections. Contrary to previous findings, ISMR shows a strong and stable correlation (0.8) with Dp at 18-month lead during the historical period. This predictability emerges from lagged synchronization between ISMR and Dp, where ISMR evolves as a delayed realization of the Dp dynamics. Our findings suggest that true EMR is stable and ISMR robustly predictable, providing clarity amid ongoing controversies.