Greenhouse gas forcing dominates the recent strengthening of North Pacific Meridional mode influence on ENSO

Abstract The North Pacific Meridional Mode (NPMM) is a key extratropical trigger of El Niño–Southern Oscillation (ENSO) events, and its influence on ENSO has increased markedly in recent decades, offering a pathway to improve ENSO predictability. Yet, the relative contributions of external forcings versus internal variability to this intensified influence remain uncertain. Using multi-model simulation outputs from the Detection and Attribution Model Intercomparison Project and a suite of numerical experiments, we demonstrate that greenhouse gas (GHG) forcing dominates over internal variability in driving the recent strengthening of the NPMM–ENSO connection, whereas aerosol and natural forcings have minimal impact. GHG forcing enhances the wind–evaporation–SST feedback over the subtropical North Pacific by elevating the background mean SST, which amplifies NPMM-induced westerly wind bursts over the western tropical Pacific and promotes ENSO development. Sensitivity experiments further demonstrate that GHG-induced SST increasing in the subtropical North Pacific enhances the atmospheric response associated with the NPMM. These findings reveal an important role of anthropogenic forcing in modulating the extratropical impact on ENSO and suggest potential opportunities for extending ENSO prediction lead times.