The North Pacific Meridional Mode (NPMM), a critical extratropical trigger for El Niño-Southern Oscillation (ENSO) events, has exhibited a pronounced increase in its influence on ENSO in recent decades, providing an important avenue for enchancing ENSO predictability. However, the relative roles of external forcings and internal variability in this intensified coupling remain poorly understood. Using multi-model simulations from the Detection and Attribution Model Intercomparison Project (DAMIP), we show that greenhouse gas (GHG) forcing substantially outweighs internal variability in driving the recent strengthening of the NPMM-ENSO connection, while aerosol and natural forcings play negligible roles. GHG forcing enhances the wind-evaporation-sea surface temperature (SST) feedback over the subtropical North Pacific by raising the background mean SST, which in turn intensifies NPMM-induced westerly wind bursts over the tropical western-central Pacific, fostering more robust ENSO development. This finding contributes to our understanding of anthropogenic impacts on ENSO variability and underscores the potential to improve subseasonal to interannual climate predictability.
 

ENSO, North Pacific, external forcing