Enhanced North Pacific impact on El Nino/Southern Oscillation under greenhouse warming

A majority of El Nino/Southern Oscillation (ENSO) events are preceded by the North Pacific Meridional Mode (NPMM), a dominant coupled ocean-atmospheric mode of variability. How the precursory NPMM forcing on ENSO responds to greenhouse warming remains unknown. Here, using climate model ensembles under high-emissions warming scenarios, we find an enhanced future impact on ENSO by the NPMM. This is manifested by increased sensitivity of boreal-winter equatorial Pacific winds and sea surface temperature (SST) anomalies to the NPMM three seasons before. The enhanced NPMM impact translates into an increased frequency of NPMM that leads to an extreme El Nino or La Nina. Under greenhouse warming, higher background SSTs cause a nonlinear evaporation-SST relationship to more effectively induce surface wind anomalies in the equatorial western Pacific, conducive to ENSO development. Thus, NPMM contributes to an increased frequency of future extreme ENSO events and becomes a more influential precursor for their predictability. The North Pacific Meridional Mode (NPMM) can trigger El Nino/Southern Oscillation (ENSO) events. Climate simulations suggest that with warming ocean temperatures, the NPMM's impact on future ENSO strengthens, contributing to increased frequency of future extreme ENSO events and their predictability.

Automated summary

Research suggests that under high-emissions warming scenarios, the North Pacific Meridional Mode (NPMM) strengthens its impact on El Nino/Southern Oscillation (ENSO), leading to increased frequency of extreme ENSO events and improved predictability.