El Niño Magnitude and Western Pacific Warm Pool Displacement. Part II: Future Changes Under Global Warming

Observations reveal a strong correlation between the magnitude of El Niño and the displacement of the eastern edge of the western Pacific warm pool (WPWP). In Part I, this relationship was examined in the Coupled Model Intercomparison Project Phase 6 (CMIP6) models using their historical simulations, and it was found to be comparable to that in the observations. The present study extends the analysis to future projections under two Shared Socioeconomic Pathway (SSP) scenarios—SSP245 and SSP585—to assess whether this strong relationship persists under global warming. It is found that El Niño magnitude and WPWP boundary displacement in most models under global warming are as strongly correlated as in the observations and their historical simulations. Moreover, most models project that stronger El Niño events will be accompanied by a greater eastward displacement of the WPWP boundary. For models with a positive response, the ensemble projects an increase in El Niño magnitude of 0.21 ± 0.03 °C (0.20 ± 0.03 °C) under the SSP245 (SSP585) scenario, accompanied by an eastward displacement of the WPWP by 11.7 ± 1.3° (11.1 ± 1.0°) in longitude. These results further support the notion that El Niño is a consequence of the eastward extension of the WPWP.