How will El Nino-Southern Oscillation change as the climate warms?
In plain words
El Nino and La Nina are swings in Pacific temperatures that shift weather worldwide. Climate models disagree on whether these swings will grow or shrink with warming, and the observed Pacific pattern has evolved differently from most models.
Precise statement
Determine the sign and magnitude of change in ENSO amplitude, frequency and spatial pattern under greenhouse warming, and resolve why the observed 1980 to 2020 eastern equatorial Pacific cooling trend and strengthened zonal SST gradient differ from the warming in most CMIP models. An answer is a projected change with mechanisms (thermocline, zonal advective and Ekman feedbacks) constrained by observations and paleo records.
What would settle it
Models that reproduce the observed tropical Pacific trend pattern and ENSO statistics, whose projected ENSO change is then consistent with paleo-ENSO records under past warm climates.