Changes in ENSO amplitude under global warming in CESM Large Ensemble project: the uncertainty due to internal variability

El Niño-Southern Oscillation (ENSO) is the dominant mode of ocean-atmospheric coupling system in the tropical oceans. Recent progresses suggested that the divergent mean state changes in the tropical Pacific, especially its spatial pattern, have an important bearing on the changes in ENSO and its diversity among the model. In this study, the changes in ENSO variability in future projection is investigated based on 30-member ensemble from CESM1 Large Ensemble (CESM-LE) community project. It is found that even though an analogous spatial pattern in SST warming appears in all the ensemble members, the uncertainty in ENSO changes among the members is large and comparable with that from CMIP5 models, illustrating that the internal variability is able to modulate the response of ENSO to global warming effectively. Further investigation suggests that the member diversity in ENSO changes is related to the ENSO-induced tropical Pacific decadal variability, which features zonal dipoles in sea surface temperature along the equator. The inter-member relationships between changes in mean state and ENSO are totally different in CESM-LE and CMIP5 ensembles, suggestive of the distinct source of uncertainty in future projections.