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Here we investigate the causal links of interannual variability between the El Nino-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) in Coupled Model Intercomparison Project Phase 5 (CMIP5) RCP8.5 future simulations. The analyses account for possible simultaneous impacts of the southern annular mode and the Indian summer monsoon rainfall on future ENSO-IOD connection. We found robust causal influence of ENSO on IOD for majority (14/22) of models. ENSO variations cause changes of tropical Indian Ocean zonal wind and sea surface temperature and thus directly influence IOD. However, the specific mechanisms of this impact remain elusive in multimodel point of view. The results show significant impact of IOD on ENSO in the 2006-2100 period for 10/22 models. These results suggest that ENSO influence on IOD is slightly more robust than vice versa. We emphasize the uncertainty in the two-way future causal relationship between ENSO and IOD.

Plain Language Summary The global climate is influenced by several major climate modes, including the El Nino-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). In the present study, we investigate the future connection between ENSO and the IOD as understanding their relationship is important for future climate extreme predictions in and around Indian Ocean and Pacific Ocean. We used data from 22 different climate model simulations for the 2006-2100 period. The results indicate significant impact of the IOD on ENSO in 10/22 models, while the influence of ENSO on the IOD is found in 14/22 models. This study allows us to gain insight into the future relationship between ENSO and the IOD, as well as understanding the consistency of climate models in simulating the links between these two climate modes.