Detecting robust responses of the ENSO teleconnection to global warming using a multi-model large-ensemble experiment

The El Niño-Southern Oscillation dominates interannual variability of the climate system, with widespread global teleconnections that influence regional precipitation and temperature. ENSO teleconnection patterns are projected to shift eastward over the Pacific-North America sector under global warming (medium confidence in IPCC AR5 report, with no uncertainty bounds and approximately 25% of models disagreeing). Better constraining future changes in ENSO teleconnections remains a challenge because of model uncertainty in how tropical convection and the midlatitude circulation will respond to global warming, as well as large internal variability of the teleconnection pattern itself, which makes it challenging to isolate the forced signal. Here, we use large-ensemble experiments (at least 100 members from 5 uncoupled CMIP models plus a 40-member coupled ensemble) to investigate the changing ENSO teleconnection under a +2°C warming scenario. In agreement with previous studies, we find a slight northeastward shift of the North Pacific teleconnection centre related to 1) an eastward shift of tropical convection that occurs even with no change in the ENSO SST forcing, and 2) mean-state changes in the midlatitude circulation. However, the shift is robust only when a substantial (at least 40) number of ENSO events are considered, suggesting that the observational record is too short to use as a baseline. Associated shifts in temperature impacts are weak, while precipitation impacts in regions along the North American west coast are accentuated and expand inland. Overall, our results help quantify the role of atmospheric internal variability in modulating the future response and impacts of the ENSO teleconnection.