Future Changes to ENSO Teleconnections over the North Pacific and North America in CMIP6 Simulations

El Niño-Southern Oscillation (ENSO) has major impacts on the weather and climate across many regions of the world. Understanding how these teleconnections may change in the future is therefore an important area of research. Here, we use simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to investigate future changes to ENSO teleconnections in the North Pacific/North America sector.

Precipitation over the equatorial Pacific associated with ENSO is projected to shift eastwards under global warming as a result of greater warming in the east Pacific, which reduces the barrier to convection as the warm pool expands eastwards. As a result, there is medium confidence (IPCC AR5 report) that ENSO teleconnections will shift eastwards in the North Pacific/North America sector. In the CMIP6 models, the present day teleconnection is relatively well simulated, with most models showing an anomalously deep Aleutian low and associated positive temperature anomalies over Alaska and northern North America in El Niño years. In the future warming simulations (we use abrupt-4xCO2, in which CO2 concentrations are immediately quadrupled from the global annual mean 1850 value), in agreement with the IPCC AR5 report, the North America teleconnection and associated circulation change is shifted eastwards. However, it is also weaker in most models, and the combination of these changes means that the positive temperature anomalies in El Niño years over North America are much reduced. Barotropic model experiments, run using different combinations of basic state and forcing from individual CMIP6 models, suggest that changes to the forcing in the equatorial Pacific between the pre-industrial control and abrupt-4xCO2 are the main cause of these changes, and this will be discussed in further detail.