Similar North Pacific variability despite suppressed El Niño variability in the warm mid-Pliocene climate

Abstract. The mid-Pliocene is the most recent geological period with similar atmospheric CO₂ concentration to the present-day, and similar surface temperatures as projected at the end of this century for a moderate warming scenario. While not a perfect analogue, the mid-Pliocene can be used to study the functioning of the Earth system under similar forcings as a near future, especially regarding features in the climate system for which uncertainties exist in future projections. According to the mid-Pliocene modelling ensemble PlioMIP2, the variability of El Niño-Southern Oscillation (ENSO) was suppressed. In this study, we investigate how teleconnections of ENSO, specifically variability in the North Pacific atmosphere, responds to a suppressed ENSO, according to the PlioMIP2. The multi-model mean shows a similar sea-level pressure (SLP) variability in the Aleutian Low (AL) in the mid-Pliocene and pre-industrial, but a per-model view reveals that the change in AL variability is related to the change in ENSO variability. Even though ENSO is suppressed, the teleconnection between ENSO sea-surface temperature anomalies, tropical precipitation and North Pacific SLP anomalies is quite robust in the mid-Pliocene. We split AL variability in a part that is ENSO-related, and a residual variability which is related to internal stochastic variability, and find that the change in ENSO-related AL variability is strongly related to the change in ENSO variability itself, while the change in residual AL variability is unrelated to ENSO change. Since the internal atmospheric variability, which is the dominant forcing of the AL variability, is largely unchanged, we are able to understand that the AL variability is largely similar even though ENSO variability is suppressed. We find that the specific change in ENSO and AL variability depends on both the model equilibrium climate sensitivity ánd Earth system sensitivity. Finally, we present a perspective of (extra-)tropical Pacific variability in the PlioMIP2, combining our results with literature findings on changes in the tropical mean climate as well as the Pacific Decadal Oscillation (PDO).