North Atlantic Oscillation (NAO) in the Paleoclimate Modelling Intercomparison Project (PMIP)

Abstract. The North Atlantic Oscillation (NAO) is one of the main modes of climate variability and the dominant mode of large-scale atmospheric variability in the North Atlantic basin and has large impacts on the European climate, whose future behaviour remains uncertain. Here we assess the NAO response in past and future climates by looking at a comprehensive set of coupled model simulations performed by the Paleoclimate Model Intercomparison Project (PMIP) and the Coupled Model Intercomparison Project (CMIP) for four experiments: the mid-Holocene (6 ka; midHolocene), the Last Glacial Maximum (21 ka; lgm), the last interglacial (127 ka; lig127k) and an idealised future warming scenario with abrupt quadrupled CO₂. Although there are various setups across experiments, the midHolocene and lig127k are mainly characterised by altered orbital configurations, inducing variations in the seasonal cycle, and the lgm and abrupt4xCO2 are mainly characterised by various GHG forcing that induces great global temperature change. Our results show that the NAO is sensitive to GHG-forcing-induced temperature changes but not the orbital configurations. NAO weakens in response to cooling and strengthens to warming. The associated teleconnections change consistently with the theory and are sensitive to the change in NAO amplitude. The two orbital experiments do not show a clear change in associated temperature and precipitation. The weakened NAO in the lgm is associated with a cooler and drier northern Europe, while the enhanced NAO in the abrupt4xCO2 causes a warmer and wetter northern Europe as compared to the piControl. No clear relationship is found in the ENSO-NAO teleconnection.