Assessment of the summer Asian–Pacific Oscillation pattern in CMIP6 models: historical simulations and future projections

The Asian–Pacific Oscillation (APO), a zonal teleconnection pattern dominating in Asian–North Pacific sector, is highly variable and considerably impacts the climate, economy, society, and environment on regional and global scales. Using 22 outputs of global climate models (GCMs) from Phase six of the Coupled Model Intercomparison Project (CMIP6), we investigated the summer APO pattern and examined its projected changes under different Shared Socioeconomic Pathways (SSPs). Results show that most CMIP6 GCMs can accurately capture the spatial features of the APO for 1950–2014, while model ability to reproduce APO interannual variability and long-term trend is relatively low. The multi-model ensemble (MME) is more representative in reproducing reproduce APO features in the reanalysis data than the single climate model, although the long-term trend remains unsatisfactory. Furthermore, the MME under four SSPs project an average decrease in APO intensity during the late 21st century, with the largest decrease occurring under SSP5-8.5, which is the scenario with the highest radiative forcing. The models project cooling over continental Asia and warming over the Pacific relative to historical observations and tilting of the vertical axis of the APO pattern, which results in a slight eastward shift of the APO in the future. According to the MME and relative to 1965–2014, the APO is likely to weaken during the mid and late 21st century. In addition, although considerable uncertainties remain, there is substantial agreement between models in their projected changes of the APO index under high emissions scenarios.