Intensification of the Western North Pacific Anticyclone Response to the Short Decaying El Nino Event due to Greenhouse Warming

Two types of El Nno evolution have been identified in terms of the lengths of their decaying phases: the first type is a short decaying El Nino that terminates in the following summer after the mature phase, and the second type is a long decaying one that persists until the subsequent winter. The responses of the western North Pacific anticyclone (WNPAC) anomaly to the two types of evolution are remarkably different. Using experiments from phase 5 of the Coupled Model Intercomparison Project (CMIP5), this study investigates how well climate models reproduce the two types of El Nino evolution and their impacts on the WNPAC in the historical period (1950-2005) and how they will change in the future under anthropogenic global warming. To reduce uncertainty in future projection, the nine best models are selected based on their performance in simulating El Nino evolution. In the historical run, the nine best models' multimodel ensemble (B9MME) well reproduces the enhanced (weakened) WNPAC that is associated with the short (long) decaying El Nino. The comparison between results of the historical run for 1950-2005 and the representative concentration pathway 4.5 run for 2050-99 reveals that individual models and the B9MME tend to project no significant changes in the two types of El Nino evolution for the latter half of the twenty-first century. However, the WNPAC response to the short decaying El Nino is considerably intensified, being associated with the enhanced negative precipitation anomaly response over the equatorial central Pacific. This enhancement is attributable to the robust increase in mean and interannual variability of precipitation over the equatorial central Pacific under global warming.