Inter-El Niño variability in CMIP5 models: Model deficiencies and future changes

Abstract

Inter-El Niño variability, which represents the diversity in spatiotemporal evolution among El Niño events, has been identified using the first two leading modes of sea surface temperature anomalies along the equator. The first mode represents the transition from El Niño into La Niña and the second mode reveals El Niño’s persistence through the following spring. Here we examine the ability of models to capture inter-El Niño variability and predict future changes due to global warming using historical and Representative Concentration Pathway 8.5 simulations of phase 5 of the Coupled Model Intercomparison Project (CMIP5). Most CMIP5 models realistically reproduce the first mode, but three fifths of the models fail to capture the second mode, with considerable intermodel diversity. The 10 best models are therefore selected according to a measurement of pattern correlation coefficients and normalized root-mean-square errors with respect to reproduction of the secondmode. The results aggregated fromthe bestmodels indicate that the first “transition” mode will remain unchanged fromthe present climate to the future climate; in contrast, the second “persistence” mode changes stochastically across the CMIP5 models. Consequently, we conclude that El Niño’s transition into La Niña is the most dominant characteristic of simulated inter-El Niño variability and will remain unswayed under global warming conditions. Model deficiency in simulating El Niño’s persistence is a key source of uncertainty in modeling inter-El Niño variability, resulting in difficulty predicting how certain characteristics of El Niño events may change with global warming.