Effects of Large-Scale Ocean Dynamics on the Uncertainty in Projecting Tropical Pacific SST Warming Pattern

Abstract

This chapter investigates how inter-model differences in large-scale ocean dynamics affect that in the tropical Pacific SST warming (TPSW) pattern. After removal of the effect of cloud radiation feedback, inter-model differences associated with large-scale ocean dynamics play another important role, explaining around 14% of the total inter-model variance in TPSW pattern. Of particular importance are differences in the climatological ocean zonal overturning circulation. With the robust enhancement of ocean stratification across models, models with stronger than multi-model ensemble mean (MME) climatological upwelling tend to have weaker than MME SST warming in the eastern Pacific. Meanwhile, the pronounced inter-model differences in the changes of zonal overturning circulation contribute little to uncertainty in the TPSW pattern. In addition, the inter-model differences in climatological zonal overturning circulation turn out to be associated with the inter-model spreads in climatological SST. In most CMIP5 models, there is a common overly-strong cold tongue associated with an overly-strong overturning circulation in the climatology simulation, implying a La Nina-like bias in the MME projection of the TPSW pattern by CMIP5 models.