Changes in Independency between Two Types of El Niño Events under a Greenhouse Warming Scenario in CMIP5 Models

This study uses archives from phase 5 of the Coupled Model Intercomparison Project (CMIP5) to investigate changes in independency between two types of El Nino events caused by greenhouse warming. In the observations, the independency between cold tongue (CT) and warm pool (WP) El Nino events is distinctively increased in recent decades. The simulated changes in independency between the two types of El Nino events according to the CMIP5 models are quite diverse, although the observed features are simulated to some extent in several climate models. It is found that the climatological change after global warming is an essential factor in determining the changes in independency between the two types of El Nino events. For example, the independency between these events is increased after global warming when the climatological precipitation is increased mainly over the equatorial central Pacific. This climatological precipitation increase extends convective response to the east, particularly for CT El Nino events, which leads to greater differences in the spatial pattern between the two types of El Nino events to increase the El Nino independency. On the contrary, in models with decreased independency between the two types of El Nino events after global warming, climatological precipitation is increased mostly over the western Pacific. This confines the atmospheric response to the western Pacific in both El Nino events; therefore, the similarity between them is increased after global warming. In addition to the changes in the climatological state after global warming, a possible connection of the changes in the El Nino independency with the historical mean state is discussed in this paper.