Asymmetric Changes of ENSO Diversity Modulated by the Cold Tongue Mode Under Recent Global Warming

Abstract

Instead of the La Niña events with no significant change in their surface expressions, the recent increasing frequency of central Pacific El Niño events is suggested to be related to global warming. There is yet no consensus on the impacts of the recent global warming on such asymmetric changes of El Niño-Southern Oscillation (ENSO) events. Here we show the frequency of the extreme cold/moderate warm events both increases in the central equatorial Pacific over the past decades. We attribute the change of ENSO diversity to the positive cold tongue mode under recent global warming, which gives rise to an intensification, contraction, and westward shift of Walker circulation accompanied by an uplift of the thermocline. Our results propose a unified explanation for the changes of ENSO diversity under the recent global warming, which carries important implications for the relationship between global warming and ENSO.