Nonlinear ENSO Warming Suppression (NEWS)

AbstractIn global warming experiments, the majority of global climate models warm faster in the eastern equatorial Pacific than in the west and produce a weakening of the Walker circulation. In contrast, GFDL-ESM2M is an exception that exhibits a La Nina–like mean-state warming with a strengthening of the Walker circulation. This study explores the cause of this exceptional response and proposes a new mechanism, the nonlinear ENSO warming suppression (NEWS), where the transient heating rate difference between the atmospheric and oceanic reservoirs annihilates extreme El Ninos, causing a suppression of mean-state warming in the east. Heat budget analyses of GFDL-ESM2M robustly show that nonlinear dynamical heating, which is necessary for extremely warm El Ninos, becomes negligible under warming. An idealized nonlinear recharge oscillator model suggests that, if the temperature difference between the atmospheric and oceanic reservoirs becomes larger than some threshold value, the upwelling becomes too effic...