Hysteresis in ENSO teleconnections under a CO2 removal pathway

Abstract

Abstract El Niño-Southern Oscillation (ENSO) is the strongest interannual phenomenon occurring in tropical Pacific, significantly affecting the entire world. Until now, the response of ENSO to increasing CO2 concentrations has been extensively studied, but the reverse scenario is still not well comprehended. Here, we investigate the hysteresis of ENSO teleconnections in a CO2 removal simulation of an earth system model. During both the ramp-up and ramp-down periods of CO2 concentrations, Pacific-North American and Pacific-South American patterns are intensified, with their poles being shifted eastward. Even more significant alterations of teleconnection pattern during the ramp-down period lead to the ENSO teleconnection hysteresis. The ENSO teleconnection hysteresis is closely linked to the hysteresis of the dominant ENSO type, ENSO skewness and the zonal shift of ENSO-induced tropical atmospheric convection. The hysteresis in the eastern Hemispheric ENSO teleconnections is primarily caused by the prevalence of eastern-Pacific type El Niño during the ramp-down periods, while in the western Hemisphere, the hysteresis effect is attributed to both the enhanced ENSO skewness and the eastward shift of anomalous atmospheric convection during the ramp-down period. The alterations originating in the tropics are predominantly associated with irreversible and intensified southward migration of the Intertropical Convergence Zone, along with a stronger El Niño-like warming trend during the ramp-down period compared to the ramp-up period.