Is climate sensitivity related to dynamical sensitivity? A Southern Hemisphere perspective

Abstract This study examines whether the spread in the climate sensitivity of CoupledModel Intercomparison Project Phase 5 (CMIP5) models also captures the spread in the Southern Hemisphere dynamical response to greenhouse gas forcing. Three metrics are proposed to quantify the “dynamical sensitivity” of the Southern Hemisphere: the poleward expansion of the Hadley circulation, the poleward expansion of the subtropical dry zone, and the poleward shift of themidlatitude jet. In the CMIP5 abrupt 4×CO2 integrations, the expansion of the Hadley circulation is well correlated with climate sensitivity in all seasons; in contrast, the shifts in the subtropical dry zone and midlatitude jet are significantly correlated with climate sensitivity only in summer and fall. In winter, those responses are more strongly linked to the control climatology in each model. Thus, a narrow focus on traditional climate sensitivity alonemightmiss out on important features of the atmospheric circulation’s response to increasing greenhouse gases, particularly in the extratropics.