Zonally variable response of the intertropical convergence zone and energy flux equator in CMIP6 future climate

Abstract:

Despite recent studies projecting a robust future narrowing of the intertropical convergence zone (ITCZ) during the 21^st century in response to climate change, projections remain highly uncertain with respect to its future position, with most past work focusing on the zonal-mean ITCZ shift. Here we use outputs from 27 state-of-the-art climate models (CMIP6) to investigate future ITCZ shifts in all seasons and longitudes of the globe, under increased CO₂ emissions (scenario SSP3-7.0). We document a robust zonally asymmetric response of the ITCZ, with a northward shift over eastern Africa and the Indian Ocean, and a southward shift in the eastern Pacific and Atlantic Ocean basins. From an energetics perspective, we show that the ITCZ response is consistent with future changes in the divergent atmospheric energy transport over the tropics, and sector-mean shifts of the energy flux equator (EFE). The changes in the EFE appear to be the result of zonally asymmetric imbalances in the hemispheric atmospheric heating over the two sectors, consisting of increases in atmospheric heating over Eurasia and cooling over the Southern Ocean, which contrast with atmospheric cooling over the North Atlantic Ocean due to a model-projected weakening of the Atlantic meridional overturning circulation (AMOC). The asymmetric responses of the ITCZ and of the EFE have not been reported and thoroughly explored in the literature and are of high importance, since they could substantially alter atmospheric circulation and precipitation patterns in the tropics and subtropics, and greatly affect the vulnerability of ecosystems and rainforests.