Zonally opposing shifts of the intertropical convergence zone in response to climate change

TL;DR

This study uses climate model projections to reveal a zonally opposing shift of the ITCZ in response to climate change, with a northward movement over some regions and southward over others, driven by hemispheric heating imbalances.

Contribution

It provides a detailed analysis of the longitudinal and seasonal shifts of the ITCZ using CMIP6 models, highlighting the importance of energy transport and hemispheric heating in these changes.

Findings

Northward ITCZ shift over eastern Africa and Indian Ocean

Southward ITCZ shift in eastern Pacific and Atlantic

Linked to hemispheric atmospheric heating imbalances

Abstract

Future changes in the location of the intertropical convergence zone (ITCZ) due to climate change are of high interest since they could substantially alter precipitation patterns in the tropics and subtropics. Although models predict a future narrowing of the ITCZ during the 21st century in response to climate warming, uncertainties remain large regarding its future position, with most past work focusing on the zonal-mean ITCZ shifts. Here we use projections from 27 state-of-the-art climate models (CMIP6) to investigate future changes in ITCZ location as a function of longitude and season, in response to climate warming. We document a robust zonally opposing 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 by 2100, for the SSP3-7.0 scenario. Using a two-dimensional energetics framework, we find that the revealed 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 opposing 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.