With the unprecedented rate of global warming in this century, whether or not human-made climate change is irreversible is the most critical question. Based on idealized CO2 ramp-up and -down experiments, we show here that the intertropical convergence zone (ITCZ) exhibits irreversible changes. While the ITCZ location does not change much during the CO2 increasing period, the ITCZ sharply moves south as soon as CO2 begins to decrease, and its center eventually resides in the Southern Hemisphere. The pattern of the irreversible precipitation changes manifests a permanent extreme El Nino-like pattern, which has distinctive impacts on the global hydrological cycle. It was revealed that the hysteresis behavior of the Atlantic meridional overturning circulation and the delayed energy exchanges between the tropics and extratropics are responsible for the peculiar evolution of the hemispheric temperature contrast, leading to irreversible ITCZ changes.