Increased extreme swings of Atlantic intertropical convergence zone in a warming climate

Interannual variability of the Atlantic intertropical convergence zone (ITCZ) affects hydrological cycles, extreme weather events, ecosystems, agriculture and livelihoods in Atlantic-rim countries. It can experience an interannual extreme swing, moving hundreds of kilometres northwards during boreal spring, causing severe droughts in central-eastern Amazon and floods in northern South America. How its interannual variability will respond to global warming remains unknown. Here using state-of-the-art climate models under a high-emission scenario, we project a more-than-doubling increase of extreme northward swings. This increase from one event per 20.4 years in the twentieth century to one per 9.3 years in the twenty-first century is underpinned by a mean state change of sea surface temperature, with faster warming north of the Equator. The warming differential facilitates the increased frequency of extreme swings, as the ITCZ follows the maximum sea surface temperature. Our finding suggests a substantial increase in ITCZ swing-induced severe droughts/floods in the Atlantic-rim countries.