Tropical response to ocean circulation slowdown raises future drought risk

Projections of tropical rainfall under global warming remain highly uncertain, largely because of an unclear climate response to a potential weakening of the Atlantic meridional overturning circulation (AMOC). Although an AMOC slowdown can substantially alter tropical rainfall patterns, the physical mechanisms linking high-latitude changes to tropical hydroclimate are poorly understood. Here we demonstrate that an AMOC slowdown drives widespread shifts in tropical rainfall through the propagation of high-latitude cooling into the tropical North Atlantic. We identify and validate this mechanism using climate model simulations and palaeoclimate records from Heinrich Stadial 1 (HS1)—a past period marked by pronounced AMOC weakening. In models, prevailing easterly and westerly winds communicate the climate signal to the Pacific Ocean and Indian Ocean through the transport of cold air generated over the tropical and subtropical North Atlantic. Air–sea interactions transmit the response across the Pacific Ocean and Indian Ocean, altering rainfall patterns as far as Indonesia, the tropical Andes and northern Australia. A similar teleconnection emerges under global warming scenarios, producing a consistent multi-model pattern of tropical hydroclimatic change. These palaeo-validated projections show widespread drying across Mesoamerica, the Amazon and West Africa, highlighting an elevated risk of severe drought for vulnerable human and ecological systems.