Drying Tropical America Under Global Warming: Mechanism and Emergent Constraint

Abstract Tropical America (TAM) is typically humid but has recently experienced frequent droughts. Using 42 climate models from the Coupled Model Intercomparison Project Phase 6, we show that amplified equatorial Pacific warming induces a Gill‐type atmospheric response that suppresses precipitation across TAM by weakening ascent, explaining over half of the inter‐model spread in projected rainfall changes. The magnitude of projected TAM drying depends strongly on the simulated present‐day zonal sea surface temperature gradient over the tropical Pacific, but climate models systematically underestimate this gradient, likely leading to an underestimation of equatorial Pacific warming and TAM drying. An emergent constraint suggests a regional mean annual rainfall decline of 46 mm over TAM per 1 K of global warming, approximately 1.5 times the raw projection, with a 30% reduction in uncertainty. These findings highlight that drought‐related risks in the Amazon and American monsoon regions may become more severe than previously estimated.