Impacts of a Reduced AMOC on the South America Mean Climate and Extremes

Abstract

The Atlantic meridional overturning circulation (AMOC) plays a crucial role in regulating global and regional climate by distributing heat meridionally across the planet. Future projections indicate a weakening of the AMOC in response to increased greenhouse gas concentrations. In this study, we investigate the impact of AMOC weakening on South America's mean climate, as well as temperature and precipitation extremes. We analyze targeted sensitivity experiments using the EC-Earth3 climate model. Our findings reveal that AMOC weakening induces cooling and wetting in the tropics of South America, contrasted by warming and dryness in the extratropics. This pattern weakens the meridional temperature gradient, shifts the intertropical convergence zone and the high-latitude winter and summer jets southward, and reduces midlatitude storm tracks, particularly in austral winter. We analyze extreme events in two representative regions—La Plata Basin and northeast Brazil—which exhibit contrasting responses. In La Plata Basin, summer heat waves become more frequent, intense, and prolonged, while winter cold spells occur more frequently but with decreased intensity and duration when the AMOC reduces. In contrast, northeast Brazil experiences an increase in the frequency and intensity of heat waves, while cold spells become less frequent but more intense. Extreme precipitation events weaken in the La Plata Basin but intensify in northeast Brazil in both seasons under AMOC weakening. Some of these climate impacts may exacerbate global warming effects, while others may partially offset them. These findings underscore the critical need to refine climate models' representation of AMOC dynamics to improve predictions of future climate scenarios.