A country-level storyline attribution of global warming on heat-related extremes in South America

Due to rising global temperatures accompanied by ENSO influences, the 2015–2024 decade featured multiple high-impact heat extremes that caused water scarcity, wildfires, power outages, and mortality in South America. In this systematic, country-based study, we use spectrally nudged storylines to examine how anthropogenic global warming modifies the occurrence of heat-related extremes across South America at a national scale. Extending the approach beyond single events, we simulate the 2015–2024 decade under counterfactual (pre-industrial), present-day, and +2K, +3K, and +4K global warming levels. We analyze climate indices relevant to human health (warm days, warm nights, hot-humid days) and water security (extreme droughts). Results show that under pre-industrial conditions, few countries would have experienced heat extremes. In contrast, persistent extreme conditions already emerge at +2K, including saturation of warm nights in Colombia and extreme droughts in Brazil and Bolivia. In warmer climates, all tropical and subtropical countries approach saturation in at least one index, while Uruguay exhibits low sensitivity to global warming. Moreover, different to present-day climate, under warmer conditions, years with or without the influence of El Niño show a comparable behavior. Based on events of the last decade, our study highlights how continued warming could shift several South American countries towards increasingly persistent heat and drought conditions, emphasizing the need for mitigation and adaptation planning.