Since the start of 2024, several countries in South America have experienced a rapid increase in cases of dengue, a viral disease transmitted by the aedes aegypti mosquito. According to the Pan American Health Organization (PAHO), this year alone at least 18 countries in the Americas have reported cases, with more than 400 deaths. In Peru, at the end of February, the government declared an emergency in 20 districts, setting up makeshift clinics and sending additional financial and human resources to affected areas. Dr. Andrés (Willy) Lescano, who leads the Emerging Infections and Climate Change Research Unit at Cayetano Heredia University in Lima, Peru and was one of the co-authors of the Lancet Countdown on Health and Climate Change 2022 report on South America, explains why it has been so challenging to control aedes aegypti mosquitoes in the region, the extent to which urbanization, global warming, and the el Niño phenomenon are driving the current outbreaks, and steps that can be taken to better prepare the health sector for future crises associated with a changing climate.