On Köppen’s classification, the central part of Northeastern Brazil has a semi-arid climate. This climate is generally associated with famine and internal migration to the coastal cities and to the South. Since the beginning of the 20th century it is also associated with political backwardness, due to the federal government mitigation policies based on dam construction and water and food distribution, both of them controlled by the local politicians and landowners. However, the social representations of the “sertão” associating its climate with poverty and political lag are quite recent. The turning point was the Brazilian great drought of 1877-1880, which raised a scientific controversy within the Polytechnic Institute in Rio de Janeiro involving the most prestigious scientists of the time. This paper explores the controversy between those who argued that the Northeastern climate was changing and those who claimed that the droughts were cyclical natural phenomena. On the one hand, the engineer Manuel Buarque de Macedo and the geographer Tomas Pompeu de Souza Brasil, then senator by one of the provinces stricken by the drought, were among the ones who believed that human action, and especially deforestation, had diminished the frequency and intensity of the rain. They believed that the construction of large dams could improve the climate by stimulating the evaporation and causing rain. On the other hand stood alone João Ernesto Viriato de Medeiros, an engineer who argued that climate could not be changed but could rather be predicted. To achieve the latter, he proposed to collect meteorological data through a network of stations created and maintained by the Imperial government. Another engineer, André Pinto Rebouças, also shared the opinion that Brazilian droughts were periodic and above human intervention. In recent years a consensus has emerged within the climatological community that the so-called Great Drought that between 1876 and 1879/80 afflicted Brazil, India and Australia was caused by Nature, specifically by a natural fact now well established and known as the El Niño-Southern Oscillation (ENSO). The question raised at the end of the 19th century by some Brazilian scientists remains thus rather actual: in face of the news of an inevitable drought, should the inhabitants of the “sertão” simply leave their houses and wait for charity and governmental aid?