The Role of Climate Change in the Expansion of Dengue

Climate change–related weather and extreme events are increasing in intensity and frequency, affecting the transmission of infectious diseases worldwide. Dengue, a climate-sensitive vector-borne disease to which more than half of the global population is at risk, has expanded its geographical range over recent decades. The 2023/24 season marked the largest dengue outbreak ever recorded in the Americas, with over 6 million cases in Brazil, and more than 5,000 deaths, coinciding with the hottest year on record in the region. To investigate the effect of climate on dengue transmission, we fit a Poisson generalized linear model for more than 5,000 municipalities in Brazil, using over 20 years of data available from DATASUS, to investigate the 2023/24 dengue season and attribute the role of anthropogenic climate change. We use simulations from the UK Met Office HadGEM3-A model, which includes two scenarios: a natural-forcing-only scenario (NAT) and a scenario including both natural and anthropogenic forcings (ACT). Temperature and precipitation from these simulations are then used as inputs to the Poisson model to estimate differences in dengue case counts between the NAT and ACT scenarios. We find that observed temperature anomalies in municipalities in southeastern and southern Brazil pushed these regions into optimal thermal conditions for dengue transmission during the 2023/24 season, amplifying the epidemic. In contrast, in northern Brazil, temperatures during the same period became too high for effective transmission, resulting in lower dengue incidence compared to a counterfactual scenario without anthropogenic climate change, although uncertainties remain high due to the lower number of cases in this region. We further test the generalizability of our model in high-altitude regions of Mexico, where dengue has been expanding. Overall, our results provide empirical evidence that climate change–related temperature anomalies contributed to the expansion and intensification of dengue transmission across diverse ecological and socio-economic contexts, with important implications for preparedness, adaptation, mitigation, and resilience planning.