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Southeast Brazil has great economic importance for Brazil and is highly vulnerable to extreme events like floods and droughts. Studies have shown an increase of temperature in this region. Using a new detection and attribution framework (Ribes et al., 2017, ) and Coupled Model Intercomparison Project Phase 5 models, this change is found to be largely due to greenhouse gases. We estimate that greenhouse gases contribute a warming of 0.95 to 1.5 degrees C to the observed warming trend of 1.1 degrees C between 1955 and 2004. Temperature changes from natural and nongreenhouse gas anthropogenic forcing are estimated to be small over this period. Results are robust using different time windows. Using the Community Earth System Model ensembles to evaluate the impacts of internal variability, observational and model error shows that most uncertainty arises from model error.

Plain Language Summary Southeast Brazil has great economic importance for Brazil and is highly vulnerable to extreme events like floods, droughts, and heat waves. Many studies link those kind of events with an increase in temperature due to climate change, largely caused by increasing atmospheric concentrations of greenhouse gases. This study tested whether or not human-induced climate change is responsible for the observed increase in temperature in Southeast Brazil. The observed 1.1 degrees C per 50-year trend is largely due to increasing greenhouse gases, which means that they have a significant role in observed changes in Southeast Brazilian temperatures.