Estimating summer temperature fluctuations over long timescales in southern South America is essential for better understanding the past climate variations in the Southern Hemisphere. Here we developed robust 212 year long basal area increment (BAI) and δ13C chronologies from living temperature‐sensitive Fitzroya cupressoideson the eastern slope of the northern Patagonian Andes (41°S). After removing the increasing trend from the growth records likely due to the CO2fertilization effect, we tested the potential to reconstruct past summer temperature variations using BAI and δ13C as predictors. The reconstruction based on δ13C records has the strongest predictive skills and explains as much as 62% of the total variance in instrumental summer temperature (n= 81, p< 0.001). The temperature signal recorded in tree‐ring growth is not substantially different to that present in δ13C and consequently does not provide additional information to improve the regression models. Our δ13C‐based reconstruction shows cold summer temperatures in the second part of the 19th century and in the mid‐20th century followed by a warmer period. Notably, the 20th and the early 21st centuries were warmer (+0.6°C) than the 19th century. Reconstructed summer temperature variations are modulated by low‐latitude (El Niño–Southern Oscillation) and high‐latitude (Southern Annular Mode) climate forcings. Our reconstruction based on δ13C agrees well with previous ring width based temperature reconstructions in the region and comparatively enhances the low‐frequency variations in the records. The present study provides the first reconstruction of summer temperature in South America south of 40°S for the period 1800–2011 entirely based on isotopic records. The Southern Hemisphere, and particularly southern South America, are very under‐represented in global climate reconstructions due to a lack of robust paleoclimatic data. Here, we reconstruct summer temperature variations on the eastern slope of the Andes in north Patagonia over the last two centuries using tree rings of one of the longest‐living species from South America, Fitzroya cupressoides. This reconstruction highlights that the 20th and 21st centuries were warmer (+ 0.6°C) than the 19th century. Our work thus contributes to improve the assessment of the intensity of current climate changes in remote regions from the Southern Hemisphere. Summer temperatures on the eastern slope of the Northern Patagonian Andes were +0.6°C warmer during the 20th than the 19th centuryThe temperature signal is better recorded in cellulose δ13C values than in tree growth of F. cupressoidesThe recent increase in tree growth on the eastern slope of the Northern Patagonian Andes is likely due to the CO2fertilization effect