Substantial effort has recently been put into the development of climate reconstructions from tree-ring stable carbon isotopes, though the interpretation of long-term trends retained in such timeseries remains challenging. Here we use detrended δ¹³C measurements in Pinus uncinata tree-rings, from the Spanish Pyrenees, to reconstruct decadal variations in summer temperature back to the 13^th century. The June-August temperature signal of this reconstruction is attributed using decadally as well as annually resolved, 20^th century δ¹³C data. Results indicate that late 20^th century warming has not been unique within the context of the past 750 years. Our reconstruction contains greater am-plitude than previous reconstructions derived from traditional tree-ring density data, and describes particularly cool conditions during the late 19^th century. Some of these differences, including early warm periods in the 14^th and 17^th centuries, have been retained via δ¹³C timeseries detrending - a novel approach in tree-ring stable isotope chronology development. The overall reduced variance in earlier studies points to an underestimation of pre-instrumental summer temperature variability de-rived from traditional tree-ring parameters.