Between 1970 and 1984, ground surveys were carried out along a flowline extending from the top of the south dome of Barnes Ice Cap to the margin. Over this time span, the ice cap thinned an average of 1.7 m, or 0.12 m yr−1. By comparing the 1984 survey with elevations derived from satellite imagery in 2006, we find that it has now thinned an additional 16.8 ± 7.7 m, or an average of ∼0.76 ± 0.35 m yr−1. Laser altimeter profiles show that between 2004 and 2006, the thinning rate was 1.0 ± 0.14 m yr−1. A correlation between mass balance and mean summer temperature at nearby weather stations, developed over the period of the ground surveys, permits independent estimates of the thinning rate. These estimates are in excellent agreement with those based on satellite imagery. The acceleration in thinning is consistent with meteorological records documenting an increase in the number of positive degree-days (atmospheric warming) in the region.