We construct a mid-latitude (30¿--60 ¿ N) reduced temperature-depth profile from a global borehole temperature database compiled for climate reconstruction. This reduced temperature profile is interpreted in terms of past surface ground temperature change and indicates warming on the order of 1 ¿C over the past 100 to 200 years. The combination of an initial temperature (the primary free parameter) with the last 140 years of gridded surface air temperature (SAT) data yields a synthetic temperature profile that is an excellent fit to observations, accounting for 99% of the observed variance and a RMS misfit of only 12 mK. The good correlation suggests that this reduced temperature profile shares much information with the mean SAT record over large areas and long time-scales. Our analysis indicates 0.7¿¿0.1¿C of ground warming between pre-industrial time and the 1961--1990 mean SAT. ¿ 2001 American Geophysical Union