FIGURE 8-2 Here, six climate reconstructions have been used to predict ground subsurface temperature. For each curve in the upper panel, the temperature reconstruction is used as the surface temperature for a thermal model to predict the temperature at depth. The top panel shows the six reconstructions, with zero defined as the 1961–1990 mean. The reconstruction shown in black (labeled POM-SAT) uses the borehole temperatures to constrain the Pre-Observational Mean (POM) and uses the instrumental temperature record from 1856 onward. The measured subsurface temperature pattern (bottom panel, black circles) is explained almost perfectly by the instrumental record and preceding cool centuries (black curve in the top panel). SOURCE: Harris and Chapman (2001). Reproduced by permission of American Geophysical Union; copyright 2001.