Deriving century-long trends of surface temperature change from borehole temperatures

We have employed a few‐parameter estimation (FPE) technique to derive information on past surface temperature variations from present‐day borehole temperatures. Synthetic experiments show that the FPE technique can separate reasonably well information on century‐long trends of surface temperature change from borehole temperatures within a wide range of noise levels. The technique also allows a simple illustration and comparison of the inversion results, both spatially and temporally. We illustrate this technique by analyzing seventeen borehole temperature profiles from eleven sites in northeast USA and southeast Canada, utilizing a ground surface temperature model of five ramps of century‐long duration.