Geothermal record of climate change

Abstract

Temperature-depth profiles measured in boreholes can be an important record of surface temperature change and can be summarized as follows: 1. Thermal diffusion results in low-pass filtering of changes in surface temperature trends to be related to subsurface curvature. Unfortunately, annual means are not apparent. Further, the depth distribution of borehole temperature anomalies is related to the timing of surface temperature changes. 2. Both globally and regionally, ground temperatures show a predominantly warming signal consistent with surface temperature warming over the past two centuries. 3. Repeated temperature measurements in the same borehole can help improve the confidence in separating and interpreting steady-state and transient sources of curvature. 4. Geothermal climate change reconstruction techniques show approximately 1º C of ground warming over the past one to two centuries, consistent with proxy methods of paleoclimate reconstruction.