Geothermics of Climate Change: Linking Ground and Air Temperature Change Through Repeat Temperature Measurements in Boreholes From Northwest Utah

Temperature-depth profiles measured in boreholes contain important information about the Earth's changing surface temperature and provide a direct method for reconstructing surface temperature variations over the past several centuries. Differences between temperature-depth logs, on annual to decadal timescales, provide an important test of borehole thermometry. Twelve temperature-depth logs at the northwestern Utah Emigrant Pass Observatory (EPO) borehole, GC-1, seven at borehole SI-1 and five at borehole DM-1, were acquired between the years 1978 and 2007. Differences in temperature logs extend to about 100 m. Below 100 m, differences between temperature logs are effectively zero. SAT data from the meteorological station at EPO and nearby Historical Climatology Network stations are used as a forcing function at the Earth's surface and diffused into the subsurface. These transients reproduce observed subsurface temperature variations reasonably well at each borehole. Comparisons between repeated temperature-depth profiles and diffused SAT transients over the same time period offer strong support for using GST histories to complement SAT data and multi-proxy reconstructions in climate change studies.