BOREHOLE TEMPERATURES AND A BASE-LINE FOR 20TH-CENTURY GLOBAL WARMINGESTIMATES

Lack of a 19th-century baseline temperature against which 20th-century warming can be referenced constitutes a deficiency in understanding r ecent climate change. Combination of borehole temperature profiles, wh ich contain a memory of surface temperature changes in previous centur ies, with the meteorological archive of surface air temperatures can p rovide a 19th-century baseline temperature tied to the current observa tional record. A test case in Utah, where boreholes are interspersed w ith meteorological stations belonging to the Historical Climatological Network, yields a noise reduction in estimates of 20th-century warmin g and a baseline temperature that is 0.6 degrees +/- 0.1 degrees C bel ow the 1951 to 1970 mean temperature for the region.