Ground Surface Warming History in Northern Canada Inferred from Inversions of Temperature Logs and Comparison with Other Proxy Climate Reconstructions

Well temperature logs from 61 sites located in discontinuous and continuous permafrost regions of northern Canada are analyzed. The method of functional space inversion (FSI) is applied to the set of precise temperature logs from wells located between 60 and 82 N. There is strong evidence of extensive ground surface temperature (GST) warming beginning in the late 18th century and lasting until the 20th century. This was preceded by a lengthy period of cooling. The approximate average increase of the surface temperature of Canadian Arctic, based on all individual GST histories, is > 1.3 C for the last 200 years. Simultaneous inversion of all well temperature data suggests an even higher warming (approximately 2 C). There has been no strong south-to-north gradient in the ground warming magnitude when northern Canadian data are compared with eastern and central Canadian data south of 60 N which also shows warming close to 2 C. In Alaska, warming of some 2 C has been restricted mainly to the 20th century. In general, however, a high warming magnitude is common for most of Canada and Alaska for the previous century. The averaged GST history (GSTH) for the Canadian Arctic is calibrated with and compares visually with a variety of recently published regional and hemispheric proxy climate reconstructions. These show that GST warming derived from well temperature logs is generally higher than one shown by other proxy (mainly tree-ring reconstructions).