East to west retardation in the onset of the recent warming across Canada inferred from inversions of temperature logs

[1] Canadian well temperature logs for 141 sites are analyzed and show evidence of extensive ground surface temperature (GST) warming beginning in the eighteenth and nineteenth centuries following a lengthy period of cooling (the Little Ice Age) over most of the past millennium. The method of functional space inversion (FSI) is applied to the complete set of 141 well precise temperature logs from wells located in low-conductivity clastic sediments of the western Canadian Sedimentary basin and higher thermal conductivity crystalline rocks of the Canadian Shield in central and eastern Canada. Marked regional differences in the onset of recent warming are evident (nineteenth century compared to the seventeenth to eighteenth centuries, respectively), following a prolonged cold period through earlier centuries. Analysis of spatial patterns of GST history changes across Canada based on the individual inversions of temperature logs shows a systematic east-to-west retardation in the onset of the recent warming yet a higher overall warming magnitude in western Canada in the twentieth century.