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

Abstract

[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. INDEX TERMS:0915 Exploration Geophysics: Downhole methods; 1610 Global Change: Atmosphere (0315, 0325); KEYWORDS: Canada climate warming, borehole temperature, geothermics Citation: Majorowicz, J., J. Safanda, and W. Skinner, East to west retardation in the onset of the recent warming across Canada inferred from inversions of temperature logs,

Impact of maximum borehole depths on inverted temperature histories in borehole paleoclimatology

“…For instance, some studies have used boreholes as shallow as 100-150 m (e.g. Majorowicz et al, 1999;Majorowicz and Safanda, 2001;Majorowicz et al, 2002;Hamza et al, 2007), while the many global analyses typically set the minimum depth criterion at 200 m thus employing boreholes 200 m or deeper Harris and Chapman, 2001;Beltrami, 2002;Beltrami and Bourlon, 2004;Pollack and Smerdon, 2004). Our calculations suggest that these depths are likely too shallow, but several caveats are necessary and discussed below.…”

“…It is important to note, however, that the numerical experiments on which this conclusion was based used synthetic borehole profiles generated with a surface temperature history comprising a linear increase in temperature over 150 years. Given the realistic thermophysical properties used by Majorowicz et al (2002) to model their subsurface profiles, such a surface temperature history would never yield perturbations below about 100-150 m. As we show in this study, temperature fluctuations that occur prior to the advent of the instrumental record can impact borehole profiles well below such depths and therefore require much deeper maximum borehole depths to adequately identify an unperturbed background steady-state signal. Such considerations make the Majorowicz et al (2002) study difficult to interpret.…”

“…Given the realistic thermophysical properties used by Majorowicz et al (2002) to model their subsurface profiles, such a surface temperature history would never yield perturbations below about 100-150 m. As we show in this study, temperature fluctuations that occur prior to the advent of the instrumental record can impact borehole profiles well below such depths and therefore require much deeper maximum borehole depths to adequately identify an unperturbed background steady-state signal. Such considerations make the Majorowicz et al (2002) study difficult to interpret. Notably, Harris and Chapman (1995) and Roy et al (2002) both propose means of estimating the depth to which surface perturbations have significantly affected temperature profiles, below which they argue that the background thermal regime can be safely estimated.…”

“…Harris and Chapman (2001) estimate the background thermal regime in all analysed boreholes using data below 160 m, a depth that is argued to be "sufficient to avoid more recent climate change effects, but that retains enough data in the deeper subsurface to obtain robust estimates" of the background regime. Similarly, Majorowicz et al (2002) perform synthetic experiments that tested inversions for different maximum borehole depths. They report depths below 150-200 m to be sufficient for their analyses of boreholes in Canada.…”

Spatial distribution of Pleistocene/Holocene warming amplitudes in Northern Eurasia inferred from geothermal data

“…The result from Outokumpu may be also irrelevant as it was obtained for shallow boreholes (790-1100 m) and under 2-D heat transfer conditions. Our analysis shows that insufficient depths may lead to underestimation of paleotemperature changes (Golovanova et al, 2002; this effect was also mentioned in Majorowicz et al, 2002Majorowicz et al, , 2006. However, it must not be ruled out that comparatively low PHW amplitudes in these sites reflect the spatial temperature variations at the base of the Scandinavian Ice Sheet.…”