Differences in recent ground surface warming in eastern and western Canada: Evidence from borehole temperatures

Because of the perturbation caused by a recent climatic warming, most borehole temperature‐depth profiles in Canada show reduced or negative gradients at shallow depths. However, the onset time and magnitude of the warming are different in eastern and western (British Columbia and southern Yukon) Canada. We determined the average subsurface temperature perturbations associated with the recent warming from borehole data for 34 and 51, respectively, well distributed sites in these two regions of Canada. If the ground surface temperature is assumed to have increased linearly since an onset time, the results indicate that the ground surface has warmed by 1.5 K since the mid‐19th century in eastern Canada but only by 0.8 K since the late 19th century in British Columbia and southern Yukon.