Based on two field surveys of permafrost distribution, conducted 26 years apart, along the Mackenzie Highway south of Great Slave Lake, Canada, the southern limit of the sporadic discontinuous permafrost zone in the region has migrated northward by about 120 km. To substantiate that the disappearance of perennial frozen ground is largely caused by climatic warming, a detailed trend analysis of monthly air temperature records from nine weather stations was performed using the non-parametric Kendall's test. The results show that the region experienced a general warming trend for the period 1949–1989 and warming is more prominent in the minimum than the maximum temperature series. From estimates of the magnitude of warming trends on a monthly basis, the resultant increase in mean annual air temperature could readily lead to the observed northward migration of permafros
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