Permafrost is a thermal condition and therefore its occurrence is dependent on climate. Climate, however, is not constant and historically has undergone significant changes detectable at time scales from decades or centuries to millennia. During periods of cooling, permafrost may increase in both areal extent and thickness, while a warmer climate may cause an increase in active layer thickness, permafrost thinning, and in some cases, disappearance.

Not all permafrost present today is in equilibrium with the current climate. Thick permafrost beneath the Beaufort Shelf is a relic of periods of lower sea level associated with the last glaciation. During this time, large areas of the continental shelf were above sea level and exposed to the intense cold of a full glacial climate. This allowed the formation of permafrost up to 700 metres in thickness. During interglacial periods and in postglacial time, these areas have been covered by Arctic Ocean water with a mean annual temperature 10 to 15°C higher than air temperatures during glacial periods. The thermal regime of the subsea permafrost is thus in disequilibrium with the present marine environment. The sediments therefore are warming gradually, causing the permafrost to slowly degrade.

A general warm period followed the disappearance of glacial ice with temperatures peaking during the middle Holocene between 6000 and 9000 years ago. Macrofossil analysis and radiocarbon dating of peat cores has been used to reconstruct the permafrost distribution in western Canada 6000 years ago. The results of this analysis suggest that mean annual temperatures were about 5°C warmer than present and the southern limit of permafrost was 300 to 500 km northward of its current position. Much of the present discontinuous permafrost zone may have been free of permafrost. Where permafrost did exist during this time, active layer thickness was probably greater than at present. Many thermokarst lakes also developed in the Mackenzie Delta during this time.

Cooler conditions followed the mid-Holocene warm period and permafrost became more extensive. Permafrost was probably established in northwestern Alberta by 3700 years ago and the climate at this time probably resembled the present climate regime. In the Mackenzie Delta region, permafrost aggradation (growth) and pingo development occurred in response to the deterioration in climate that began about 5000 BP.

Frozen peatlands occur today in the southern fringe of the discontinuous permafrost zone at relatively warm ground temperatures (> 0.5°C). Permafrost likely formed when slightly colder climatic conditions prevailed in the northern hemisphere during the Little Ice Age. Between 1550 and 1850 AD, temperatures were about 1°C cooler than present and permafrost occurred farther south than it does today. Much of this permafrost has generally degraded in response to warming but has been preserved in some areas due to the insulating properties of the thick peat cover.

 

Permafrost is melting and receding toward the North in many locations in Canada. The photo was taken at the James Bay, Ontario.

Evidence also exists for climate-induced changes to permafrost response during the last several decades to a century. During the last 100 years, air temperatures in the Mackenzie District (western Arctic) have warmed by about 1.5°C. This warming has caused an increase in permafrost temperatures in the Yukon and western N.W.T. In Manitoba, permafrost continues to degrade in the southern fringe of the permafrost region especially where there is no surface peat layer. In the eastern Arctic, however, recent cooling and aggradation (growth) of permafrost has occurred. Air temperature records for northern Quebec, show a decrease in temperature between 1947 and 1992 ranging from .02 to .03°C per year which has been accompanied by a cooling of the upper 20 m of permafrost between 1988-1993.

Material for this section was provided by Sharon Smith and Margo Burgess, Geological Survey of Canada, and extracted from the following sources:

• Smith, S.L., Burgess, M.M., and Heginbottom, J.A., (in press). Permafrost in Canada, a challenge to northern development; in A Synthesis of Geological Hazards in Canada, (ed.) G.R. Brooks; Geological Survey of Canada, Bulletin 548.
• Smith, S.L. and Burgess, M.M. (in prep.) Sensitivity of permafrost to climate warming in Canada; Contribution to Geological Survey of Canada’s "Impact of global climate change on geological processes", Geological Survey of Canada Bulletin.