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Future of Canadian Permafrost
Permafrost is a thermal condition of the ground, and is therefore its existence is dependent on climate. Thus, permafrost will be profoundly affected by global warming. Over many thousands of square kilometres, permafrost is within one or two degrees of its melting point. The behaviour and stability of soils in cold regions is strongly influenced by temperature and therefore changes in ground thermal conditions are of great importance.
General circulation models predict that mean annual air temperatures may rise by several °C over much of the Arctic during the 21st century if there is a doubling in the concentration of atmospheric carbon dioxide due to fossil fuel burning. Arctic regions are especially sensitive to global warming, and some researchers predict the temperature to rise by 5 to 10°C (or more) during the winter months. Large areas of the Canadian north are underlain by permafrost at temperatures greater than -2°C (Figure 1) and it is expected that most of this permafrost, which is generally less than 75 m thick, may ultimately disappear under anticipated climate warming scenarios. In areas of thicker and colder permafrost, warming would likely result in a thickening of the active layer, an increase in permafrost temperature and a decrease in permafrost thickness.
 Figure 1: Spatial variation in mean annual near-surface ground temperature for the Canadian permafrost region. The discontinuous permafrost zone includes the area shown to have a ground temperature warmer than -2°C. Within this zone there are areas where the ground temperature is above 0°C (from Smith and Burgess, 1998 and 1999). (Image courtesy Sharon Smith, GSC).
The impacts of permafrost warming and degradation will be important in regions where permafrost is ice-rich. Thawing of ground ice can result in loss of soil strength and lead to ground instability which has important implications for many landscape processes and hazards such as increased terrain, slope and coastal stability. These changes as well as associated alterations to surface hydrology, groundwater regimes, and surface vegetation have consequent socio-economic impacts for ecosystems, infrastructure and development. In addition, climate warming in permafrost regions will also affect the carbon cycle through changes in greenhouse gas sources and sinks associated with thawing or burning of permafrost-affected peatlands. An assessment of the impact of climate change on permafrost is necessary to determine whether adaptation measures will be required.
The sensitivity of permafrost to climate warming is a component of a series of national syntheses of geological responses to climate change currently being prepared by the Geological Survey of Canada. The GSC study examines the sensitivity of permafrost to warming by considering the main factors that determine the response of the permafrost thermal regime to warming and the impact of any permafrost thaw that occurs. Geographic Information System (GIS) techniques have been used to produce maps classifying areas according to A) the thermal response to warming: the relative rate and magnitude of ground temperature change (Figure 2), and B) the physical response: the relative magnitude of the impact of permafrost thaw (Figure 3).
 Figure 2: The relative thermal response of permafrost to climate warming (from Smith and Burgess, 1998). Ground temperature has been classified into three zones. The potential for permafrost thaw would be greatest in areas underlain by permafrost that currently has a temperature close to 0°C (zone 3) and which also would exhibit a high thermal response to warming. Permafrost thaw and the disappearance of permafrost would be expected to occur first in these regions. (Image courtesy Sharon Smith, GSC).
 Figure 3: The relative physical response of permafrost to climate warming (from Smith and Burgess, 1998). Thaw subsidence will be greatest where ice-rich sediments are present. The structural ice content (pore ice and ice lenses) will generally be higher in fine-grained and organic material. In areas where massive ice is abundant the consequences of permafrost thaw could be more severe than indicated by the shading which reflects the structural ice content of the surficial material. (Image courtesy Sharon Smith, GSC).
Scientists at the Geological Survey of Canada have used site specific one-dimensional thermal modelling to determine the impact of climate warming on thaw depth and permafrost thickness at selected sites in the Mackenzie Valley. The results for Norman Wells and Fort Simpson are shown in Figure 4. Thaw depths are plotted as a function of time for three scenarios: a linear air temperature increase, an exponential air temperature increase, and a linear increase with 10% more snowfall. The plots show the increase in maximum annual thaw depth over the 50-year simulation period and the rise in the base of permafrost. In all simulations, the rate of change in thaw depth is very slow in the first 10 to 20 years but significantly greater thereafter. These results suggest that detection of the early impacts of warming by monitoring thaw depth may be difficult, particularly when allowing for seasonal variations and when dealing with permafrost temperatures near 0°C.
 Figure 4: Predicted increase in thaw depth and permafrost degradation for two sites in the Mackenzie Valley under three climate warming scenarios. (Image courtesy GSC).
The GSC is also developing a GIS based modelling and mapping techniques which integrate key environmental factors for predicting the occurrence of permafrost. These are being validated for the Mackenzie Valley and are being applied to the regional prediction of equilibrium permafrost distribution temperature and thickness under various climate warming scenarios (Figure 5).
 Figure 5: Predicted permafrost occurrence in the Fort Simpson study area under a 1°C and 2°C increase in mean annual air temperature, and current climate conditions (mean annual air temperature of -4°C). Blue indicates rivers or lakes, green corresponds to unfrozen material, and white indicates permafrost thicknesses between 1 and 5 m, light grey between 5 and 10 m, and dark grey between 10 and 15 m. The Norman Wells pipeline is shown in yellow and Mackenzie Highway in red (Wright et al., 2000). (Image courtesy GSC)
References
- Burgess M.M., Desrochers, D.T. and Saunders, R., 2000. Potential changes in thaw depth and thaw settlement for three locations in the Mackenzie Valley; in The physical environment of the Mackenzie Valley: a baseline for the assessment of environmental change, L.D. Dyke and G.R. Brooks (eds.), Chapter 19, Geological Survey of Canada Bulletin 547.
- Smith, S.L. and Burgess, M.M., 1999. Mapping the sensitivity of Canadian permafrost to climate warming; in Interactions Between the Cryosphere, Climate and Greenhouse Gases (Proceedings of IUGG 99 Symposium HS2, Birmingham, July 1999); IAHS Publication no. 256, p. 71-80.
- Smith, S.L. and Burgess, M.M., 1998. Mapping the response of permafrost in Canada to climate warming; in Current Research 1998-E; Geological Survey of Canada, p. 163-171.
- Wright, J.F., Smith, M.W. and Taylor, A.E. , 2000 Potential changes in permafrost distribution in the Fort Simpson and Norman Wells Areas; in The physical environment of the Mackenzie Valley: a baseline for the assessment of environmental change, L.D. Dyke and G.R. Brooks (eds.), Chapter 20, Geological Survey of Canada Bulletin 547.
The above material was provided by Margo Burgess and Sharon Smith, Geological Survey of Canada.
A model calculating the Temperature at the Top Of Permafrost (TTOP) has also been developed by Smith and Riseborough (1996). Because snow cover and ground thermal properties significantly modulate the relation between air temperature and permafrost, this model links permafrost with the surface climatology through seasonal surface transfer functions and subsurface thermal properties. The model is exact for equilibrium conditions, and provides a reasonably accurate estimate of subsurface temperatures under transient conditions.
Results of the TTOP model indicate that Canadian permafrost will become largely confined to the northern portions of the mainland Territories and the Arctic Islands if there is adoubling of atmospheric carbon dioxide. Baffin Island will no longer have a complete cover of permafrost, and it will disappear completely in northern Quebec. According to the model, the total area of permafrost would be reduced eventually to less than half its current extent.
References
- Smith, M.W. and D.W. Riseborough (1996) Ground temperature monitoring and detection of climate change. Permafrost and Periglacial Processes, 7(4): 301-310.
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