IMPACTS ON PERMAFROST

The terrestrial environment of the north, in which permafrost plays such a major role, would be profoundly disrupted during the transition to a warmer world.  With climatic warming there would be long-term changes in the distribution of permafrost, as extensive areas of warm permafrost eventually disappeared. While complete thawing of permafrost might take centuries (IPCC 1990), there will be rapid onset effects over periods of several decades. As ice-rich permafrost degrades from the surface, widespread thaw settlement and terrain disturbance is likely, which raises concerns for the stability of roads and various other structures.

The existence of permafrost affects numerous properties of the ground, from its strength to its hydrology. Since permafrost is defined by temperature and not by the state of moisture in the soil, it can contain both ice and unfrozen water simultaneously (Williams and Smith 1989). As the proportions of ice and water change as the temperature changes, permafrost is a very dynamic substance. The physical and mechanical properties of permafrost are temperature dependent, and  particularly so within one or two degrees of 0^oC. With a temperature increase due to climate warming, permafrost soils will weaken. On complete thawing, the ground will lose its strength from ice cementation, with implications for the stability of slopes, structures and foundations.

Geotechnical Issues

The stability of the ground is of serious concern for building and maintaining roads, pipelines and other structures. As such, geotechnical issues regarding the strength of the ground and its effect on structures are significant. The geotechnical consequences of climate warming in permafrost regions have been summarized by Esch and Osterkamp (1990).

Infrastructure in Canada’s north often depends critically upon permafrost as a foundation material, or as a contaminant barrier, among other functions. Under stable climate conditions, these factors can be assessed by geotechnical evaluation and professional judgment. Current engineering practice accommodates climate variability through consideration of the historical climatic record. Given the expectation of global climate change, practice must be adjusted to accommodate expected trends in climate variables relevant to the design. This requires consideration of the lifetime of the project, to determine the extent to which a climate trend will have significant impact during the useful life of the project.

The report by the CRISIS Impact Assessment Research Group (Paoli et al. 1998) focuses on the impact of climate warming on the use of permafrost as a structural material in engineering design. Warming of the ground as a result of climate change will degrade the performance of many existing and planned structures including roads, foundations, embankments and open pit mines. Of particular concern are mine tailings retention structures.

Greenhouse gases

Permafrost is a potential source of greenhouse gases and thawing of the ground could affect the global carbon cycle to a significant degree. Organic material in thawing permafrost decays rapidly, releasing large quantities of carbon dioxide and methane, and the permafrost regions could change from a global carbon sink to a source of carbon. This, in turn, would act as a positive feedback loop to global climate warming.

Studies in Alaska (REF?) have found that the tundra has switched during the last few decades from absorbing carbon dioxide to releasing it. Moreover, large summer methane releases are closely correlated to warming temperatures. Because large amounts of organic carbon, the precursor for carbon dioxide and methane emissions, are sequestered within permafrost, a thicker active layer could affect global-warming predictions, Nelson notes. 

Therefore, the impact of climate change on permafrost conditions is of concern and significance to Canada and the globe.