Stuart A. Harris

Permafrost is ground that remains below 0°C for more than two consecutive years. This condition is widespread in polar regions and near the top of high mountains (Figure 1).

In permafrost that is in equilibrium with the present-day climate, the negative heat balance of the soil is the result of the interaction between the low mean annual temperatures cooling the ground surface not being adequately modified by the relatively small but stable geothermal heat flow coming from the interior of the earth. Obviously, a change in the mean annual air temperature will modify the adjacent ground temperatures, but the relationship is not simple.

 The factors affecting permafrost distribution can be broadly divided into two groups: climatic and terrain. Climatic factors control the rate and duration of heat transfer to the ground surface. Altitude, latitude, snow cover, temperature, cold air drainage, and temperature inversions are examples, and these are dominant over the terrain factors in the Far North. Terrain factors modify climatic factors and control permafrost distribution along the southern border of the permafrost zone. Examples would include local relief, vegetation, hydrology, the nature of soil or rock, and fire. However, factors such as vegetation, hydrology, and fire frequency may also vary with changes in climatic factors.

Increasingly, man is becoming a factor in permafrost terrain. When the sole inhabitants of the region were native hunters living in harmony with the environment, there were few problems. However, with the increased population resulting from better health care, the discovery and development of northern resources, and the coming of modern equipment such as snowmobiles,  rifles, and aircraft, land use has been modified to the point of no return. The fragile environment cannot sustain the population pressure with a subsistence style of living; increasingly, modern technology is being called on to solve problems associated with other types of land use in the permafrost environment.

The Nature of Permafrost Ground

To understand the consequences of climatic change on permafrost, we must first examine the nature of permafrost. Permafrost merely implies a temperature condition, and, if the permafrost is dry, then there are minimal problems. Unfortunately, most permafrost contains large quantities of moisture in the form of ground-ice.

The upper layer, which thaws in summer and freezes in winter each year, is called the active layer. In summer, it tends to produce a very wet, sloppy surface, since the underlying frozen layers prevent water from the melting snow and ground-ice from percolating downward to any great extent.

Beneath the active layer is the upper surface pf the permafrost, called the permafrost table. The highest moisture content in the permafrost tends to be found in this layer. Moisture content of more than 1000 per cent by volume is common in silts and peats in regions such as the lower Mackenzie Valley. If these are thawed, they produce a fluid with the consistency of dishwater. Very quickly, a pond appears, followed by enlargement into a lake. This will grow in size until it intersects a drainage-way, or is bounded by dry permafrost.

 The permafrost generally becomes less icy and warmer toward its base layer. At Hay River, this would be at 10 metres, whereas at Tuktoyaktuk it may be at 250 metres in depth. Unfrozen zones within the permafrost body are known as taliks and commonly contain water.

Effect of Climatic Change

Climatic change produces a very rapid increase (warming) or decrease (cooling) in the active layer. Thus, the 2°C cooling of mean annual air temperature since 1940 at Tuktoyaktuk has resulted in a 40 per cent reduction in the thickness of the active layer. The thermal changes gradually spread through the mass of the permafrost, with the slowest changes occurring at the permafrost base. The latter will rise as a result of warming, or descend deeper if there is cooling.

 The temperature of the permafrost also alters its strength. The colder the permafrost, the greater its strength and the better the bonding between the permafrost and man-made structures such as foundations. Warming of the permafrost reduces its load-bearing strength, even though thawing does not actually occur.

 Areas most vulnerable to a warming of the climate are shown in Figure 2. A 2°C warming would eventually move the outer boundary of permafrost to that of the metastable permafrost region. A 5°C increase in temperature would ultimately result in melting of the permafrost everywhere except in the Far North.

 In contrast, cooling would expand the area of permafrost southward and result in moisture accumulation (ground-ice) where enough moisture is available. This would be accompanied by variable heaving of the ground surface. In general, climatic change would produce greater effects on the works of man in the ice-rich permafrost of western arctic Canada than in the drier, rockier areas of the eastern Arctic. The following section outlines some of the major consequences.

Foundations

Roads, railways, airstrips, pipelines, buildings, and other structures rest on foundations of one sort or another placed in the upper layers of the ground. In general, a cooling trend will not seriously affect the performance of foundations unless differential heaving occurs. This would tend to occur on the margins of permafrost bodies where taliks would become frozen.

 Warming of the climate would produce a rapid increase in the thickness of the active layer. Foundations are designed with only a limited safety factor to cope with unusually warm years and are certainly not built to cope with the effects of climatic change. A small increase in temperature would greatly reduce the load-bearing strength of the ground and tend to produce structural failures in foundations; larger temperature increases would mean that almost all of the structures would have to be rebuilt. The effects would be worst in the areas of discontinuous permafrost, due, in part, to the variation in thaw settlement from place to place. Rebuilding would be easiest for certain types of pile construction where deeper piles could be added to support linear structures such as pipelines or utilidors before complete failure occurred.

Winter Roads

Climatic warming would reduce the time for their use each winter, especially on the southern margin of the permafrost zone. Conversely, climatic cooling would make these of greater use in a wider area.

 Use of the Sea

Climatic warming would increase the season for open-sea operations and probably modify the zones of the different ice types (landfast ice, polar pack ice, seasonal ice) in the offshore areas. There would be changes in the distribution and frequency of release of ice islands and icebergs from the far North which would alter design requirements for offshore structures such as oil wells and shipping terminals. Shorelines in icy permafrost would retreat more rapidly than today, creating problems for coastal settlements along the north coast of Yukon.

 Mining

 Climatic warming would aid in placer and open-pit mining, as the amount of permafrost encountered would be reduced. Higher temperatures would reduce the strength of the permafrost and force underground mines to use larger rock pillars to support the roofs of the workings. The risk of rock bursts and flooding from taliks would increase, and the cost of cooling the air put into deep mines would rise. Conversely, cooling would hinder placer and openpit mining and favour underground mining.

 Water Supply and Waste Disposal

For health reasons, these must be kept apart. In general, waste is disposed of in pits on the permafrost surface, where it becomes refrigerated, while the best and safest water supplies come from beneath the permafrost. A climatic warming would tend to thaw the waste piles and allow bacteria to migrate through the thawed soil; the risk of contamination of water supplies would be greatly increased. On the other hand, climatic cooling would make water supplies harder to find and would make it necessary to modify the water distribution systems in the larger settlements to prevent water freezing in the pipes.

 Landscape

 Climatic warming would cause thawing of ice-rich permafrost, resulting in thaw lakes and subsidence of the land surface. This would damage the forests and make land use and agriculture more difficult until thawing was complete. Contrary to popular belief, increased farming might be difficult in the North due to the tendency to produce saline soils on the flatter land during cultivation (e.g., around Fort Simpson and Whitehorse). Distance from markets would be a limiting factor in the development of agriculture.

Trends in Climatic Change

 Although there is an increasing concentration of carbon dioxide in the atmosphere, other climatic changes are occurring constantly. Current studies of ground temperatures in areas of permafrost show different regimes from place to place. Along the Rocky Mountains, temperatures have dropped 3°C in the last 10 years, and recent cooling is also indicated along the north coast of Yukon. The lower and middle Mackenzie Valley show stable ground temperatures at present, whereas the higher levels of the Nahanni Range are undergoing a warming, Perhaps due to temperature inversion. Thus, there is not a simple correspondence of trends in ground temperatures from place to place in northern Canada nor evidence of the extreme climatic changes predicted by some climatologists. Nevertheless, the situation warrants close attention.

Amelioration of the Effects of Climatic Change

 Little can be done to modify the effects of substantial changes in climate, but it is possible to make minor changes to the heat balance in small areas. Thus, peat acts as a natural insulator and can be used to prevent excessive thawing in man-made disturbances. Wood chips have recently been tried along the Zama Lake-Norman Wells pipeline but have been less successful. Thermal piles can be used to cool the ground by about 1°C around foundations and have proved successful in stabilizing certain structures (e.g., Churchill Railroad, Ross River School).

 The thawing of winter snow and ice can be accelerated by placing soot or other dark substances on the surface to promote heat absorption, and snow fences have proved successful in inducing thawing of patches of permafrost at the Iron Ore Co. of Canada mines at Schefferville. Snow has also been used to insulate the ground from winter cold to prevent contraction cracking at Garry Island.

 Conclusions

 Permafrost distribution directly reflects climate, and the response of ground temperature to any climatic change will affect the works of man very quickly. A substantial climatic warming would devastate most engineering structures built on permafrost such as roads, railways, pipelines, and buildings, except in the Far North or where foundations rest on bedrock. The effects on mining would depend on the type of mine, but there could be extreme problems with water supplies and leakage from waste disposal sites.

Available evidence does not support the concept of a major warming trend having commenced in the permafrost areas, but this will have to be monitored carefully. Should there be a major change in climate, we can only make minor modifications to ameliorate its effects at specific sites. Trying to design northern facilities to protect against a large3/4 4°C3/4 climatic warming is not feasible due to the high costs involved.

Stuart A. Harris is a professor of geography at the University of Calgary.