Permafrost in Canada and climate change Source: NRC

Source: Hinzman et al. (2005)

Time to form deep permafrost Time (yr) Permafrost depth 1 4.44 m 350 79.9 m 3,500 219.3 m 35,000 461.4 m 100,000 567.8 m 225,000 626.5 m 775,000 687.7 m Source: Wikipedia

Snow & permafrost warming Source: Stieglitz et al. (2003)

Source: Hinzman et al. (2005)

Permafrost and climate change During the past few thousand years, Earth's climate has been subject of fairly small changes and world temperatures have fluctuated only within a couple of degrees. However, higher levels of carbon dioxide and other greenhouse gases in the atmosphere may progressively increase global temperature by as much as 2 to 4oC over the next century.

In addition to temperature changes, the patterns of precipitation would undoubtedly change - annual totals would likely increase over the arctic mainland, although current regional projections are again quite variable between models. Increase of 10 to 50% in summer and as much as 60% in winter may be anticipated for parts of the Canadian Arctic. Such large and rapid climatic changes would have serious and far-reaching environmental and socio-economic effects in permafrost regions and for the arctic environment as a whole.

Some might look on the transition to a warmer Arctic with happy anticipation; in the long term, it would undoubtedly result in greatly reduced costs of living and operating there. New resources could become available, and mining and agriculture, for example, might expand; however the terrestrial environment of the north, in which permafrost plays a major role, would be profoundly disrupted during the transition.

Permafrost degradation may lead to another, potentially disastrous, positive feedback on climate. Degrading permafrost may allow the release of greenhouse gases such as CO2 and CH4 that are currently trapped in frozen ground (especially in peat bogs).

Let us imagine some change in climatic conditions which causes the mean annual surface temperature to fall below 0oC, so that the depth of winter freezing will exceed the depth of summer thaw. A layer of permafrost would grow downward from the base of the seasonal frost, thickening progressively with each succeeding winter.

Was it not for the effect of heat escaping from Earth's interior (the geothermal heat flux), the permafrost would grow to depths in response to surface temperatures only slightly below 0oC. However, this outward heat flow results in a temperature increase of about 30 K km-1, the figure varying with regional geological conditions.

Thus the base of permafrost approaches an equilibrium depth where the temperature increase caused by this geothermal gradient just offsets the amount by which the surface temperature is below freezing. Whereas the base of permafrost is determined by the mean surface temperature and geothermal heat flow, the upper layers of permafrost are influenced more by seasonal and interannual fluctuations of temperature and snowpack.

The major variation in surface temperature has a period of one year, corresponding to the annual cycle of solar radiation (there is also a diurnal variation corresponding to the daily cycle of radiation). Temperature variations experienced with the passage of the seasons at the surface extend in a progressively dampened manner to a depth of some 10-20 m.

Within the layer of annual variation, maximum and minimum figures form an envelope about the mean, and the top of permafrost is that depth where the maximum annual temperature is 0oC. Superimposed on normal periodic variations are other fluctuations with durations from seconds to years; causes may included sporadic cloudiness, variations in weather and changes in climate.

Let us now imagine some change in climatic conditions which causes mean annual surface temperature to rise. The result would be deepening of the active layer, as both the mean annual temperature and the envelope of maximum (summer) temperatures shift to higher values. If climatic warming were sustained, the permafrost table would recede further year by year and the base of the permafrost would begin to rise as surface warming propagated to greater depths.

If the progressive warming were great enough, then permafrost could eventually disappear altogether. Since permafrost is a thermal condition, it is potentially sensitive to changes in climate. However changes in the thermal regime of the ground that lead to degradation (or formation) of permafrost can result from environmental changes other than fluctuations in climate.

For example, removal, damage, or compaction of surface vegetation, peat, and soil alters the balance of surface energy transfers, generally raising mean summer surface temperature and thawing the upper layer of permafrost. In winter, increases in snow cover accumulation, as can result from barriers, structures, and depressions or changes in wind patterns, can lead to significant warming of the ground. Decreases in snow cover, in contrast, lead to cooling of the ground, other things being equal.

While the effects of surface environmental changes are usually restricted in areal extent, climatic change can affect extensive areas of permafrost. Even modest climatic warming could have drastic effects for terrain conditions and northern engineering, since thousands of square kilometers of warm permafrost would be directly affected. While many centuries would be required for complete degradation of the affected permafrost, thawing from the surface would begin immediately, with many potentially serious results.

There is some evidence that permafrost has been retreating during the past decades: Syslov (1961) reports that the permafrost extent at Mezen (Russia) has retreated northward at an average rate of 400 m per year since 1837, whereas similar findings have been reported for the Mackenzie Valley of Canada. Although permafrost is temperature dependent, the relation with climate is not straightforward, since the surface temperature regime does not depend solely on geographic location.

Local surface conditions such as the type of vegetation, depth of snow cover, soil type, and moisture content, profoundly affect the surface energy regime, being interposed between the atmosphere and the ground. Thus myriad local variations of vegetation, topography, and soil conditions can cause differences in mean ground temperatures of several degrees over quite small areas. Wherever average temperature is within a few degrees of 0oC, such variation mean that permafrost occurs in patches, or discontinuously.

These circumstances, together with the scattered nature of direct observations, make precise mapping of permafrost difficult. While cold is usually seen as the singular feature of high latitudes, problems resulting from thaw are generally of greater practical concern.

Where permafrost contains ground ice, considerable thaw settlement can occur and such action has been responsible for significant damage to buildings, roads, runways, etc. and increased action would undoubtedly cause additional and severe maintenance and repair problems. Special concern might be directed to existing water-retaining structures, such as reservoirs, and hydrodams, especially in areas of thaw-sensitive permafrost.

Erosion of lake, river, and reservoir shorelines may increase because of permafrost thawing and a longer open-water season. Greater sediment transport in rivers could shorten the operating life of hydro-electric projects, for example. The expected rise in sea level accompanying global warming could accelerate coastal retreat in permafrost regions and combined with thaw settlement as permafrost melts, could produce inundation of low-lying areas.

Source: Déry et al. (2005), JHM. Potential Changes in the Components of the Surface Water Budget, Kuparuk River Basin Source: Déry et al. (2005), JHM.

Source: Anisimov (2006)

Slaymaker and Kelly (2007)

Source: Lawrence and Slater (2005)

Source: Lawrence and Slater (2005)

Source: Vavrus (2007)