Climate Change Canada

 

5.6: Permafrost

Permafrost temperature has increased over the past 3-4 decades (very high confidence). Regional observations identify warming rates of about 0.1ºC per decade in the central Mackenzie Valley and 0.3ºC to 0.5ºC per decade in the high Arctic. Active layer thickness has increased by approximately 10% since 2000 in the Mackenzie Valley. Widespread formation of thermokarst landforms have been observed across northern Canada.

Increases in mean air temperature over land underlain with permafrost are projected under all emissions scenarios, resulting in continued permafrost warming and thawing over large areas by mid-century (high confidence) with impacts on northern infrastructure and the carbon cycle.

Permafrost is an important component of the Canadian landscape, underlying about 40% of the landmass and extending under the ocean in parts of the Canadian Arctic. Soil properties (including both the deep mineral soil and any overlying layers of organic matter), ground cover, and the thickness of overlying snow cover (because of snow’s insulating properties) have important influences on ground temperatures and, therefore, permafrost characteristics. The soil layer above the permafrost that thaws and freezes annually is referred to as the “active layer.”

Understanding current permafrost conditions and how they may evolve in response to a changing climate is essential for the assessment of climate change impacts and the development of adaptation strategies in northern Canada. Permafrost conditions are linked to hydrological (e.g., drainage) and land surface processes (e.g., erosion and slope movements); ground warming and thawing can therefore affect ecosystems. Thawing of ice-rich permafrost results in ground instability; if not considered in the design phase, this can affect the integrity of infrastructure such as buildings and airstrips. Coastal communities face unique challenges because of processes related to thawing of the shore face (Ford et al., 2016). The northern circumpolar permafrost region holds reserves of carbon (approximately 1000 petagrams [Pg] in the upper 3 m) as large as the total amount of carbon in the atmosphere (Hugelius et al., 2014; Olefeldt et al., 2016). If permafrost thaws, it could therefore release massive amounts of greenhouse gases (carbon dioxide and methane) into the atmosphere (Romanovsky et al., 2017a). Northern soils efficiently store mercury, which is vulnerable to release as a consequence of permafrost thaw (Schuster et al., 2018). Permafrost thawing can also release other compounds and dissolved material (e.g., Kokelj and Jorgenson, 2013; Kokelj et al., 2013), including contaminants associated with waste facilities that may depend on permafrost for containment (e.g., Prowse et al., 2009; Thienpont et al., 2013).

 

5.6.1: Observed changes in permafrost

Permafrost conditions are challenging to monitor because they cannot be directly determined using satellite measurements. They are therefore determined largely from in situ monitoring, which results in gaps in the spatial distribution of measurement sites because of the relative inaccessibility of large portions of northern Canada and historical emphasis in monitoring regions with infrastructure development potential (such as the Mackenzie Valley; Smith et al., 2010). Changes in permafrost conditions over the last few decades can be assessed by tracking changes in two key indicators: permafrost temperature and thickness of the active layer. Ground temperature, measured below the depth where it varies from one season to the next, is a good indicator of decadal to century changes in climate, while the active layer responds to shorter-term climate fluctuations (Romanovsky et al., 2010).

Ground temperature is measured in boreholes, generally up to 20 m deep, across northern Canada. Some of these monitoring sites have been operating for more than two decades, while many others were installed during the International Polar Year (IPY, 2007–2009) to establish baseline measurements of the temperature of permafrost (Smith et al., 2010; Derksen et al., 2012). A comparison of data collected for about five years after the establishment of the IPY baseline indicates that permafrost has warmed at many sites from the boreal forest to the tundra (Smith et al., 2015a), with greater changes in the colder permafrost of the eastern and high Arctic, where temperatures increased by more than 0.5ºC at some sites over this short time period. Continued data collection has extended the time series beyond 30 years for some sites, allowing researchers to place the changes since IPY in the context of a longer record.

The temperature of warm permafrost (above −2ºC) in the central and southern Mackenzie Valley (i.e., Norman Wells, Wrigley) has increased since the mid-1980s, but the rate of temperature increase has generally been lower since 2000 — less than about 0.2ºC per decade. The low rate of increase is observed because permafrost temperatures are already close to 0ºC in this region, so energy is directed toward the latent heat required to melt ground ice rather than raising the temperature further. In the Yukon, comparison of recent ground temperature measurements with those made in the late 1970s and early 1980s suggests similar warming of approximately 0.2ºC per decade (Duguay, 2013; Smith et al., 2015b). In contrast, in the northern Mackenzie Valley (sites designated Norris Ck and KC-07, recent increases in permafrost temperature have been up to 0.9ºC per decade, likely associated with the greater increases in surface air temperature in this region over the last decade when compared with the southern Mackenzie Valley (Wrigley, Norman Wells in Figure 5.17; Smith et al., 2017).

Since 2000, high Arctic permafrost temperatures have increased at higher rates than those observed in the sub-Arctic, ranging between 0.7ºC and 0.9ºC at 24 m depth and more than 1.0ºC per decade at 15 m depth, consistent with greater increases in air temperature since 2000 (Smith et al., 2015a). Short records from sites in the Baffin region indicate warming at 10–15 m depth since 2000 (see Figure 5.17 and Table 5.1), but there has been a decline in permafrost temperatures since 2012 (Ednie and Smith, 2015) that likely reflects lower air temperatures in this region since 2010. In northern Quebec, where measurements at some sites began in the early 1990s, permafrost continues to warm at rates between 0.5ºC to 1.0ºC per decade (Smith et al., 2010; Allard et al., 2016). Permafrost can exist at high elevations in more southerly locations. Canada’s most southerly occurrence of permafrost, at Mont Jacques-Cartier on the Gaspé Peninsula, shows an overall warming trend at 14 m depth of 0.2ºC per decade since 1977 (Gray et al., 2017).

A network of thaw tubes throughout the Mackenzie Valley has provided information on trends in the active layer thickness (ALT) between 1991 and 2016 (see Figure 5.18; Smith et al., 2009). ALT exhibits greater variability among years than does deeper ground temperature, with higher values of ALT in extremely warm years such as 1998 (Duchesne et al., 2015). ALT generally increased between 1991 and 1998 but decreased over the following decade in response to lower annual air temperatures in the region. Since 2008, there has been a general increase in ALT in Mackenzie Valley, with peak values in 2012 (Duchesne et al., 2015; Smith et al., 2017). At sites where the permafrost is ice-rich, increases in summer thawing have been accompanied by significant settlement (subsidence) of the ground surface (Duchesne et al., 2015).

A number of recent studies provide other evidence of changing permafrost conditions. Observations of landscape change over time, often based on air photo or satellite imagery interpretation, have identified areas undergoing thermokarst processes, such as lake formation and collapse of peat plateaus and palsas (e.g., Olefeldt et al., 2016; Kokelj and Jorgenson, 2013). Over the last 50 years in northern Quebec, there has been a loss of permafrost mounds, collapse of lithalsas, and increases in the size of thermokarst ponds (Bouchard et al., 2014; Beck et al., 2015; Jolivel and Allard, 2017), while palsa decay has been observed in the Mackenzie mountains of the Northwest Territories (Mamet et al., 2017). A recent repeat of a 1964 survey of permafrost conditions along the Alaska Highway corridor between Whitehorse and Fort St. John indicated that permafrost continues to persist in organic-rich soils, but is no longer found at other sites (James et al., 2013). Changes in lake area in Old Crow Flats since 1951 have also been linked to thermokarst processes (Lantz and Turner, 2015). A recent intensification of thaw slumping may also be tied to changes in climate, including increases in precipitation (Kokelj et al., 2015, 2017a; Segal et al., 2016; Rudy et al., 2017). In the southern Northwest Territories, forest die-off has been attributed to permafrost thawing and ground subsidence (Sniderhan and Baltzer, 2016). Erosion of Arctic coasts in the form of retrogressive thaw slumps can result from a combination of mechanical (wave action) and thermal (warming permafrost) processes, potentially exacerbated by sea-level rise (see Chapter 7, Section 7.5; Ford et al., 2016; Lamoureux et al., 2015; Lantuit and Pollard, 2008).