Technical Thematic Report No. 9. - Trends in permafrost conditions and ecology in northern Canada
Trends in Permafrost Conditions in Each Ecozone+
- Taiga Plains Ecozone+
- Taiga Shield Ecozone+
- Taiga Plains Ecozone+
- Boreal Plains Ecozone+
- Boreal Shield Ecozone+
- Arctic Ecozone+
- Taiga Cordillera Ecozone+
Recent results from permafrost thermal monitoring sites indicate that warming of permafrost is occurring across the permafrost region (for example Smith et al., 2005b), although the magnitude of this warming varies regionally. Since the 1980s, warming of shallow permafrost of 0.3 to 0.6°C per decade has occurred in the central and northern Mackenzie region in response to a general increase in air temperature. Warming of shallow permafrost has been observed in the eastern and high Arctic but this mainly occurred in the late 1990s. Further evidence of permafrost warming and thawing in recent decades, in particular the southern portions of permafrost zone, is provided by investigations of loss of frozen peatlands. A summary of observed recent changes in permafrost conditions for each ecozone+ is provided below.
Taiga Plains Ecozone+
An extensive permafrost monitoring network in the Mackenzie Valley region of western Canada provides records of permafrost temperature in the upper 20 to 30 m. Some of these records are over 20 years long. In the central Mackenzie Valley (near Norman Wells), where permafrost is up to 50 m thick and at temperatures of about −1°C, warming of 0.3°C per decade since the mid-1980s at a depth of 10 m has been observed, as shown in Figure 2 (Smith et al., 2005b; Romanovsky et al., 2007). Similar rates of permafrost temperature increases of 0.1 to 0.2°C per decade at a depth of 15 m have occurred since the 1960s in colder permafrost (−2 to −3°C) at spruce forested sites in the northern portion of the ecozone+ in the Mackenzie Delta (Kanigan et al., 2008). Kokelj et al. (2007b) found that ice wedges were inactive in spruce forests of the eastern Mackenzie Delta, suggesting that winter conditions have become warmer.
Figure 2. Ground temperatures between 1984 and 2007 at depths near 10 metres in the Mackenzie valley south of Norman Wells.
Long Description for Figure 2
This line graph shows ground temperatures between 1984 and 2007 at depths near 10 metres in the MacKenzie valley south of Norman Wells. The sites at Norman Wells and Wrigley (both measured at 12 metres) show temperatures around -1°C with a warming trend of 0.3°C and 0.1°C per decade, respectively. The sites at Fort Simpson and northern Alberta (both measured at 10 metres) show temperatures around 0°C.
Note that the frequency of measurements was reduced in the mid-1990s at the two most southern sites.
Source: adapted and updated from Smith et al. (2005b)
In the southern Mackenzie Valley (near Fort Simpson) and northern Alberta where permafrost becomes patchy and warmer (temperatures close to 0°C), increases in permafrost temperatures have been much less (Figure 2). This absence of a trend or reduced increase in permafrost temperature in warm permafrost is probably due to the large amount of latent heat required for phase change in the ice-rich unconsolidated sediments (Smith et al., 2005b). In the southern portion of the ecozone+, permafrost is largely confined to organic terrain. Much of this permafrost likely formed during the Little Ice Age and has been preserved under warmer climatic conditions by a thick layer of insulating peat (for example Halsey et al., 1995). Since permafrost in these peatlands is generally ice-rich, ground temperatures at depth become isothermal as temperatures approach 0°C (Smith et al., 2008). Increases in thaw depth have been observed (Burgess and Smith, 2003), and some sites with thin permafrost (<5 m thick) have completely degraded over the last one to two decades (Figure 3) (Burgess and Smith, 2003).
Figure 3. September ground temperature profiles between 1985 and 2001 for a site in a degrading peatland near Fort Simpson Northwest Territories.
Long Description for Figure 3
This line graph displays September ground temperature profiles between 1985 and 2001 for a site in a degrading peatland near Fort Simpson, Northwest Territories. Profiles for five years show a clear overall warming trend for the period. In 1998, temperature at 0.5 metres spikes, reaching approximately 4.6°C, but returns back to 1°C, similar to previous years, in 2000. The profile for 2001 shows significant change from 2000 for depth measurements of 1.5, 2, and 2.5 metres, increasing approximately 1.6, 2, and 0.8°C, respectively.
Source: adapted from Smith et al. (2008)
Other evidence of changes in permafrost conditions in the southern Taiga Plains comes from analysis of air photos to determine the change in the area of frozen peatlands over time. Beilman and Robinson (2003) examined four sites in the southern Mackenzie Valley and found that over the latter half of the 20th century, the area of frozen peatlands decreased by 10 to 50%, with an average of 22% of the peat plateaus degrading over this period.
While these changes in permafrost distribution and thermal state within the Taiga Plains are consistent with changes in air temperature over the last few decades, changes in snow cover are also important in determining the response of permafrost to a warming climate. Snow cover acts as an insulator and reduces heat loss from the ground during winter resulting in warmer winter ground temperatures compared to areas of minimal snow cover (for example Goodrich, 1982; Burgess and Smith, 2000; Burn et al., 2009). Also, frozen peatlands progress through a natural evolution from an early stage of permafrost development to a mature stable stage and an overmature stage during which thermal degradation results in thawing of permafrost and collapse of peatland surfaces (Burgess and Tarnocai, 1997). Wildfires within the region may also result in changes in permafrost conditions (Mackay, 1995). Where burning is severe, damage to the surface organic layer may occur in addition to removal of vegetation. This reduction in surface insulation together with an increase in surface albedo can result in warming and thawing of the ground such as that observed in organic terrain of northern Alberta following fires in 2004 (Smith et al., 2008).
Taiga Shield Ecozone+
A quantification of changes in the distribution of frozen peatlands of northern Quebec on the east coast of Hudson Bay is presented by Payette et al. (2004). Air photos were utilized to characterize the changing patterns of permafrost and thermokarst ponds between 1957 and 2003. Their results show that permafrost has degraded since 1957 with the rate of loss of frozen peatland area being greater after 1993 (5.3% per year) as shown in Table 1. Surface subsidence of 1 to 1.5 m has occurred in response to melting of ground ice. Payette et al. (2004) concluded that the main driver for the accelerated rate in permafrost thawing was increases in snow precipitation and air temperature. An increase in thermokarst ponds is also found over this period (Beaulieu and Allard, 2003; Vallee and Payette, 2007). Fortier and Aubé-Maurice (2008) report, based on analysis of air photos and satellite imagery, that this loss of permafrost is continuing in this region with a decrease in permafrost extent between 1957 and 2005 of 40% near Umiujaq and an increase in thermokarst of 175%. Additional evidence of changing permafrost conditions in northern Quebec is provided by observations of shallow permafrost temperatures that indicate warming since 1993 (Allard et al., 2007).
|Period||Rate of permafrost loss|
|1957-1983||2.5% per yr|
|1983-1993||2.8% per yr|
|1993-2003||5.3% per yr|
Source: Payette et al.(2004)
Boreal Plains Ecozone+
In the Boreal Plains, permafrost is patchy and confined to peatlands. Permafrost within this zone has been highly dynamic over the last millennium (Vitt et al., 2000). Permafrost likely formed during the colder climate of the Little Ice Age and has persisted due to the insulation provided by the peat. Through analysis of air photos, Beilman et al. (2001) and Beilman and Robinson (2003) have concluded that in some locations permafrost has completely thawed over the last century especially at the southern limit of the permafrost zone. Beilman and Robinson (2003) found that 32 to 70% of the frost mound area at field sites in Alberta has degraded over the last 100 to 150 years.
Boreal Shield Ecozone+
Similar to the permafrost distribution in the Boreal Plains, permafrost in this zone is also largely confined to organic terrain. Air photo analysis and measurements of rates of peatland collapse provide evidence that thawing has occurred over the last 50 to 100 years (Beilman et al., 2001; Beilman and Robinson, 2003; Camill, 2005) in northern Saskatchewan and Manitoba. Beilman and Robinson (2003) found that 53 to 64% of the frost mound area at field sites in Saskatchewan and Manitoba degraded over the last 100 to 150 years. This permafrost degradation has been attributed to changes in climate, although frozen peatlands go through a natural cycle of permafrost formation and thawing (see Taiga Plains section).
Boreal Cordillera Ecozone+
Limited information is available to characterize trends in permafrost in the southern Yukon and northern British Columbia. Some information however is available for sites along the Alaska Highway corridor. In the Takhini River Valley, Yukon, records of shallow permafrost temperatures collected between 1983 and 1996 showed no clear trend (Burn, 1998). In the central Yukon at Mayo, measurements of thaw depths collected in the 1990s at a forested site have showed no increase in thaw depth (Haeberli and Burn, 2002).
Preliminary results of field investigations in 2007 along the Alaska Highway corridor between Whitehorse, Yukon and Fort St. John, British Columbia of depths to the top of permafrost (James et al., 2008), indicate greater thaw depths than were measured in 1964 by Brown (1967). The results also indicate that some degradation of permafrost has occurred over four decades at more than half of the observation points.
Information on recent trends in permafrost temperatures in the Arctic Ecozone+ comes from a number of monitoring sites from the western Arctic to the eastern Arctic and the high Arctic. In general, changes in shallow permafrost temperatures over the last decade are greater in the Arctic compared to those areas below the treeline (Taiga and Boreal) due to the lack of a buffer layer provided by vegetation and thick snow covers. The presence of colder permafrost also means that phase change and the presence of unfrozen water do not obscure the climate signal. There is therefore a more direct link between changes in air temperature and changes in permafrost temperature.
In the western Arctic, permafrost temperature data collected since the late 1990s from the northern Mackenzie Basin indicate that warming of permafrost has occurred since the early 1990s. On the Tuktoyaktuk Peninsula for example, at a depth of 28 m, permafrost temperatures increased between 1990 and 2002 at a rate between 0.02 and 0.06°C per year (Smith et al., 2005b). Analysis by Burn and Kokelj (2009) indicates that near surface ground temperatures in the tundra uplands of the Mackenzie Delta region have increased 1 to 2°C from the early 1970s to 2007. Modelling analysis conducted for a permafrost monitoring site at Herschel Island in the Yukon indicate that permafrost temperature at a depth of 20 m has increased by 1.9°C over the past 100 years (Burn and Zhang, 2009). Recent field observations at this monitoring site also indicate an increase in active layer thickness since 1985.
In the central southern portion of the Arctic Ecozone+, permafrost temperatures to 3 m depth have been collected since 1997 at Baker Lake, Nunavut. Between 1997 and 2007, a general increase in thaw depth (Figure 4) has been observed although there is some interannual variability within the short record (Smith et al., 2005b; Throop et al., 2008). The largest increase in thaw depth occurred between 1997 and 1998 and this was related to the longer thaw season in 1998 (Smith et al., 2001b).
Figure 4. Maximum summer thaw depth for a site (BH4) at Baker Lake, 1997 to 2007.
Long Description for Figure 4
This bar graph shows maximum summer thaw depth for a site (BH4) at Baher Lake from 1997 to 2007. A general increase in thaw depth has been observed although there is some interannual variability within the short record. The largest increase in thaw depth occurred between 1997 and 1998 increasing 0.45 metres. There was also a large increase in thaw depth of 0.39 metres occurred between 2004 and 2005, following a decrease between 2003 and 2004 of 0.27 metres.
Source: adapted and updated from Smith et al. (2005b) and Throop et al. (2008)
Permafrost temperature data collected since 1978 at CFS Alert, Nunavut can be used to characterize trends in permafrost in the high Arctic. Although a general increase in air temperatures has been observed since the 1980s, distinct warming in shallow permafrost temperatures has only been observed since the mid-1990s. Between 1994 and 2001, an increase in permafrost temperatures of about 0.15°C per year occurred at a depth of 15 m (Smith et al., 2005b). Although some cooling of permafrost was observed between 2000 and 2002, recent data collected from the site indicates that warming of permafrost is continuing at an overall rate of approximately 0.1°C per year since 1994 (Figure 5). Recent increases in shallow ground temperatures have also been observed in other Arctic regions such as Scandinavia and Svalbard (Isaksen et al., 2007a; Isaksen et al., 2007b; Harris and Isaksen, 2008). Although snow cover is generally thin at these high Arctic sites, its variability can be an important factor affecting the response of permafrost temperatures to changes in air temperature (Smith et al., 2003). Changes in snow cover may counteract changes in air temperature occurring over the same period such that permafrost temperatures may increase in the high Arctic during periods of higher snow cover but lower air temperature (Taylor et al., 2006).
Figure 5. Observed and mean annual ground temperatures (MAGT) at a depth of 15 metres at Alert (BH5), 1978 to summer 2008.
Long Description for Figure 5
This line graph displays observed and mean annual ground temperatures (MAGT) at a depth of 15 metres at Alert (BH5) from 1978 to summer 2008. Prior to July 2000, measurements were made manually at approximately monthly intervals. After July 2000, monthly mean temperatures were determined from data logger records. Although some cooling of permafrost was observed between 1992 and 1994, and again 2000 and 2002, recent data collected from the site indicates that warming of permafrost is continuing at an overall rate of approximately 0.1°C per year since 1994.
Note that prior to July 2000, measurements were made manually at approximately monthly intervals. After July 2000, monthly mean temperatures were determined from data logger records.
Source: adapted and updated from Smith et al. (2005b)
In the eastern Arctic, cooling of shallow permafrost was observed until the early 1990s in response to the general decrease in air temperature that occurred until 1992. An increase in air temperatures began in 1993. Shallow (5 m) permafrost temperatures at Iqaluit also began to warm in 1993 with warming continuing through the 1990s (Figure 6). Temperatures at a depth of 5 m increased at a rate of 0.4°C per year between 1993 and 2000. A similar trend has been observed in northern Quebec, where cooling of about 0.1°C per year was observed between the mid-1980s and mid-1990s at a depth of 10 m (Allard et al., 1995). An increase in air temperatures commencing in 1993 in northern Quebec has been associated with warming of permafrost since 1993 to depths of 20 m (Allard et al., 2002; Ouranos, 2004; Chouinard et al., 2007) and an increase in active layer thickness (Brown et al., 2000).
Figure 6. Monthly ground temperatures at a depth of 5 metres at Environment Canada’s borehole at Iqaluit, 1988 to 2002.
Long Description for Figure 6
This graph displays monthly ground temperatures at a depth of 5 metres at Environment Canada’s borehole at Iqaluit from 1988 to 2002. Monthly ground temperatures vary seasonally, although the running mean shows a warming trend, from -8.9°C in 1989 to -7.4°C in 2001. The air temperature running mean follows similar fluctuations, with a cooling trend from 1988 to 1993, followed by a general warming trend to 2001.
The 12-month running mean for both ground and air temperature is also shown.
Source: adapted from Smith et al. (2005b)
Taiga Cordillera Ecozone+
Limited information is available on changes in permafrost conditions in this ecozone+. Analysis of sequential air photos beginning in the early 1940s and field surveys by Kershaw (2003) have facilitated an examination of permafrost landform degradation. A reduction in the area covered by frozen peat plateaus and palsas of greater than 1% per year has been determined for the Macmillan Pass area of the Northwest Territories. This permafrost degradation has been accompanied by the formation of thermokarst ponds. Temperatures measured near the top of the permafrost between 1991 and 2000 have also shown an increase of about 0.1°C per year (Kershaw, 2003).
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