Ice Across Biomes

Permafrost

Permafrost (rock or soil that remains below 0°C throughout the year) is warming across the northern half of Canada.50 Since the 1980s, shallow permafrost has warmed at a rate of 0.3 to 0.6°C per decade in the central and northern Mackenzie Valley in response to an increase in air temperature.51 In the Eastern and High Arctic, shallow permafrost has also warmed, by about 1°C per decade, mainly since the late 1990s.52 In southern parts of the permafrost zone, the area of frozen ground and frozen peatlands has shrunk or disappeared in several ecozones+ – for example, along the Alaska Highway in the Boreal Cordillera,53 in the northern peatlands of the Boreal Plains, and Boreal Shield54, 55 and in the peatlands of the eastern Taiga Shield56, 57 and the peatlands of Nunavik in the Arctic.58

Ecological consequences of changes in permafrost conditions are evident now, especially along the southern edges of its distribution in Canada. In colder regions of the country, it is likely that widespread impacts will occur in coming decades as frozen ground and the ice within it continue to warm. In subarctic and boreal regions, thawing permafrost and collapse of frozen peatlands may flood the land, replacing forest ecosystems with wet sedge meadows, bogs, ponds, and fens59, 60 – as is happening now in northern Quebec.57, 61, 62 In colder areas, on the other hand, deepening of the ground layer that thaws in the summer (the active layer) or melting of ground ice can lead to collapse and drainage of channels and wetlands63 or lower the water table and dry out the land,64, 65 altering plant species and affecting wildlife.64 There are signs of these ecological impacts now, especially in the Western Arctic.66-68

Permafrost zones

Map: permafrost zones. Click for graphic description (new window).
Source: adapted from Smith, 2010,50 based on Heginbottom et al., 199569

Permafrost temperatures in the central Mackenzie Valley

Temperature (°C) at 10 to 12 m depth, 1984 to 2008
Graph: permafrost temperatures in the central Mackenzie Valley. Click for graphic description (new window).
 
Source: adapted from Smith et al., 201052

Permafrost in the south-central Mackenzie Valley (Fort Simpson and Northern Alberta) is likely being preserved by an insulating layer of peat.70 Frozen peatlands are, however, decreasing in the southern part of the Mackenzie Valley, with an estimated loss of 22% at four study sites over the latter half of the 20th century. Permafrost further north (in the Mackenzie Delta) has warmed at a rate of 0.1 to 0.2°C per decade at a depth of 15 m since the 1960s.71, 72 While these changes are consistent with changes in air temperature over the past few decades, changes in snow cover73, 74 and in wildfires75 are also affecting rates and locations of warming and thawing of permafrost.

Photo: lichen and shrub-covered palsas © Serge Payette
Lichen and shrub-covered palsas surrounded by a pond resulting from thawing permafrost in a bog near the village of Radisson, Quebec

Permafrost temperatures at Alert, Nunavut

Temperature (°C) at 15 m depth, 1978 to 2008
Graph: permafrost temperatures at Alert, Nunavut. Click for graphic description (new window).
Source: adapted from Smith et al., 201052

Trends at Alert are characteristic of the High Arctic – although air temperatures have been increasing since the 1980s, distinct warming of permafrost has only been observed since the mid-1990s. In the eastern Arctic51 and Nunavik (northern Quebec),76-78 shallow permafrost cooled up to the early 1990s in response to a period of cooler air temperatures, then it started to warm as air temperatures increased.

Changes in land cover with loss of permafrost, northern Quebec

Percent of land cover at study site, 1957 to 2003
Graph: changes in land cover with loss of permafrost, northern Quebec. Click for graphic description (new window).
Note: based on ground surveys and 1957 air photos.
Source: adapted from Payette et al., 200461

Permafrost has thawed at a rapid rate over the past 50 years in northern Quebec and the southern permafrost limit has retreated about 130 km north.62 As a result, the landscape is changing from frozen peat plateaus and palsas (mounds of peat and soil containing ice lenses) which support dry, lichen-heath ecosystems and black spruce trees, to wetter landscapes characterized by ponds, fens, and bogs. The changes are widespread – from east of the southern part of James Bay north to the southern boundary of the “continuous” permafrost zone on the Ungava Peninsula, where, in a study area along the Boniface River, palsas decreased by 23% in area and permafrost-thaw ponds increased by 76% between 1957 and 2001.57 Lichen, an important forage for caribou, is expected to decrease in abundance along with this transition.

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