What is permafrost in Canada?

Permafrost is ground (soil, sediment, or rock) that remains at or below 0 degrees Celsius for at least two consecutive years. About 50 per cent of Canada's land area is underlain by some form of permafrost, including all of Yukon, the Northwest Territories, and Nunavut, most of Labrador, northern Quebec, and northern Manitoba, Ontario, Saskatchewan, and Alberta. Permafrost extends to depths exceeding 1,000 metres in the high Arctic and only a few metres in the southern margins.

Permafrost is divided into three zones based on areal coverage. The continuous permafrost zone (more than 90 per cent of the land underlain by permafrost) covers the high Arctic islands and the northern mainland north of about 60 degrees north. The discontinuous permafrost zone (50 to 90 per cent) covers most of the Yukon, NWT, and northern provinces. The sporadic permafrost zone (10 to 50 per cent) covers a band across central Quebec, Ontario, the Prairies, and northern British Columbia. The southern permafrost limit varies seasonally and over decades.

Permafrost is closely linked to surface features. The seasonally thawing top layer (the active layer) is typically 30 centimetres to 3 metres thick. Below the active layer, ice-rich permafrost can include large ice wedges, ice lenses, and massive ice (some accumulated more than 100,000 years ago). Distinctive permafrost landforms include pingos (ice-cored hills, with the Tuktoyaktuk Peninsula in the NWT containing about 1,350 pingos including Ibyuk Pingo, the second-largest in the world), polygonal ground patterns, thermokarst lakes, palsas, and frost mounds.

Permafrost thaw caused by climate change is the largest infrastructure challenge in Canada's North. Buildings, roads, airports, pipelines, and the Inuvik-Tuktoyaktuk Highway built on permafrost foundations have all been destabilised by thaw, with hundreds of millions of dollars in repair costs already incurred. The Yukon River, Mackenzie River, and Slave River banks are slumping as permafrost thaws. Federal investment includes the Climate-Resilient Buildings and Core Infrastructure Initiative ($102 million, 2018) and the Northern REACHE programme. Permafrost thaw also releases stored carbon (estimated 1,460 to 1,600 billion tonnes globally, including a substantial Canadian share) as carbon dioxide and methane, accelerating climate change. The Canadian Permafrost Association coordinates research, including federal investment in the Permafrost Carbon Network and the Northern Climate Change Adaptation Programme.