Let it be continuous, discontinuous, sporadic or isolated, permafrost covers about a quarter of the northern hemisphere, or some 22.8 million square kilometers: 50% of the land surface of Russia and Canada, 22% of China and 82%. of Alaska (approximately 15% of the total land mass of the continental United States). Additionally, nearly 90% of the circumpolar peatlands that formed after the last ice age, approximately 10,000 years ago, are currently trapped in permafrost; of these, the Hudson Bay Lowlands of northern Manitoba, Ontario, and Quebec constitute one of the largest continuous regions of its type. These numbers are important for global climate change scenarios and for Canada’s role in these scenarios, particularly because organic matter trapped in permafrost represents 50% of the global underground carbon store, four times the amount of carbon released by all human activities since 1850. If significant areas of permafrost thawed and released even a fraction of this carbon as greenhouse gases (GHGs), scientists warn it would would create a feedback loop that could accelerate the rapid climate changes we are already experiencing.
Let’s start with the bad news: the permafrost thaw is already underway; it is widespread, accelerates and is irreversible. While not as exciting in a short-term news cycle as the Antarctic ice shelf breaking up, a record heat wave in Alaska, or a catastrophic Atlantic storm, the process by which millions of square kilometers of frozen ground becoming dangerously spongy is well underway. It is accompanied by visible effects on the ecology, hydrology and landscapes of the North, as well as environmental, food and infrastructure concerns for communities.
Now for the less bad news: studies are indeed revealing the complex nature of the disappearance of permafrost and, although concern remains, it may not be the ticking time bomb that some have predicted. On the contrary, the disappearance of permafrost is probably just another phenomenon of global warming that we must pay attention to, adapt to and seek to remedy.
The scientist I met at Churchill was Peter Kershaw, a retired University of Alberta researcher and specialist in human disturbance of tundra and forests. Peter Kershaw has monitored ecosystem response to changes in permafrost near Churchill for over 15 years and was principal investigator on a 45-year study that also included several sites on Mount Selwyn and Mount Mackenzie in the Territories. of the North-West. It monitored both the decline of permafrost and the migration of the tree line toward the North Pole. Vacationing volunteers like me, eager to see with their own eyes how global warming is undermining the planet’s natural carbon storage systems, provided the human energy for his work.
I spent a week kneeling on the tundra amid clouds of mosquitoes, wielding a magnifying glass to find tree seedlings no taller than the spongy moss in which they grew, and measuring annual growth. larger trees, previously marked. The evening presentations, peppered with graphs, tables and before-and-after photos, offered a sad litany of rising temperatures, retreating glaciers, shrinking sea ice and changing snow cover. None of this is new except the scale of these phenomena, all of which indicate rapid, unidirectional climate change: the climate is warming everywhere, twice as fast in the Arctic and even faster underground. . It is therefore clear that permafrost is not just the one-dimensional concept that its name implies.
The simple definition of permafrost – rock or soil whose temperature remains at or below 0°C for at least two consecutive years – ends there. Permafrost consists of an active layer of variable thickness that thaws and refreezes each year, and which rests on a deeper, more permanent layer. The distribution of permafrost in a landscape is considered continuous if it covers 91 to 100% of the area, discontinuous if this coverage is 51 to 90%, sporadic if it is 10 to 50% and isolated if it is less. at 10% (as is the case for much of the Alpine permafrost). Permafrost can be dry, with low water content, or ice-rich, when the ice content exceeds the saturated moisture capacity of the soil. The latter case of excess ice is responsible for most of the characteristics of permafrost: the interrelated ice wedges that form in vertical cracks to create polygonal shapes on the ground; the distinct conical ice-cored pingos common to the Mackenzie Delta; the separate ice lenses that underlie peat mound structures such as palsas.
Rapid thawing of ice-rich permafrost causes land subsidence in a variety of ways; These processes, known as thermokarst, cause peatlands to collapse into watery craters, also causing land subsidence, landslides and the enlargement (or occasional drying) of lakes.
Peter Kershaw argued that the active layer was warming significantly and therefore expanding to release more GHGs, such as carbon dioxide and methane. The permanent layer, which extends 10 to 20 meters deep, warms more slowly. Much of the permafrost is deeply buried (more than a kilometer deep in some parts of Siberia), so few people expect it will ever release all the stored carbon; models generally suggest that at best only 10-20% of it could escape in the future, even under the most pessimistic emissions scenarios. But there is a problem with the models.
My trip to Churchill took place in June 2012 and in the six years since then, five of them have been the hottest on Earth’s record. Recent observations in Alaska and Siberia show that active layers are warming much faster than models predict. Supporting this claim, a landmark study published in 2017 in the journal Nature Climate Change looked at how quickly permafrost actually thawed between 1960 and 1990 and found that it was about 20% more sensitive to warming. than the models suggested.
This highlights the limitations of models currently used to predict future climate scenarios – they simply cannot capture all the nuances involved in major changes to permafrost. “The divergence between some of the world’s best models is enormous, but there is no simple answer to the question why,” says Antoni Lewkowicz, professor in the department of geography, environment and geomatics at the University of Ottawa and President of the Canadian Permafrost Association.
Professor Lewkowicz is a dean of permafrost science in Canada, having worked across the North since 1976, from Labrador to the Yukon to the High Arctic. “Permafrost loss is an incredibly complicated system with many moving parts. We explore it primarily through modeling and site-specific studies, but we would like to be able to expand it. »
Professor Lewkowicz questions how much carbon is actually present, how mobile it is, and whether some of it is absorbed by plants. He notes that some parts of the tundra are already greening – a de facto absorption of carbon – but the resulting shrubs are also deepening the snow cover, which can lead to additional warming that would release more gases to the earth. greenhouse. “Some changes are happening faster than expected and are not trivial, but they also do not appear to be catastrophic,” he says. We need to explore this further, because to meet climate goals we will ultimately need to include permafrost loss and the resulting carbon release in our calculations. »
Although studies pointing to climate catastrophe tend to make headlines, the consensus in Canada seems to follow the Lewkowicz doctrine of certain but gradual effects. “The distribution of permafrost in the North is like a puzzle,” he explains. The top three rows – the continuous permafrost – are complete, the next three rows are incomplete, but represent perhaps 80% of the picture, and at the very bottom – the southern fringe of the discontinuous permafrost – there are scattered pieces that disappear slowly. »
David Olefeldt, an assistant professor in the Faculty of Agricultural, Life and Environmental Sciences at the University of Alberta who studies carbon cycling in boreal and Arctic wetlands, agrees. “We have more or less ruled out any catastrophe scenario, but we are receiving a lot of information indicating that the climate will nevertheless be modified,” he explains. Simply put, this would add another Germany or United States to the list of sources of GHGs in the atmosphere. Permafrost thawing alone does not move the climate in a direction it is not already heading, but it should be taken seriously. It is still up to us to manage future emissions – our choices have not been taken away from us. »
