Climate change is one of the most substantial and widespread environmental phenomena of our immediate future, with the effects of global climate change projected to be most severe at high latitudes. Permafrost landscapes make up a large portion of the Northern hemisphere. JEAN HOLLOWAY says understanding the impacts of change for the people, ecosystems and infrastructure in these areas is important.
JEAN HOLLOWAY is a PhD candidate in the Dept. of Geography at Ottawa University focusing on the impacts of forest fires on permafrost in the southern Northwest Territories, Canada. This article appeared in The Circle 04.15.
THERE HAS BEEN substantial winter and spring warming in west-central and northwestern Canada and virtually all of Siberia over the past three decades.
How permafrost is affected by these temperature changes depends on complex interactions among topography, surface water, soil, vegetation, and snow, which vary greatly between sites, even over short distances. Vegetation, in particular, can insulate permafrost from the atmosphere, making it resilient to increases in air temperature, at least in the short term. This ecosystem-protected permafrost covers millions of square kilometres worldwide and is particularly sensitive to climate and environmental change as it is just below 0°C, thin and usually cannot be re-established after disturbance. The most widespread source of disturbance of this permafrost is forest fire.
Forest fires are a natural and essential part of the boreal forest ecosystem, and typically locations burn every 50-300 years. Global warming and greater human activities have increased the frequency and magnitude of forest fires, which generally occur in warm and dry summers. The number of recorded forest fires in Canada has increased substantially in the last 30 years. In Siberia 1.5% of the total forested area burns annually. The response of permafrost to forest fires depends on the degree to which the permafrost is protected by the ecosystem.
The heat from the fire itself does not directly affect permafrost. The damage occurs when intense fires destroy the organic layer that is insulating the ground. This exposes the underlying mineral soil, which is more conductive than the surface organic mat, and allows more heat to get into the ground. Similarly, fire removes trees, which catch snow thus creating a deeper layer of snow that shields the ground from necessary cold winter temperatures. The active layer deepens until the upper layers of permafrost begin to thaw. Other factors that aid in this degradation include decreasing albedo due to surface darkening, and loss of shading from the tree canopy. Soils with permafrost in the coldest and wettest landscape positions (e.g. valleys) usually do not thaw as deeply after fires as soils in warmer and drier positions, such as hilltops or south-facing slopes. Fire severity is also significant, especially the degree to which the ground surface layer is burned. Complete destruction of the forest and the surface organic layer by hot, slow-moving fires will have the greatest impact, while fast-moving fires may skip over patches of forest, and low intensity fires can leave much of the organic layer intact. While the general influence on permafrost is therefore clear, how it will respond at a particular site depends on numerous local factors.
Thaw and degradation of burned areas is expected to continue until sufficient re-vegetation occurs to reestablish the insulating organic mat.
Vegetation recovery after forest fires has a major influence on stabilization of permafrost thaw. Growth is rapid in the first few years, and then slows down with time, as there is more competition for moisture and sunlight. The complete recovery of the ecosystem to pre-burn conditions can take up to 50 years. However, this depends on the climate still being suitable for permafrost. If the permafrost is ecosystem-protected and the climate is warming, permafrost degradation may continue until it disappears entirely.
Forest fires also affect permafrost landscapes in ways that are more noticeable. In the first and second years after a fire, landslides can occur on hill-slopes. Progressive uneven surface subsidence of the ground (called thermokarst) may also occur for years because of melting ground ice within the permafrost. This can affect current infrastructure as well as future development, especially as the frequency of fire means that many developments in the boreal forest may expect to be affected by fire at some point during the lifespan of infrastructure.
Another important effect of forest fires is carbon release during the fires and from thaw of permafrost post-fire. Boreal permafrost soils store large amounts of organic carbon, and fire disturbance influences the amount and type of carbon in the soil. Forest fires release approximately 53 million tonnes of carbon from North American boreal forests each year. Vegetation re-growth post-fire actually ends up storing large amounts of carbon, but in a warming climate with a higher frequency and magnitude of forest fires, this is expected to change. Furthermore, thaw of permafrost following forest fires allows carbon that has been trapped in frozen soils to become available for decomposition by soil microbes. Both these phenomena create a positive-feedback loop: climate change results in a greater frequency and magnitude of forest fires, which release greenhouse gases into the atmosphere, which results in more climate change, and so on.
How permafrost responds to forest fire is a complex issue, but it is clear that a warming climate and the expected increase in the frequency and magnitude of fires will have a substantial impact on permafrost thaw and degradation, especially in the discontinuous zone. It is important that we understand these impacts so we can make informed decisions on fire-management and how to deal with post-fire issues such as landslides and positive feedback adding to climate change.

BRONWYN BENKERT is a research project coordinator with the Northern Climate ExChange, Yukon Research Centre, Yukon College, Whitehorse. This article appeared in The Circle 04.15.
In the North, we live on permafrost. Much of our infrastructure is built on ground that is at or below 0°C for two years or more. We travel across permafrost, and it supports our homes and workplaces. Northerners have long had to contend with permafrost in construction and economic development – in the Klondike gold fields, prospectors at the turn of the 20th century actively thawed frozen ground to reach pay dirt, while workers constructing the Alaska Highway during the Second World War battled thawing ground that never stabilized, forcing on-the-fly adaptation of construction processes.
Northerners continue to adapt to our permafrost environment, which forces us to use ingenuity and innovation as we invest in and maintain infrastructure on permafrost. This task has become increasingly challenging, as a result of compounding factors that include heightened development intensity and a changing climate.
The goal of preserving costly northern infrastructure prompts us to develop a thorough understanding of permafrost characteristics and its dynamic responses to anthropogenic and environmental stressors. In Yukon, research focuses on identifying solutions to permafrost thaw impacts on infrastructure. As the only dedicated permafrost research group in northern Canada, the Northern Climate ExChange (NCE), part of the Yukon Research Centre at Yukon College, is working with community, government and industry partners to assess permafrost vulnerability to thaw, and to identify suitable measures to keep it stable.
Yukoners have regularly witnessed impacts of permafrost thaw on infrastructure. In January 2015, a 15-year-old Yukon school was closed due to concerns about its structural integrity. Shifts in the foundation were attributed, at least in part, to permafrost thaw under the building. Substantial investment was required to repair the building before it could be re-opened in September. Prior to the closure of the school, NCE partnered with Yukon government to assess permafrost conditions and recommend practices that could be used to slow or prevent thaw. These ranged from modified snow clearing practices to engineering solutions. Permafrost cores, ground temperature records and geophysics profiles were collected and analyzed by NCE researchers. Together, these approaches form the basis of our understanding of conditions that contributed to infrastructure vulnerability and damage, and may contribute to the preservation and longevity of our buildings.
Increasingly, permafrost-related information is being integrated as part of the planning process for local development. In Yukon, many communities are proactively adopting adaptive planning approaches, based in part on landscape hazard maps the NCE and its partners have developed. These maps integrate current and future hazards associated with permafrost, surficial geology and hydrology into easy-to-interpret, community-scale maps. The hazard risk maps have assisted Yukon communities and other agencies in choosing suitable locations for new infrastructure by helping them avoid key thaw-sensitive areas, and by allowing them to assess the suitability of development projects for local conditions.
In some cases, choosing stable or non-permafrost locations for infrastructure is impractical. Twenty-five percent of Yukon’s 4800 km highway network is built on permafrost. The maintenance of these sections can cost in excess of 5 times that of non-permafrost sections. Where permafrost is already degrading, the management of nearby water and on-going remediation are continually required to reduce infrastructure deterioration. Further, sections of highway overlying permafrost that are currently stable may be affected by future permafrost degradation – it is likely that permafrost impacts on linear infrastructure will become more significant with time.
Fortunately, modified construction practices and thaw mitigation techniques can be used to preserve permafrost and reduce degradation impacts on linear infrastructure like highways.
However, because variability is inherent in permafrost characteristics and distribution, a reasonable solution for one place may be completely ineffective or even damaging at a nearby location. Recently, NCE completed an assessment of permafrost vulnerability to thaw along the northern 200 km of the Alaska Highway, where ice-rich permafrost is located under much of the highway alignment. This characterization has informed the design of solutions that are tailored to local permafrost conditions. Results will guide Yukon government in making strategic investments in the most promising, effective thaw mitigation techniques adapted to local conditions, reducing on-going maintenance costs and preserving highway integrity.
Promoting resilience to permafrost change in the North is a multi-faceted process. It requires basic information regarding the nature, thermal state, and extent of permafrost, as well as ongoing monitoring of permafrost change. Thaw mitigation techniques can also offer protective benefits to infrastructure. Importantly, the development of northern capacity to respond to northern problems like permafrost impacts on infrastructure is helping to ensure improved infrastructure resiliency for our communities.

Soils from the northern circumpolar permafrost zone contain almost twice as much carbon as is currently in the atmosphere. Temperatures in this region are already rising twice as fast as the global average and are expected to keep warming as a result of emissions of carbon from coal, oil, gas and deforestation around the globe. Ted Schuur says a warmer climate causes permafrost ground to thaw, and exposes organic carbon to decomposition by soil microbes.
TED SCHUUR is a Professor of Ecosystem Ecology at Northern Arizona University, USA. This article appeared in The Circle 04.15.

THIS PERMAFROST CARBON is the decomposed remains of plants and animals that have accumulated in perennially frozen ground over hundreds to thousands of years. Thawing permafrost is like having the power cut to your freezer. Just like frozen food that will spoil when thawed, organic carbon in soil is metabolized by bacteria and fungi and transformed into carbon dioxide and methane as part of the natural metabolic cycle of these microorganisms. Carbon dioxide and methane both contain carbon but are produced in different environments by microorganisms depending on how much oxygen is available. Carbon dioxide and methane are also greenhouse gases, trapping heat when released into the atmosphere. Release of permafrost carbon into the atmosphere by this process has the potential to accelerate climate change, making it go faster than we expect based on projections from human emissions alone.
New research has helped solidify the tremendous quantities of permafrost carbon stored in the north. The known pool of permafrost carbon is 1330-1580 billion tons, accounting both for carbon in the surface three meters of soil, and for carbon that is stored much deeper. These deep deposits occur in areas of Siberia and Alaska that remained unglaciated during the last Ice Age, as well as in Arctic river deltas. Even beyond the deep carbon that has been documented, there are permafrost carbon pools that at this point still remain largely a mystery. In particular, there are deep permafrost sediments outside of Siberia and Alaska as well as permafrost that is now beneath the ocean. Ocean permafrost is located on the shallow Arctic sea shelves that were exposed during the last glacial period when the ocean was 120 meters lower than today, since ground must be exposed to frigid air temperatures in order for permafrost to form. These additional deposits are poorly quantified but could add several hundred billions tons more carbon to the known permafrost carbon pool described here.

Thawing permafrost is like having the power cut to your freezer.

The critical question is how much of this permafrost carbon is susceptible to climate change on a timescale that matters to our decision-making. The strength of the permafrost carbon feedback to climate depends on how much carbon is released, how fast it happens, and the form of carbon (carbon dioxide, methane) that makes it to the atmosphere. Research has measured the tremendous quantities of carbon in permafrost soils, but some of this carbon is stored deep in permafrost and will take time before a warmer climate can affect temperatures deep in the ground. Even when thawed, some fraction of organic carbon is susceptible to rapid breakdown and release as greenhouse gases, while another fraction will remain in soil even when the temperatures rise due to other factors that preserve carbon in soils.
Still, initial estimates of potential greenhouse gas release point towards the potential for significant emissions of Carbon from permafrost to the atmosphere in a warmer world. The most recent scientific efforts put the vulnerable fraction about 5-15% of the vast permafrost carbon pool in scenarios where human-caused climate change progresses on its current trajectory. While that vulnerable fraction is on the smaller rather than the larger side of the total pool, it still would result in the addition of billions of tons of additional carbon into the atmosphere. Ten per cent of the known terrestrial permafrost carbon pool is equivalent to 130– 160 billion tons carbon. That amount, if released primarily in the form of CO2 at a constant rate over a century, would make it similar in magnitude to other historically important biospheric sources, such as deforestation, but far less than current and future fossilfuel emissions. Considering CH4 as a fraction of permafrost carbon release would increase the warming impact of these emissions.
Permafrost carbon emissions are likely to occur over decades and centuries as the Arctic warms, making climate change happen even faster than we project on the basis of emissions from human activities alone. Because of momentum in the system and the continued warming and thawing of permafrost, permafrost carbon emissions are likely not only during this century but also beyond. Although never likely to overshadow emissions from fossil fuel, each additional ton of carbon released from the permafrost region to the atmosphere will probably incur additional costs to society. Understanding of the magnitude and timing of permafrost carbon emissions based on new observations and the synthesis of existing data needs to be integrated into policy decisions about the management of carbon in a warming world.