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Wednesday, May 27, 2015
What is Permafrost
Permafrost is permanently frozen soil, and occurs mostly in high latitudes. Permafrost comprises 24% of the land in the Northern Hemisphere, and stores massive amounts of carbon. As a result of climate change, permafrost is at risk of melting, releasing the stored carbon in the form of carbon dioxide and methane, which are powerful heat-trapping gases. In addition, permafrost is structurally important, and its melting has been known to cause erosion, disappearance of lakes, landslides, and ground subsidence. It will also cause changes in plant species composition at high latitudes.
What is permafrost?
The Effect of Climate Change on Permafrost
Melting Permafrost Causes Greenhouse Gas Emissions
Other Impacts of Melting Permafrost
What is permafrost?
Figure 1. Idealized permafrost cross section.
Permafrost is permanently frozen soil, sediment, or rock. Its classification is solely based on temperature, not moisture or ground cover. The ground must remain at or below 0°C for at least two years in order to be considered permafrost. Although new permafrost is forming, it can be over thousands of years old. For example, some of the permafrost in western Canada's boreal peatlands has been there since the Little Ice Age of the 1600's (Turetsky et al., 2007).
Permafrost has layers, of which frozen ground is just one portion (Figure 1). The active layeris ground that is seasonally frozen, typically lying above the perennially frozen permafrost layer. Talik is unfrozen ground that lies below the permafrost and between the active layer and permafrost.
Where is permafrost found?
Most frequently, permafrost is found in high latitudes near the north and south poles. However, it can also be found at high altitudes in other locations around the world. Roughly 37% of the Northern Hemisphere permafrost occurs in western North America, mainly in Alaska and northern Canada, but also further south in the Rocky Mountains. The majority of permafrost in the Northern Hemisphere occurs in the Eastern Hemisphere, in Siberia and the Far East of Russia, as well as northern Mongolia, northeastern China and the Tibetan Qinghai-Xizang Plateau (Zhang et al., 1999).
In the Southern Hemisphere, permafrost is found in Antarctica, the Antarctic islands, and the Andes Mountains. In areas where the conditions are such that the ground is cold enough year-round, continuous permafrost forms. Discontinuous and sporadic permafrost occurs in locations where temperatures only get cold enough in certain areas, such as in the shade, or on the northern side of a hill or mountain. Seasonal permafrost occurs during colder seasons and thaws or disappears during warmer times of the year.
The Effect of Climate Change on Permafrost
Climate change will significantly affect the complex interactions between above- and below-ground climate regimes. However, even changes in temperature at the surface take time to impact permafrost at depth; According to the Geological Survey of Canada (GSC), "for thick permafrost this lag may be on the order of hundreds to thousands of years, for thin permafrost, years to decades" (GSC, 2007).
In a recent study using freezing/thawing index, trend analysis of spatial data since 1970 indicates that in recent decades, there has been a decrease in freezing during the cold season throughout North America's permafrost regions. Additionally, coastal areas and eastern Canada have started to see "significant" increases in warm season thawing of permafrost (Frauenfeld et al., 2007). Overall, this means there has been a decrease in freeze depths and in the amount of permanent permafrost. Conversely, there has been an increase in seasonal permafrost. This increase in seasonal permafrost is not due to increases in acres frozen, but to the decrease in permanent permafrost which is not remaining frozen all year anymore. Since it is no longer perennially frozen, it loses its distinction as 'permanent' and becomes 'seasonal'.
Figure 2. Permafrost distribution in the Arctic. Image credit: Philippe Rekacewicz, 2005, UNEP/GRID-Arendal Maps and Graphics Library based on International Permafrost Association (1998) Circumpolar Active-Layer Permafrost System (CAPS), version 1.0.
Decreasing freeze depths have also been recorded in a separate study of deep boreholes in mountain permafrost in Svalbard and Scandinavia. Results from the study show that the permafrost has "warmed considerably" at the study sites and that "significant warming is detectable down to at least 60m depth, and present decadal warming rates at the permafrost surface are on the order of 0.04°.0.07°C [per year], with greatest warming in Svalbard and in northern Scandinavia. The present regional trend shows accelerated warming during the last decade" (Isaksen et al., 2007).
Although many studies, programs, and research, including the Global Terrestrial Network for Permafrost (GTNP), indicate a warming trend throughout the permafrost zone, some have found no significant changes have occurred in permanent Russian permafrost regions. According to the authors of the study mentioned earlier, spatial trend analysis shows that while permanent permafrost areas in Russia have remained largely within the same freezing regime, seasonally frozen ground areas are experiencing "significant warming trends" (Frauenfeld et al., 2007).
All of these changes in permafrost areas are attributed to increases in air temperature and changes in snow cover, specifically in Canada and Alaska. This echoes the conclusions of numerous other reports, such as those from the Geological Survey of Canada and the Arctic Climate Impact Assessment, which attribute the northern polar region's permafrost thaw to dramatic warming over the past half-century. In regions of discontinuous and seasonal permafrost, ground temperatures are generally right around freezing. With even 1-2 degrees increase in temperature, these areas of permafrost will "likely ultimately disappear as a result of ground thermal changes associated with global climate warming" (GSC, 2007). Based on trends and forecasts predicted by climate models, however, we could be facing a much steeper increase in air temperature, leading to more significant effects on permafrost regions across the globe. As Charles Harris, one of the authors of the Svalbard study, a geologist at the University of Cardiff, UK, and a coordinator of Permafrost and Climate in Europe (PACE), said in a 2004 interview, "Boreholes in Svalbard, Norway, for example, indicate that ground temperatures rose 0.4°C over the past decade, four times faster than they did in the previous century. What took a century to be achieved in the 20th Century will be achieved in 25 years in the 21st Century, if this trend continues" (Bently, 2004).
Additionally, thawing and warming permafrost areas do not seem to be reversing the trend from year to year. Instead, they keep warming. Researchers of Canada's peatland permafrost regions mentioned "The permafrost underlying Canada's peatlands show no sign of regeneration" (Turetsky et al., 2007). According to the IPCC, by the mid-21st century, the area of permafrost in the northern hemisphere is expected to decline by around 20 per cent to 35 per cent. The depth of thawing is likely to increase by 30 percent to half its current depth by 2080 (UNEP, 2007). The end result could look something like the scenario depicted in the figure "Map of Permafrost in the Future".
Impacts of Melting Permafrost: Physical and Ecological
Thawing permafrost has significant effects on surface and subsurface regimes, including those governing hydrology and energy and moisture balance. Ecosystem diversity, composition, and productivity are not only impacted by increasing air temperatures, but by the associated effects of increasing ground temperatures as well. Because of this, thawing permafrost has significant impacts on infrastructure and ecosystems. Where ground ice contents are comparatively high, permafrost degradation can have significant impacts, some of which may take not be as readily apparent as others.
The Geological Survey of Canada states "Of greatest concern are soils with the potential for instability upon thaw (thaw settlement, creep or slope failure). Such instabilities may have implications for the landscape, ecosystems, and infrastructure" (GSC, 2007). Erosion, landslides, and subsidence can all result from permafrost degradation.
Figure 6. Sishmaref photo series: “Only two hours separate the first photo from the second. For reference, red arrows mark the barrel. By the time the second photograph was taken, the coastline in the foreground had retreated past the barrel. Although coastal erosion was significant, this was not a particularly strong storm. Image courtesy of Tony Weyiouanna Sr.” Image credit: NSIDC.
Erosion is especially evident and worrisome in coastal areas, may of which are also being ravaged by winter storm surge as the protective barrier of sea ice appears later and later (if at all) during the year. Intact permafrost is extremely resilient. However, when it becomes compromised, it and the ground above and below it become much more vulnerable to the erosive forces of wind and water. On our Sea Ice page, you can see a picture of a house in Shismaref, Alaska that has had its foundation washed away by storm surge. These pictures to the right in Figure 4 were also taken in Shishmaref, Alaska, during a storm in 2003.
In some areas, erosion has been so much enhanced by exposed and degraded permafrost, the inhabitants might have to be evacuated. Costs to relocate are hefty . for towns such as Kivalina, Alaska, they have been estimated at upwards of $400 million. Due to the heavy toll climate change is taking on Kivalina, the town recently sued two dozen oil, power, and coal companies for their contributions to global warming (CNN, 2008).
As permafrost thaws, the friction needed between the frozen and thawing permafrost regions to maintain stability disappears. On ice, you don't need a very sloped surface before you start to slip and slide . and that's exactly what happens with the permafrost and overlying land, resulting in landslides. This happened in July of 1988 on the Fosheim Peninsula of Canada's Ellesmere Island after a few years of increasingly warmer temperatures during the summers. Hundreds of landslides, some of which were the size of over three football fields, carried tons of soil into a number of creek valleys.
According to the Permafrost and Climate in Europe (PACE) project, thawing permafrost is likely to have similar effects on the slopes of Europe's Alps and Pyrenees as global temperatures continue to rise. Landslides, such as the Val Pola landslide of July 1987 in the Italian Alps are predicted to become more common as the permafrost underlying the slopes of Europe's mountains degrades due to rising ground temperatures.
Figure 7. Permafrost distribution in the Arctic. Image credit: Philippe Rekacewicz, 2005, UNEP/GRID-Arendal Maps and Graphics Library based on International Permafrost Association (1998) Circumpolar Active-Layer Permafrost System (CAPS), version 1.0.
Ground subsidence can occur when permafrost thaws and the soil previously held up by the ice collapses. The resulting landscape is characterized by irregular surfaces of marshy hollows and small hummocks called thermokarst. Visitors and residents all over permafrost regions have been struck by the effects of this phenomenon when they see a wooded landscape affected by subsidence from permafrost thaw. They call these areas "drunken forests" because of the way that the trees lean, as shown in Figure 5.
However, subsidence can have other effects on vegetation. A group of scientists studying the effect of permafrost thawing on vegetation in Alaska noted, "This effect of warming acts on vegetation indirectly by creating localized variability in moisture conditions as lower karst areas accumulate moisture and may have the water table near the soil surface, while nearby higher areas become drier" (Schuur et al., 2007). In some of these areas, these changing conditions allow new plant species to grow. In other pockets, water collects and they become thermokarst lakes or ponds. Once the underlying permafrost has thawed completely away, however, this water sinks back in to the empty space and disappears. According to a 2005 article in Science, this is what has been happening in Western Siberia, where thawing permafrost is the likely cause behind of the disappearance of Siberian Arctic lakes during the past three decades over an area of 500,000 square km (see Figure 6).
In addition to its ecological effects, subsidence caused by thawing can significantly compromise infrastructure built on top of permafrost. Many permafrost areas are permanently inhabited by humans, and as such have roads, buildings, and other structures built on it. In places where these structures were not designed to withstand changes in permafrost, subsidence has created sinkholes that swallow up houses and small buildings, and has also caused foundations to shift and drop and roads and railroads to crack and heave (such as the building and railroad in Figure 7 at right). In some permafrost areas, engineers are coming up with new ways to build on permafrost such that the ground is insulated from the heat created by whatever is on the ground above it. Additionally, these new engineering techniques are making it possible for the infrastructure built upon it to weather changes in permafrost a little bit better. The world's longest high-elevation railroad, the Qinghai-Tibet Railway or "Permafrost Express", in China and the 800-mile long Trans Alaska Pipeline in Alaska both involved engineering and design techniques sensitive to the permafrost environment in which they were constructed.
Figure 8. A railroad in Alaska (left) and building (right), both buckled due to thawing permafrost. Image credit: (left) NASA and U.S. Geological Survey, (right) Vladimir Romanovsky, Geophysical Institute, University of Alaska Fairbanks.
The changes brought about by thawing permafrost will also have significant impacts on the ecosystems of the Arctic. In addition to impacting migration routes and patterns in birds, reindeer, and caribou, it is expected that the effects of thawing permafrost will change the plant species composition of the area, as well as its productivity.
Changes in plant species composition
Increasing temperatures are expected to have significant impacts on the species composition world wide. This is also true of permafrost areas in northern latitude ecosystems, where plant species composition and productivity will change as increasing temperatures will allow new, warmer-climate species to grow. Tundra is usually characterized by sedges and grasses. However, with warming temperatures, these typical tundra species are being overtaken by evergreen shrubs and trees. The IPCC projects that by 2100, between 10 and 50% of the Arctic tundra could be replaced by forests (UNEP, 2007).
Warming can affect plants directly, through its influences over plant growth, and indirectly, through changes in nutrient availability. In permafrost areas, where increasing temperatures and subsequent thawing causes the development of thermokarst, warming can drastically change the hydrologic profile of an ecosystem. Researchers working at permafrost sites across Alaska and at peatland sites overlaying permafrost across boreal regions in Canada found changes in community composition, biomass, and productivity as a result of warmer air and soil temperatures as well as associated changes in the hydrologic structure of the soil (Schuur et al., 2007; Turetsky et al., 2007). Plant biomass shifted away from traditional species to plants associated with warmer, wetter biotypes. Additionally, plant productivity increased due to improved availability of nitrogen and other nutrients from altered hydrological patterns caused by thawing permafrost.
As a warming climate allows snow and ice to thaw, and tundra species are replaced with evergreens, albedo changes. Instead of reflecting sunlight, the landscape begins to absorb more heat than it did previously, further increasing the warming and thawing trends in the area.
Not all ecosystems in permafrost regions will respond the same way. Turetsky herself cautioned in an interview earlier this year, "It will depend on the history of the permafrost and the nature of both vegetation and soils" (Physorg.com, 2007). The quantity, distribution, and composition of the organic matter in permafrost areas are important in determining their effect on emissions. Some permafrost, such as yedoma permafrost found mostly in northern and eastern Siberia as well as in smaller amounts in Canada and Alaska, have more concentrated carbon and methane stores than others.
Additionally, records and data for many regions are incomplete or of short-term duration, with the exception of Russia's long-term permafrost monitoring. There has been a push to extend current monitoring programs and enlarge their scope. Programs such as the Global Terrestrial Network for Permafrost (GTNP) are working to organize data collection so that there is a global network for detecting and monitoring changes in permafrost regions, and predicting climate change's impact on these affected areas. Advances in spatial analysis have contributed greatly, as evidenced by the research conducted for the 2005 article on Siberian lake methane emissions. You can even monitor permafrost thaw with Google Earth!