Photograph by Bernhard Edmaier, National Geographic December 2007

Permafrost is perennially frozen ground that remains at or below zero degrees Celsius (32 degrees Fahrenheit) for two or more years and forms in regions where the mean annual temperature is colder than zero degrees Celsius. Permafrost underlies about 20 percent of the land in the Northern Hemisphere and is widespread within the Arctic Ocean’s vast continental shelves and in parts of Antarctica. Most of the world’s permafrost has been frozen for millennia and can be up to 5,000 feet thick.

In addition to occurring in cold landscapes of the higher latitudes, permafrost is found at high elevations in the lower latitudes. Known as alpine or mountain permafrost, it exists all over the world, including on the Tibetan Plateau, in the Rocky Mountains of North America, and in the Andes in South America. Permafrost can occur at elevations as low as 8,000 feet in the northern states of the United States and at 11,500 feet in southwestern states such as Arizona.

The International Permafrost Association created a map of permafrost’s extent in the Northern Hemisphere, which can be viewed here.


Lopez, Barry. “Coldscapes.” National Geographic (December 2007), 136-155.

International Permafrost Assocation

Circum-Arctic Map of Permafrost

Permafrost: Where Does It Occur?

The Active Layer: Freezing and Thawing

Permafrost’s thickness is affected by snow cover, vegetation, bodies of water, heat from the Earth’s interior, and especially the temperature of the air near the ground. The active layer of permafrost, the uppermost ground layer, thaws in the summer and freezes in the winter. Plant growth is restricted largely to this active layer, since roots can’t penetrate the frozen ground beneath. Many types of plants exist in permafrost regions, depending on the climate and hydrology. Common plants include dwarf shrubs, birch and spruce trees, mosses, and lichens.

The permafrost zone ranges from continuous, occurring in 90 to 100 percent of an area, to isolated, occurring in up to 10 percent of the region. In the polar and high-mountain regions, where winter is severe and the temperature is below freezing, permafrost underlies nearly all the landscape, except perhaps deep lakes and rivers that don’t freeze to the bottom. Such landscapes are referred to as the continuous permafrost zone. The thickness of the active layer varies according to the temperature. In colder areas, continuous permafrost is topped with an active layer less than a foot thick.

In warmer regions, where the permafrost tends to be discontinuous, the temperature remains above freezing nearly as long as below, and local factors such as vegetation, soil type, and snow cover determine whether permafrost can form or be maintained. This discontinuous permafrost zone has a thicker active layer, which can become up to ten feet thick. Permafrost has the lowest ice content and the thickest active layer in isolated areas. Whether permafrost forms depends on how well the surface is insulated from the underlying soil or rock. Peat bogs are remarkable in this respect: Dry peat is an excellent thermal insulator, and in the summer it prevents heat from penetrating the ground. However, when peat is wet or frozen, it transmits heat efficiently from the ground into the atmosphere. Consequently, permafrost is found in peatlands throughout the vast discontinuous permafrost zone of North America, Europe, and Asia. These peatlands serve as an enormous reservoir of organic carbon, which may be released in the form of greenhouse gases if the permafrost thaws.

Many permafrost regions now have shorter winters, which means the active layer is growing thicker and warmer. And as the organic-rich top layer thaws, it’s more likely to decompose. As the organic material breaks down, it forms methane, which could contribute to the carbon already in the atmosphere.


Lopez, Barry. “Coldscapes.” National Geographic (December 2007), 136-155.

Kimble, J. M., ed. Cryosols: Permafrost-Affected Soils. Springer-Verlag, 2004.

Permafrost and Climate Change

Climate change may threaten the natural freeze and thaw cycles of permafrost. According to our supplement map (October 2007), “The Arctic is experiencing the fastest rate of warming as its reflective covering of ice and snow shrinks.” This includes some places where permafrost is most abundant. The Arctic’s continued loss of sea ice, retreat of glaciers, and thawing of permafrost will likely have consequences for the planet and its inhabitants. Temperature measurements have shown that in some places permafrost has fallen out of sync with the normal seasonal climate, suggesting that increased thawing may be occurring. A recent United Nations report, “Confronting Climate Change: Avoiding the Unmanageable and Managing the Unavoidable,” details the work of the Scientific Expert Group on Climate Change and Sustainable Development. It can be viewed at

Changes in the seasonal thaw depth and ground temperature of permafrost, measured at different locations around the world, indicate that as warming trends continue, the active layer of permafrost will thaw more readily, affecting ecosystems, carbon reservoirs in the upper part of permafrost, hydrology, and Arctic infrastructure such as roads. More information on the warming trend over the past 30 years can be found at


Lopez, Barry. “Coldscapes.” National Geographic (December 2007), 136-155.

United Nations Environmental Programme

International Permafrost Association

Carbon Reservoir

Greenhouse gases such as carbon dioxide and methane could be released as permafrost thaws. When organic material in the active layer of permafrost thaws and decomposes, it can add to the carbon in the atmosphere. As the temperature rise accelerates, more thawing occurs. The amount of carbon currently estimated to be in the upper part of the permafrost ranges from 500 billion to 1,000 billion metric tons. There are already 800 billion metric tons of carbon in the atmosphere.


Lopez, Barry. “Coldscapes.” National Geographic (December 2007), 136-155.

Walter, Katey, and others. Nature, (September 2006), 71-75.

Human Impact

Permafrost changes can affect people as well as the environment. They may force changes in land-use planning and in infrastructure design, construction, and maintenance. More information on climate change, permafrost, and their impact on infrastructure can be found at

“These changes [in the Arctic] will have consequences for all of us,” says Ron Sletten, a permafrost scientist at the University of Washington. He says that in addition to “climate feedbacks and opening of the northwest passage,” he expects that changes in the Earth’s unique environment will lead to changes for both the people who’ve evolved in them and for the wildlife that has adapted and thrived there.

The Geological Survey of Canada has gathered climate data from more than 500 national, university, and industry databases. The data—on, among other things, air temperature, snow cover, vegetation—can be accessed at


United Nations Environmental Programme

Geological Survey of Canada

Ice Wedges and Polygons

Ice wedges grow as the ice-rich frozen ground contracts during the winter and forms open cracks below the surface. As the ground surface warms and the snow thaws in the spring, meltwater flows into the open cracks and freezes. But the ground beneath is still frozen, and as the freezing water expands, it forces the surrounding soil upward and outward. This process creates the ridges and troughs typically seen on either side of the ice wedges.

Networks of ice wedges form the distinctive polygonal patterns that mark the surface of permafrost. These features, commonly found in areas of both permafrost and seasonal frost, are formed by contraction cracks enlarged by ice wedges. The wedges exert pressure that forces soil around the crack upward to relieve the tensile stresses, creating two small ridges. The ridges form the raised edges of polygonal shapes, which can be 100 feet (30 meters) across. This is similar to the way columnar basalt is formed as volcanic rock cools, according to Ron Sletten.

Some polygons are lower in the center and have a pond in the middle. Water from the ponds absorbs more solar heat than the soil, which can increase thawing of the underlying soil. Over time, as ground ice melts below the small water bodies, the ponds combine to create larger lakes, as they have on Alaska’s north slope.

In other places, subtle changes in the thaw and drainage patterns cause ponds of water to develop at the intersection of ice wedges. Small rivulets running between the ridges often link these ponds, and they develop into networks called beaded streams, because the ponds are connected like beads on a necklace.


Sletten, R. S., and others. “Resurfacing Time of Terrestrial Surfaces by the Formation and Maturation of Polygonal Patterned Ground.” Journal of Geophysical Research (2003), 8044.


The pingo, or ice-cored mound, is one of the most remarkable permafrost landforms, rising high above the tundra, sometimes more than a hundred feet high. These mounds are created as water freezes beneath the ground’s surface and forms ice masses that force the frozen ground layers upward.

Pingos fall into two categories: open-system and closed-system.

Closed-system pingos are most common in tundra areas of continuous permafrost. They form in level areas where unfrozen groundwater is trapped by permafrost, which exerts pressure through soil pores, forcing the water inward. When the water freezes, it expands upward, heaving the frozen overburden of ground into a mound.

The open-system pingo, typically smaller than the closed-system variety, forms when groundwater flows downhill and becomes trapped beneath permafrost. The water eventually forces itself up through the cracks of the permafrost and freezes, which pushes the soil above it into a cone-shaped mound.

Some of the biggest pingos in the world are found on the Tuktoyaktuk Peninsula in Canada. The largest, Ibyuk, is about 160 feet tall and is surrounded by more than a thousand other pingos.


Parks Canada

Mackay, J. R. “The pingos of the Pleistocene Mackenzie Delta area.” Geographical Bulletin 18:21-63.

Mackay, J. R. “Pingos in Canada.” Permafrost International Conference, Proceedings. National Academy of Science - National Research Council, Publication 1287:71-76.

Thermokarst Topography and Beaded Streams

Thermokarst terrain forms when warming at the surface causes thawing to extend into the upper layers of ice-rich permafrost. Melting of the ground ice creates a series of irregular hollows and hills. The hollows deepen and form meltwater pools, which absorb more solar radiation than do ice and snow. As the depressions fill with water, thermokarst ponds form. The frozen permafrost beneath the ponds protects them from draining away, and eventually the ponds join to form larger lakes. If the underlying permafrost thaws completely, the lakes drain away underground.

Thermokarst topography includes mounds, depressions, sinkholes, tunnels, and caverns. Widespread thermokarst terrain can form in response to the warmer temperatures associated with climate change. It can also occur locally in response to changes at the surface caused by human activity, such as removing vegetation, modifying drainage patterns, and constructing roads, airfields, and buildings.

Parts of the north slope of Alaska, for example, have a long, linear thermokarst topography, which has formed in places where old roads have damaged the organic top layer. The layer no longer loses its ability to insulate, and meltwater pools form, linking together into beaded streams.


Permafrost in Alaska

Arctic Long Term Ecological Research Site

Frost Action and Patterned Ground

“Frost heave” is defined as an upward thrusting of the ground due to the freezing of moist soil—something the soil of the active layer are vulnerable to.

Repeated sorting and shifting of rocks in the active layer of permafrost creates unique horizontal, alternating rows of rock fragments and fine soil. Though scientists are still learning about the exact processes involved in such pattern formations, it’s generally accepted that they’re affected by gravity and different rates of freezing, expansion, and contraction.

In the deep cold of winter, moist soil freezes, increasing in volume and lifting heavy stones, which don’t compress, to the surface—a process known as “frost sorting.” The water-filled, fine-grained soil tends to expand and contract, moving surface stones laterally across the ground.

Initially, isolated circles build in places with adequate moisture, soil texture, and snow cover. As more of them form, a field of sorted circles is created.

Sorted stone stripes can also form in permafrost, as parallel lines of stones and intervening lines of finer material extend down the slope of a hill. Many scientists believe that sorted stripes form as sorted circles are deformed by processes such as solifluction, the slow downslope flow of saturated soil. Since the ground beneath the active layer is frozen and impermeable, the active layer can become saturated with moisture during the summer. Gravity propels this fluid soil slowly downhill, taking vegetative material with it.


Rosato, A., and others. "Why the Brazil Nuts Are on Top: Size Segregation of Particulate Matter by Shaking." Physical Review (1987), 1038-1040.

Permafrost in Alaska


Arctic Geobotanical Atlas

Stone Circles

On Norway’s Spitsbergen Island are mysterious stone circles that look like giant stone doughnuts, with a diameter of up to ten feet (below). Centuries of seasonal freezing and thawing have caused the ground to shift and settle, forming these labyrinthine Arctic patterns. These circles are likely caused by frost heave, the upward thrusting of the ground. In the deep cold of winter, moist soil freezes, increasing in volume and lifting heavy stones, a process also known as vertical sorting.

During the spring thaw, as the ice melts, the fine-grained silt particles settle more rapidly, while the bigger, gravelly chunks that remain on top get pushed toward the rim. At first the circles build in isolation in places with snow cover, adequate moisture, and the proper soil texture. Eventually they merge and grow into a field of circles.

“More than 40,000 years ago, this area was just a sandy, gravelly beach with absolutely no structure or organization,” says Bernard Hallet, a professor of earth and space sciences at the University of Washington (he took the photograph). Like a box of granola shaken during shipping, he says, the bigger chunks tend to stay on top. “The distinct patterns and the segregation of material according to size,” he says, “constitute striking examples of self-organization.”

To Pier Paul Overduin, a scientist at Germany’s Alfred Wegener Institute for Polar and Marine Research, that statement doesn’t go far enough. In his view, “It is one of the most startling and dramatic examples of sorted rock circles in the known universe.”


Illustration from “Coldscapes.” National Geographic (December 2007), 146-47.

Permafrost Thawing and Arctic Communities

Permafrost isn’t just a faraway phenomenon that exists in isolation at the Poles. It directly affects the lives of people who live today in Arctic villages and communities. As the Arctic continues to warm, the decline of permafrost will change the way they live in these cold landscapes.

According to a recent report from the UN Intergovernmental Panel on Climate Change, increased thawing of Arctic permafrost is “likely to have significant implications for infrastructure, including houses, buildings, roads, railways and pipelines. A combination of reduced sea ice, thawing permafrost and storm surges also threatens erosion of Arctic coastlines with impacts on coastal communities, culturally important sites and industrial facilities.”

One study suggests that “a three degree C increase in average summer air temperatures could increase erosion rates in the eastern Siberia Arctic by three to five meters a year.” And experts estimate that by the mid-21st century, permafrost will decline by 20 to 35 percent in the Northern Hemisphere. Some changes have already occurred, including the draining and disappearance of Arctic lakes in Siberia—likely the result of thermokarst conditions, which occur when rising temperatures melt all the permafrost, allowing lakes to drain away underground.

Relocating towns will carry a hefty price tag: Moving a village like Kivalina, in northwestern Alaska, could cost 54 million dollars.

In some parts of the Arctic toxic materials have reportedly been stored in the permafrost. These substances might be released into the local environment, posing a risk to humans and wildlife and adding to the clean-up costs.

Biodiversity will also be affected by changing river patterns and increased sedimentation from permafrost thaw. The declining species could include the broad whitefish, Arctic char, Arctic grayling, and Arctic cisco. Freshwater and estuary-dependent marine food sources could also be affected.

“The communities and Indigenous peoples of this region are skilled in adapting to harsh and often dramatic changing conditions, including sharp fluctuations in the scarcity and in the abundance of land and marine resources,” Achim Steiner, executive director of the UN Environment Programme, has said. “However, the rapid changes likely in the future may overwhelm traditional coping strategies. It is thus also vital that communities are assisted in climate proofing centuries-old lifestyles in order to survive and to thrive through the 21st century.”


Science Daily (April 11, 2007).

United Nations Environment Programme

Intergovernmental Panel on Climate Change

Contribution of Working Group II to the Fourth Assessment Report

“Climate Warning as Siberia Melts.” New Scientist (August 11, 2005).

Carmichael, Mary. “Making Sense of Melting Ice: How Long Will the Poles Stay Frozen? The Search for Answers.” Newsweek (April 2, 2007).

Kimble, J. M., ed. Cryosols: Permafrost-Affected Soils. Springer-Verlag, 2004.

Perkins Sid. “On the Rise.” Science News (September 9, 2006).

Perkins, Sid. “Not-So-Perma Frost.” Science News (March 10, 2007).

Rosato, A., and others. "Why the Brazil Nuts Are on Top: Size Segregation of Particulate Matter by Shaking." Physical Review (1987), 1038-1040.

Sletten, R. S., and others. “Resurfacing Time of Terrestrial Surfaces by the Formation and Maturation of Polygonal Patterned Ground.” Journal of Geophysical Research (2003), 8044.

Washburn, A. L. Geocryology: A Survey of Periglacial Processes and Environments. Edward Arnold, 1979.

Werner, B. T. and Hallet, B. “Sorted Stripes: A Numerical Study of Textural Self-Organization.” Nature (January 14, 1993), 142-145.

Young, Steven B. To the Arctic. Wiley, 1989.

Other Resources

National Geographic Photo Gallery, Climate Change

DNA from the oldest known living bacteria in the world—more than half a millions years old—has been found in permafrost. University of Copenhagen researchers led by Professor Eske Willersley made the discovery.

Research cartographer Benjamin M. Jones, of the Alaska Science Center, USGS, took fascinating video of permafrost landscapes along the coastline of the Beaufort Sea in the Arctic during the summer of 2007 and of the changes the landscape had undergone.

Most of Alaska sits on top of permafrost, and as the climate has warmed, the permafrost has started to melt. In this video Torre Jorgenson, a landscape ecologist at Alaska Biological Research, shows a spot in Alaska where the melting permafrost has turned the forest into ponds.

For the first time in tens of thousands of years, Siberia's frozen land is undergoing a thaw. Scientists warn that the process could release billions of tons of carbon, which could quickly turn into greenhouse gases in the atmosphere and further accelerate global warming.

The planet’s cryosphere consists of those parts of the Earth's surface where water is found in solid form, including areas of snow, sea ice, glaciers, permafrost, ice sheets, and icebergs. Using satellite observations, scientists monitor changes in the global and regional climate by observing how regions of the Earth's cryosphere shrink and expand. This animation shows fluctuations in the cryosphere using observations collected from satellite-based sensors. It begins in Antarctica, showing ice shelves, ice streams, glaciers, and the formation of massive icebergs, then moves on to show areas of permafrost in South America, a mostly tropical continent. Then it shifts north to show daily changes in snow cover over the North American continent.
NASA Goddard Space Flight Center: A Tour of the Cryosphere

“Our Planet in Transition: Pole to Pole,” a short film that focuses on climate change in the Arctic and around the globe; made by Greenpeace International

Photos and video of permafrost and the effects of methane release, posted by researchers at the University of Alaska Fairbanks

International Permafrost Association
The association has information about permafrost and about the scientists and international organizations with expertise on the subject.

Natural Resources Canada
Includes a good map of where permafrost exists

Center for International Climate and Environmental Research
Information about how climate change affects permafrost

Canadian Pingo Landmark
Learn more about Canada’s biggest pingo, Ibyuk.

National Oceanic and Atmospheric Association
Vladimir Romanovsky, a professor at the University of Alaska Fairbanks, describes how and why permafrost is changing.

Polar Landscape Studies
Discover more about polar landscape studies.

“Permafrost Thaw.” Science Daily.
An interesting article about the changes that will affect humans and the environment as permafrost continues to thaw

United Nations Environment Programme: Permafrost Thaw
Describes the intergovernmental panel’s climate-change predictions about how permafrost thawing will affect Arctic communities

People and Global Heritage on Our Last Wild Shores
A compilation of illustrations and case studies concerning the Arctic, the livelihoods of Arctic indigenous peoples, and the future well-being of this region

Circumpolar Active Layer Monitoring

United States Arctic Research Commission
Information on climate change, permafrost, and the impact on civil infrastructure

Last updated: December 14, 2007