What Is Permafrost?

A quarter of the entire northern hemisphere is permafrost.

In this photo you can see a collapsed block of ice-rich permafrost along Drew Point, Alaska. Coastal bluffs in this region can erode 20 meters/year (~65 feet). USGS scientists continually research the causes of major permafrost thaw and bluff retreat along the Arctic coast of Alaska.

Permafrost is soil or rocks that remain frozen below 0 degrees Celsius year-round. Permafrost soils can remain intact for hundreds of thousands of years and can extend several meters to 1.5 km below the Earth’s surface. Permafrost usually forms in cold climates where the average annual temperature is less than the freezing point of water. Such climates occur near the North and South poles and in some Alpine regions.

Permafrost Formation

Image: Alexander Oboimov.

Just as a puddle freezes on a cold winter night, water trapped in sediment, soil or rock cracks, crevices and pores turns to ice when the ground temperature drops below 0°C. When this soil remains frozen for at least two consecutive years, permafrost has formed.

A quarter of the entire northern hemisphere is permafrost. About 85% of Siberia, Canada, Greenland and the Arctic regions of Alaska lie on permafrost. There is also submarine permafrost on the Tibetan plateau, in high-altitude areas such as the Rocky Mountains and on the floor of the Arctic Ocean. In the southern hemisphere, where there is much less ground to freeze, there is permafrost in mountainous regions such as the South American Andes and the Southern Alps of New Zealand, and under Antarctica.

Permafrost in the northern hemisphere covers an area of 23 million km2, equivalent to the US, China and Canada combined. But this area is shrinking rapidly. Global warming is increasing temperatures worldwide and the Arctic is melting twice as fast as anywhere else and warming faster than it has in the last 3 million years. As surface air temperatures rise, permafrost is thawing. Scientists estimate that there was 10% less permafrost in the northern hemisphere today than in the early 1900s. A recent study showed that for every additional 1°C of warming, 3.9 million km2 of permafrost is destroyed.” Even if we meet the climate targets set out during the 2015 Paris climate talks, the Earth will still lose more than 9 million km2 of permafrost.

Impact of Permafrost Thaw on Earth

Emission of Greenhouse Gases

When plants and animals die, the bacteria that break down their bodies release carbon dioxide, methane, and other greenhouse gases into the air. Permafrost acts like a pause button in this process, trapping the organisms and gases emitted underground. However, when the permafrost moves, microbes decompose these organic materials, and the release of greenhouse gases begins again. Therefore, it is crucial for our Earth that the permafrost layer does not melt.

Permafrost is one of the largest stores of global warming gases on Earth, preserving everything from human bodies that died thousands of years ago to the bodies of woolly mammoths. Arctic permafrost alone is estimated to hold almost twice as much carbon as the atmosphere by mass. The same applies to methane, a powerful greenhouse gas that traps 80 times more heat on our planet. As permafrost thaws, it is estimated that 92 billion tons of carbon will be released into the atmosphere from the thawing permafrost by 2100. That is equivalent to 20% of all the carbon released since the beginning of the Industrial Revolution.

New Diseases

Just as permafrost traps carbon and other greenhouse gases, it also hides ancient microbes. Some bacteria and viruses are believed to have been dormant in permafrost for thousands of years. While the concept of ‘zombie’ pathogens, referring to these ancient microbes, may sound scary, they may pose a risk. The 2016 anthrax outbreak in Siberia was found to have been caused by a decades-old reindeer carcass exposed to thawed permafrost filled with bacteria. However, it is not yet known whether pathogens in this permafrost, where people who died from smallpox or the Spanish flu of 1918 may be hiding, could cause another outbreak. What is certain is that millions of tons of permafrost disturbed in the Arctic to extract precious metals and oil have increased human contact with ancient and possibly zombie pathogens.

The Earth Will Be Filled With Mercury

Carbon and methane are not the only pollutants trapped in permafrost. In addition to new diseases, a recent study shows that Arctic permafrost is a huge natural storehouse of mercury, a potent neurotoxin. Indeed, about 15 million gallons of mercury—almost twice the amount found in the ocean, atmosphere, and all other soils—are hidden in permafrost soils. Once released, this mercury can enter the environment through water or air, and potentially even into the food supply.

Damage to Infrastructure in Cities and Roads

Glacial soils begin to lose their structure.
Glacial soils begin to lose their structure. Image: Climate Change (Third Edition).

City buildings are collapsing in northern Russia. In Alaska, roads turn into amusement park rides. When water underground freezes, it expands and causes the soil to swell, creating surface cracks similar to potholes in spring. Approximately 35 million people live in towns and cities built in areas once considered ‘permanently frozen ground’ within permafrost zones. As this solid ground softens, the infrastructure on which people stand deteriorates.

In Canada, the annual disappearance of permafrost is estimated to cause tens of millions of dollars in damage to infrastructure in the Northwest Territories. In Alaska, a study shows that by the end of this century, roads, rail lines, buildings, and airports damaged by permafrost thaw and other climate impacts will cost $5.5 billion in repairs. The fossil fuel industry continues to drive climate change, contributing to the warming of the planet and the melting of the world’s permafrost.

Changing Natural Landscapes

Drunken trees, tilted trees, or a drunken forest is a serious environmental problem.
Drunken trees, tilted trees, or a drunken forest is a serious environmental problem.

Thawing permafrost also changes ecosystems. Thermokarst can create areas of sagging ground and shallow puddles, often resulting in the phenomenon known as ‘drunken trees.’ An example of a drunken forest can be found in the photo above, and more can be found here.

When these frozen soils start to deteriorate or soften, soil erosion occurs first. As a result, new sediments are formed that alter the flow of rivers and streams, leading to reduced water quality (including carbon content) and affecting aquatic wildlife. The visible landscape undergoes dramatic changes.

By reducing our carbon footprint, investing in energy-efficient products, and supporting climate-friendly businesses, laws, and policies, we can help preserve the world’s permafrost—the climate—and prevent the vicious cycle that contributes to the continuous warming of the planet.


pingo soil permafrost
Ibyuk, the largest pingo in Canada and the second largest in the world after Kadleroshilik Pingo in Alaska. Source: Adam Jones – Flickr.

Some soils exposed to warm weather thaw for a short period during these months. Thawing is limited to the top layer of the soil, and the permafrost layer remains frozen a few inches below the surface. The soil layer in these areas, known as the active layer, can warm up enough to support plant growth in the summer. The permafrost beneath the active layer retains water near the soil’s surface, resulting in high soil moisture content. Permafrost also contributes to cooler soil temperatures, slower plant growth, and slower decay processes. When the permafrost layer contains a significant amount of water, pingo soil formations occur. When the water freezes, it expands and saturates the soil, forming large mounds known as pingos.



Thawing is a process that leads to the formation of new soil. It occurs when thawed soils slope over the permafrost layer and slide down. When this happens, the soils form wave patterns, as seen in the photo above.

Thermokarst Collapse Formation

Thermokarst lakes near Cape Krusenstern, Alaska. Photograph by J. Giardino (2005).

Thermokarst subsidence often occurs in areas that have been cleared of vegetation due to human error, such as irregular land use. This phenomenon leads to the melting of the permafrost layer, causing the ground to collapse or become unstable. These collapses are commonly found in Arctic regions and occasionally occur in the Swiss Alps.

Permafrost Distribution in the Northern Hemisphere

Permafrost covers 85% of Alaska, 55% of Russia and Canada, and likely the entire continent of Antarctica. The extent and thickness of permafrost are generally greater in the northern regions compared to the south. In northern Siberia, permafrost can reach a thickness of up to 1,500 meters, while in northern Alaska, it can be up to 740 meters thick. However, the thickness gradually decreases as you move south.

Permafrost can be broadly categorized into two zones: continuous and discontinuous, based on the lateral continuity of permafrost. In the continuous zone, which extends far north, permafrost is present in most areas except at the bottoms of lakes and waterways that never freeze over. In the discontinuous zone, permafrost-free areas become more extensive and abundant as you move from north to south. Some rare ice fields have been discovered near certain southern borders.

Permafrost is not limited to Arctic and subarctic regions; it can also be found at lower altitudes in higher mountainous areas. Alpine permafrost refers to the permanent icy soil in mountains. While data from high plateaus and mountains are limited, measurements from deeper within the Earth’s crust reveal regions where temperatures remain below freezing for two years or more. Western China has the world’s largest alpine tundra region, covering 1.5 million square kilometers of permafrost. The western high ranges of the continental United States contain approximately 100,000 square kilometers of alpine permafrost. In northern states, permafrost can be found at altitudes as low as 2,500 meters, while in Arizona, it can be found at around 3,500 meters.

In the Arctic Ocean, along the continental margins of North America and Eurasia, a unique case of permafrost exists without a counterpart on land. This phenomenon is referred to as submarine or offshore permafrost.

Permafrost at a Glance

What Is Permafrost?

Permafrost is soil that remains frozen for two or more years and is found in areas with temperatures below 0°C.

What Are the Different Types of Permafrost?

The statement “There are three types of permafrost: continuous, discontinuous, and irregular” is accurate and grammatically correct. It introduces the three types of permafrost based on their characteristics. Continuous permafrost is described as occurring in areas where the temperature remains below freezing year-round. Discontinuous permafrost is characterized by variations in temperature above and below freezing. Irregular permafrost is defined as permafrost that is intermixed with unfrozen ground.

What Is the Importance of Permafrost in the Global Climate System?

Permafrost plays a critical role in the global climate system because it stores large amounts of carbon in the form of organic matter that has been frozen for thousands of years. When permafrost thaws, organic matter decomposes and releases carbon dioxide and methane, powerful greenhouse gases that contribute to climate change.

How Does Permafrost Form?

Permafrost forms when the ground temperature remains below freezing for a long period of time. This causes the water in the soil to freeze, forming a layer of ice. Over time, the ice layer thickens and gradually transforms into permafrost.

What Factors Affect Permafrost Distribution and Stability?

The distribution and stability of permafrost are influenced by several factors, including air and ground temperature, snow cover, vegetation, and water content.

Featured Image: Benjamin Jones, U.S. Geological Survey.