Permafrost (from perma- 'permanent', and frost) is soil or underwater sediment which continuously remains below 0 °C (32 °F) for two or more years. Land-based permafrost can include the surface layer of the soil, but if the surface is too warm, it may still occur within a few centimeters of the surface down to hundreds of meters. It usually consists of ice holding in place a combination of various types of soil, sand, and rock, though in ice-free ground, perennially frozen non-porous bedrock can serve the same role.[1]

Circum-Arctic Map of Permafrost and Ground Ice Conditions.png
Map showing extent and types of permafrost in the Northern Hemisphere
Used inInternational Permafrost Association
ClimateHigh latitudes, alpine regions

Around 15% of the Northern Hemisphere or 11% of the global surface is underlain by permafrost,[2] with the total area of around 18 million km2 (6.9 million sq mi).[3] This includes substantial areas of Alaska, Greenland, Canada, and Siberia. It is also located in high mountain regions, with the Tibetan Plateau a prominent example. Only a minority of permafrost exists in the Southern Hemisphere, where it is consigned to mountain slopes like in the Andes or the Southern Alps of New Zealand, and beneath the massive ice sheets of the Antarctic.[4]

Permafrost contains large amounts of dead biomass that had accumulated throughout millennia without having had the chance to fully decompose and release its carbon, making tundra soil a carbon sink.[4] As global warming heats the ecosystem, frozen soil thaws and becomes warm enough for decomposition to start anew, accelerating permafrost carbon cycle. Depending on conditions at the time of thaw, decomposition can either release carbon dioxide or methane, and these greenhouse gas emissions act as a climate change feedback.[5][6][7] The emissions from thawing permafrost will have a sufficient impact on the climate to impact global carbon budgets. Exact estimates of permafrost emissions are hard to model because of the uncertainty about different thaw processes. There's a widespread agreement they will be smaller than human-caused emissions and not large enough to result in "runaway warming".[8]

Slope failure of permafrost soil, revealing the top of an ice wedge.

In addition to its climate impact, permafrost thaw brings additional risks. Formerly frozen ground often contains enough ice that when it thaws, hydraulic saturation is suddenly exceeded, so the ground shifts substantially and may even collapse outright. Many buildings and other infrastructure were built on permafrost when it was frozen and stable, and so are vulnerable to collapse if it thaws.[9] Estimates suggest nearly 70% of such infrastructure is at risk by 2050, and that the associated costs could rise to tens of billions of dollars in the second half of the century.[10] Furthermore, around 20,000 sites contaminated with toxic waste are present in the permafrost,[11] as well as the natural mercury deposits,[12] which are all liable to leak and pollute the environment as the warming progresses.[13] Lastly, there have been concerns about potentially pathogenic microorganisms surviving the thaw and contributing to future epidemics and pandemics,[14][15][16] although this risk is speculative and is considered implausible by much of the scientific community.[17][18][19]

Classification and extentEdit

Red lines: Seasonal temperature extremes (dotted=average).

Permafrost is soil, rock or sediment that is frozen for more than two consecutive years. In areas not covered by ice, it exists beneath a layer of soil, rock or sediment, which freezes and thaws annually and is called the "active layer".[20] In practice, this means that permafrost occurs at an mean annual temperature of −2 °C (28.4 °F) or below. Active layer thickness varies with the season, but is 0.3 to 4 meters thick (shallow along the Arctic coast; deep in southern Siberia and the Qinghai-Tibetan Plateau).[citation needed]

The extent of permafrost is displayed in terms of permafrost zones, which are defined according to the area underlain by permafrost as continuous (90%–100%), discontinuous (50%–90%), sporadic (10%–50%), and isolated patches (10% or less).[21] These permafrost zones cover together approximately 22% of the Northern Hemisphere. Continuous permafrost zone covers slightly more than half of this area, discontinuous permafrost around 20 percent, and sporadic permafrost together with isolated patches little less than 30 percent.[22] Because permafrost zones are not entirely underlain by permafrost, only 15% of the ice-free area of the Northern Hemisphere is actually underlain by permafrost.[2] Most of this area is found in Siberia, northern Canada, Alaska and Greenland. Beneath the active layer annual temperature swings of permafrost become smaller with depth. The deepest depth of permafrost occurs where geothermal heat maintains a temperature above freezing. Above that bottom limit there may be permafrost with a consistent annual temperature—"isothermal permafrost".[23]

Continuity of coverageEdit

Permafrost typically forms in any climate where the mean annual air temperature is lower than the freezing point of water. Exceptions are found in humid boreal forests, such as in Northern Scandinavia and the North-Eastern part of European Russia west of the Urals, where snow acts as an insulating blanket. Glaciated areas may also be exceptions. Since all glaciers are warmed at their base by geothermal heat, temperate glaciers, which are near the pressure-melting point throughout, may have liquid water at the interface with the ground and are therefore free of underlying permafrost.[24] "Fossil" cold anomalies in the Geothermal gradient in areas where deep permafrost developed during the Pleistocene persist down to several hundred metres. This is evident from temperature measurements in boreholes in North America and Europe.[25]

Discontinuous permafrostEdit

The below-ground temperature varies less from season to season than the air temperature, with mean annual temperatures tending to increase with depth as a result of the geothermal crustal gradient. Thus, if the mean annual air temperature is only slightly below 0 °C (32 °F), permafrost will form only in spots that are sheltered—usually with a northern or southern aspect (in north and south hemispheres respectively) —creating discontinuous permafrost. Usually, permafrost will remain discontinuous in a climate where the mean annual soil surface temperature is between −5 and 0 °C (23 and 32 °F). In the moist-wintered areas mentioned before, there may not be even discontinuous permafrost down to −2 °C (28 °F). Discontinuous permafrost is often further divided into extensive discontinuous permafrost, where permafrost covers between 50 and 90 percent of the landscape and is usually found in areas with mean annual temperatures between −2 and −4 °C (28 and 25 °F), and sporadic permafrost, where permafrost cover is less than 50 percent of the landscape and typically occurs at mean annual temperatures between 0 and −2 °C (32 and 28 °F).[26] In soil science, the sporadic permafrost zone is abbreviated SPZ and the extensive discontinuous permafrost zone DPZ.[27] Exceptions occur in un-glaciated Siberia and Alaska where the present depth of permafrost is a relic of climatic conditions during glacial ages where winters were up to 11 °C (20 °F) colder than those of today.

Continuous permafrostEdit

Estimated extent of alpine permafrost by region[28]
Locality Area
Qinghai-Tibet Plateau 1,300,000 km2 (500,000 sq mi)
Khangai-Altai Mountains 1,000,000 km2 (390,000 sq mi)
Brooks Range 263,000 km2 (102,000 sq mi)
Siberian Mountains 255,000 km2 (98,000 sq mi)
Greenland 251,000 km2 (97,000 sq mi)
Ural Mountains 125,000 km2 (48,000 sq mi)
Andes 100,000 km2 (39,000 sq mi)
Rocky Mountains (US and Canada) 100,000 km2 (39,000 sq mi)
Alps 80,000 km2 (31,000 sq mi)
Fennoscandian mountains 75,000 km2 (29,000 sq mi)
Remaining <50,000 km2 (19,000 sq mi)

At mean annual soil surface temperatures below −5 °C (23 °F) the influence of aspect can never be sufficient to thaw permafrost and a zone of continuous permafrost (abbreviated to CPZ) forms. A line of continuous permafrost in the Northern Hemisphere[29] represents the most southern border where land is covered by continuous permafrost or glacial ice. The line of continuous permafrost varies around the world northward or southward due to regional climatic changes. In the southern hemisphere, most of the equivalent line would fall within the Southern Ocean if there were land there. Most of the Antarctic continent is overlain by glaciers, under which much of the terrain is subject to basal melting.[30] The exposed land of Antarctica is substantially underlain with permafrost,[31] some of which is subject to warming and thawing along the coastline.[32]

Alpine permafrostEdit

Alpine permafrost occurs at elevations with low enough average temperatures to sustain perennially frozen ground; much alpine permafrost is discontinuous.[33] Estimates of the total area of alpine permafrost vary. Bockheim and Munroe[28] combined three sources and made the tabulated estimates by region, totaling 3,560,000 km2 (1,370,000 sq mi).

Alpine permafrost in the Andes has not been mapped.[34] Its extent has been modeled to assess the amount of water bound up in these areas.[35] In 2009, a researcher from Alaska found permafrost at the 4,700 m (15,400 ft) level on Africa's highest peak, Mount Kilimanjaro, approximately 3° south of the equator.[36]

Changes in subsea permafrost extent and structure between the Last Glacial Maximum and now.[3]

Subsea permafrostEdit

Subsea permafrost occurs beneath the seabed and exists in the continental shelves of the polar regions.[37] These areas formed during the last ice age, when a larger portion of Earth's water was bound up in ice sheets on land and when sea levels were low. As the ice sheets melted to again become seawater, the permafrost became submerged shelves under relatively warm and salty boundary conditions, compared to surface permafrost. Therefore, subsea permafrost exists in conditions that lead to its diminishment. According to Osterkamp, subsea permafrost is a factor in the "design, construction, and operation of coastal facilities, structures founded on the seabed, artificial islands, sub-sea pipelines, and wells drilled for exploration and production."[38] It also contains gas hydrates in places, which are a "potential abundant source of energy" but may also destabilize as subsea permafrost warms and thaws, producing large amounts of methane gas, which is a potent greenhouse gas.[38][39][3] Scientists report with high confidence that the extent of subsea permafrost is decreasing, and 97% of permafrost under Arctic ice shelves is currently thinning.[40][8]: 1281 

Past extent of permafrostEdit

At the Last Glacial Maximum, continuous permafrost covered a much greater area than it does today, covering all of ice-free Europe south to about Szeged (southeastern Hungary) and the Sea of Azov (then dry land)[41] and East Asia south to present-day Changchun and Abashiri.[42] In North America, only an extremely narrow belt of permafrost existed south of the ice sheet at about the latitude of New Jersey through southern Iowa and northern Missouri, but permafrost was more extensive in the drier western regions where it extended to the southern border of Idaho and Oregon.[43] In the southern hemisphere, there is some evidence for former permafrost from this period in central Otago and Argentine Patagonia, but was probably discontinuous, and is related to the tundra. Alpine permafrost also occurred in the Drakensberg during glacial maxima above about 3,000 metres (9,840 ft).[44][45]


Time required for permafrost to reach depth at Prudhoe Bay, Alaska[46]
Time (yr) Permafrost depth
1 4.44 m (14.6 ft)
350 79.9 m (262 ft)
3,500 219.3 m (719 ft)
35,000 461.4 m (1,514 ft)
100,000 567.8 m (1,863 ft)
225,000 626.5 m (2,055 ft)
775,000 687.7 m (2,256 ft)

Base depthEdit

Permafrost extends to a base depth where geothermal heat from the Earth and the mean annual temperature at the surface achieve an equilibrium temperature of 0 °C.[47] The base depth of permafrost reaches 1,493 m (4,898 ft) in the northern Lena and Yana River basins in Siberia.[48] The geothermal gradient is the rate of increasing temperature with respect to increasing depth in the Earth's interior. Away from tectonic plate boundaries, it is about 25–30 °C/km (124–139 °F/mi) near the surface in most of the world.[49] It varies with the thermal conductivity of geologic material and is less for permafrost in soil than in bedrock.[47]

Calculations indicate that the time required to form the deep permafrost underlying Prudhoe Bay, Alaska was over a half-million years.[46][50] This extended over several glacial and interglacial cycles of the Pleistocene and suggests that the present climate of Prudhoe Bay is probably considerably warmer than it has been on average over that period. Such warming over the past 15,000 years is widely accepted.[46] The table to the right shows that the first hundred metres of permafrost forms relatively quickly but that deeper levels take progressively longer.

Massive ground iceEdit

Massive blue ground ice exposure on the north shore of Herschel Island, Yukon, Canada.

When the ice content of a permafrost exceeds 250 percent (ice to dry soil by mass) it is classified as massive ice. Massive ice bodies can range in composition, in every conceivable gradation from icy mud to pure ice. Massive icy beds have a minimum thickness of at least 2 m and a short diameter of at least 10 m.[51] First recorded North American observations were by European scientists at Canning River, Alaska in 1919.[52] Russian literature provides an earlier date of 1735 and 1739 during the Great North Expedition by P. Lassinius and Kh. P. Laptev, respectively.[53] Two categories of massive ground ice are buried surface ice and intrasedimental ice[54] (also called constitutional ice).[53]

Buried surface ice may derive from snow, frozen lake or sea ice, aufeis (stranded river ice) and—probably the most prevalent—buried glacial ice.[55]

Intrasedimental ice forms by in-place freezing of subterranean waters and is dominated by segregational ice which results from the crystallizational differentiation taking place during the freezing of wet sediments, accompanied by water migrating to the freezing front.[53]

Intrasedimental or constitutional ice has been widely observed and studied across Canada and also includes intrusive and injection ice.[52][53]

Additionally, ice wedges—a separate type of ground ice—produce recognizable patterned ground or tundra polygons. Ice wedges form in a pre-existing geological substrate and were first described in 1919.[52][53]

Several types of massive ground ice, including ice wedges and intrasedimental ice within the cliff wall of a retrogressive thaw slump located on the southern coast of Herschel Island within an approximately 22-metre (72 ft) by 1,300-metre (4,300 ft) headwall.


Permafrost processes manifest themselves in large-scale land forms, such as palsas and pingos[56] and smaller-scale phenomena, such as patterned ground found in arctic, periglacial and alpine areas.[57] In ice-rich permafrost areas, melting of ground ice initiates thermokarst landforms such as thermokarst lakes, thaw slumps, thermal-erosion gullies, and active layer detachments.[58][59]


Only plants with shallow roots can survive in the presence of permafrost. Black spruce tolerates limited rooting zones, and dominates flora where permafrost is extensive. Likewise, animal species which live in dens and burrows have their habitat constrained by the permafrost, and these constraints also have a secondary impact on interactions between species within the ecosystem.[60]

While permafrost soil is frozen, it is not completely inhospitable to microorganisms, though their numbers can vary widely, typically from 1 to 1000 million per gram of soil.[61] Most of these bacteria and fungi in permafrost soil cannot be cultured in the laboratory, but the identity of the microorganisms can be revealed by DNA-based techniques. For instance, analysis of 16S rRNA genes from late Pleistocene permafrost samples in eastern Siberia's Kolyma Lowland revealed eight phylotypes, which belonged to the phyla Actinomycetota and Pseudomonadota.[62] “Muot-da-Barba-Peider”, an alpine permafrost site in eastern Switzerland, was found to host a diverse microbial community in 2016. Prominent bacteria groups included phylum Acidobacteriota, Actinomycetota, AD3, Bacteroidota, Chloroflexota, Gemmatimonadota, OD1, Nitrospirota, Planctomycetota, Pseudomonadota, and Verrucomicrobiota, in addition to eukaryotic fungi like Ascomycota, Basidiomycota, and Zygomycota. In the presently living species, scientists observed a variety of adaptations for sub-zero conditions, including reduced and anaerobic metabolic processes.[63] In 2015, researchers had taken 1,017 feet (310 m) ice core samples from a glacier at Qinghai–Tibet Plateau: due to extremely low biomass in those 15,000-year-old samples, it had taken around 5 years of research to extract 33 viruses, of which 28 were new to science, and all were killed during the extraction. Phylogenetic analysis suggests those viruses infected plants or other microorganisms.[64][65]

The permafrost carbon cycle (Arctic Carbon Cycle) deals with the transfer of carbon from permafrost soils to terrestrial vegetation and microbes, to the atmosphere, back to vegetation, and finally back to permafrost soils through burial and sedimentation due to cryogenic processes. Some of this carbon is transferred to the ocean and other portions of the globe through the global carbon cycle. The cycle includes the exchange of carbon dioxide and methane between terrestrial components and the atmosphere, as well as the transfer of carbon between land and water as methane, dissolved organic carbon, dissolved inorganic carbon, particulate inorganic carbon and particulate organic carbon.[66]

Construction on permafrostEdit

Building on permafrost is difficult because the heat of the building (or pipeline) can warm the permafrost and destabilize the structure. Warming can result in thawing of the soil and its consequent weakening of support for a structure as the ice content turns to water; alternatively, where structures are built on piles, warming can cause movement through creep because of the change of friction on the piles even as the soil remains frozen.[67] Additionally, there is no ground water available in an area underlain with permafrost. Any substantial settlement or installation needs to make some alternative arrangement to obtain water.[68] Three common solutions include: using foundations on wood piles, a technique pioneered by Soviet engineer Mikhail Kim in Norilsk;[69] building on a thick gravel pad (usually 1–2 metres/3.3–6.6 feet thick); or using anhydrous ammonia heat pipes.[70] The Trans-Alaska Pipeline System uses heat pipes built into vertical supports to prevent the pipeline from sinking and the Qingzang railway in Tibet employs a variety of methods to keep the ground cool, both in areas with frost-susceptible soil. Permafrost may necessitate special enclosures for buried utilities, called "utilidors".[71]

The Melnikov Permafrost Institute in Yakutsk, found that the sinking of large buildings into the ground can be prevented by using pile foundations extending down to 15 metres (49 ft). At this depth the temperature does not change with the seasons, remaining at about −5 °C (23 °F).[72]

Yakutsk is one of two large cities in the world built in areas of continuous permafrost—that is, where the frozen soil forms an unbroken, below-zero sheet. The other is Norilsk, in Krasnoyarsk Krai, Russia.[68]

Impacts of climate changeEdit

Recently thawed Arctic permafrost and coastal erosion on the Beaufort Sea, Arctic Ocean, near Point Lonely, Alaska in 2013.

Globally, permafrost warmed by about 0.3 °C between 2007 and 2016, with stronger warming observed in the continuous permafrost zone relative to the discontinuous zone. This inevitably causes permafrost to thaw. Permafrost extent has been diminishing for decades, and more decline is expected in the future.[8]: 1280  This causes a wide range of issues, and International Permafrost Association (IPA) exists to help address them. It convenes International Permafrost Conferences and maintains Global Terrestrial Network for Permafrost, which undertakes special projects such as preparing databases, maps, bibliographies, and glossaries, and coordinates international field programmes and networks.[73]

Thaw-induced ground instabilityEdit

Thawing permafrost in Herschel Island, Canada, 2013.

As the water drains or evaporates, soil structure weakens and sometimes becomes viscous until it regains strength with decreasing moisture content. One visible sign of permafrost degradation is the random displacement of trees from their vertical orientation in permafrost areas.[74] Global warming has been increasing permafrost slope disturbances and sediment supplies to fluvial systems, resulting in exceptional increases in river sediment. [75] On the other hands, disturbance of formerly hard soil increases drainage of water reservoirs in northern wetlands. This can dry them out and compromise the survival of plants and animals used to the wetland ecosystem.[76]

In high mountains, much of the structural stability can be attributed to glaciers and permafrost.[77] As climate warms, permafrost thaws, decreasing slope stability and increasing stress through buildup of pore-water pressure, which may ultimately lead to slope failure and rockfalls.[78][79] Over the past century, an increasing number of alpine rock slope failure events in mountain ranges around the world have been recorded, and some have been attributed to permafrost thaw induced by climate change. The 1987 Val Pola landslide that killed 22 people in the Italian Alps is considered one such example.[80] In 2002, massive rock and ice falls (up to 11.8 million m3), earthquakes (up to 3.9 Richter), floods (up to 7.8 million m3 water), and rapid rock-ice flow to long distances (up to 7.5 km at 60 m/s) were attributed to slope instability in high mountain permafrost.[81]

Permafrost and ice in Herschel Island, Canada, 2012.

Permafrost thaw can also result in the formation of frozen debris lobes (FDLs), which are defined as "slow-moving landslides composed of soil, rocks, trees, and ice".[82] This is a notable issue in the Alaska's southern Brooks Range, where some FDLs measured over 100 m (110 yd) in width, 20 m (22 yd) in height, and 1,000 m (1,100 yd) in length by 2012.[83][84] As of December 2021, there were 43 frozen debris lobes identified in the southern Brooks Range, where they could potentially threaten both the Trans Alaska Pipeline System (TAPS) corridor and the Dalton Highway, which is the main transport link between the Interior Alaska and the Alaska North Slope.[85]


Map of likely risk to infrastructure from permafrost thaw expected to occur by 2050.[86]

As of 2021, there are 1162 settlements located directly atop the Arctic permafrost, which host an estimated 5 million people. By 2050, permafrost layer below 42% of these settlements is expected to thaw, affecting all their inhabitants (currently 3.3 million people).[87] Consequently, a wide range of infrastructure in permafrost areas is threatened by the thaw.[9][88]: 236  By 2050, it's estimated that nearly 70% of global infrastructure located in the permafrost areas would be at high risk of permafrost thaw, including 30-50% of "critical" infrastructure. The associated costs could reach tens of billions of dollars by the second half of the century.[10] Reducing greenhouse gas emissions in line with the Paris Agreement is projected to stabilize the risk after mid-century; otherwise, it'll continue to worsen.[86]

In Alaska alone, damages to infrastructure by the end of the century would amount to $4.6 billion (at 2015 dollar value) if RCP8.5, the high-emission climate change scenario, were realized. Over half stems from the damage to buildings ($2.8 billion), but there's also damage to roads ($700 million), railroads ($620 million), airports ($360 million) and pipelines ($170 million).[89] Similar estimates were done for RCP4.5, a less intense scenario which leads to around 2.5 °C (4.5 °F) by 2100, a level of warming similar to the current projections.[90] In that case, total damages from permafrost thaw are reduced to $3 billion, while damages to roads and railroads are lessened by approximately two thirds (from $700 and $620 million to $190 and $220 million) and damages to pipelines are reduced more than ten-fold, from $170 million to $16 million. Unlike the other costs stemming from climate change in Alaska, such as damages from increased precipitation and flooding, climate change adaptation is not a viable way to reduce damages from permafrost thaw, as it would cost more than the damage incurred under either scenario.[89]

In Canada, Northwest Territories have a population of only 45,000 people in 33 communities, yet permafrost thaw is expected to cost them $1.3 billion over 75 years, or around $51 million a year. In 2006, the cost of adapting Inuvialuit homes to permafrost thaw was estimated at $208/m2 if they were built at pile foundations, and $1,000/m2 if they didn't. At the time, the average area of a residential building in the territory was around 100 m2. Thaw-induced damage is also unlikely to be covered by home insurance, and to address this reality, territorial government currently funds Contributing Assistance for Repairs and Enhancements (CARE) and Securing Assistance for Emergencies (SAFE) programs, which provide long- and short-term forgivable loans to help homeowners adapt. It is possible that in the future, mandatory relocation would instead take place as the cheaper option. However, it would effectively tear the local Inuit away from their ancestral homelands. Right now, their average personal income is only half that of the median NWT resident, meaning that adaptation costs are already disproportionate for them.[91]

By 2022, up to 80% of buildings in some Northern Russia cities had already experienced damage.[10] By 2050, the damage to residential infrastructure may reach $15 billion, while total public infrastructure damages could amount to 132 billion.[92] This includes oil and gas extraction facilities, of which 45% are believed to be at risk.[86]

Detailed map of Qinghai–Tibet Plateau infrastructure at risk from permafrost thaw under the RCP4.5 scenario.[93]

Outside of the Arctic, Qinghai–Tibet Plateau (sometimes known as "the Third Pole"), also has an extensive permafrost area. It is warming at twice the global average rate, and 40% of it is already considered "warm" permafrost, making it particularly unstable. Qinghai–Tibet Plateau has a population of over 10 million people - double the population of permafrost regions in the Arctic - and over 1 million m2 of buildings are located in its permafrost area, as well as 2,631 km of power lines, and 580 km of railways.[93] There are also 9,389 km of roads, and around 30% are already sustaining damage from permafrost thaw.[10] Estimates suggest that under the scenario most similar to today, SSP2-4.5, around 60% of the current infrastructure would be at high risk by 2090 and simply maintaining it would cost $6.31 billion, with adaptation reducing these costs by 20.9% at most. Holding the global warming to 2 °C (3.6 °F) would reduce these costs to $5.65 billion, and fulfilling the optimistic Paris Agreement target of 1.5 °C (2.7 °F) would save a further $1.32 billion. In particular, fewer than 20% of railways would be at high risk by 2100 under 1.5 °C (2.7 °F), yet this increases to 60% at 2 °C (3.6 °F), while under SSP5-8.5, this level of risk is met by mid-century.[93]

Toxic pollutionEdit

Graphical representation of leaks from various toxic hazards caused by the thaw of formerly stable permafrost.[11]

For much of the 20th century, it was believed that permafrost would "indefinitely" preserve anything buried there, and this made deep permafrost areas popular locations for hazardous waste disposal. In places like Canada's Prudhoe Bay oil field, procedures were developed documenting the "appropriate" way to inject waste beneath the permafrost. This means that as of 2023, there are ~4500 industrial facilities in the Arctic permafrost areas which either actively process or store hazardous chemicals. Additionally, there are between 13,000 and 20,000 sites which have been heavily contaminated, 70% of them in Russia, and their pollution is currently trapped in the permafrost. About a fifth of both the industrial and the polluted sites (1000 and 2200–4800) are expected to start thawing in the future even if the warming does not increase from its 2020 levels. Only about 3% more sites would start thawing between now and 2050 under the climate change scenario consistent with the Paris Agreement goals, RCP2.6, but by 2100, about 1100 more industrial facilities and 3500 to 5200 contaminated sites are expected to start thawing even then. Under the very high emission scenario RCP8.5, 46% of industrial and contaminated sites would start thawing by 2050, and virtually all of them would be affected by the thaw by 2100.[11] Organochlorines and other persistent organic pollutants are of a particular concern, due to their potential to repeatedly reach local communities after their re-release through biomagnification in fish. At worst, future generations born in the Arctic would enter life with weakened immune systems due to pollutants accumulating across generations.[13]

Distribution of toxic substances currently located at various permafrost sites in Alaska, by sector. The number of fish skeletons represents the toxicity of each substance.[11]

A notable example of pollution risks associated with permafrost was the 2020 Norilsk oil spill, caused by the collapse of diesel fuel storage tank at Norilsk-Taimyr Energy's Thermal Power Plant No. 3. It spilled 6,000 tonnes of fuel into the land and 15,000 into the water, polluting Ambarnaya, Daldykan and many smaller rivers on Taimyr Peninsula, even reaching lake Pyasino, which is a crucial water source in the area. State of emergency at the federal level was declared.[94][95] The event has been described as the second-largest oil spill in modern Russian history.[96][97]

Another issue associated with permafrost thaw is the release of natural mercury deposits. An estimated 800,000 tons of mercury are frozen in the permafrost soil. According to observations, around 70% of it is simply taken up by vegetation after the thaw.[13] However, if the warming continues under RCP8.5, then permafrost emissions of mercury into the atmosphere would match the current global emissions from all human activities by 2200. Mercury-rich soils also pose a much greater threat to humans and the environment if they thaw near rivers. Under RCP8.5, enough mercury will enter the Yukon River basin by 2050 to make its fish unsafe to eat under the EPA guidelines. By 2100, mercury concentrations in the river will double. Contrastingly, even if mitigation is limited to RCP4.5 scenario, mercury levels will increase by about 14% by 2100, and will not breach the EPA guidelines even by 2300.[12]

Climate change feedbackEdit

Permafrost thaw ponds on peatland in Hudson Bay, Canada in 2008.[98]

In the northern circumpolar region, permafrost contains 1700 billion tons of organic material equaling almost half of all organic material in all soils.[99][100] This pool was built up over thousands of years and is only slowly degraded under the cold conditions in the Arctic. The amount of carbon sequestered in permafrost is four times the carbon that has been released to the atmosphere due to human activities in modern time.[101] One manifestation of this is yedoma, which is an organic-rich (about 2% carbon by mass) Pleistocene-age loess permafrost with ice content of 50–90% by volume.[102] Thawing can also influence the rate of change of soil gases with the atmosphere.[103][76]

Carbon is continually cycling between soils, vegetation, and the atmosphere. As climate change increases mean annual air temperatures throughout the Arctic, it extends permafrost thaw and deepens the active layer, exposing old carbon that has been in storage for decades to millennia to biogenic processes which facilitate its entrance into the atmosphere. In general, the volume of permafrost in the upper 3 m of ground is expected to decrease by about 25% per 1 °C (1.8 °F)of global warming.[104]: 1283  According to the IPCC Sixth Assessment Report, there is high confidence that global warming over the last few decades has led to widespread increases in permafrost temperature.[104]: 1237  Observed warming was up to 3 °C (5.4 °F) in parts of Northern Alaska (early 1980s to mid-2000s) and up to 2 °C (3.6 °F) in parts of the Russian European North (1970–2020), and active layer thickness has increased in the European and Russian Arctic across the 21st century and at high elevation areas in Europe and Asia since the 1990s.[104]: 1237  In Yukon, the zone of continuous permafrost might have moved 100 kilometres (62 mi) poleward since 1899, but accurate records only go back 30 years. Based on high agreement across model projections, fundamental process understanding, and paleoclimate evidence, it is virtually certain that permafrost extent and volume will continue to shrink as global climate warms.[104]: 1283 

Greater summer precipitation increases the depth of permafrost layer subject to thaw, in different Arctic permafrost environments.[105]

Carbon emissions from permafrost thaw contribute to the same warming which facilitates the thaw, making it a positive climate change feedback. The warming also intensifies Arctic water cycle, and the increased amounts of warmer rain are another factor which increases permafrost thaw depths.[105] The amount of carbon that will be released from warming conditions depends on depth of thaw, carbon content within the thawed soil, physical changes to the environment[106] and microbial and vegetation activity in the soil. Microbial respiration is the primary process through which old permafrost carbon is re-activated and enters the atmosphere. The rate of microbial decomposition within organic soils, including thawed permafrost, depends on environmental controls, such as soil temperature, moisture availability, nutrient availability, and oxygen availability.[107] In particular, sufficient concentrations of iron oxides in some permafrost soils can inhibit microbial respiration and prevent carbon mobilization: however, this protection only lasts until carbon is separated from the iron oxides by Fe-reducing bacteria, which is only a matter of time under the typical conditions.[108] Depending on the soil type, Iron(III) oxide can boost oxidation of methane to carbon dioxide in the soil, but it can also amplify methane production by acetotrophs: these soil processes are not yet fully understood.[109]

Altogether, the likelihood of the entire carbon pool mobilizing and entering the atmosphere is low despite the large volumes stored in the soil. Although temperatures will increase, this does not imply complete loss of permafrost and mobilization of the entire carbon pool. Much of the ground underlain by permafrost will remain frozen even if warming temperatures increase the thaw depth or increase thermokarsting and permafrost degradation.[110] Moreover, other elements such as iron and aluminum can adsorb some of the mobilized soil carbon before it reaches the atmosphere, and they are particularly prominent in the mineral sand layers which often overlay permafrost.[111] On the other hand, once the permafrost area thaws, it will not go back to being permafrost for centuries even if the temperature increase reversed, making it one of the best-known examples of tipping points in the climate system.

Impact on global temperaturesEdit

Carbon dioxide and methane (in CO2 equivalent) emissions from subsea permafrost alone under the different Representative Concentration Pathway scenarios over time.[112]

In 2011, preliminary computer analyses suggested that permafrost emissions could be equivalent to around 15% of anthropogenic emissions.[113]

A 2018 perspectives article discussing tipping points in the climate system activated around 2 °C (3.6 °F) of global warming suggested that at this threshold, permafrost thaw would add a further 0.09 °C (0.16 °F) to global temperatures by 2100, with a range of 0.04–0.16 °C (0.072–0.288 °F)[114] In 2021, another study estimated that in a future where zero emissions were reached following an emission of a further 1000 Pg C into the atmosphere (a scenario where temperatures ordinarily stay stable after the last emission, or start to decline slowly) permafrost carbon would add 0.06 °C (0.11 °F) (with a range of 0.02–0.14 °C (0.036–0.252 °F)) 50 years after the last anthropogenic emission, 0.09 °C (0.16 °F) (0.04–0.21 °C (0.072–0.378 °F)) 100 years later and 0.27 °C (0.49 °F) (0.12–0.49 °C (0.22–0.88 °F)) 500 years later.[115] However, neither study was able to take abrupt thaw into account.

In 2020, a study of the northern permafrost peatlands (a smaller subset of the entire permafrost area, covering 3.7 million km2 out of the estimated 18 million km2[112]) would amount to ∼1% of anthropogenic radiative forcing by 2100, and that this proportion remains the same in all warming scenarios considered, from 1.5 °C (2.7 °F) to 6 °C (11 °F). It had further suggested that after 200 more years, those peatlands would have absorbed more carbon than what they had emitted into the atmosphere.[116]

The IPCC Sixth Assessment Report estimates that carbon dioxide and methane released from permafrost could amount to the equivalent of 14–175 billion tonnes of carbon dioxide per 1 °C (1.8 °F) of warming.[104]: 1237  For comparison, by 2019, annual anthropogenic emission of carbon dioxide alone stood around 40 billion tonnes.[104]: 1237 

Permafrost peatlands under varying extent of global warming, and the resultant emissions as a fraction of anthropogenic emissions needed to cause that extent of warming.[116]

A 2021 assessment of the economic impact of climate tipping points estimated that permafrost carbon emissions would increase the social cost of carbon by about 8.4% [117] However, the methods of that assessment have attracted controversy: when researchers like Steve Keen and Timothy Lenton had accused it of underestimating the overall impact of tipping points and of higher levels of warming in general,[118] the authors have conceded some of their points.[119]

In 2021, a group of prominent permafrost researchers like Merritt Turetsky had presented their collective estimate of permafrost emissions, including the abrupt thaw processes, as part of an effort to advocate for a 50% reduction in anthropogenic emissions by 2030 as a necessary milestone to help reach net zero by 2050. Their figures for combined permafrost emissions by 2100 amounted to 150–200 billion tonnes of carbon dioxide equivalent under 1.5 °C (2.7 °F) of warming, 220–300 billion tonnes under 2 °C (3.6 °F) and 400–500 billion tonnes if the warming was allowed to exceed 4 °C (7.2 °F). They compared those figures to the extrapolated present-day emissions of Canada, the European Union and the United States or China, respectively. The 400–500 billion tonnes figure would also be equivalent to the today's remaining budget for staying within a 1.5 °C (2.7 °F) target.[120] One of the scientists involved in that effort, Susan M. Natali of Woods Hole Research Centre, had also led the publication of a complementary estimate in a PNAS paper that year, which suggested that when the amplification of permafrost emissions by abrupt thaw and wildfires is combined with the foreseeable range of near-future anthropogenic emissions, avoiding the exceedance (or "overshoot") of 1.5 °C (2.7 °F) warming is already implausible, and the efforts to attain it may have to rely on negative emissions to force the temperature back down.[121]

An updated 2022 assessment of climate tipping points concluded that abrupt permafrost thaw would add 50% to gradual thaw rates, and would add 14 billion tons of carbon dioxide equivalent emissions by 2100 and 35 by 2300 per every degree of warming. This would have a warming impact of 0.04 °C (0.072 °F) per every full degree of warming by 2100, and 0.11 °C (0.20 °F) per every full degree of warming by 2300. It also suggested that at between 3 °C (5.4 °F) and 6 °C (11 °F) degrees of warming (with the most likely figure around 4 °C (7.2 °F) degrees) a large-scale collapse of permafrost areas could become irreversible, adding between 175 and 350 billion tons of CO2 equivalent emissions, or 0.2–0.4 °C (0.36–0.72 °F) degrees, over about 50 years (with a range between 10 and 300 years).[122][123]

Revival of ancient microorganismsEdit

Some of the ancient amoeba-eating viruses revived by the research team of Jean-Michel Claverie. Clockwise from the top: Pandoravirus yedoma; Pandoravirus mammoth and Megavirus mammoth; Cedratvirus lena; Pithovirus mammoth; Megavirus mammoth; Pacmanvirus lupus.[15]

In 1999, researchers were able to extract potentially viable microscopic fungi, as well as tomato mosaic virus, from Greenland ice cores up to 140,000 years old.[124][125] In 2004, it was estimated that between 1017 and1021 microorganisms, ranging from fungi and bacteria in addition to viruses, were already released every year due to ice melt, often directly into the ocean. However, only viruses with high abundance, ability to be transported through ice, and ability to resume disease cycles after the thaw would be of any concern. Caliciviruses of Vesivirus genus were hypothesized as the most likely to spread from ancient ice, due to their high abundance and using ocean animals as hosts, where the migratory nature of many species of fish and birds could potentially enable a high transmission rate. Caliciviruses are poorly adapted to humans, and the only known infections were of marine biologists who worked closely with infected seals. However, Enteroviruses (a group which includes polioviruses, echoviruses and Coxsackie viruses) and even influenza A were also considered less likely but still plausible candidates.[14] On the other hand, Johan Hultin made multiple attempts during the 20th century to culture 1918 influenza virus he found in the frozen corpses of pandemic victims at Brevig Mission in Alaska, yet all of them failed, suggesting that the influenza virus is incapable of surviving the thaw.[18]

In 2014, a completely unknown plant virus was revived from a frozen caribou feces deposit which was only 700 years old. It was named "ancient caribou feces associated virus" (aCFV) by the researchers, and it was able to successfully replicate in Nicotiana benthamiana, a common model species for plant pathogens. aCFV couldn't cause more than an asymptomatic infection, which either suggests large genetic distance between it and modern plants, or that N. benthamiana was simply a suboptimal host for it.[126] Also in 2014, two ~30,000 years old giant virus species, Pithovirus sibericum[127] and Mollivirus sibericum,[128] were discovered in the Siberian permafrost and they retained their infectivity. Like the other giant viruses with large genomes, they are larger in size than most bacteria and pose no risk to humans, as they infect other microorganisms like Acanthamoeba, a genus of amoebas.[128] In 2023, the same team of French researchers managed to revive 8 more ancient amoeba-infecting viral species, four of which were from the pandoravirus, cedratvirus (sometimes classified as a subgroup of pithovirus), megavirus and pacmanvirus (part of Asfarviridae) families, which weren't previously revived from the permafrost. In addition, five more species from these families were found in already thawed permafrost, with no way to tell their age. The oldest revived virus was a 48,500-year-old Pandoravirus yedoma.[15][16]

Ancient bacteria (red) possess a remarkable range of antibiotic resistance, but it is also generally lower than of modern bacteria from the same area (black).[129]

Scientists are split on whether revived microorganisms from the permafrost can pose a significant threat to humans. Jean-Michel Claverie, who led the only successful attempts to revive such "zombie viruses", believes that the public health threat from them is underestimated, and that while his research focused on amoeba-infecting viruses, this decision was in part motivated by the desire to avoid viral spillover as well as convenience, and "one can reasonably infer" other viral species would also remain infectious.[15][16] On the other hand, University of British Columbia virologist Curtis Suttle argued that "people already inhale thousands of viruses every day, and swallow billions whenever they swim in the sea". In his view, the odds of a frozen virus replicating and then circulating to a sufficient extent to threaten humans "stretches scientific rationality to the breaking point".[17] While there have already been outbreaks of anthrax from formerly frozen soil, such as the 2016 Yamal Peninsula outbreak,[130] anthrax is a non-contagious pathogen which has been known for its ability to hibernate in the soil since the Middle Ages, and does not require the cold to do so.[18] Some scientists have argued that Hultin's inability to revive thawed influenza virus, as well as other researchers' failure to revive pneumonia-causing bacteria or smallpox viruses show that pathogens adapted to warm-blooded hosts cannot survive being frozen for a prolonged period of time.[18][19] However, many of the amoeba-infecting viruses revived in Claverie's 2023 research were taken from a ~27,000-year-old site with "a large amount of mammoth wool", and one species, Pacmanvirus lupus, was found in the intestine of an equally old Siberian wolf carcass.[15]

There is some agreement that revived bacteria would be less dangerous than the revived viruses, since they would still be affected by broad-spectrum antibiotics and would not require wholly new treatments.[15] However, they would not be completely vulnerable either, due to the discovery of ancient antibiotic resistance genes in permafrost samples. Antibiotics to which permafrost bacteria have displayed at least some resistance include chloramphenicol, streptomycin, kanamycin, gentamicin, tetracycline, spectinomycin and neomycin.[13] Some scientists consider horizontal gene transfer of novel antibiotic resistance sequences from otherwise harmless ancient bacteria into modern pathogens to be a far more realistic threat than a revival of an ancient pathogen.[131] At the same time, other studies show that resistance levels in ancient bacteria to modern antibiotics remain lower than in the contemporary bacteria from the active (thawed) layer above them, [129] suggesting that this risk is "no greater" than in any other soil.[19]

Preservation of plantsEdit

In 2012, Russian researchers proved that permafrost can serve as a natural repository for ancient life forms by reviving of Silene stenophylla from 30,000 year old tissue found in an Ice Age squirrel burrow in the Siberian permafrost. This is the oldest plant tissue ever revived. The plant was fertile, producing white flowers and viable seeds. The study demonstrated that tissue can survive ice preservation for tens of thousands of years.[132]

History of scientific researchEdit

Southern limit of permafrost in Eurasia according to Karl Ernst von Baer (1843), and other authors.

Prior to World War II, there were not many scientific publications on frozen ground in North America. In contrast, a vast literature on basic permafrost science and the engineering aspects of permafrost was available in Russian. Some Russian authors relate permafrost research with the name Alexander von Middendorff (1815–1894). However, Russian scientists also realized that Karl Ernst von Baer must be given the attribute "founder of scientific permafrost research". In 1843, Baer's original study “materials for the study of the perennial ground-ice” was ready to be printed. Baer's detailed study consists of 218 pages and was written in German language, as he was a Baltic German scientist. He was teaching at the University of Königsberg and became a member of the St Petersburg Academy of Sciences. This world's first permafrost textbook was conceived as a complete work and ready for printing in 1843. But it remained lost for around 150 years. However, from 1838 onwards, Baer published several individual publications on permafrost. The Russian Academy of Sciences honoured Baer with the publication of a tentative Russian translation of his study in 1942.[133]

These facts were completely forgotten after the Second World War. Thus in 2001 the discovery of the typescript from 1843 in the library archives of the University of Giessen and its annotated publication was a scientific sensation. The full text of Baer's original work is available online (234 pages).[133] The editor added to the facsimile reprint a preface in English, two colour permafrost maps of Eurasia and some figures of permafrost features. Baer's text is introduced with detailed comments and references on additional 66 pages written by the Estonian historian Erki Tammiksaar. The work is notable because Baer's observations on permafrost distribution and periglacial morphological descriptions are seen as largely correct to the present day.[133] With his compilation and analysis of all available data on ground ice and permafrost, Baer laid the foundation for the modern permafrost terminology. Baer's southern limit of permafrost in Eurasia drawn in 1843 corresponds well with the actual southern limit on the Circum-Arctic Map of Permafrost and Ground Ice Conditions of the International Permafrost Association (edited by J. Brown et al.).[21]

Beginning in 1942, Siemon William Muller delved into the relevant Russian literature held by the Library of Congress and the U.S. Geological Survey Library so that he was able to furnish the government an engineering field guide and a technical report about permafrost by 1943",[134] the year in which he coined the term as a contraction of permanently frozen ground.[135] Although originally classified (as U.S. Army. Office of the Chief of Engineers, Strategic Engineering Study, no. 62, 1943),[135][136][137][138] in 1947 a revised report was released publicly, which is regarded as the first North American treatise on the subject.[134][138]

See alsoEdit


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  137. ^ Occurrences on Google Books.
  138. ^ a b Muller, Siemon William (1947). Permafrost. Or, Permanently Frozen Ground and Related Engineering Problems. Ann Arbor, Michigan: Edwards. ISBN 978-0-598-53858-1. OCLC 1646047.

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Permafrost institutionsEdit

Additional informationEdit