Вечная мерзлота: распространение, влияние и риски оттаивания.

Soil frozen for a duration of at least two years
frozen ground

Permafrost is soil or underwater sediment which continuously remains below for two years or more: the oldest permafrost had been continuously frozen for around 700,000 years. While the shallowest permafrost has a vertical extent of below a meter (3 ft), the deepest is greater than The ground beneath glaciers and ice sheets is not usually defined as permafrost, so on land, permafrost is generally located beneath a so called active layer of soil which freezes and thaws depending on the season. Around 15% of the Northern Hemisphere or 11% of the global surface is underlain by permafrost, with the total area of around This includes large areas of Alaska, Canada, Greenland, 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 of Patagonia, the Southern Alps of New Zealand, or the highest mountains of Antarctica. The emissions from thawing permafrost will have a sufficient impact on the climate to impact global carbon budgets. It is difficult to accurately predict how much greenhouse gases the permafrost releases because of the different thaw processes are still uncertain. There is widespread agreement that the emissions will be smaller than human caused emissions and not large enough to result in runaway warming. Instead, the annual permafrost emissions are likely comparable with global emissions from deforestation, or to annual emissions of large countries such as Russia, the United States or China. 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. as of 2018, the average thickness in the Northern Hemisphere is ~, but there are significant regional differences. Northeastern Siberia, Alaska and Greenland have the most solid permafrost with the lowest extent of active layer (less than on average, and sometimes only ), while southern Norway and the Mongolian Plateau are the only areas where the average active layer is deeper than , with the record of The border between active layer and permafrost itself is sometimes called permafrost table. 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 greatest depth of permafrost occurs right before the point where geothermal heat maintains a temperature above freezing. Above that bottom limit there may be permafrost with a consistent annual temperature—"isothermal permafrost".

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. "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.

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 , 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 In the moist wintered areas mentioned before, there may not be even discontinuous permafrost down to 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 , and sporadic permafrost, where permafrost cover is less than 50 percent of the landscape and typically occurs at mean annual temperatures between
In soil science, the sporadic permafrost zone is abbreviated SPZ and the extensive discontinuous permafrost zone DPZ. 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 colder than those of today.

A range of elevations in both the Northern and Southern Hemisphere are cold enough to support perennially frozen ground: some of the best known examples include the Canadian Rockies, the European Alps, Himalaya and the Tien Shan. In general, it has been found that extensive alpine permafrost requires mean annual air temperature of , though this can vary depending on local topography, and some mountain areas are known to support permafrost at It is also possible for subsurface alpine permafrost to be covered by warmer, vegetation supporting soil. [[File:Sayedi 2020 post LGM permafrost. jpg|thumb|Changes in subsea permafrost extent and structure between the Last Glacial Maximum and now. In 2014, a collection of regional estimates of alpine permafrost extent had established a global extent of Yet, by 2014, alpine permafrost in the Andes has not been fully mapped, although its extent has been modeled to assess the amount of water bound up in these areas.

Subsea permafrost occurs beneath the seabed and exists in the continental shelves of the polar regions. 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 during the Holocene glacial retreat, coastal permafrost became submerged shelves under relatively warm and salty boundary conditions, compared to surface permafrost. Since then, these conditions led to the gradual and ongoing decline of subsea permafrost extent. Subsea permafrost can also overlay deposits of methane clathrate, which were once speculated to be a major climate tipping point in what was known as a clathrate gun hypothesis, but are now no longer believed to play any role in projected climate change.

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) and East Asia south to present day Changchun and Abashiri. 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. 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 .

[[File:Schuur 2022 century scale permafrost projections. jpeg|thumb|Nine probable scenarios of greenhouse gas emissions from permafrost thaw during the 21st century, which show a limited, moderate and intense and emission response to low, medium and high emission Representative Concentration Pathways. The vertical bar uses emissions of selected large countries as a comparison: the right hand side of the scale shows their cumulative emissions since the start of the Industrial Revolution, while the left hand side shows each country's cumulative emissions for the rest of the 21st century if they remained unchanged from their 2019 levels. while a 2022 review concluded that every of global warming would cause and from abrupt thaw by the year 2100 and 2300. Around of global warming, abrupt (around 50 years) and widespread collapse of permafrost areas could occur, resulting in an additional warming of .

thumb|Severe coastal erosion on the Arctic Ocean coast of Alaska. 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. Global warming has been increasing permafrost slope disturbances and sediment supplies to fluvial systems, resulting in exceptional increases in river sediment. 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. In high mountains, much of the structural stability can be attributed to glaciers and permafrost. 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. 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. 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. thumb|left|Thawing permafrost in Herschel Island, Canada, 2013. 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". This is a notable issue in the Alaska's southern Brooks Range, where some FDLs measured over in width, in height, and in length by 2012. 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.

[[File:Hjort 2018 permafrost infrastructure. png|thumb|Map of likely risk to infrastructure from permafrost thaw expected to occur by 2050. Consequently, a wide range of infrastructure in permafrost areas is threatened by the thaw. 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. 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. Similar estimates were done for RCP4.5, a less intense scenario which leads to around by 2100, a level of warming similar to the current projections. 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. By 2022, up to 80% of buildings in some Northern Russia cities had already experienced damage. This includes oil and gas extraction facilities, of which 45% are believed to be at risk. [[File:Ran 2022 QTP Permafrost damages 2050. png|thumb|left|Detailed map of Qinghai–Tibet Plateau infrastructure at risk from permafrost thaw under the SSP2 4.5 scenario.

[[File:Langer 2023 thawed pollution. png|thumb|Graphical representation of leaks from various toxic hazards caused by the thaw of formerly stable permafrost. 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. [[File:Langer 2023 alaska distributions. png|thumb|left|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. The event has been described as the second largest oil spill in modern Russian history. 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.

[[File:Alempic 2023 permafrost viruses. jpg|thumb|left|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. Further, some scientists argue that horizontal gene transfer could occur between the older, formerly frozen bacteria, and modern ones, and one outcome could be the introduction of novel antibiotic resistance genes into the genome of current pathogens, exacerbating what is already expected to become a difficult issue in the future. and other scientists argue that the risk of ancient microorganisms being both able to survive the thaw and to threaten humans is not scientifically plausible. Likewise, some research suggests that antimicrobial resistance capabilities of ancient bacteria would be comparable to, or even inferior to modern ones.

In 2012, Russian researchers proved that permafrost can serve as a natural repository for ancient life forms by reviving a sample 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 resultant plant was fertile, producing white flowers and viable seeds. The study demonstrated that living tissue can survive ice preservation for tens of thousands of years.

[[File:Schuur 2022 permafrost carbon literature. jpeg|thumb|The annual number of scientific research papers published on the subject of permafrost carbon has grown from next to nothing around 1990 to around 400 by 2020. Baer is also known to have composed the world's first permafrost textbook in 1843, "materials for the study of the perennial ground ice", written in his native language. However, it was not printed at the time, and a Russian translation wasn't ready until 1942. The original German textbook was believed to be lost until the typescript from 1843 was discovered in the library archives of the University of Giessen. The 234 page text was made available online, with additional maps, preface and comments. That report coined the English term as a contraction of permanently frozen ground, in what was considered a direct translation of the Russian term vechnaia merzlota (вечная мерзлота). In 1953, this translation was criticized by another USGS researcher Inna Poiré, as she believed the term had created unrealistic expectations about its stability: more recently, some researchers have argued that "perpetually refreezing" would be a more suitable translation. The report itself was classified (as U. S. Army. Office of the Chief of Engineers, Strategic Engineering Study, no. 62, 1943), until a revised version was released in 1947, which is regarded as the first North American treatise on the subject. Between 11 and 15 November 1963, the First International Conference on Permafrost took place on the grounds of Purdue University in the American town of West Lafayette, Indiana. It involved 285 participants (including "engineers, manufacturers and builders" who attended alongside the researchers) from a range of countries (Argentina, Austria, Canada, Germany, Great Britain, Japan, Norway, Poland, Sweden, Switzerland, the US and the USSR). This marked the beginning of modern scientific collaboration on the subject. Conferences continue to take place every five years. During the Fourth conference in 1983, a special meeting between the "Big Four" participant countries (US, USSR, China and Canada) had officially created the International Permafrost Association. In the recent decades, permafrost research has attracted more attention than ever due to the role it plays in climate change. Consequently, there has been a massive acceleration in published scientific literature. Around 1990, almost no papers were released containing the words "permafrost" and "carbon": by 2020, around 400 such papers were published every year. thumb|center|upright=1.2|Southern limit of permafrost in Eurasia according to Karl Ernst von Baer (1843), and other authors.