Permafrost: an Important Carbon Reservoir
Permafrost is permanently frozen ground whose temperature stays at 0°C (32°F) or below, for at least two years in a row. 1 The fact that it’s frozen, makes it part of Earth’s cryosphere as well as an important part of Earth’s climate system.
In addition, due to the high carbon content of its peat layer, permafrost is an important reservoir in the global carbon cycle. But, if permafrost continues to thaw – as many climate models suggest it will – the resulting emissions of carbon dioxide (CO2) and methane (CH4) would act as powerful climate feedbacks, raising temperatures in the atmosphere and across the surface of the planet. See also: Which is the Largest Carbon Reservoir?
Most permafrost is found in high latitudes around the polar regions. At lower latitudes it exists only at higher elevations. The thickness of permafrost varies enormously depending on temperature and local conditions, ranging in depth from 1 meter (3 feet) to more than 1,000 meters (3,281 feet).
Permafrost Extent & Coverage
“Continuous permafrost” (underlying more than 90 percent of the terrain) is typically found in places with mean annual ground surface temperatures (MAGST) of between 0°C and minus 6°C or colder (32-21°F). “Discontinuous permafrost” (underlying 50-90 percent of the terrain) is typically found in places with MAGST of between minus 5°C and minus 2°C (23-32°F). “Sporadic permafrost” (permafrost covers less than 50 percent), is typically found in places with MAGST of between 0°C and minus 2°C (32-28°F). 2 “Seasonally frozen ground” describes those places where soil freezes for 15 days or more per year. “Intermittently frozen ground” means those areas where the soil freezes for fewer than 15 days. At present, the maximum average extent of seasonally frozen ground in the Northern Hemisphere is about 55 million sq km (21 million sq mi) or 55 percent of the total land area. 3
- Permafrost: an Important Carbon Reservoir
- Where Is Permafrost Found?
- What Is Permafrost Made Of?
- How Does The Ground Freeze?
- How Does Climate Change Affect Permafrost?
- What Happens If Large Areas Of Permafrost Start Thawing?
- Emissions of Nitrous Oxide: A New Danger
- Unfortunately, The Arctic Is Getting Much Hotter
- How High Do Temperatures Need To Rise In Order To Thaw The Permafrost?
- How Does Thawing Permafrost Spread Disease?
- Will Mercury Be Released Into The Food Chain?
- Financial Consequences Of Permafrost Loss
Where Is Permafrost Found?
Permafrost is found mostly in the Northern Hemisphere, where roughly 24 percent of ice-free land has permafrost underneath it, equivalent to 19 million sq km (7,336,000 sq mi), although this varies with temperature and climate. 4 5 Of this, just over half is continuous permafrost, about 20 percent is discontinuous permafrost, and just under 30 percent is sporadic permafrost. 6 Large tracts of permafrost exist in the Canadian Arctic, Alaska, Siberia, the Qinghai-Tibetan Plateau, and other higher mountain regions. Ground ice is a frequent though not a constant feature. See also: Glaciers: Slow Moving Ice Giants.
Permafrost is also located in the Southern Hemisphere. It underlies Antarctica, although in what quantities is difficult to say, as more than 99.5 percent of its surface is covered by the Antarctic ice sheet, parts of which are several thousand feet thick. In addition to Antarctica, it can be found in South America’s Patagonia region and New Zealand’s Southern Alps.
Permafrost also exists beneath the sea (sub-sea permafrost) in the continental shelves of the northern polar region. 7 Some of the ocean floor underneath the Arctic is permanently frozen to a depth of 100 meters (328 feet).
What Is Permafrost Made Of?
Permafrost consists of soil, silt, sand, gravel, clay, small stones, or particles of rock, all bound together by frozen water (ice). Upper layers of permafrost typically contain large amounts of partially decomposed plant material that died but didn’t rot completely because of the cold and a lack of oxygen. This organic peat matter consists of partly decayed roots, whole roots, and other plant material. (It can also contain frozen animals and animal material.) This dead vegetation represents one of the Planet’s largest single reservoirs of carbon. Lower levels of permafrost contain soils made up mostly of minerals.
The layer of earth that sits on top of permafrost – called the “active layer” – does not freeze all year. This layer freezes during the cold winter months but thaws during the spring or summer, only to re-freeze in the fall. The depth of the active layer varies with climate. In colder regions, where the ground rarely thaws – even during the summer – the active layer is typically quite thin – perhaps only 15 centimeters (6 inches) or less. In warmer regions, by contrast, it can be several meters thick. (See also; Why is Soil So Important to the Planet?)
What is Yedoma?
Yedoma is an organic-rich, Pleistocene-epoch type of permafrost peat containing syngenetic ice-wedges that give it a high ice content of between 50 and 90 percent. When yedoma thaws, it emits large amounts of methane greenhouse gas. Yedoma is found across the circumpolar Arctic region, especially in eastern Siberia, as well as in Alaska and the Yukon. Arctic yedoma is estimated to contain roughly 130 gigatons of organic carbon, up to 10 percent of which is particularly decomposable. The large amount of ice in Yedoma makes it highly vulnerable to disturbances like thermokarst and thermo-erosion processes. 8
How Does The Ground Freeze?
Why and how does the earth freeze in the first place? Well it freezes because the water inside and around it, freezes. And the water freezes because the temperature reaches freezing point – 0°C (32°F) or below. When this happens, all the water between the rocks, soil, and pebbles (known as “pore ice”) freezes solid and turns into ice.
Conversely, when the temperature rises, the pore ice “melts” and the earth “thaws”, leaving behind water and soil. Because earth remains a solid at all times, frozen ground is described as “thawing”, rather than “melting”. Only when solids become liquids do they melt.
When water freezes and turns to ice it occupies more space. This is because water molecules are more tightly packed than ice molecules. So, as water freezes it expands. For example, sometimes part of a road surface will sometimes rise up in severe cold weather, due to an underground stream turning to ice. Conversely, when sub-surface frozen water melts, it will ‘shrink’, which sometimes causes the ground to subside. In fact, the rapid increase in the rate of global warming has led to widespread thawing in the permafrost region, putting buildings and other infrastructure at risk of subsidence or collapse. In one area of Canada, for instance, scientists have recorded a 60-fold increase in massive ground slumps from 1984 to 2013. 9 10
How Does Climate Change Affect Permafrost?
The unprecedented rising temperatures in the Arctic during the last two decades – driven by record heatwaves – combined with other effects of climate change such as loss of albedo, is causing more and more permafrost to thaw. As permafrost thaws, so too does the plant material inside it. And so do the microbes inside it, who can now begin decomposing the material. (Studies have identified microbes more than 400,000 years old in thawed permafrost.) This decomposition process emits greenhouse gases into the atmosphere, such as carbon dioxide (if oxygen present during decomposition), or methane (if no oxygen present).
In its annual report on the state of the Arctic’s climate, the U.S. National Oceanic and Atmospheric Administration (NOAA) warns that thawing permafrost throughout the Arctic could be releasing an estimated 1.1 billion to 2.2. billion tons of carbon dioxide annually into the atmosphere. These emissions are likely to be “two to three times bigger by the end of the century” says Ted Schuur, author of the section entitled “Permafrost and the Global Carbon Cycle”. 11
According to the Second State of the Carbon Cycle Report, between 5 and 15 percent of the organic carbon stored in the circumpolar permafrost zone is vulnerable to release by the year 2100. This is the equivalent of 146 to 160 billion tonnes of carbon, or 535 to 587 billion tonnes of carbon dioxide. 12
Decomposition takes place during the winter as well as the summer. A new study using data from more than 100 Arctic study sites by dozens of institutions, suggests that as global temperatures rise, the decomposition of organic matter in the permafrost peat layer during the winter months can be substantially greater than previously thought. The new numbers indicate a release of CO2 that far exceeds the corresponding summer uptake.
The scientists found that these winter carbon emissions could increase 41 percent by 2100 if human-caused greenhouse gas emissions continue at their current pace. 13 “Given that a major process responsible for CO2 emissions – microbial respiration – increases with warming even at sub-zero temperatures, winter is a critical period for carbon cycling,” said study co-author Dr. Fereidoun Rezanezhad.
What Happens If Large Areas Of Permafrost Start Thawing?
The impact of large emissions of methane or carbon dioxide from thawing peatlands would be dire. These heat-trapping gases would significantly boost the greenhouse effect, causing more damage to the climate system and leading to significant sea level rise around the globe. For example, if global warming is not brought under control, soil studies indicate that tens to hundreds of billions of tonnes of carbon could be transferred from the permafrost “carbon pool” into the atmosphere. 14 This would almost certainly trigger an unstoppable destabilization of the permafrost with potentially catastrophic effects.
Emissions of Nitrous Oxide: A New Danger
If you thought that Arctic permafrost was only a source of carbon dioxide and methane, think again. According to a recent study, which surveyed 120 square miles of the permafrost surface, during the month of August, using the airborne eddy-covariance method, nitrous oxide – one of the world’s worst greenhouse gases – is being emitted by the permafrost and at roughly 12 times the rate previously assumed.
It’s a double whammy, because – as study co-author Ron Dobosy, of the NOAA, says – until now, the Arctic was considered to be nitrogen poor. Now it’s clear that nitrous oxide emissions are present, and need to be studied further. 15
Unfortunately, The Arctic Is Getting Much Hotter
The Arctic region is warming twice as fast as the global average. 16 In its Special Report on the Ocean and Cryosphere, the IPCC itself admitted that the region was experiencing temperature increases of between 2°C and 3°C. According to another study, published in Geophysical Research Letters, temperatures in the region are higher now than they have been for 44,000 years, perhaps even for 120,000 years. 17 See also: What is Earth’s Temperature?
Meantime, a Washington Post analysis has found that parts of Yakutia in eastern Siberia have warmed by more than 3°C since preindustrial times – that’s about three times the global average. 18 In August 2019, average surface temperatures in the Beaufort, Chukchi, and Laptev seas as well as Baffin Bay were 1-7°C warmer than the August average during the three decades 1982-2010. 19
These elevated temperatures, caused by global warming, are directly responsible for the tinderbox conditions that led to the Arctic fires that raged across the region in 2019, releasing huge clouds of black carbon and soot as well as vast quantities of carbon dioxide and methane. (See also: Why Are Methane Levels Rising?)
How High Do Temperatures Need To Rise In Order To Thaw The Permafrost?
Actually, it’s melting already – in Alaska, Canada, Siberia and all the way around the circumpolar region. 20
Okay, so how much warming is needed for large areas of permafrost to start thawing? According to a study led by the paleoclimate specialist Anton Vaks, an increase in global temperature of 1.5°C (2.7 °F) above current levels would be enough to kickstart the thawing of permafrost in Siberia. The study, which used radiometric dating techniques on Siberian rock formations to measure historic melting rates, shows that a 1.5C rise is enough to thaw an extensive expanse of permafrost. 21
The IPCC’s Special Report on the Ocean and Cryosphere is no more optimistic. The report says that even if the world manages to limit global warming to 2°C, roughly one quarter of the near-surface (3-4-meter depth) permafrost will be lost by 2100. In a more pessimistic scenario where greenhouse gas emissions continue to increase strongly, resulting in warming of 5°C, roughly 69 percent is likely to be lost. This would be potentially catastrophic. 22
Global warming does not have to heat up the permafrost directly, to pose a threat. It may trigger as many as three climate feedbacks instead: surface albedo feedback (SAF), permafrost carbon feedback (PCF) and wildfire feedback.
For example, if global warming melts more sea ice, the region will lose albedo and attract more sunlight, and become even warmer. 23 24 Or, if it causes more permafrost to thaw, the resulting greenhouse gas emissions would make the Earth (including the Arctic) even warmer. 25 A third pathway is for global warming to continue drying out the boreal forest. This inevitably will lead to more Arctic fires, and the region will get even warmer. In all three cases, the result is the same. The Arctic gets warmer which causes more permafrost to thaw.
How Does Thawing Permafrost Spread Disease?
When permafrost thaws, the newly-defrosted microbes (which include ancient bacteria and viruses) can pass on their viruses to humans and animals.
In 2014, a research team thawed out two viruses that had been trapped 100-feet deep inside Siberian permafrost for 30,000 years. Known as “Pithovirus sibericum” and “Mollivirus sibericum”, they were both what are called “giant viruses”. Once revived, they quickly became infectious. Fortunately, the viruses were only able to infect single-celled organisms. Nonetheless, the study’s findings indicated that other viruses, which could infect humans, might be revitalized in the same way. The bad news, according to lead author Jean-Michel Claverie, is that so-called ‘giant viruses’ tend to be immune to degradation, even after thousands of years. 26
Will Mercury Be Released Into The Food Chain?
Greenhouse gases and viruses aren’t the only health hazards locked up in the Arctic. A new study in Geophysical Research Letters estimates that the Northern Hemisphere permafrost contains 15 million gallons of the neurotoxin mercury. That’s nearly twice the amount of mercury found in all the world’s soils, atmosphere, and ocean put together. The more global warming, the more likely that this mercury, or a part of it, will be released into the ocean and end up in the food chain. 27
Financial Consequences Of Permafrost Loss
Thawing permafrost may add nearly $70 trillion to the overall costs of climate change – even if the world succeeds in limiting global warming to 2°C. However, if climate change can be limited to 1.5°C (2.7 °F), the extra cost of Arctic warming falls to $25 trillion. That’s according to new research published in Nature Communications. For context, global GDP in 2016 was roughly $76 trillion. 28
- “Encyclopedia of Geomorphology. 2.” Andrew Goudie, ed. (2004). New York: Routledge. p.777. ISBN 0-415-32738-5.
- “Distribution of permafrost in North America and its relationship to the environment: A review, 1963–1973.” Brown, Roger J.E.; Pewe, Troy L. (1973) Permafrost: North American Contribution – Second International Conference, 2: 71–100.
- “Statistics and characteristics of permafrost and ground ice distribution in the Northern Hemisphere.” Zhang, T., Roger G. Barry, K. Knowles, J. A. Heginbottom, and J. Brown: Volume 31, 2008, pp. 47-68. July 2008.
- “Observations: Changes in Snow, Ice and Frozen Ground.” Lemke et al; IPCC Working Group I GI, 2007, pages 242-243.
- “Soil organic carbon pools in the northern circumpolar permafrost region”. C. Tarnocai, J. G. Canadell, E. A. G. Schuur, P. Kuhry, G. Mazhitova, S. Zimov. (2009). Global Biogeochemical Cycles. 23 (2): GB2023.
- “State of the Earth’s cryosphere at the beginning of the 21st century: glaciers, global snow cover, floating ice, and permafrost and periglacial environments: Chapter A in Satellite image atlas of glaciers of the world.” Edited by: Richard S. Williams Jr. and Jane G. Ferrigno. p. A435 (2013). Heginbottom, J. Alan, Brown, Jerry; Humlum, Ole, Svensson, Harald.
- “Sub-Sea Permafrost.” T.E. Osterkamp. (2001) Encyclopedia of Ocean Sciences, pp.2902–12, ISBN 9780122274305
- “Deep Yedoma permafrost: A synthesis of depositional characteristics and carbon vulnerability.” Jens Strauss, Lutz Schirrmeister, Guido Grosse, Daniel Fortier, Gustaf Hugelius, Christian Knoblauch, Vladimir Romanovsky, Christina Schadel, Thomas Schneider von Deimling, Edward A.G.Schuur, Denis Shmelev, Mathias Ulrich, Alexandra Veremeeva. Earth-Science Reviews, Volume 172, September 2017, Pages 75-86.
- Extremes of summer climate trigger thousands of thermokarst landslides in a High Arctic environment. Nature Communications 10, 1329 (2019). Lewkowicz, A.G., Way, R.G.
- “The Race to Save Arctic Cities As Permafrost Melts. Melody Schreiber. citylab.com/ May 10, 2018.
- “Arctic Report Card: Update for 2019.” NOAA.
- Schuur, E. A. G., and Coauthors, 2018: Chapter 11: Arctic and boreal carbon. In: Second State of the Carbon Cycle Report (SOCCR2): A Sustained Assessment Report, Cavallaro, N., G. Shrestha, R. Birdsey, M. A. Mayes, R. G. Najjar, S. C. Reed, P. Romero-Lankao, and Z. Zhu, Eds., U.S. Global Change Research Program, Washington, DC, USA, 428-468.
- Large loss of CO2 in winter observed across the northern permafrost region, Nature Climate Change (2019). Susan M. Natali et al.
- Chapter 3: Polar Regions (PDF). IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC). September 25, 2019. p. 173.
- “Permafrost nitrous oxide emissions observed on a landscape scale using the airborne eddy-covariance method.” Jordan Wilkerson, Ronald Dobosy, David S. Sayres, Claire Healy, Edward Dumas, Bruce Baker and James G. Anderson. Atmospheric Chemistry and Physics, 19, 4257–4268, 2019.
- “Permafrost and the Global Carbon Cycle.” T. Schuur. NOAA Arctic Essays. November 22, 2019.
- “Unprecedented recent summer warmth in Arctic Canada”. Miller, G. H.; Lehman, S. J.; Refsnider, K. A.; Southon, J. R.; Zhong, Y. (2013). Geophysical Research Letters. 40 (21): 5745–5751.
- “Radical warming in Siberia leaves millions on unstable ground.” Anton Troianovski, Chris Mooney. Washington Post. October 3, 2019.
- NOAA 2019 Arctic Report Card.
- “Radical warming in Siberia leaves millions on unstable ground.” Anton Troianovski, Chris Mooney. Washington Post. October 3, 2019.
- “Speleothems reveal 500,000-year history of Siberian permafrost.” Vaks A, Gutareva OS, Breitenbach SF, Avirmed E, Mason AJ, Thomas AL, Osinzev AV, Kononov AM, Henderson GM. Science. 2013 Apr 12;340(6129):183-6.
- Intergovernmental Panel on Climate Change (IPCC) Special Report on the Ocean and Cryosphere in a Changing Climate (2019). Summary for Policymakers.
- Radiative forcing and albedo feedback from the Northern Hemisphere cryosphere between 1979 and 2008. Nature Geosci 4, 151–155 (2011). Flanner, M., Shell, K., Barlage, M. et al.
- Arctic Ice Cover, Ice Thickness and Tipping Points. AMBIO 41, 23–33 (2012). Wadhams, P.
- Climate change and the permafrost carbon feedback. Nature 520, 171–179 (2015). Schuur, E., McGuire, A., Schadel, C. et al.
- “Thirty-thousand-year-old distant relative of giant icosahedral DNA viruses with a pandoravirus morphology.” Matthieu Legendre, Julia Bartoli, Lyubov Shmakova, Sandra Jeudy, Karine Labadie, Annie Adrait, Magali Lescot, Olivier Poirot, Lionel Bertaux, Christophe Bruley, Yohann Coute, Elizaveta Rivkina, Chantal Abergel, and Jean-Michel Claverie. PNAS March 18, 2014 111 (11) 4274-4279
- “Permafrost Stores a Globally Significant Amount of Mercury.” Paul F. Schuster, Kevin M. Schaefer, George R. Aiken, Ronald C. Antweiler, John F. Dewild, Joshua D. Gryziec, Alessio Gusmeroli, Gustaf Hugelius, Elchin Jafarov, David P. Krabbenhoft. Geophysical Research Letters. Feb 5, 2018.
- Climate policy implications of nonlinear decline of Arctic land permafrost and other cryosphere elements. Nat Commun 10, 1900 (2019). Yumashev, D., Hope, C., Schaefer, K. et al.