Permafrost

This article is about frozen ground. For other uses, see Permafrost (disambiguation).

Permafrost
Extent and types of permafrost in the Northern Hemisphere as per International Permafrost Association

Permafrost (from perma- 'permanent' and frost) is soil or underwater sediment which continuously remains below 0 °C (32 °F) for two years or more: the oldest permafrost had been continuously frozen for around 700,000 years.[1] Whilst the shallowest permafrost has a vertical extent of below a meter (3 ft), the deepest is greater than 1,500 m (4,900 ft).[2] Similarly, the area of individual permafrost zones may be limited to narrow mountain summits or extend across vast Arctic regions.[3] 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.[4]

Around 15% of the Northern Hemisphere or 11% of the global surface is underlain by permafrost,[5] covering a total area of around 18 million km2 (6.9 million sq mi).[6] This includes large areas of Alaska, Canada, Greenland, and Siberia. It is also located in high mountain regions, with the Tibetan Plateau being 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.[3][1]

Permafrost contains large amounts of dead biomass that have accumulated throughout millennia without having had the chance to fully decompose and release their carbon, making tundra soil a carbon sink.[3] As global warming heats the ecosystem, frozen soil thaws and becomes warm enough for decomposition to start anew, accelerating the permafrost carbon cycle. Depending on conditions at the time of thaw, decomposition can release either carbon dioxide or methane, and these greenhouse gas emissions act as a climate change feedback.[7][8][9] 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.[10] 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.[11]

Apart from its climate impact, permafrost thaw brings more 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.[12] 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.[13] Furthermore, between 13,000 and 20,000 sites contaminated with toxic waste are present in the permafrost,[14] as well as the natural mercury deposits,[15] which are all liable to leak and pollute the environment as the warming progresses.[16] Lastly, concerns have been raised about the potential for pathogenic microorganisms surviving the thaw and contributing to future pandemics.[17][18] However, this is considered unlikely,[19][20] and a scientific review on the subject describes the risks as "generally low".[21]

  1. ^ a b McGee, David; Gribkoff, Elizabeth (4 August 2022). "Permafrost". MIT Climate Portal. Retrieved 27 September 2023.
  2. ^ Cite error: The named reference IPADefinition was invoked but never defined (see the help page).
  3. ^ a b c Denchak, Melissa (26 June 2018). "Permafrost: Everything You Need to Know". Natural Resources Defense Council. Retrieved 27 September 2023.
  4. ^ Cooper, M. G.; Zhou, T.; Bennett, K. E.; Bolton, W. R.; Coon, E. T.; Fleming, S. W.; Rowland, J. C.; Schwenk, J. (4 January 2023). "Detecting Permafrost Active Layer Thickness Change From Nonlinear Baseflow Recession". Water Resources Research. 57 (1): e2022WR033154. Bibcode:2023WRR....5933154C. doi:10.1029/2022WR033154. S2CID 255639677.
  5. ^ Obu, J. (2021). "How Much of the Earth's Surface is Underlain by Permafrost?". Journal of Geophysical Research: Earth Surface. 126 (5): e2021JF006123. Bibcode:2021JGRF..12606123O. doi:10.1029/2021JF006123.
  6. ^ Sayedi, Sayedeh Sara; Abbott, Benjamin W; Thornton, Brett F; Frederick, Jennifer M; Vonk, Jorien E; Overduin, Paul; Schädel, Christina; Schuur, Edward A G; Bourbonnais, Annie; Demidov, Nikita; Gavrilov, Anatoly (22 December 2020). "Subsea permafrost carbon stocks and climate change sensitivity estimated by expert assessment". Environmental Research Letters. 15 (12): B027-08. Bibcode:2020AGUFMB027...08S. doi:10.1088/1748-9326/abcc29. S2CID 234515282.
  7. ^ Schuur, T. (22 November 2019). "Permafrost and the Global Carbon Cycle". Natural Resources Defense Council – via NOAA.
  8. ^ Koven, Charles D.; Ringeval, Bruno; Friedlingstein, Pierre; Ciais, Philippe; Cadule, Patricia; Khvorostyanov, Dmitry; Krinner, Gerhard; Tarnocai, Charles (6 September 2011). "Permafrost carbon-climate feedbacks accelerate global warming". Proceedings of the National Academy of Sciences. 108 (36): 14769–14774. Bibcode:2011PNAS..10814769K. doi:10.1073/pnas.1103910108. PMC 3169129. PMID 21852573.
  9. ^ Galera, L. A.; Eckhardt, T.; Beer C., Pfeiffer E.-M.; Knoblauch, C. (22 March 2023). "Ratio of in situ CO2 to CH4 production and its environmental controls in polygonal tundra soils of Samoylov Island, Northeastern Siberia". Journal of Geophysical Research: Biogeosciences. 128 (4): e2022JG006956. Bibcode:2023JGRG..12806956G. doi:10.1029/2022JG006956. S2CID 257700504.
  10. ^ Fox-Kemper, B., H.T. Hewitt, C. Xiao, G. Aðalgeirsdóttir, S.S. Drijfhout, T.L. Edwards, N.R. Golledge, M. Hemer, R.E. Kopp, G. Krinner, A. Mix, D. Notz, S. Nowicki, I.S. Nurhati, L. Ruiz, J.-B. Sallée, A.B.A. Slangen, and Y. Yu, 2021: Chapter 9: Ocean, Cryosphere and Sea Level Change. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1211–1362.
  11. ^ Schuur, Edward A.G.; Abbott, Benjamin W.; Commane, Roisin; Ernakovich, Jessica; Euskirchen, Eugenie; Hugelius, Gustaf; Grosse, Guido; Jones, Miriam; Koven, Charlie; Leshyk, Victor; Lawrence, David; Loranty, Michael M.; Mauritz, Marguerite; Olefeldt, David; Natali, Susan; Rodenhizer, Heidi; Salmon, Verity; Schädel, Christina; Strauss, Jens; Treat, Claire; Turetsky, Merritt (2022). "Permafrost and Climate Change: Carbon Cycle Feedbacks From the Warming Arctic". Annual Review of Environment and Resources. 47: 343–371. doi:10.1146/annurev-environ-012220-011847. S2CID 252986002.
  12. ^ Cite error: The named reference Nelson2002 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Hjort2022 was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference Langer2023 was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference Schaefer2020 was invoked but never defined (see the help page).
  16. ^ Cite error: The named reference Miner2021 was invoked but never defined (see the help page).
  17. ^ Cite error: The named reference Alempic2023 was invoked but never defined (see the help page).
  18. ^ Cite error: The named reference Alund2023 was invoked but never defined (see the help page).
  19. ^ Cite error: The named reference Yong2014 was invoked but never defined (see the help page).
  20. ^ Cite error: The named reference Doucleff2020 was invoked but never defined (see the help page).
  21. ^ Cite error: The named reference Wu2022 was invoked but never defined (see the help page).