Physics:Carbon sink

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Short description: Reservoir absorbing more carbon from, than emitting to, the air
Carbon sinks (green bars on the right) remove carbon from the atmosphere, whereas carbon sources (greenhouse gas emissions) (grey bars on the left) add them. Together, they are part of the carbon budget which is no longer in balance since the 1850s, causing a nearly 50% rise in atmospheric carbon dioxide concentration.[1]

A carbon sink is anything, natural or otherwise, that accumulates and stores some carbon-containing chemical compound for an indefinite period and thereby removes carbon dioxide (CO
2) from the atmosphere.[2] These sinks form an important part of the natural carbon cycle. An overarching term is carbon pool, which is all the places where carbon can be (the atmosphere, oceans, soil, plants, and so forth). A carbon sink is a type of carbon pool that has the capability to take up more carbon from the atmosphere than it releases.

Globally, the two most important carbon sinks are vegetation and the ocean.[3] Soil is an important carbon storage medium. Much of the organic carbon retained in the soil of agricultural areas has been depleted due to intensive farming. "Blue carbon" designates carbon that is fixed via the ocean ecosystems. Coastal blue carbon includes mangroves, salt marshes and seagrasses which make up a majority of ocean plant life and store large quantities of carbon. Deep blue carbon is located in the high seas beyond national jurisdictions and includes carbon contained in "continental shelf waters, deep-sea waters and the sea floor beneath them. As a main carbon sink, the ocean removes excess greenhouse gas emissions such as heat and energy."[4]

Many efforts are being made to enhance natural carbon sinks, mainly soils and forests, to mitigate climate change. These efforts counter historical trends caused by practices like deforestation and industrial agriculture which depleted natural carbon sinks; land use, land-use change, and forestry historically have been important human contributions to climate change. In addition to enhancing natural processes, investments in artificial sequestration initiatives are underway to store carbon in building materials or deep underground.[5][6]

Definition

In the context of climate change and in particular mitigation, a sink is defined as "Any process, activity or mechanism which removes a greenhouse gas, an aerosol or a precursor of a greenhouse gas from the atmosphere".[7]:2249

In the case of non-CO
2 greenhouse gases, sinks need not store the gas. Instead they can break it down into substances that have a reduced effect on global warming. For example, nitrous oxide can be reduced to harmless N2.[8][9]

Related terms are "carbon pool, reservoir, sequestration, source and uptake".[7]:2249 The same publication defines carbon pool as "a  reservoir in the Earth system where elements, such as carbon [...], reside in various chemical forms for a period of time."[7]:2244

Both carbon pools and carbon sinks are important concepts in understanding the carbon cycle, but they refer to slightly different things. A carbon pool can be thought of as the overarching term, and carbon sink is then a particular type of carbon pool: A carbon pool is all the places where carbon can be (for example the atmosphere, oceans, soil, plants, and fossil fuels).[7]:2244 A carbon sink, on the other hand, is a type of carbon pool that has the capability to take up more carbon from the atmosphere than it releases.[citation needed]

Types

The amount of carbon dioxide varies naturally in a dynamic equilibrium with photosynthesis of land plants. The natural carbon sinks are:

  • Soil is a carbon store and active carbon sink.[10]
  • Photosynthesis by terrestrial plants with grass and trees allows them to serve as carbon sinks during growing seasons.
  • Absorption of carbon dioxide by the oceans via solubility and biological pumps.

Artificial carbon sinks are those that store carbon in building materials or deep underground (geologic carbon sequestration).[5][6] No major artificial systems remove carbon from the atmosphere on a large scale yet.[11]

Public awareness of the significance of CO
2 sinks has grown since passage of the 1997 Kyoto Protocol, which promotes their use as a form of carbon offset.[12]

Natural carbon sinks

This diagram of the fast carbon cycle shows the movement of carbon between land, atmosphere, soil and oceans in billions of tons of carbon per year. Yellow numbers are natural fluxes, red are human contributions in billions of tons of carbon per year. White numbers indicate stored carbon.
Main page: Carbon sequestration

Soils

Soils represent a short to long-term carbon storage medium, and contain more carbon than all terrestrial vegetation and the atmosphere combined.[13][14][15] Plant litter and other biomass including charcoal accumulates as organic matter in soils, and is degraded by chemical weathering and biological degradation. More recalcitrant organic carbon polymers such as cellulose, hemi-cellulose, lignin, aliphatic compounds, waxes and terpenoids are collectively retained as humus.[16]

Organic matter tends to accumulate in litter and soils of colder regions such as the boreal forests of North America and the Taiga of Russia . Leaf litter and humus are rapidly oxidized and poorly retained in sub-tropical and tropical climate conditions due to high temperatures and extensive leaching by rainfall. Areas where shifting cultivation or slash and burn agriculture are practiced are generally only fertile for two to three years before they are abandoned. These tropical jungles are similar to coral reefs in that they are highly efficient at conserving and circulating necessary nutrients, which explains their lushness in a nutrient desert.[17]

Grasslands contribute to soil organic matter, stored mainly in their extensive fibrous root mats. Due in part to the climatic conditions of these regions (e.g. cooler temperatures and semi-arid to arid conditions), these soils can accumulate significant quantities of organic matter. This can vary based on rainfall, the length of the winter season, and the frequency of naturally occurring lightning-induced grass-fires. While these fires release carbon dioxide, they improve the quality of the grasslands overall, in turn increasing the amount of carbon retained in the humic material. They also deposit carbon directly to the soil in the form of biochar that does not significantly degrade back to carbon dioxide.[18]

Organic matter in peat bogs undergoes slow anaerobic decomposition below the surface. This process is slow enough that in many cases the bog grows rapidly and fixes more carbon from the atmosphere than is released. Over time, the peat grows deeper. Peat bogs hold approximately one-quarter of the carbon stored in land plants and soils.[19]

Enhancing soil carbon sinks

Much organic carbon retained in many agricultural areas worldwide has been severely depleted due to intensive farming practices.[20] Since the 1850s, a large proportion of the world's grasslands have been tilled and converted to croplands, allowing the rapid oxidation of large quantities of soil organic carbon. Methods that significantly enhance carbon sequestration in soil include no-till farming, residue mulching, cover cropping, and crop rotation, all of which are more widely used in organic farming than in conventional farming.[21][22]

Forests

Proportion of carbon stock in forest carbon pools, 2020[23]

Favourable factors and carbon sink saturation in forests

Forests are generally carbon dioxide sinks when they are high in diversity, density or area. However, they can also be carbon sources if diversity, density or area decreases due to deforestation, selective logging, climate change, wildfires or diseases.[24][25][26] One study in 2020 found that 32 tracked Brazilian non-Amazon seasonal tropical forests declined from a carbon sink to a carbon source in 2013 and concludes that "policies are needed to mitigate the emission of greenhouse gases and to restore and protect tropical seasonal forests".[27][28] In 2019 forests took up a third less carbon than they did in the 1990s, due to higher temperatures, droughts and deforestation. The typical tropical forest may become a carbon source by the 2060s.[29]

An assessment of European forests found early signs of carbon sink saturation, after decades of increasing strength.[30] The Intergovernmental Panel on Climate Change (IPCC) concluded that a combination of measures aimed at increasing forest carbon stocks, andsustainable timber offtake will generate the largest carbon sequestration benefit.[31]

Life expectancy of forests varies throughout the world, influenced by tree species, site conditions and natural disturbance patterns. In some forests, carbon may be stored for centuries, while in other forests, carbon is released with frequent stand replacing fires. Forests that are harvested prior to stand replacing events allow for the retention of carbon in manufactured forest products such as lumber.[32] However, only a portion of the carbon removed from logged forests ends up as durable goods and buildings. The remainder ends up as sawmill by-products such as pulp, paper and pallets, which often end with incineration (resulting in carbon release into the atmosphere) at the end of their lifecycle. For instance, of the 1,692 megatonnes of carbon harvested from forests in Oregon and Washington (state) from 1900 to 1992, only 23% is in long-term storage in forest products.[33]

The Food and Agriculure Organization (FAO) reported that: "The total carbon stock in forests decreased from 668 gigatonnes in 1990 to 662 gigatonnes in 2020".[23]:11 However, another study finds that the leaf area index has increased globally since 1981, which was responsible for 12.4% of the accumulated terrestrial carbon sink from 1981 to 2016. The CO2 fertilization effect, on the other hand, was responsible for 47% of the sink, while climate change reduced the sink by 28.6%.[34] In Canada's boreal forests as much as 80% of the total carbon is stored in the soils as dead organic matter.[35]

Carbon offset programs are planting millions of fast-growing trees per year to reforest tropical lands, for as little as $0.10 per tree. Over their typical 40-year lifetime, one million of these trees can sequester up to one million tons of carbon dioxide.[36][37]

Changes in albedo effect

This section is an excerpt from Albedo#Trees[ edit ]

Deep ocean, tidal marshes, mangroves and seagrasses

This section is an excerpt from Blue carbon[ edit ]

Enhancing natural carbon sinks

Main page: Earth:Carbon sequestration

Purpose in the context of climate change

This section is an excerpt from Climate change mitigation#Preserving and enhancing carbon sinks[ edit ]

Carbon sequestration techniques in oceans

To enhance carbon sequestration processes in oceans the following technologies have been proposed but none have achieved large scale application so far: Seaweed farming, ocean fertilisation, artificial upwelling, basalt storage, mineralization and deep sea sediments, adding bases to neutralize acids. The idea of direct deep-sea carbon dioxide injection has been abandoned.[38]

Artificial carbon sinks

Geologic carbon sequestration

Wooden buildings

Mjøstårnet, one of the tallest timber buildings, at its opening 2019

Broad-base adoption of mass timber and their role in substituting steel and concrete in new mid-rise construction projects over the next few decades has the potential to turn timber buildings into carbon sinks, as they store the carbon dioxide taken up from the air by trees that are harvested and used as mass timber.[5] This could result in storing between 10 million tons of carbon per year in the lowest scenario and close to 700 million tons in the highest scenario. For this to happen, the harvested forests would need to be sustainably managed and wood from demolished timber buildings would need to be reused or preserved on land in various forms.[5]

See also

References

  1. ↑ "Global Carbon Budget 2021". 4 November 2021. p. 57. https://www.globalcarbonproject.org/carbonbudget/21/files/GCP_CarbonBudget_2021.pdf. "The cumulative contributions to the global carbon budget from 1850. The carbon imbalance represents the gap in our current understanding of sources & sinks. ... Source: Friedlingstein et al 2021; Global Carbon Project 2021" 
  2. ↑ "What is a carbon sink?" (in en). https://www.clientearth.org//latest/latest-updates/stories/what-is-a-carbon-sink. 
  3. ↑ "Carbon Sources and Sinks" (in en). 2020-03-26. https://www.nationalgeographic.org/encyclopedia/carbon-sources-and-sinks/. 
  4. ↑ Nations, United. "The ocean – the world's greatest ally against climate change" (in en). https://www.un.org/en/climatechange/science/climate-issues/ocean. 
  5. ↑ 5.0 5.1 5.2 5.3 Churkina, Galina; Organschi, Alan; Reyer, Christopher P. O.; Ruff, Andrew; Vinke, Kira; Liu, Zhu; Reck, Barbara K.; Graedel, T. E. et al. (2020). "Buildings as a global carbon sink" (in en). Nature Sustainability 3 (4): 269–276. doi:10.1038/s41893-019-0462-4. ISSN 2398-9629. https://www.nature.com/articles/s41893-019-0462-4. 
  6. ↑ 6.0 6.1 "carbon sequestration | Definition, Methods, & Climate Change" (in en). https://www.britannica.com/technology/carbon-sequestration. 
  7. ↑ 7.0 7.1 7.2 7.3 IPCC, 2021: Annex VII: Glossary [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C.  Méndez, S. Semenov, A. Reisinger (eds.)]. 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. 2215–2256, doi:10.1017/9781009157896.022.
  8. ↑ "Soils, a sink for N2O? A review". Global Change Biology 13: 1–17. 2007. doi:10.1111/j.1365-2486.2006.01280.x. 
  9. ↑ "Sustainable scale-up of negative emissions technologies and practices: where to focus". Environmental Research Letters 18 (2): 023001. 2023. doi:10.1088/1748-9326/acacb3. 
  10. ↑ Blakemore, R.J. (2018). "Non-Flat Earth Recalibrated for Terrain and Topsoil". Soil Systems 2 (4): 64. doi:10.3390/soilsystems2040064. 
  11. ↑ "Carbon Sinks: A Brief Review" (in en-GB). https://earth.org/data_visualization/carbon-sinks-a-brief-overview/. 
  12. ↑ "carbon sink — European Environment Agency" (in en). https://www.eea.europa.eu/help/glossary/eea-glossary/carbon-sink. 
  13. ↑ Swift, Roger S. (November 2001). "Sequestration of Carbon by soil". Soil Science 166 (11): 858–71. doi:10.1097/00010694-200111000-00010. Bibcode: 2001SoilS.166..858S. 
  14. ↑ Batjes, N.H. (1996). "Total carbon and nitrogen in the soils of the world" (in en). European Journal of Soil Science 47 (2): 151–163. doi:10.1111/j.1365-2389.1996.tb01386.x. ISSN 1351-0754. https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2389.1996.tb01386.x. 
  15. ↑ Batjes, N.H. (2016). "Harmonized soil property values for broad-scale modelling (WISE30sec) with estimates of global soil carbon stocks" (in en). Geoderma 269: 61–68. doi:10.1016/j.geoderma.2016.01.034. Bibcode: 2016Geode.269...61B. https://linkinghub.elsevier.com/retrieve/pii/S0016706116300349. 
  16. ↑ Klaus Lorenza; Rattan Lala; Caroline M. Prestonb; Klaas G.J. Nieropc (15 November 2007). "Strengthening the soil organic carbon pool by increasing contributions from recalcitrant aliphatic bio(macro)molecules". Geoderma 142 (1–2): 1–10. doi:10.1016/j.geoderma.2007.07.013. Bibcode: 2007Geode.142....1L. https://zenodo.org/record/896885. 
  17. ↑ "Coral Reefs Biome "Underwater Rainforests"". https://untamedscience.com/biology/biomes/coral-reefs-biome/. 
  18. ↑ Woolf, Dominic; Amonette, James E.; Street-Perrott, F. Alayne; Lehmann, Johannes; Joseph, Stephen (2010-08-10). "Sustainable biochar to mitigate global climate change" (in en). Nature Communications 1 (5): 56. doi:10.1038/ncomms1053. ISSN 2041-1723. PMID 20975722. Bibcode: 2010NatCo...1...56W. 
  19. ↑ Chester, Bronwyn (20 April 2000). "The case of the missing sink". McGill Reporter. https://reporter-archive.mcgill.ca/32/15/roulet/index.html. 
  20. ↑ "Organic Farming Can Cool the World that Chemical Farming Overheated". 17 October 2009. https://www.cornucopia.org/2009/10/organic-farming-can-cool-the-world-that-chemical-farming-overheated/. 
  21. ↑ Susan S. Lang (13 July 2005). "Organic farming produces same corn and soybean yields as conventional farms, but consumes less energy and no pesticides, study finds". https://www.news.cornell.edu/stories/July05/organic.farm.vs.other.ssl.html. 
  22. ↑ Pimentel, David; Hepperly, Paul; Hanson, James; Douds, David; Seidel, Rita (2005). "Environmental, Energetic, and Economic Comparisons of Organic and Conventional Farming Systems". BioScience 55 (7): 573–82. doi:10.1641/0006-3568(2005)055[0573:EEAECO2.0.CO;2]. 
  23. ↑ 23.0 23.1 (in en) Global Forest Resources Assessment 2020. FAO. 2020. doi:10.4060/ca8753en. ISBN 978-92-5-132581-0. https://www.fao.org/documents/card/en/c/ca8753en. 
  24. ↑ Carolyn Gramling (28 September 2017). "Tropical forests have flipped from sponges to sources of carbon dioxide; A closer look at the world's trees reveals a loss of density in the tropics". Sciencenews.org 358 (6360): 230–234. doi:10.1126/science.aam5962. PMID 28971966. Bibcode: 2017Sci...358..230B. https://www.sciencenews.org/article/tropical-forests-have-flipped-sponges-sources-carbon-dioxide. Retrieved 6 October 2017. 
  25. ↑ "Tropical forests are a net carbon source based on aboveground measurements of gain and loss". Science 358 (6360): 230–234. 13 October 2017. doi:10.1126/science.aam5962. PMID 28971966. Bibcode: 2017Sci...358..230B. 
  26. ↑ Spawn, Seth A.; Sullivan, Clare C.; Lark, Tyler J.; Gibbs, Holly K. (December 2020). "Harmonized global maps of above and belowground biomass carbon density in the year 2010". Scientific Data 7 (1): 112. doi:10.1038/s41597-020-0444-4. PMID 32249772. Bibcode: 2020NatSD...7..112S. 
  27. ↑ "Brazilian forests found to be transitioning from carbon sinks to carbon sources" (in en). phys.org. https://phys.org/news/2020-12-brazilian-forests-transitioning-carbon-sources.html. 
  28. ↑ Maia, Vinícius Andrade; Santos, Alisson Borges Miranda; Aguiar-Campos, Natália de; Souza, Cléber Rodrigo de; Oliveira, Matheus Coutinho Freitas de; Coelho, Polyanne Aparecida; Morel, Jean Daniel; Costa, Lauana Silva da et al. (1 December 2020). "The carbon sink of tropical seasonal forests in southeastern Brazil can be under threat" (in en). Science Advances 6 (51): eabd4548. doi:10.1126/sciadv.abd4548. ISSN 2375-2548. PMID 33355136. Bibcode: 2020SciA....6.4548M. 
  29. ↑ Harvey, Fiona (2020-03-04). "Tropical forests losing their ability to absorb carbon, study finds" (in en-GB). The Guardian. ISSN 0261-3077. https://www.theguardian.com/environment/2020/mar/04/tropical-forests-losing-their-ability-to-absorb-carbon-study-finds. 
  30. ↑ Nabuurs, Gert-Jan; Lindner, Marcus; Verkerk, Pieter J.; Gunia, Katja; Deda, Paola; Michalak, Roman; Grassi, Giacomo (September 2013). "First signs of carbon sink saturation in European forest biomass" (in en). Nature Climate Change 3 (9): 792–796. doi:10.1038/nclimate1853. ISSN 1758-678X. https://www.nature.com/articles/nclimate1853. 
  31. ↑ Intergovernmental Panel on Climate Change (2007), "Forestry", Climate Change 2007 (Cambridge: Cambridge University Press): pp. 541–584, doi:10.1017/cbo9780511546013.013, ISBN 978-0-511-54601-3, https://dx.doi.org/10.1017/cbo9780511546013.013, retrieved 2024-01-05 
  32. ↑ J. Chatellier (January 2010). The Role of Forest Products in the Global Carbon Cycle: From In-Use to End-of-Life. Yale School of Forestry and Environmental Studies. https://gisf.research.yale.edu/forest_carbon_report/Chapter_13.pdf. 
  33. ↑ Harmon, M. E.; Harmon, J. M.; Ferrell, W. K.; Brooks, D. (1996). "Modeling carbon stores in Oregon and Washington forest products: 1900?1992". Climatic Change 33 (4): 521. doi:10.1007/BF00141703. Bibcode: 1996ClCh...33..521H. https://zenodo.org/record/1232389. 
  34. ↑ Chen, JM; Ciais, Philippe (18 September 2019). "Vegetation structural change since 1981 significantly enhanced the terrestrial carbon sink". Nature Communications 10 (4259): 4259. doi:10.1038/s41467-019-12257-8. PMID 31534135. Bibcode: 2019NatCo..10.4259C. 
  35. ↑ "Does harvesting in Canada's forests contribute to climate change?". Canadian Forest Service Science-Policy Notes. Natural Resources Canada. May 2007. https://www.sfmcanada.org/CMFiles/PublicationLibrary/CFS_DoesHarvestingInCanadasForestsContributeToClimateChange_English1OVA-25012010-8256.pdf. 
  36. ↑ "This Is The Impact Of 1 Million Trees". 26 November 2019. https://blog.tentree.com/this-is-the-impact-of-1-million-trees/. 
  37. ↑ Grant M. Domke; Sonja N. Oswalt; Brian F. Walters; Randall S. Morin (6 Oct 2020). "Tree planting has the potential to increase carbon sequestration capacity of forests in the United States". PNAS 117 (40): 24649–24651. doi:10.1073/pnas.2010840117. PMID 32958649. PMC 7547226. Bibcode: 2020PNAS..11724649D. https://www.fs.fed.us/nrs/pubs/jrnl/2020/nrs_2020_domke_001.pdf. 
  38. ↑ Benson, S.M.; Surles, T. (2006-10-01). "Carbon Dioxide Capture and Storage: An Overview With Emphasis on Capture and Storage in Deep Geological Formations". Proceedings of the IEEE 94 (10): 1795–1805. doi:10.1109/JPROC.2006.883718. ISSN 0018-9219. https://zenodo.org/record/1232299. Retrieved September 10, 2019. 



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