Editing Carbon sink

{{Short description|Reservoir absorbing more carbon from, than emitting to, the air}}
{{About|storage reservoirs for carbon|the processes involved for storing carbon for a long time|carbon sequestration}}
{{Use dmy dates|date=September 2024}}[[File:1850- Global carbon budget - Global Carbon Project - offset-stacked bar chart.svg|thumb|upright=1.35 |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. Since the 1850s, there are more carbon sources than sinks and therefore the [[carbon dioxide in Earth's atmosphere]] is rising.<ref name="GlobalCarbonBudget_2021">{{cite web |date=4 November 2021 |title=Global Carbon Budget 2021 |url=https://www.globalcarbonproject.org/carbonbudget/21/files/GCP_CarbonBudget_2021.pdf |url-status=live |archive-url=https://web.archive.org/web/20211211094754/https://www.globalcarbonproject.org/carbonbudget/21/files/GCP_CarbonBudget_2021.pdf |archive-date=11 December 2021 |website=Global Carbon Project |page=57 |quote=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}}</ref>]]A '''carbon sink''' is a natural or artificial [[carbon sequestration]] process that "removes a [[greenhouse gas]], an [[aerosol]] or a precursor of a [[greenhouse gas]] from the [[atmosphere]]".<ref name="IPCC AR6 WGI Glossary" />{{rp|2249}} These sinks form an important part of the natural [[carbon cycle]]. An overarching term is '''carbon pool''', which is all the places where carbon on [[Earth]] can be, i.e. the [[atmosphere of Earth|atmosphere]], [[ocean]]s, [[soil]], [[flora]]e, [[fossil fuel]] reservoirs 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]].<ref>{{Cite web|date=2020-03-26|title=Carbon Sources and Sinks|url=http://www.nationalgeographic.org/encyclopedia/carbon-sources-and-sinks/|url-status=live|access-date=2021-06-18|publisher=National Geographic Society|archive-url=https://web.archive.org/web/20201214082221/https://www.nationalgeographic.org/encyclopedia/carbon-sources-and-sinks/ |archive-date=14 December 2020 }}</ref> [[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 certain [[marine ecosystem]]s. ''Coastal blue carbon'' includes [[mangrove]]s, [[salt marsh]]es and [[seagrass]]es. These make up a majority of ocean plant life and store large quantities of carbon. ''Deep blue carbon'' is located in [[international waters]] and includes carbon contained in "continental shelf waters, deep-sea waters and the sea floor beneath them".<ref>{{Cite web |title=The ocean – the world's greatest ally against climate change |url=https://www.un.org/en/climatechange/science/climate-issues/ocean |access-date=2023-04-27 |publisher=United Nations}}</ref>

For [[climate change mitigation]] purposes, the maintenance and enhancement of natural carbon sinks, mainly soils and forests, is important.<ref>{{Cite journal |last1=Binkley |first1=Clark S. |last2=Brand |first2=David |last3=Harkin |first3=Zoe |last4=Bull |first4=Gary |last5=Ravindranath |first5=N. H. |last6=Obersteiner |first6=Michael |last7=Nilsson |first7=Sten |last8=Yamagata |first8=Yoshiki |last9=Krott |first9=Max |date=2002-05-01 |title=Carbon sink by the forest sector—options and needs for implementation |url=https://www.sciencedirect.com/science/article/pii/S1389934102000059 |journal=Forest Policy and Economics |volume=4 |issue=1 |pages=65–77 |doi=10.1016/S1389-9341(02)00005-9 |issn=1389-9341}}</ref><ref>{{Cite journal|last1=Batjes|first1=N.H.| last2=  Ceschia  |first2= E. | last3=   Heuvelink |first3= G.B.M.  |last4=   Demenois |first4= J.  |last5=   le Maire |first5= G. |last6=   Cardinael |first6= R.  | 
last7=   Arias-Navarro |first7= C. |  last8=   von Egmond |first8= F.  |date=October 2024 |title=Towards a modular, multi-ecosystem monitoring, reporting and verification (MRV) framework for soil organic carbon stock change assessment|journal=Carbon Management|volume=15|issue=1|pages=2410812|doi= 10.1080/17583004.2024.2410812 |doi-access=free|bibcode=2024CarM...1510812B }}</ref>  In the past, human practices like [[deforestation]] and [[industrial agriculture]] have depleted natural carbon sinks. This kind of [[land use change]] has been one of the [[causes of climate change]].

== Definition ==
In the context of [[climate change]] and in particular [[Climate change mitigation|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".<ref name="IPCC AR6 WGI Glossary">IPCC, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf 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 [https://www.ipcc.ch/report/ar6/wg1/ 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.</ref>{{rp|2249}}

In the case of non-{{CO2}} 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 [[nitrogen|N<sub>2</sub>]].<ref>{{cite journal | vauthors = CHAPUIS-LARDY L, WRAGE N, CHOTTE J, BERNOUX M  | title =Soils, a sink for N2O? A review | journal = [[Global Change Biology]] | volume = 13| pages =1–17  | date = 2007  | issue =1 | doi =10.1111/j.1365-2486.2006.01280.x  | bibcode =2007GCBio..13....1C | s2cid =86551302 }}</ref><ref>{{cite journal | vauthors = Cobo S, Negri V, Valente A, Reiner D, Hamelin L, Dowell N, Guillén-Gosálbez G  | title = Sustainable scale-up of negative emissions technologies and practices: where to focus | journal = [[Environmental Research Letters]] | year = 2023 | volume =18 | issue = 2 | page = 023001 | doi = 10.1088/1748-9326/acacb3 | bibcode = 2023ERL....18b3001C | s2cid = 254915878 | hdl = 20.500.11850/596686 | hdl-access = free }}</ref>

Related terms are "carbon pool, reservoir, [[Carbon sequestration|sequestration]], [[Carbon source|source]] and uptake".<ref name="IPCC AR6 WGI Glossary" />{{rp|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."<ref name="IPCC AR6 WGI Glossary" />{{rp|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:<ref>{{Cite web |title=What is a Carbon Sink? |url=https://greenly.earth/en-us/blog/company-guide/what-is-a-carbon-sink |access-date=2024-11-23 |website=greenly.earth |language=en-us}}</ref> A carbon pool is all the places where carbon can be stored (for example the atmosphere, oceans, soil, plants, and fossil fuels).<ref name="IPCC AR6 WGI Glossary" />{{rp|2244}}

==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.<ref>{{cite journal |author=Blakemore, R.J. |title=Non-Flat Earth Recalibrated for Terrain and Topsoil |journal=Soil Systems |volume=2 |issue=4 |pages=64 |year=2018 |doi=10.3390/soilsystems2040064 |doi-access=free |bibcode=2018SoiSy...2...64B }}</ref>
* [[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 pump|solubility]] and [[biological pump]]s.

Artificial carbon sinks are those that store carbon in building materials or deep underground (geologic [[carbon sequestration]]).<ref name="Churkina-2020">{{Cite journal |last1=Churkina |first1=Galina |last2=Organschi |first2=Alan |last3=Reyer |first3=Christopher P. O. |last4=Ruff |first4=Andrew |last5=Vinke |first5=Kira |last6=Liu |first6=Zhu |last7=Reck |first7=Barbara K. |last8=Graedel |first8=T. E. |last9=Schellnhuber |first9=Hans Joachim |date=2020 |title=Buildings as a global carbon sink |url=https://www.nature.com/articles/s41893-019-0462-4 |journal=Nature Sustainability|volume=3 |issue=4 |pages=269–276 |bibcode=2020NatSu...3..269C |doi=10.1038/s41893-019-0462-4 |issn=2398-9629 |s2cid=213032074}}</ref><ref name="Encyclopedia Britannica">{{Cite web |title=carbon sequestration {{!}} Definition, Methods, & Climate Change |url=https://www.britannica.com/technology/carbon-sequestration |access-date=2021-06-18 |website=Encyclopædia Britannica}}</ref> No major artificial systems [[carbon dioxide removal|remove carbon from the atmosphere]] on a large scale yet.<ref>{{Cite web|title=Carbon Sinks: A Brief Review|url=https://earth.org/data_visualization/carbon-sinks-a-brief-overview/|access-date=2020-12-02|website=Earth.Org - Past {{!}} Present {{!}} Future}}</ref>

Public awareness of the significance of {{CO2}} sinks has grown since passage of the 1997 [[Kyoto Protocol]], which promotes their use as a form of [[carbon offset]].<ref>{{Cite web |title=carbon sink – European Environment Agency |url=https://www.eea.europa.eu/help/glossary/eea-glossary/carbon-sink |access-date=2021-06-18 |website=eea.europa.eu}}</ref>

== Natural carbon sinks ==
[[File:Carbon cycle.jpg|thumb|right|upright=2|This diagram of the [[carbon cycle#Types of dynamics|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|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.<ref>{{cite journal |journal=Soil Science |volume=166 |issue=11 |pages=858–71 |last=Swift |first=Roger S. |title=Sequestration of Carbon by soil |date=November 2001 |doi=10.1097/00010694-200111000-00010 |bibcode=2001SoilS.166..858S |s2cid=96820247 }}</ref><ref>{{Cite journal |last=Batjes |first=N.H. |date=1996 |title=Total carbon and nitrogen in the soils of the world |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2389.1996.tb01386.x |journal=European Journal of Soil Science|volume=47 |issue=2 |pages=151–163 |doi=10.1111/j.1365-2389.1996.tb01386.x |bibcode=1996EuJSS..47..151B |issn=1351-0754}}</ref><ref>{{Cite journal |last=Batjes |first=N.H. |date=2016 |title=Harmonized soil property values for broad-scale modelling (WISE30sec) with estimates of global soil carbon stocks |url=https://linkinghub.elsevier.com/retrieve/pii/S0016706116300349 |journal=Geoderma|volume=269 |pages=61–68 |doi=10.1016/j.geoderma.2016.01.034|bibcode=2016Geode.269...61B }}</ref> [[Plant litter]] and other [[Biomass (ecology)|biomass]] including [[charcoal]] accumulates as [[Soil organic matter|organic matter]] in soils, and is degraded by [[chemical weathering]] and biological [[biodegradation|degradation]]. More recalcitrant [[organic material|organic]] [[Biopolymer|carbon polymers]] such as [[cellulose]], [[hemi-cellulose]], [[lignin]], aliphatic compounds, waxes and [[terpenoid]]s are collectively retained as [[humus]].<ref>{{cite journal |author1=Klaus Lorenza |author2=Rattan Lala |author3=Caroline M. Prestonb |author4=Klaas G.J. Nieropc |title=Strengthening the soil organic carbon pool by increasing contributions from recalcitrant aliphatic bio(macro)molecules |journal=Geoderma |volume=142 |issue=1–2 |pages=1–10 |date=15 November 2007 |doi=10.1016/j.geoderma.2007.07.013 |url=https://zenodo.org/record/896885 |bibcode=2007Geode.142....1L }}</ref>

Organic matter tends to accumulate in litter and soils of colder regions such as the [[boreal forest]]s 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.<ref>{{cite web | access-date=19 September 2021 | title=Coral Reefs Biome "Underwater Rainforests" | url=https://untamedscience.com/biology/biomes/coral-reefs-biome/}}</ref>

[[Grassland]]s 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 [[Wildfire|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 into the soil in the form of [[biochar]] that does not significantly degrade back to carbon dioxide.<ref>{{Cite journal|last1=Woolf|first1=Dominic|last2=Amonette|first2=James E.|last3=Street-Perrott|first3=F. Alayne|last4=Lehmann|first4=Johannes|last5=Joseph|first5=Stephen|date=2010-08-10|title=Sustainable biochar to mitigate global climate change|journal=Nature Communications|volume=1|issue=5|pages=56|doi=10.1038/ncomms1053|issn=2041-1723|pmc=2964457|pmid=20975722|bibcode=2010NatCo...1...56W}}</ref>

Much [[soil carbon|organic carbon]] retained in many agricultural areas worldwide has been severely depleted due to [[intensive farming]] practices.<ref name="cool">{{cite web |date=17 October 2009 |title=Organic Farming Can Cool the World that Chemical Farming Overheated |url=https://www.cornucopia.org/2009/10/organic-farming-can-cool-the-world-that-chemical-farming-overheated/ |access-date=18 September 2021}}</ref> 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 are called [[carbon farming]]. They include for example [[no-till farming]], residue mulching, [[cover crop]]ping, and [[crop rotation]].

=== Forests ===
{{Excerpt|Carbon sequestration#Forestry|paragraphs=1-4}}

=== Deep ocean, tidal marshes, mangroves and seagrasses ===
{{Excerpt|Blue carbon|}}

== Enhancing natural carbon sinks ==
{{Main|Carbon sequestration}}

===Purpose in the context of climate change===
{{excerpt|Climate change mitigation#Preserving and enhancing carbon sinks}}

=== Carbon sequestration techniques in oceans ===
{{Main|Carbon sequestration#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 fertilization|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.<ref name="Benson-2006">{{Cite journal |last1=Benson |first1=S.M. |last2=Surles |first2=T. |date=2006-10-01 |title=Carbon Dioxide Capture and Storage: An Overview With Emphasis on Capture and Storage in Deep Geological Formations |url=https://zenodo.org/record/1232299 |url-status=live |journal=Proceedings of the IEEE |volume=94 |issue=10 |pages=1795–1805 |doi=10.1109/JPROC.2006.883718 |issn=0018-9219 |archive-url=https://web.archive.org/web/20200611063420/https://zenodo.org/record/1232299 |archive-date=11 June 2020 |access-date=10 September 2019 |s2cid=27994746}}</ref>

== Artificial carbon sinks ==
===Geologic carbon sequestration===
{{Main|Carbon sequestration#Geologic carbon sequestration}}

=== Wooden buildings ===
{{See also|Green building and wood}}
[[File:Mjøstårnet.jpg|thumb|[[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 [[List of tallest wooden buildings|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.<ref name="Churkina-2020"/> 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 [[Sustainable forest management|sustainably managed]] and wood from demolished timber buildings would need to be reused or preserved on land in various forms.<ref name="Churkina-2020"/>

Using rapidly renewable plant materials like [[bamboo]], [[straw]] or [[hempcrete]] can be further carbon sinks.<ref>{{Cite journal |last=Jami |first=Tarun |last2=Karade |first2=S. R. |last3=Singh |first3=L. P. |date=2019-12-01 |title=A review of the properties of hemp concrete for green building applications |url=https://www.sciencedirect.com/science/article/abs/pii/S0959652619327222?via=ihub |journal=Journal of Cleaner Production |volume=239 |pages=117852 |doi=10.1016/j.jclepro.2019.117852 |issn=0959-6526}}</ref><ref>{{Cite journal |last=Arrigoni |first=Alessandro |last2=Pelosato |first2=Renato |last3=Melià |first3=Paco |last4=Ruggieri |first4=Gianluca |last5=Sabbadini |first5=Sergio |last6=Dotelli |first6=Giovanni |date=2017-04-15 |title=Life cycle assessment of natural building materials: the role of carbonation, mixture components and transport in the environmental impacts of hempcrete blocks |url=https://www.sciencedirect.com/science/article/abs/pii/S0959652617303876 |journal=Journal of Cleaner Production |volume=149 |pages=1051–1061 |doi=10.1016/j.jclepro.2017.02.161 |issn=0959-6526|hdl=10446/131799 |hdl-access=free }}</ref>

==See also==
{{Portal|Climate change|Energy|Engineering|Environment}}
*[[Carbon budget]]
*[[Forest management]]
* [[Reforestation]]

== References ==
{{Reflist|30em}}

{{Global warming}}
{{Authority control}}

{{DEFAULTSORT:Carbon Sink}}
[[Category:Carbon dioxide]]
[[Category:Carbon dioxide removal]]
[[Category:Photosynthesis]]
[[Category:Gas technologies]]