View source for Carbon sequestration

{{Short description|Storing carbon in a carbon pool}}
{{About|storing carbon so that it is not in the atmosphere|removing carbon dioxide from industrial point sources before it enters the atmosphere|Carbon capture and storage|removing carbon dioxide from the atmosphere (and negative emissions)|Carbon dioxide removal}}
{{Use mdy dates|date=June 2019}}
[[File:Carbon sequestration-2009-10-07.svg|right|thumb|upright=1.2| Geologic and biologic carbon sequestration of excess [[Carbon dioxide in Earth's atmosphere|carbon dioxide in the atmosphere]] emitted by human activities.<ref>{{Cite web|title=CCS Explained|url=https://ukccsrc.ac.uk/ccs-explained/|access-date=2020-06-27|website=UKCCSRC|archive-date=June 28, 2020|archive-url=https://web.archive.org/web/20200628232607/https://ukccsrc.ac.uk/ccs-explained/|url-status=live}}</ref>]]

'''Carbon sequestration''' is the process of storing carbon in a [[carbon pool]].<ref name="Masson-Delmotte">{{Cite book|author=IPCC|url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf|title=Climate Change 2021: The Physical Science Basis|publisher=Cambridge University Press (In Press)|year=2021|isbn=|editor1-last=Masson-Delmotte|editor1-first=V.|series=Contribution of Working Group I to the [[IPCC Sixth Assessment Report|Sixth Assessment Report]] of the Intergovernmental Panel on Climate Change|place=|ref={{harvid|IPCC AR6 WG1|2021}}|author-link=IPCC|editor2-last=Zhai|editor2-first=P.|editor3-last=Pirani|editor3-first=A.|editor4-last=Connors|editor4-first=S. L.|editor5-last=Péan|editor5-first=C.|editor6-last=Berger|editor6-first=S.|editor7-last=Caud|editor7-first=N.|editor8-last=Chen|editor8-first=Y.|editor9-last=Goldfarb|editor9-first=L.|display-editors=4|editor10-first=M. I.|editor10-last=Gomis|access-date=June 3, 2022|archive-date=June 5, 2022|archive-url=https://web.archive.org/web/20220605175306/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf|url-status=live}}</ref>{{Rp|page=2248}} It plays a crucial role in [[Climate change mitigation|limiting climate change]] by reducing the amount of [[Carbon dioxide in Earth's atmosphere|carbon dioxide in the atmosphere]]. There are two main types of carbon sequestration: biologic (also called ''biosequestration'') and geologic.<ref name=":8" />  

Biologic carbon sequestration is a naturally occurring process as part of the [[carbon cycle]]. Humans can enhance it through deliberate actions and use of technology. Carbon dioxide ({{chem|CO|2}}) is naturally captured from the [[atmosphere]] through biological, chemical, and physical processes. These processes can be accelerated for example through changes in land use and agricultural practices, called [[carbon farming]]. Artificial processes have also been devised to produce similar effects. This approach is called [[carbon capture and storage]]. It involves using technology to capture and sequester (store) {{chem|CO|2}} that is produced from human activities underground or under the sea bed. 

Plants, such as forests and [[kelp bed]]s, absorb carbon dioxide from the air as they grow, and bind it into biomass. However, these biological stores may be temporary [[carbon sink]]s, as long-term sequestration cannot be guaranteed. [[Wildfire]]s, disease, economic pressures, and changing political priorities may release the sequestered carbon back into the atmosphere.<ref name="auto">{{Cite web |last=Myles |first=Allen |date=September 2020 |title=The Oxford Principles for Net Zero Aligned Carbon Offsetting |url=https://www.smithschool.ox.ac.uk/publications/reports/Oxford-Offsetting-Principles-2020.pdf |url-status=live |archive-url=https://web.archive.org/web/20201002083510/https://www.smithschool.ox.ac.uk/publications/reports/Oxford-Offsetting-Principles-2020.pdf |archive-date=October 2, 2020 |access-date=10 December 2021}}</ref>

Carbon dioxide that has been removed from the atmosphere can also be stored in the Earth's crust by injecting it underground, or in the form of [[insoluble]] [[carbonate]] salts. The latter process is called [[Carbon capture and storage#Mineral storage/mineral carbonation|mineral sequestration]]. These methods are considered ''non-volatile'' because they not only remove carbon dioxide from the atmosphere but also sequester it indefinitely. This means the carbon is "locked away" for thousands to millions of years.

To enhance carbon sequestration processes in oceans the following chemical or physical technologies have been proposed: [[ocean fertilization]], [[artificial upwelling]], basalt storage, mineralization and deep-sea sediments, and adding bases to neutralize acids.<ref>{{cite journal |last1=Renforth |first1=Phil |last2=Henderson |first2=Gideon |title=Assessing ocean alkalinity for carbon sequestration |journal=Reviews of Geophysics |date=15 June 2017 |volume=55 |issue=3 |pages=636–674 |doi=10.1002/2016RG000533 |bibcode=2017RvGeo..55..636R |s2cid=53985208 |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016RG000533 |access-date=3 March 2024}}</ref> However, none have achieved large scale application so far. Large-scale [[seaweed farming]] on the other hand is a biological process and could sequester significant amounts of carbon.<ref name=":152" /> The potential growth of seaweed for carbon farming would see the harvested seaweed transported to the deep ocean for long-term burial.<ref name=":73" /> The IPCC [[Special Report on the Ocean and Cryosphere in a Changing Climate]] recommends "further research attention" on seaweed farming as a mitigation tactic.<ref name=":242" />

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== Terminology ==
<noinclude>{{Carbon cycle|Carbon sequestration}}</noinclude>
The term ''carbon sequestration'' has diverse meanings in the literature and media. The [[IPCC Sixth Assessment Report]] defines carbon sequestration as "The process of storing carbon in a carbon pool".<ref name=":6">{{Cite journal |last1=Warner |first1=Emily |last2=Cook-Patton |first2=Susan C. |last3=Lewis |first3=Owen T. |last4=Brown |first4=Nick |last5=Koricheva |first5=Julia |last6=Eisenhauer |first6=Nico |last7=Ferlian |first7=Olga |last8=Gravel |first8=Dominique |last9=Hall |first9=Jefferson S. |last10=Jactel |first10=Hervé |last11=Mayoral |first11=Carolina |last12=Meredieu |first12=Céline |last13=Messier |first13=Christian |last14=Paquette |first14=Alain |last15=Parker |first15=William C. |date=2023 |title=Young mixed planted forests store more carbon than monocultures—a meta-analysis |journal=Frontiers in Forests and Global Change |volume=6 |bibcode=2023FrFGC...626514W |doi=10.3389/ffgc.2023.1226514 |issn=2624-893X |doi-access=free}}</ref>{{Rp|page=2248}} Subsequently, a ''pool'' is defined as "a reservoir in the Earth system where elements, such as carbon and nitrogen, reside in various chemical forms for a period of time".<ref name=":6" />{{Rp|page=2244}}

The [[United States Geological Survey]] (USGS) defines ''carbon sequestration'' as follows: "Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide."<ref name=":8">{{Cite web |title=What is carbon sequestration? {{!}} U.S. Geological Survey |url=https://www.usgs.gov/faqs/what-carbon-sequestration |access-date=2023-02-06 |website=www.usgs.gov |archive-date=February 6, 2023 |archive-url=https://web.archive.org/web/20230206141017/https://www.usgs.gov/faqs/what-carbon-sequestration |url-status=live }}</ref> Therefore, the difference between carbon sequestration and [[carbon capture and storage]] (CCS) is sometimes blurred in the media.{{Citation needed|date=May 2024}} The IPCC, however, defines CCS as "a process in which a relatively pure stream of [[carbon dioxide]] (CO<sub>2</sub>) from industrial sources is separated, treated and transported to a long-term storage location".<ref name=":9">IPCC, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf Annex VII: Glossary] {{Webarchive|url=https://web.archive.org/web/20220605175306/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf |date=June 5, 2022 }} [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C.&nbsp; 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] {{Webarchive|url=https://web.archive.org/web/20210809131444/https://www.ipcc.ch/report/ar6/wg1/ |date=August 9, 2021 }} [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, US, pp. 2215–2256, doi:10.1017/9781009157896.022.</ref>{{Rp|page=2221}}

== Roles ==

=== In nature ===
Carbon sequestration is part of the natural [[carbon cycle]] by which [[carbon]] is exchanged among the [[biosphere]], [[pedosphere]] (soil), [[geosphere]], [[hydrosphere]], and [[atmosphere of Earth]].{{citation needed|date=July 2023}} Carbon dioxide is naturally captured from the atmosphere through biological, chemical, or physical processes, and stored in long-term reservoirs.

Plants, such as forests and [[kelp bed]]s, absorb carbon dioxide from the air as they grow, and bind it into [[Biomass (ecology)|biomass]]. However, these biological stores are considered ''volatile [[carbon sink]]s'' as long-term sequestration cannot be guaranteed. Events such as [[wildfire]]s or disease, economic pressures, and changing political priorities can result in the sequestered carbon being released back into the atmosphere.<ref name="auto"/>

=== In climate change mitigation and policies ===
{{Further|Climate change mitigation|Politics of climate change}}

Carbon sequestration - when acting as a [[carbon sink]] -{{Clarify|reason=why do we need the phrase which is between the dashes? Does it not always help to mitigate climate change?|date=May 2024}} helps to [[Climate change mitigation|mitigate climate change]] and thus reduce harmful [[effects of climate change]]. It helps to slow the atmospheric and marine accumulation of [[greenhouse gas]]es, which is mainly carbon dioxide released by burning [[fossil fuel]]s.<ref name="Hodrien">{{cite conference |last=Hodrien |first=Chris |date=October 24, 2008 |title=Squaring the Circle on Coal – Carbon Capture and Storage |url=http://www.claverton-energy.com/download/137/ |format=PDF |conference=Claverton Energy Group Conference, Bath |archive-url=https://web.archive.org/web/20090531162754/http://www.claverton-energy.com/download/137/ |archive-date=May 31, 2009 |access-date=May 9, 2010 }}</ref>

Carbon sequestration for climate change mitigation can involve either enhancing natural carbon sinks or employing technological methods to capture and store carbon.

Within the carbon capture and storage approaches, ''carbon sequestration'' refers to the ''storage'' component. Artificial carbon storage technologies can be applied, such as gaseous storage in deep geological formations (including saline formations and exhausted gas fields), and solid storage by reaction of CO<sub>2</sub> with metal [[oxide]]s to produce stable [[carbonate]]s.<ref>{{Cite journal |last1=Bui |first1=Mai |last2=Adjiman |first2=Claire S. |last3=Bardow |first3=André |last4=Anthony |first4=Edward J. |last5=Boston |first5=Andy |last6=Brown |first6=Solomon |last7=Fennell |first7=Paul S. |last8=Fuss |first8=Sabine |last9=Galindo |first9=Amparo |last10=Hackett |first10=Leigh A. |last11=Hallett |first11=Jason P. |last12=Herzog |first12=Howard J. |last13=Jackson |first13=George |last14=Kemper |first14=Jasmin |last15=Krevor |first15=Samuel |date=2018 |title=Carbon capture and storage (CCS): the way forward |url=http://xlink.rsc.org/?DOI=C7EE02342A |journal=Energy & Environmental Science |language=en |volume=11 |issue=5 |pages=1062–1176 |doi=10.1039/C7EE02342A |bibcode=2018EnEnS..11.1062B |issn=1754-5692 |access-date=February 6, 2023 |archive-date=March 17, 2023 |archive-url=https://web.archive.org/web/20230317201308/https://pubs.rsc.org/en/content/articlelanding/2018/EE/C7EE02342A |url-status=live |hdl=10044/1/55714 |hdl-access=free }}</ref>

For carbon to be sequestered artificially—that is, outside the natural processes of the carbon cycle—it must first be captured, or its release into the atmosphere must be significantly delayed or prevented. This can be achieved by incorporating carbon-rich materials into long-lasting applications, such as construction, thereby avoiding release through processes like combustion or decay. Thereafter it can be passively stored or remain productively utilized over time in a variety of ways. For instance, upon harvesting, wood (as a carbon-rich material) can be incorporated into construction or a range of other durable products, thus sequestering its carbon over years or even centuries.<ref name=":10">{{cite journal |author=Ning Zeng |date=2008 |title=Carbon sequestration via wood burial |journal=Carbon Balance and Management |volume=3 |issue=1 |page=1 |doi=10.1186/1750-0680-3-1 |pmc=2266747 |pmid=18173850 |doi-access=free |bibcode=2008CarBM...3....1Z }}</ref> In industrial production, engineers typically capture carbon dioxide from emissions from power plants or factories.

For example, in the [[Climate change policy of the United States|United States]], the [[Executive Order 13990]] (officially titled "Protecting Public Health and the Environment and Restoring Science to Tackle the Climate Crisis") from 2021, includes several mentions of carbon sequestration via conservation and restoration of carbon sink ecosystems, such as wetlands and forests. The document emphasizes the importance of farmers, landowners, and coastal communities in carbon sequestration. It directs the [[United States Department of the Treasury|Treasury Department]] to promote conservation of carbon sinks through market based mechanisms.<ref>{{Cite web |date=2021-01-27 |title=Executive Order on Tackling the Climate Crisis at Home and Abroad |url=https://bidenwhitehouse.archives.gov/briefing-room/presidential-actions/2021/01/27/executive-order-on-tackling-the-climate-crisis-at-home-and-abroad/ |url-status=live |archive-url=https://web.archive.org/web/20210217015733/https://www.whitehouse.gov/briefing-room/presidential-actions/2021/01/27/executive-order-on-tackling-the-climate-crisis-at-home-and-abroad/ |archive-date=February 17, 2021 |access-date=2021-04-28 |website=The White House |language=en-US}}</ref>

== Biological carbon sequestration on land ==
Biological carbon sequestration (also called ''biosequestration'') is the capture and storage of the atmospheric greenhouse gas carbon dioxide by continual{{Contradictory inline|reason='continual' seems to contradict 'increased' in next sentence? Also perhaps next word should be 'and' not 'or'?|date=May 2024}}or enhanced biological processes. This form of carbon sequestration occurs through increased rates of [[photosynthesis]] via [[Land use|land-use]] practices such as [[reforestation]] and [[Sustainability|sustainable]] [[forest management]].<ref name="Beerling">{{cite book |author=Beerling, David |title=The Emerald Planet: How Plants Changed Earth's History |publisher=Oxford University Press |year=2008 |isbn=978-0-19-954814-9 |pages=194–5 |author-link=David Beerling}}</ref><ref>{{Cite book |last1=National Academies Of Sciences |first1=Engineering |title=Negative Emissions Technologies and Reliable Sequestration: A Research Agenda |publisher=National Academies of Sciences, Engineering, and Medicine |year=2019 |isbn=978-0-309-48452-7 |location=Washington, D.C. |pages=45–136 |language=en |doi=10.17226/25259 |pmid=31120708 |s2cid=134196575}}</ref> [[Land-use change]]s that enhance natural carbon capture have the potential to capture and store large amounts of carbon dioxide each year. These include the conservation, management, and restoration of [[ecosystems]] such as forests, [[peatlands]], [[wetlands]], and [[grasslands]], in addition to carbon sequestration methods in agriculture.<ref>*{{Cite book|ref= {{harvid|IPCC AR6 WG3 Summary for Policymakers|2022| Sections C.9.1, D.2.2}}|author= IPCC|author-link= IPCC|chapter= Summary for Policymakers|chapter-url= https://report.ipcc.ch/ar6wg3/pdf/IPCC_AR6_WGIII_SummaryForPolicymakers.pdf|year= 2022|title= Mitigation of Climate Change|series= Contribution of Working Group III to the [[IPCC Sixth Assessment Report|Sixth Assessment Report]] of the Intergovernmental Panel on Climate Change|access-date= May 20, 2022|archive-date= August 7, 2022|archive-url= https://web.archive.org/web/20220807023536/https://report.ipcc.ch/ar6wg3/pdf/IPCC_AR6_WGIII_SummaryForPolicymakers.pdf}}</ref> Methods and practices exist to enhance [[soil carbon]] sequestration in both [[agriculture]] and [[forestry]].<ref>{{cite web |title=World Soil Resources Reports |url=https://www.fao.org/3/bl001e/bl001e.pdf |access-date=19 December 2023}}</ref><ref>{{cite web | url= https://irc-orcasa.eu | title= ORCaSa because soil organic matters - A Horizon Europe initiative that aims to bring together international stakeholders working on techniques for capturing and storing carbon in the soil}}</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>

=== Forestry ===

[[File:Proportion of carbon stock in forest carbon pools, 2020.svg|thumb|Proportion of carbon stock in forest carbon pools, 2020<ref name="FAO-2020">{{Cite book |url=http://www.fao.org/documents/card/en/c/ca8753en |title=Global Forest Resources Assessment 2020 |date=2020 |publisher=FAO |isbn=978-92-5-132581-0 |language=en |doi=10.4060/ca8753en|s2cid=130116768 }}</ref>]]

Forests are an important part of the [[global carbon cycle]] because trees and plants absorb [[carbon dioxide]] through [[photosynthesis]]. Therefore, they play an important role in [[climate change mitigation]].<ref name="AR6 WGIII Ch 13">IPCC (2022) [https://www.ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6_WGIII_SPM.pdf Summary for policy makers] in [https://www.ipcc.ch/report/ar6/wg3/ Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change], Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA</ref>{{rp|37}} By removing the [[greenhouse gas]] carbon dioxide from the air, forests function as terrestrial [[carbon sink]]s, meaning they store large amounts of carbon in the form of biomass, encompassing roots, stems, branches, and leaves. By doing so, forests sequester approximately 25% of human carbon emissions annually, playing a critical role in Earth's climate.<ref name=":15">{{Cite web |last=Barnett |first=Lauren |date=January 15, 2024 |title=Climate change threatens global forest carbon sequestration, study finds |url=https://news.clas.ufl.edu/climate-change-threatens-global-forest-carbon-sequestration-study-finds/ |access-date=May 9, 2025 |website=UF Liberal Arts and Sciences}}</ref> Throughout their lifespan, trees continue to sequester carbon, storing atmospheric CO<small><sub>2</sub></small> long-term.<ref name="Sedjo, R. 2012">Sedjo, R., & Sohngen, B. (2012). Carbon sequestration in forests and soils. Annu. Rev. Resour. Econ., 4(1), 127-144.</ref> [[Sustainable forest management]], [[afforestation]], [[reforestation]] are therefore important contributions to climate change mitigation.  

An important consideration in such efforts is that forests can turn from sinks to carbon sources.<ref>{{Cite journal |last1=Baccini |first1=A. |last2=Walker |first2=W. |last3=Carvalho |first3=L. |last4=Farina |first4=M. |last5=Sulla-Menashe |first5=D. |last6=Houghton |first6=R. A. |date=October 2017 |title=Tropical forests are a net carbon source based on aboveground measurements of gain and loss |url=https://www.science.org/doi/10.1126/science.aam5962 |journal=Science |language=en |volume=358 |issue=6360 |pages=230–234 |doi=10.1126/science.aam5962 |pmid=28971966 |bibcode=2017Sci...358..230B |issn=0036-8075|url-access=subscription }}</ref><ref>{{Cite journal |last1=Spawn |first1=Seth A. |last2=Sullivan |first2=Clare C. |last3=Lark |first3=Tyler J. |last4=Gibbs |first4=Holly K. |date=2020-04-06 |title=Harmonized global maps of above and belowground biomass carbon density in the year 2010 |journal=Scientific Data |language=en |volume=7 |issue=1 |pages=112 |doi=10.1038/s41597-020-0444-4 |issn=2052-4463 |pmc=7136222 |pmid=32249772|bibcode=2020NatSD...7..112S }}</ref><ref>{{cite journal |author=Carolyn Gramling |date=28 September 2017 |title=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 |url=https://www.sciencenews.org/article/tropical-forests-have-flipped-sponges-sources-carbon-dioxide |journal=[[Sciencenews.org]] |volume=358 |issue=6360 |pages=230–234 |bibcode=2017Sci...358..230B |doi=10.1126/science.aam5962 |pmid=28971966 |access-date=6 October 2017 |doi-access=free|url-access=subscription }}</ref> In 2019 forests took up a third less carbon than they did in the 1990s, due to higher temperatures, [[drought]]s<ref>{{Cite news |last=Greenfield |first=Patrick |date=2024-10-14 |title=Trees and land absorbed almost no CO2 last year. Is nature's carbon sink failing? |url=https://www.theguardian.com/environment/2024/oct/14/nature-carbon-sink-collapse-global-heating-models-emissions-targets-evidence-aoe |access-date=2024-11-02 |work=The Guardian |language=en-GB |issn=0261-3077}}</ref> and [[deforestation]]. National-scale forest inventory data also shows trends from 1999 to 2020 that some forests were already approaching climate thresholds shifting them from carbon sinks to carbon sources.<ref name=":15" /> The typical tropical forest may become a carbon source by the 2060s.<ref>{{Cite news |last=Harvey |first=Fiona |author-link=Fiona Harvey |date=2020-03-04 |title=Tropical forests losing their ability to absorb carbon, study finds |url=https://www.theguardian.com/environment/2020/mar/04/tropical-forests-losing-their-ability-to-absorb-carbon-study-finds |access-date=2020-03-05 |work=The Guardian |language=en-GB |issn=0261-3077}}</ref>

Researchers have found that, in terms of [[environmental services]], it is better to avoid deforestation than to allow for deforestation to subsequently reforest, as the latter leads to irreversible effects in terms of [[biodiversity loss]] and [[soil degradation]].<ref>{{cite web |title=Press corner |url=https://ec.europa.eu/commission/presscorner/detail/en/MEMO_08_632 |access-date=28 September 2020 |website=European Commission – European Commission |language=en}}</ref> Furthermore, the probability that legacy carbon will be released from soil is higher in younger boreal forest.<ref>{{cite journal |last1=Walker |first1=Xanthe J. |last2=Baltzer |first2=Jennifer L. |last3=Cumming |first3=Steven G. |last4=Day |first4=Nicola J. |last5=Ebert |first5=Christopher |last6=Goetz |first6=Scott |last7=Johnstone |first7=Jill F. |last8=Potter |first8=Stefano |last9=Rogers |first9=Brendan M. |last10=Schuur |first10=Edward A. G. |last11=Turetsky |first11=Merritt R. |last12=Mack |first12=Michelle C. |author-link12=Michelle Cailin Mack |date=August 2019 |title=Increasing wildfires threaten historic carbon sink of boreal forest soils |url=https://www.nature.com/articles/s41586-019-1474-y |journal=Nature |language=en |volume=572 |issue=7770 |pages=520–523 |bibcode=2019Natur.572..520W |doi=10.1038/s41586-019-1474-y |issn=1476-4687 |pmid=31435055 |s2cid=201124728 |access-date=28 September 2020|url-access=subscription }}</ref> Global greenhouse gas emissions caused by damage to tropical rainforests may have been substantially underestimated until around 2019.<ref>{{cite news |date=31 October 2019 |title=Climate emissions from tropical forest damage 'underestimated by a factor of six' |url=https://www.theguardian.com/environment/2019/oct/31/climate-emissions-from-tropical-forest-damage-underestimated-by-a-factor-of-six |access-date=28 September 2020 |work=The Guardian |language=en}}</ref> Additionally, the effects of afforestation and reforestation will be farther in the future than keeping existing forests intact.<ref>{{cite web |title=Why Keeping Mature Forests Intact Is Key to the Climate Fight |url=https://e360.yale.edu/features/why-keeping-mature-forests-intact-is-key-to-the-climate-fight |access-date=28 September 2020 |website=Yale E360}}</ref> It takes much longer − several decades − for the benefits for global warming to manifest to the same carbon sequestration benefits from mature trees in tropical forests and hence from limiting deforestation.<ref>{{cite web |date=1 September 2012 |title=Would a Large-scale Reforestation Effort Help Counter the Global Warming Impacts of Deforestation? |url=https://blog.ucsusa.org/elliott-negin/would-reforestation-help-counter-deforestation |access-date=28 September 2020 |website=Union of Concerned Scientists}}</ref> Therefore, scientists consider "the protection and recovery of carbon-rich and long-lived ecosystems, especially natural forests" to be "the major climate [[Nature-based solutions|solution]]".<ref>{{cite web |title=Planting trees is no substitute for natural forests |url=https://phys.org/news/2019-08-trees-substitute-natural-forests.html |access-date=2 May 2021 |website=phys.org |language=en}}</ref>

The planting of trees on marginal crop and [[pasture]] lands helps to incorporate carbon from atmospheric {{chem|CO|2}} into [[biomass]].<ref>{{cite web |last=McDermott |first=Matthew |date=August 22, 2008 |title=Can Aerial Reforestation Help Slow Climate Change? Discovery Project Earth Examines Re-Engineering the Planet's Possibilities |url=http://www.treehugger.com/files/2008/08/aerial-reforestation-explored-in-discovery-project-earth-premiere.php |url-status=live |archive-url=https://web.archive.org/web/20100330031042/http://www.treehugger.com/files/2008/08/aerial-reforestation-explored-in-discovery-project-earth-premiere.php |archive-date=March 30, 2010 |access-date=May 9, 2010 |website=TreeHugger}}</ref><ref>{{Cite journal |last1=Lefebvre |first1=David |last2=Williams |first2=Adrian G. |last3=Kirk |first3=Guy J. D. |last4=Paul |last5=Burgess |first5=J. |last6=Meersmans |first6=Jeroen |last7=Silman |first7=Miles R. |last8=Román-Dañobeytia |first8=Francisco |last9=Farfan |first9=Jhon |last10=Smith |first10=Pete |date=2021-10-07 |title=Assessing the carbon capture potential of a reforestation project |journal=Scientific Reports |language=en |volume=11 |issue=1 |page=19907 |bibcode=2021NatSR..1119907L |doi=10.1038/s41598-021-99395-6 |issn=2045-2322 |pmc=8497602 |pmid=34620924}}</ref> For this carbon sequestration process to succeed the carbon must not return to the atmosphere from biomass burning or rotting when the trees die.<ref>{{Cite book |last=Gorte |first=Ross W. |url=https://sgp.fas.org/crs/misc/RL31432.pdf |title=Carbon Sequestration in Forests |publisher=Congressional Research Service |year=2009 |edition=RL31432 |access-date=January 9, 2023 |archive-date=November 14, 2022 |archive-url=https://web.archive.org/web/20221114182920/http://sgp.fas.org/crs/misc/RL31432.pdf |url-status=live }}</ref> 

Earth offers enough room to plant an additional 0.9 billion ha of tree canopy cover, although this estimate has been criticized,<ref>{{Cite journal |last1=Lewis |first1=Simon L. |last2=Mitchard |first2=Edward T. A. |last3=Prentice |first3=Colin |last4=Maslin |first4=Mark |last5=Poulter |first5=Ben |date=2019-10-18 |title=Comment on "The global tree restoration potential" |url=https://www.science.org/doi/10.1126/science.aaz0388 |journal=Science |language=en |volume=366 |issue=6463 |doi=10.1126/science.aaz0388 |pmid=31624179 |issn=0036-8075|hdl=10044/1/74650 |hdl-access=free |url-access=subscription }}</ref><ref>{{Cite journal |last1=Friedlingstein |first1=Pierre |last2=Allen |first2=Myles |last3=Canadell |first3=Josep G. |last4=Peters |first4=Glen P. |last5=Seneviratne |first5=Sonia I. |date=2019-10-18 |title=Comment on "The global tree restoration potential" |url=https://www.science.org/doi/10.1126/science.aay8060 |journal=Science |language=en |volume=366 |issue=6463 |doi=10.1126/science.aay8060 |pmid=31624183 |issn=0036-8075|hdl=10871/39954 |hdl-access=free }}</ref> and the true area that has a net cooling effect on the climate when accounting for biophysical feedbacks like albedo is 20-80% lower.<ref>{{Cite journal |last1=Hasler |first1=Natalia |last2=Williams |first2=Christopher A. |last3=Denney |first3=Vanessa Carrasco |last4=Ellis |first4=Peter W. |last5=Shrestha |first5=Surendra |last6=Terasaki Hart |first6=Drew E. |last7=Wolff |first7=Nicholas H. |last8=Yeo |first8=Samantha |last9=Crowther |first9=Thomas W. |last10=Werden |first10=Leland K. |last11=Cook-Patton |first11=Susan C. |date=2024-03-26 |title=Accounting for albedo change to identify climate-positive tree cover restoration |journal=Nature Communications |language=en |volume=15 |issue=1 |pages=2275 |doi=10.1038/s41467-024-46577-1 |issn=2041-1723 |pmc=10965905 |pmid=38531896|bibcode=2024NatCo..15.2275H }}</ref><ref name=":7" /> Planting and protecting these trees would sequester 205 billion tons of carbon if the trees survive future climate stress to reach maturity.<ref>{{Cite journal |last1=Anderegg |first1=William R. L. |last2=Trugman |first2=Anna T. |last3=Badgley |first3=Grayson |last4=Anderson |first4=Christa M. |last5=Bartuska |first5=Ann |last6=Ciais |first6=Philippe |last7=Cullenward |first7=Danny |last8=Field |first8=Christopher B. |last9=Freeman |first9=Jeremy |last10=Goetz |first10=Scott J. |last11=Hicke |first11=Jeffrey A. |last12=Huntzinger |first12=Deborah |last13=Jackson |first13=Robert B. |last14=Nickerson |first14=John |last15=Pacala |first15=Stephen |date=2020-06-19 |title=Climate-driven risks to the climate mitigation potential of forests |url=https://www.science.org/doi/10.1126/science.aaz7005 |journal=Science |language=en |volume=368 |issue=6497 |doi=10.1126/science.aaz7005 |pmid=32554569 |issn=0036-8075|url-access=subscription }}</ref><ref name=":7">{{Cite journal |last1=Bastin |first1=Jean-Francois |last2=Finegold |first2=Yelena |last3=Garcia |first3=Claude |last4=Mollicone |first4=Danilo |last5=Rezende |first5=Marcelo |last6=Routh |first6=Devin |last7=Zohner |first7=Constantin M. |last8=Crowther |first8=Thomas W. |date=July 5, 2019 |title=The global tree restoration potential |journal=Science |volume=365 |issue=6448 |pages=76–79 |bibcode=2019Sci...365...76B |doi=10.1126/science.aax0848 |pmid=31273120 |doi-access=free |s2cid=195804232}}</ref> To put this number into perspective, this is about 20 years of current global carbon emissions (as of 2019) .<ref>{{Cite web |last=Tutton |first=Mark |date=July 4, 2019 |title=Restoring forests could capture two-thirds of the carbon humans have added to the atmosphere |url=https://www.cnn.com/2019/07/04/world/forests-capture-two-thirds-of-carbon-emissions-scn-intl/index.html |url-status=live |archive-url=https://web.archive.org/web/20200323221053/https://www.cnn.com/2019/07/04/world/forests-capture-two-thirds-of-carbon-emissions-scn-intl/index.html |archive-date=March 23, 2020 |access-date=January 23, 2020 |website=CNN}}</ref> This level of sequestration would represent about 25% of the atmosphere's carbon pool in 2019.<ref name=":7" /> 

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]].<ref>{{cite book |author=J. Chatellier |url=http://gisf.research.yale.edu/forest_carbon_report/Chapter_13.pdf |title=The Role of Forest Products in the Global Carbon Cycle: From In-Use to End-of-Life |date=January 2010 |publisher=Yale School of Forestry and Environmental Studies |archive-url=https://web.archive.org/web/20100705163108/http://gisf.research.yale.edu/forest_carbon_report/Chapter_13.pdf |archive-date=5 July 2010 |url-status=dead}}</ref> 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.<ref>{{Cite journal |last1=Harmon |first1=M. E. |last2=Harmon |first2=J. M. |last3=Ferrell |first3=W. K. |last4=Brooks |first4=D. |year=1996 |title=Modeling carbon stores in Oregon and Washington forest products: 1900?1992 |url=https://zenodo.org/record/1232389 |journal=Climatic Change |volume=33 |issue=4 |pages=521 |bibcode=1996ClCh...33..521H |doi=10.1007/BF00141703 |s2cid=27637103}}</ref> If all new construction globally utilized 90% wood products, largely via adoption of [[mass timber]] in [[low rise]] construction, this could sequester 700&nbsp;million net tons of carbon per year.<ref>{{Cite web |last=Toussaint |first=Kristin |date=2020-01-27 |title=Building with timber instead of steel could help pull millions of tons of carbon from the atmosphere |url=https://www.fastcompany.com/90456328/building-with-timber-instead-of-steel-could-help-pull-millions-of-tons-of-carbon-from-the-atmosphere |url-status=live |archive-url=https://web.archive.org/web/20200128214740/https://www.fastcompany.com/90456328/building-with-timber-instead-of-steel-could-help-pull-millions-of-tons-of-carbon-from-the-atmosphere |archive-date=January 28, 2020 |access-date=2020-01-29 |website=Fast Company |language=en-US}}</ref><ref>{{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=2020-01-27 |title=Buildings as a global carbon sink |url=https://www.nature.com/articles/s41893-019-0462-4 |url-status=live |journal=Nature Sustainability |language=en |volume=3 |issue=4 |pages=269–276 |bibcode=2020NatSu...3..269C |doi=10.1038/s41893-019-0462-4 |issn=2398-9629 |s2cid=213032074 |archive-url=https://web.archive.org/web/20200128124454/https://www.nature.com/articles/s41893-019-0462-4 |archive-date=January 28, 2020 |access-date=January 29, 2020|url-access=subscription }}</ref> This is in addition to the elimination of carbon emissions from the displaced construction material such as steel or concrete, which are carbon-intense to produce.

A meta-analysis found that mixed species plantations would increase carbon storage alongside other benefits of diversifying planted forests.<ref name=":6" />

Although a bamboo forest stores less total carbon than a mature forest of trees, a [[Bamboo cultivation|bamboo plantation]] sequesters carbon at a much faster rate than a mature forest or a tree plantation. Therefore, the farming of bamboo timber may have significant carbon sequestration potential.<ref>{{Cite journal |last1=Devi |first1=Angom Sarjubala |last2=Singh |first2=Kshetrimayum Suresh |date=2021-01-12 |title=Carbon storage and sequestration potential in aboveground biomass of bamboos in North East India |journal=Scientific Reports |language=en |volume=11 |issue=1 |page=837 |doi=10.1038/s41598-020-80887-w |issn=2045-2322 |pmc=7803772 |pmid=33437001}}</ref>

The [[Food and Agriculture Organization]] (FAO) reported that: "The total carbon stock in forests decreased from 668 gigatonnes in 1990 to 662 gigatonnes in 2020".<ref name="FAO-2020" />{{rp|11}} In [[Boreal forest of Canada|Canada's boreal forests]] as much as 80% of the total carbon is stored in the soils as dead organic matter.<ref name="cfs.nrcan.gc.ca">{{cite web |date=May 2007 |title=Does harvesting in Canada's forests contribute to climate change? |url=http://www.sfmcanada.org/CMFiles/PublicationLibrary/CFS_DoesHarvestingInCanadasForestsContributeToClimateChange_English1OVA-25012010-8256.pdf |url-status=live |archive-url=https://web.archive.org/web/20130730163912/http://www.sfmcanada.org/CMFiles/PublicationLibrary/CFS_DoesHarvestingInCanadasForestsContributeToClimateChange_English1OVA-25012010-8256.pdf |archive-date=2013-07-30 |work=Canadian Forest Service Science-Policy Notes |publisher=Natural Resources Canada}}</ref>{{Globalize inline|date=May 2024}}

The [[IPCC Sixth Assessment Report]] says: "Secondary forest regrowth and restoration of degraded forests and non-forest ecosystems can play a large role in carbon sequestration (high confidence) with high resilience to disturbances and additional benefits such as enhanced biodiversity."<ref>{{Cite web|url=https://www.ipcc.ch/report/ar6/wg1/downloads/factsheets/IPCC_AR6_WGI_Sectoral_Fact_Sheet_Forestry.pdf|title=Climate information relevant for Forestry}}</ref><ref>Ometto, J.P., K. Kalaba, G.Z. Anshari, N. Chacón, A. Farrell, S.A. Halim, H. Neufeldt, and R. Sukumar, 2022: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_CCP7.pdf CrossChapter Paper 7: Tropical Forests]. In: [https://www.ipcc.ch/report/ar6/wg2/chapter/ccp7/ Climate Change 2022: Impacts, Adaptation and Vulnerability]. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA, pp. 2369–2410, doi:10.1017/9781009325844.024.</ref>

Impacts on temperature are affected by the location of the forest. For example, reforestation in boreal or [[subarctic]] regions has less impact on climate. This is because it substitutes a high-[[albedo]], snow-dominated region with a lower-albedo forest canopy. By contrast, tropical reforestation projects lead to a positive change such as the formation of [[clouds]]. These clouds then [[albedo|reflect the sunlight]], lowering temperatures.<ref name="Canadell">{{Cite journal |last=Canadell |first=J.G. |author2=M.R. Raupach |date=2008-06-13 |title=Managing Forests for Climate Change |url=http://www.globalcarbonproject.org/global/pdf/canadell%26raupach2008_managingforests.science.pdf |journal=Science |volume=320 |issue=5882 |pages=1456–1457 |bibcode=2008Sci...320.1456C |citeseerx=10.1.1.573.5230 |doi=10.1126/science.1155458 |pmid=18556550 |s2cid=35218793}}</ref>{{rp|1457}}

Planting trees in [[tropical climate]]s with [[wet season]]s has another advantage. In such a setting, trees grow more quickly (fixing more carbon) because they can grow year-round. Trees in tropical climates have, on average, larger, brighter, and more abundant leaves than non-tropical climates. A study of the [[:wikt:girth|girth]] of 70,000 trees across [[Africa]] has shown that tropical forests fix more carbon dioxide pollution than previously realized. The research suggested almost one-fifth of fossil fuel emissions are absorbed by forests across Africa, [[Amazonia]] and [[Asia]]. Simon Lewis stated, "Tropical forest trees are absorbing about 18% of the carbon dioxide added to the atmosphere each year from burning fossil fuels, substantially buffering the rate of change."<ref>{{cite news| url=http://www.guardian.co.uk/environment/2009/feb/18/trees-tropics-climate-change | work=The Guardian | location=London | title=Fifth of world carbon emissions soaked up by extra forest growth, scientists find | first=David | last=Adam | date=2009-02-18 | access-date=2010-05-22}}</ref>{{Obsolete source|date=May 2024}}

=== Wetlands ===
{{See also|Blue carbon|Wetland#Climate change mitigation}}
[[File:Wetland in Skippack Township, MontCo PA.jpg|thumb|A healthy wetland ecosystem]]
[[File:Journal.pone.0043542.g001.TIF|thumb|{{center|Global distribution of blue carbon (rooted vegetation in the coastal zone): tidal marshes, mangroves and seagrasses.<ref name=Pendleton2012>{{Cite journal| last1 = Pendleton| first1 = Linwood| last2 = Donato| first2 = Daniel C.| last3 = Murray| first3 = Brian C.| last4 = Crooks| first4 = Stephen| last5 = Jenkins| first5 = W. Aaron| last6 = Sifleet| first6 = Samantha| last7 = Craft| first7 = Christopher| last8 = Fourqurean| first8 = James W.| last9 = Kauffman| first9 = J. Boone| title = Estimating Global "Blue Carbon" Emissions from Conversion and Degradation of Vegetated Coastal Ecosystems| journal = PLOS ONE| volume = 7| issue = 9| doi = 10.1371/journal.pone.0043542| pmc = 3433453| pmid = 22962585| pages=e43542| year=2012| bibcode = 2012PLoSO...743542P| doi-access = free}}</ref>}}]]
Wetland restoration involves restoring a wetland's natural biological, geological, and chemical functions through re-establishment or rehabilitation.<ref>{{Cite web|last=US EPA|first=OW|date=2018-07-27|title=Basic Information about Wetland Restoration and Protection|url=https://www.epa.gov/wetlands/basic-information-about-wetland-restoration-and-protection|access-date=2021-04-28|website=US EPA|language=en|archive-date=April 28, 2021|archive-url=https://web.archive.org/web/20210428154040/https://www.epa.gov/wetlands/basic-information-about-wetland-restoration-and-protection|url-status=live}}</ref> It is a good way to reduce climate change.<ref name=":4">{{Cite web|last=US Department of Commerce|first=National Oceanic and Atmospheric Administration|title=What is Blue Carbon?|url=https://oceanservice.noaa.gov/facts/bluecarbon.html|access-date=2021-04-28|website=oceanservice.noaa.gov|language=EN-US|archive-date=April 22, 2021|archive-url=https://web.archive.org/web/20210422222157/https://oceanservice.noaa.gov/facts/bluecarbon.html|url-status=live}}</ref> Wetland soil, particularly in coastal wetlands such as [[mangroves]], [[Seagrass|sea grasses]], and [[salt marsh]]es,<ref name=":4" /> is an important carbon reservoir; 20–30% of the world's [[soil carbon]] is found in wetlands, while only 5–8% of the world's land is composed of wetlands.<ref>{{Cite journal|last1=Mitsch|first1=William J.|last2=Bernal|first2=Blanca|last3=Nahlik|first3=Amanda M.|last4=Mander|first4=Ülo|last5=Zhang|first5=Li|last6=Anderson|first6=Christopher J.|last7=Jørgensen|first7=Sven E.|last8=Brix|first8=Hans|date=2013-04-01|title=Wetlands, carbon, and climate change|journal=Landscape Ecology|language=en|volume=28|issue=4|pages=583–597|doi=10.1007/s10980-012-9758-8|bibcode=2013LaEco..28..583M |s2cid=11939685|issn=1572-9761}}</ref> Studies have shown that restored wetlands can become productive [[Carbon sink|{{CO2}} sinks]]<ref>{{Cite journal|last1=Valach|first1=Alex C.|last2=Kasak|first2=Kuno|last3=Hemes|first3=Kyle S.|last4=Anthony|first4=Tyler L.|last5=Dronova|first5=Iryna|last6=Taddeo|first6=Sophie|last7=Silver|first7=Whendee L.|last8=Szutu|first8=Daphne|last9=Verfaillie|first9=Joseph|last10=Baldocchi|first10=Dennis D.|date=2021-03-25|title=Productive wetlands restored for carbon sequestration quickly become net CO<sub>2</sub> sinks with site-level factors driving uptake variability|journal=PLOS ONE|language=en|volume=16|issue=3|pages=e0248398|doi=10.1371/journal.pone.0248398|issn=1932-6203|pmc=7993764|pmid=33765085|bibcode=2021PLoSO..1648398V|doi-access=free}}</ref><ref>{{Cite journal|last1=Bu|first1=Xiaoyan|last2=Cui|first2=Dan|last3=Dong|first3=Suocheng|last4=Mi|first4=Wenbao|last5=Li|first5=Yu|last6=Li|first6=Zhigang|last7=Feng|first7=Yaliang|date=January 2020|title=Effects of Wetland Restoration and Conservation Projects on Soil Carbon Sequestration in the Ningxia Basin of the Yellow River in China from 2000 to 2015|journal=Sustainability|language=en|volume=12|issue=24|page=10284|doi=10.3390/su122410284|doi-access=free|bibcode=2020Sust...1210284B }}</ref><ref>{{Cite journal|last1=Badiou|first1=Pascal|last2=McDougal|first2=Rhonda|last3=Pennock|first3=Dan|last4=Clark|first4=Bob|date=2011-06-01|title=Greenhouse gas emissions and carbon sequestration potential in restored wetlands of the Canadian prairie pothole region|journal=Wetlands Ecology and Management|language=en|volume=19|issue=3|pages=237–256|doi=10.1007/s11273-011-9214-6|bibcode=2011WetEM..19..237B |s2cid=30476076|issn=1572-9834}}</ref> and many are being restored.<ref>{{Cite web|title=Restoring Wetlands - Wetlands (U.S. National Park Service)|url=https://www.nps.gov/subjects/wetlands/restoring-wetlands.htm|access-date=2021-04-28|website=www.nps.gov|language=en|archive-date=April 28, 2021|archive-url=https://web.archive.org/web/20210428072509/https://www.nps.gov/subjects/wetlands/restoring-wetlands.htm|url-status=live}}</ref><ref>{{Cite web|title=A new partnership for wetland restoration {{!}} ICPDR – International Commission for the Protection of the Danube River|url=https://www.icpdr.org/main/publications/new-partnership-wetland-restoration|access-date=2021-04-28|website=www.icpdr.org|archive-date=April 28, 2021|archive-url=https://web.archive.org/web/20210428072511/https://www.icpdr.org/main/publications/new-partnership-wetland-restoration|url-status=live}}</ref> Aside from climate benefits, wetland restoration and conservation can help preserve biodiversity, improve [[water quality]], and aid with [[flood control]].<ref name=":5">{{Cite web|title=Fact Sheet: Blue Carbon|url=https://www.american.edu/sis/centers/carbon-removal/fact-sheet-blue-carbon.cfm|access-date=2021-04-28|website=American University|language=en|archive-date=April 28, 2021|archive-url=https://web.archive.org/web/20210428062528/https://www.american.edu/sis/centers/carbon-removal/fact-sheet-blue-carbon.cfm|url-status=live}}</ref>

The plants that makeup wetlands absorb carbon dioxide ({{CO2}}) from the atmosphere and convert it into organic matter. The waterlogged nature of the soil slows down the decomposition of organic material, resulting in the accumulation of carbon-rich sediments,{{Clarify|reason=is not all peat carbon-rich?|date=May 2024}} that ast as a long-term [[carbon sink]].<ref>{{Cite journal |last1=Bansal |first1=Sheel |last2=Creed |first2=Irena F. |last3=Tangen |first3=Brian A. |last4=Bridgham |first4=Scott D. |last5=Desai |first5=Ankur R. |last6=Krauss |first6=Ken W. |last7=Neubauer |first7=Scott C. |last8=Noe |first8=Gregory B. |last9=Rosenberry |first9=Donald O. |last10=Trettin |first10=Carl |last11=Wickland |first11=Kimberly P. |last12=Allen |first12=Scott T. |last13=Arias-Ortiz |first13=Ariane |last14=Armitage |first14=Anna R. |last15=Baldocchi |first15=Dennis |date=2023-11-28 |title=Practical Guide to Measuring Wetland Carbon Pools and Fluxes |journal=Wetlands |language=en |volume=43 |issue=8 |pages=105 |doi=10.1007/s13157-023-01722-2 |issn=1943-6246 |pmc=10684704 |pmid=38037553|bibcode=2023Wetl...43..105B }}</ref><ref name=":11">Harris, L. I., Richardson, K., Bona, K. A., Davidson, S. J., Finkelstein, S. A., Garneau, M., ... & Ray, J. C. (2022). The essential carbon service provided by northern peatlands. Frontiers in Ecology and the Environment, 20(4), 222-230.</ref> Additionally, anaerobic conditions in waterlogged soils hinder the complete breakdown of organic matter, promoting the conversion of carbon into more stable forms.<ref name=":11" />

As with forests, for the sequestration process to succeed, the wetland must remain undisturbed. If it is disturbed the carbon stored in the plants and sediments will be released back into the atmosphere, and the ecosystem will no longer function as a carbon sink.<ref>{{Cite web|title=Carbon Sequestration in Wetlands {{!}} MN Board of Water, Soil Resources|url=http://bwsr.state.mn.us/carbon-sequestration-wetlands|access-date=2021-04-28|website=bwsr.state.mn.us|archive-date=April 28, 2021|archive-url=https://web.archive.org/web/20210428154040/http://bwsr.state.mn.us/carbon-sequestration-wetlands|url-status=live}}</ref> Additionally, some wetlands can release non-{{CO2}} greenhouse gases, such as [[methane]]<ref>{{Cite journal |last1=Bridgham |first1=Scott D. |last2=Cadillo-Quiroz |first2=Hinsby |last3=Keller |first3=Jason K. |last4=Zhuang |first4=Qianlai |date=May 2013 |title=Methane emissions from wetlands: biogeochemical, microbial, and modeling perspectives from local to global scales |url=https://onlinelibrary.wiley.com/doi/10.1111/gcb.12131 |journal=Global Change Biology |language=en |volume=19 |issue=5 |pages=1325–1346 |doi=10.1111/gcb.12131 |pmid=23505021 |bibcode=2013GCBio..19.1325B |s2cid=14228726 |access-date=January 5, 2023 |archive-date=January 20, 2023 |archive-url=https://web.archive.org/web/20230120150913/https://onlinelibrary.wiley.com/doi/10.1111/gcb.12131 |url-status=live |url-access=subscription }}</ref> and [[nitrous oxide]]<ref>{{Cite journal |last1=Thomson |first1=Andrew J. |last2=Giannopoulos |first2=Georgios |last3=Pretty |first3=Jules |last4=Baggs |first4=Elizabeth M. |last5=Richardson |first5=David J. |date=2012-05-05 |title=Biological sources and sinks of nitrous oxide and strategies to mitigate emissions |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |language=en |volume=367 |issue=1593 |pages=1157–1168 |doi=10.1098/rstb.2011.0415 |issn=0962-8436 |pmc=3306631 |pmid=22451101}}</ref> which could offset potential climate benefits. The amounts of carbon sequestered via [[blue carbon]] by wetlands can also be difficult to measure.<ref name=":5" />

Wetland soil is an important [[carbon sink]]; 14.5% of the world's [[soil carbon]] is found in wetlands, while only 5.5% of the world's land is composed of wetlands.<ref>{{Cite web |last=US EPA |first=ORD |date=2017-11-02 |title=Wetlands |url=https://www.epa.gov/report-environment/wetlands |access-date=2020-04-01 |website=US EPA |language=en |archive-date=February 9, 2023 |archive-url=https://web.archive.org/web/20230209115924/https://www.epa.gov/report-environment/wetlands |url-status=live }}</ref> Not only are wetlands a great carbon sink, they have many other benefits like collecting floodwater, filtering out air and water pollutants, and creating a home for numerous birds, fish, insects, and plants.<ref name=":032">{{Cite web |title=Wetlands |url=https://www.nrcs.usda.gov/conservation-basics/natural-resource-concerns/land/wetlands |url-status=live |archive-url=https://web.archive.org/web/20221020012506/https://www.nrcs.usda.gov/wps/portal/nrcs/main/national/water/wetlands/ |archive-date=October 20, 2022 |access-date=1 April 2020 |website=United States Department of Agriculture}}</ref>

Climate change could alter wetland soil carbon storage, changing it from a sink to a source.<ref name=":14">{{Cite journal |last1=Zedler |first1=Joy B. |last2=Kercher |first2=Suzanne |date=2005-11-21 |title=WETLAND RESOURCES: Status, Trends, Ecosystem Services, and Restorability |journal=[[Annual Review of Environment and Resources]] |language=en |volume=30 |issue=1 |pages=39–74 |doi=10.1146/annurev.energy.30.050504.144248 |issn=1543-5938 |doi-access=free}}</ref>{{Obsolete source|reason=This old source is just about wetlands I guess - can we generalize or should sentence be more specific. Or are there newer sources?|date=May 2024}}With rising temperatures comes an increase in [[greenhouse gas]]ses from wetlands especially locations with [[permafrost]]. When this permafrost melts it increases the available oxygen and water in the soil.<ref name=":14" /> Because of this, bacteria in the soil would create large amounts of carbon dioxide and methane to be released into the atmosphere.<ref name=":14" />{{Obsolete source|date=May 2024}}

The link between climate change and wetlands is still not fully known.<ref name=":14" />{{Obsolete source|date=May 2024}}It is also not clear how restored wetlands manage carbon while still being a contributing source of methane. However, preserving these areas would help prevent further release of carbon into the atmosphere.<ref name=":23">{{Cite web |date=August 2017 |title=The Peatland Ecosystem: The Planet's Most Efficient Natural Carbon Sink |url=https://www.worldatlas.com/articles/the-peatland-ecosystem-the-planet-s-most-efficient-natural-carbon-sink.html |access-date=2020-04-03 |website=WorldAtlas |language=en |archive-date=February 9, 2023 |archive-url=https://web.archive.org/web/20230209115925/https://www.worldatlas.com/articles/the-peatland-ecosystem-the-planet-s-most-efficient-natural-carbon-sink.html |url-status=live }}</ref>

==== Peatlands, mires and peat bogs ====
Despite occupying only 3% of the global land area, [[Mire|peatlands]] hold approximately 30% of the carbon in our ecosystem - twice the amount stored in the world's forests.<ref name=":23" /><ref>{{Cite web |last=IUCN UK Peatland Programme |title=About Peatlands |url=https://www.iucn-uk-peatlandprogramme.org/about-peatlands |access-date=2024-09-11 |website=IUCN Peatland Programme |language=en}}</ref> Most peatlands are situated in high latitude areas of the northern hemisphere, with most of their growth occurring since the last [[ice age]],<ref name=":12">{{Cite journal |last1=Loisel |first1=J. |last2=Gallego-Sala |first2=A. V. |last3=Amesbury |first3=M. J. |last4=Magnan |first4=G. |last5=Anshari |first5=G. |last6=Beilman |first6=D. W. |last7=Benavides |first7=J. C. |last8=Blewett |first8=J. |last9=Camill |first9=P. |last10=Charman |first10=D. J. |last11=Chawchai |first11=S. |last12=Hedgpeth |first12=A. |last13=Kleinen |first13=T. |last14=Korhola |first14=A. |last15=Large |first15=D. |date=January 2021 |title=Expert assessment of future vulnerability of the global peatland carbon sink |url=https://www.nature.com/articles/s41558-020-00944-0 |journal=Nature Climate Change |language=en |volume=11 |issue=1 |pages=70–77 |doi=10.1038/s41558-020-00944-0 |bibcode=2021NatCC..11...70L |issn=1758-678X|hdl=10871/123307 |hdl-access=free }}</ref> but they are also found in tropical regions, such as the Amazon and Congo Basin.<ref>{{Cite journal |last1=Ribeiro |first1=Kelly |last2=Pacheco |first2=Felipe S. |last3=Ferreira |first3=José W. |last4=de Sousa-Neto |first4=Eráclito R. |last5=Hastie |first5=Adam |last6=Krieger Filho |first6=Guenther C. |last7=Alvalá |first7=Plínio C. |last8=Forti |first8=Maria C. |last9=Ometto |first9=Jean P. |date=2020-12-04 |title=Tropical peatlands and their contribution to the global carbon cycle and climate change |url=http://dx.doi.org/10.1111/gcb.15408 |journal=Global Change Biology |volume=27 |issue=3 |pages=489–505 |doi=10.1111/gcb.15408 |pmid=33070397 |issn=1354-1013|hdl=20.500.11820/98ca9a07-f1be-4808-aa55-8dc7ebb5072b |hdl-access=free |url-access=subscription }}</ref>

Peatlands grow steadily over thousands of years, accumulating dead plant material – and the carbon contained within it – due to waterlogged conditions which greatly slow rates of decay.<ref name=":12" /> If peatlands are drained, for [[farmland]] or development, the plant material stored within them decomposes rapidly, releasing stored carbon. These degraded peatlands account for 5-10% of global [[Greenhouse gas emissions|carbon emissions]] from human activities.<ref name=":12" /><ref name=":13">{{Cite journal |last1=Leifeld |first1=J. |last2=Menichetti |first2=L. |date=2018-03-14 |title=The underappreciated potential of peatlands in global climate change mitigation strategies |url=http://dx.doi.org/10.1038/s41467-018-03406-6 |journal=Nature Communications |volume=9 |issue=1 |page=1071 |doi=10.1038/s41467-018-03406-6 |pmid=29540695 |issn=2041-1723|pmc=5851997 |bibcode=2018NatCo...9.1071L }}</ref> The loss of one peatland could potentially produce more carbon than 175–500 years of [[methane emissions]].<ref name=":14" />

Peatland protection and restoration are therefore important measures to mitigate carbon emissions, and also provide benefits for biodiversity,<ref name=":13" /> freshwater provision, and flood risk reduction.<ref>{{Cite journal |last1=Strack |first1=Maria |last2=Davidson |first2=Scott J. |last3=Hirano |first3=Takashi |last4=Dunn |first4=Christian |date=2022-06-13 |title=The Potential of Peatlands as Nature-Based Climate Solutions |url=http://dx.doi.org/10.1007/s40641-022-00183-9 |journal=Current Climate Change Reports |volume=8 |issue=3 |pages=71–82 |doi=10.1007/s40641-022-00183-9 |bibcode=2022CCCR....8...71S |issn=2198-6061|url-access=subscription |hdl=10012/19410 |hdl-access=free }}</ref>

=== Agriculture ===
{{See also|Carbon sink#Soils|Greenhouse gas emissions from agriculture}}
[[File:Panicum_virgaturn_heavy_metal_switch_grass_MN_2007.JPG|thumb|''[[Panicum virgatum]]'' switchgrass, valuable in [[biofuel]] production, soil conservation, and carbon sequestration in soils.]]
Compared to natural vegetation, cropland soils are depleted in soil organic carbon (SOC). When soil is converted from natural land or semi-natural land, such as forests, woodlands, grasslands, steppes, and savannas, the SOC content in the soil reduces by about 30–40%.<ref name=":3">{{Cite journal|last1=Poeplau|first1=Christopher|last2=Don|first2=Axel|date=2015-02-01|title=Carbon sequestration in agricultural soils via cultivation of cover crops – A meta-analysis|journal=Agriculture, Ecosystems & Environment|volume=200|issue=Supplement C|pages=33–41|doi=10.1016/j.agee.2014.10.024|bibcode=2015AgEE..200...33P }}</ref> This loss is due to [[harvest]]ing, as plants contain carbon. When [[land use change]]s, the carbon in the soil will either increase or decrease, and this change will continue until the soil reaches a new equilibrium. Deviations from this equilibrium can also be affected by variated{{Clarify|reason=do we mean 'climate change' or if not what does 'variated' mean here?|date=May 2024}} climate.<ref>{{Cite journal|last1=Goglio|first1=Pietro|last2=Smith|first2=Ward N.|last3=Grant|first3=Brian B.|last4=Desjardins|first4=Raymond L.|last5=McConkey|first5=Brian G.|last6=Campbell|first6=Con A.|last7=Nemecek|first7=Thomas|date=2015-10-01|title=Accounting for soil carbon changes in agricultural life cycle assessment (LCA): a review|url=https://www.deepdyve.com/lp/elsevier/accounting-for-soil-carbon-changes-in-agricultural-life-cycle-7fKGPeVfUr|journal=Journal of Cleaner Production|language=en|volume=104|pages=23–39|doi=10.1016/j.jclepro.2015.05.040|bibcode=2015JCPro.104...23G |issn=0959-6526|access-date=November 27, 2017|archive-date=October 30, 2020|archive-url=https://web.archive.org/web/20201030235106/https://www.deepdyve.com/lp/elsevier/accounting-for-soil-carbon-changes-in-agricultural-life-cycle-7fKGPeVfUr|url-status=live|url-access=subscription}}</ref>

The decreasing of SOC content can be counteracted by increasing the carbon input. This can be done with several strategies, e.g. leave harvest residues on the field, use manure as fertilizer, or include perennial crops in the rotation. [[Perennial crop]]s have a larger below-ground biomass fraction, which increases the SOC content.<ref name=":3" />

Perennial crops reduce the need for [[tillage]] and thus help mitigate soil erosion, and may help increase soil organic matter. Globally, soils are estimated to contain >8,580&nbsp;gigatons of organic carbon, about ten times the amount in the atmosphere and much more than in vegetation.<ref>{{cite journal |last=Blakemore |first=R.J. |journal= Soil Systems|volume=2 |issue=4 |page=64 |title=Non-flat Earth Recalibrated for Terrain and Topsoil |date=Nov 2018 |doi=10.3390/soilsystems2040064 |doi-access=free |bibcode=2018SoiSy...2...64B }}</ref>

Researchers have found that rising temperatures can lead to population booms in soil microbes, converting stored carbon into carbon dioxide. In laboratory experiments heating soil, fungi-rich soils released less carbon dioxide than other soils.<ref>{{Cite web|last=Kreier|first=Freda|date=2021-11-30|title=Fungi may be crucial to storing carbon in soil as the Earth warms|url=https://www.sciencenews.org/article/fungi-carbon-storage-soil-earth-warm-climate|url-status=live|access-date=2021-12-01|website=Science News|language=en-US|archive-url=https://web.archive.org/web/20211130153839/https://www.sciencenews.org/article/fungi-carbon-storage-soil-earth-warm-climate |archive-date=November 30, 2021 }}</ref>

Following carbon dioxide (CO<small>2</small>) absorption from the atmosphere, plants deposit organic matter into the soil.<ref name="Sedjo, R. 2012"/> This organic matter, derived from decaying plant material and root systems, is rich in carbon compounds. [[Microorganisms]] in the soil break down this organic matter, and in the process, some of the carbon becomes further stabilized in the soil as [[humus]] - a process known as [[humification]].<ref>Guggenberger, G. (2005). Humification and mineralization in soils. In Microorganisms in soils: roles in genesis and functions (pp. 85-106). Berlin, Heidelberg: Springer Berlin Heidelberg.</ref>

On a global basis, it is estimated that soil contains about 2,500 gigatons of carbon.{{Contradictory inline|reason=contradicts number above of over 8000|date=May 2024}}This is greater than 3-fold the carbon found in the atmosphere and 4-fold of that found in living plants and animals.<ref>{{Cite web |title=Soil carbon: what we've learned so far |url=https://cawood.co.uk/blog/soil-carbon-what-weve-learned-so-far/ |url-status=live |archive-url=https://web.archive.org/web/20230120064406/https://cawood.co.uk/blog/soil-carbon-what-weve-learned-so-far/ |archive-date=January 20, 2023 |access-date=2023-01-20 |website=Cawood |language=en}}</ref> About 70% of the global soil organic carbon in non-permafrost areas is found in the deeper soil within the upper metre and is stabilized by mineral-organic associations.<ref>{{Cite journal |last1=Georgiou |first1=Katerina |last2=Jackson |first2=Robert B. |last3=Vindušková |first3=Olga |last4=Abramoff |first4=Rose Z. |last5=Ahlström |first5=Anders |last6=Feng |first6=Wenting |last7=Harden |first7=Jennifer W. |last8=Pellegrini |first8=Adam F. A. |last9=Polley |first9=H. Wayne |last10=Soong |first10=Jennifer L. |last11=Riley |first11=William J. |last12=Torn |first12=Margaret S. |date=2022-07-01 |title=Global stocks and capacity of mineral-associated soil organic carbon |journal=Nature Communications |language=en |volume=13 |issue=1 |page=3797 |bibcode=2022NatCo..13.3797G |doi=10.1038/s41467-022-31540-9 |issn=2041-1723 |pmc=9249731 |pmid=35778395}}</ref>

==== Carbon farming ====
{{excerpt|Carbon farming|file=no}}

==== Prairies ====
[[Prairie restoration]] is a [[Conservation biology|conservation]] effort to restore [[prairie]] lands that were destroyed due to industrial, [[Agriculture|agricultural]], commercial, or residential development.<ref>{{Cite web |title=Restoration |url=https://www.dnr.state.mn.us/prairie/restore/restoration.html |access-date=2023-04-06 |website=Minnesota Department of Natural Resources |language=en}}</ref> The primary aim is to return areas and ecosystems to their previous state before their depletion.<ref>{{Cite journal |last=Allison |first=Stuart K. |date=2004 |title=What "Do" We Mean When We Talk About Ecological Restoration? |journal=Ecological Restoration |volume=22 |issue=4 |pages=281–286 |doi=10.3368/er.22.4.281 |jstor=43442777 |bibcode=2004EcoRe..22..281A |s2cid=84987493 |issn=1543-4060}}</ref> The mass of SOC able to be stored in these restored plots is typically greater than the previous crop, acting as a more effective carbon sink.<ref>{{Cite journal |last1=Nelson |first1=J. D. J. |last2=Schoenau |first2=J. J. |last3=Malhi |first3=S. S. |date=2008-10-01 |title=Soil organic carbon changes and distribution in cultivated and restored grassland soils in Saskatchewan |journal=Nutrient Cycling in Agroecosystems |language=en |volume=82 |issue=2 |pages=137–148 |doi=10.1007/s10705-008-9175-1 |bibcode=2008NCyAg..82..137N |s2cid=24021984 |issn=1573-0867}}</ref><ref>{{Cite journal |last1=Anderson-Teixeira |first1=Kristina J. |last2=Davis |first2=Sarah C. |last3=Masters |first3=Michael D. |last4=Delucia |first4=Evan H. |date=February 2009 |title=Changes in soil organic carbon under biofuel crops |journal=GCB Bioenergy |language=en |volume=1 |issue=1 |pages=75–96 |doi=10.1111/j.1757-1707.2008.01001.x|s2cid=84636376 |doi-access=free |bibcode=2009GCBBi...1...75A }}</ref>

==== Biochar ====
{{Main|Biochar}}

[[Biochar]] is [[charcoal]] created by [[pyrolysis]] of [[biomass]] waste. The resulting material is added to a [[landfill]] or used as a soil improver to create [[terra preta]].<ref>{{cite journal |author1=Lehmann, J. |author2=Gaunt, J. |author3=Rondon, M. |year=2006 |title=Bio-char sequestration in terrestrial ecosystems – a review |url=http://www.css.cornell.edu/faculty/lehmann/publ/MitAdaptStratGlobChange%2011%2C%20403-427%2C%20Lehmann%2C%202006.pdf |url-status=live |journal=Mitigation and Adaptation Strategies for Global Change |type=Submitted manuscript |volume=11 |issue=2 |pages=403–427 |citeseerx=10.1.1.183.1147 |doi=10.1007/s11027-005-9006-5 |bibcode=2006MASGC..11..403L |archive-url=https://web.archive.org/web/20181025075921/http://www.css.cornell.edu/faculty/lehmann/publ/MitAdaptStratGlobChange%2011,%20403-427,%20Lehmann,%202006.pdf |archive-date=October 25, 2018 |access-date=July 31, 2018 |s2cid=4696862}}</ref><ref>{{cite web |title=International Biochar Initiative &#124; International Biochar Initiative |url=http://www.biochar-international.org/ |url-status=live |archive-url=https://web.archive.org/web/20120505085711/http://www.biochar-international.org/ |archive-date=May 5, 2012 |access-date=May 9, 2010 |publisher=Biochar-international.org}}</ref> Adding biochar may increase the soil-C stock for the long term and so mitigate global warming by offsetting the atmospheric C (up to 9.5 Gigatons C annually).<ref>{{cite journal |last1=Yousaf |first1=Balal |last2=Liu |first2=Guijian |last3=Wang |first3=Ruwei |last4=Abbas |first4=Qumber |last5=Imtiaz |first5=Muhammad |last6=Liu |first6=Ruijia |year=2016 |title=Investigating the biochar effects on C-mineralization and sequestration of carbon in soil compared with conventional amendments using stable isotope (δ13C) approach |journal=GCB Bioenergy |volume=9 |issue=6 |pages=1085–1099 |doi=10.1111/gcbb.12401 |doi-access=free}}</ref> In the soil, the biochar carbon is unavailable for [[oxidation]] to {{chem|CO|2}} and consequential atmospheric release. However concerns have been raised about biochar potentially accelerating release of the carbon already present in the soil.<ref>{{Cite journal |last1=Wardle |first1=David A. |last2=Nilsson |first2=Marie-Charlotte |last3=Zackrisson |first3=Olle |date=2008-05-02 |title=Fire-Derived Charcoal Causes Loss of Forest Humus |url=https://www.science.org/doi/10.1126/science.1154960 |url-status=live |journal=Science |language=en |volume=320 |issue=5876 |page=629 |bibcode=2008Sci...320..629W |doi=10.1126/science.1154960 |issn=0036-8075 |pmid=18451294 |archive-url=https://web.archive.org/web/20210808091854/https://science.sciencemag.org/content/320/5876/629 |archive-date=August 8, 2021 |access-date=August 8, 2021 |s2cid=22192832|url-access=subscription }}</ref>{{Update inline|date=May 2024}}

[[Terra preta]], an [[human impact on the environment|anthropogenic]], high-carbon soil, is also being investigated as a sequestration mechanism. By [[Pyrolysis|pyrolysing]] biomass, about half of its carbon can be reduced to [[charcoal]], which can persist in the soil for centuries, and makes a useful soil amendment, especially in tropical soils (''biochar'' or ''agrichar'').<ref>{{cite web |author=Johannes Lehmann |title=Biochar: the new frontier |url=http://www.css.cornell.edu/faculty/lehmann/biochar/Biochar_home.htm |archive-url=https://web.archive.org/web/20080618231424/http://www.css.cornell.edu/faculty/lehmann/biochar/Biochar_home.htm |archive-date=18 June 2008 |access-date=8 July 2008}}</ref><ref name="abc.net.au/catalyst/s2012892">{{cite news |last=Horstman |first=Mark |date=23 September 2007 |title=Agrichar – A solution to global warming? |work=ABC TV Science: Catalyst |publisher=Australian Broadcasting Corporation |url=http://www.abc.net.au/catalyst/stories/s2012892.htm |access-date=8 July 2008 |archive-date=April 30, 2019 |archive-url=https://web.archive.org/web/20190430061147/http://www.abc.net.au/catalyst/stories/s2012892.htm |url-status=live }}</ref>

=== Burial of biomass ===
[[Image:Charcoal2.jpg|right|thumb|[[Biochar]] can be landfilled, used as a [[soil improver]] or burned using [[carbon capture and storage]].]]Burying biomass (such as trees) directly mimics the natural processes that created [[fossil fuels]].<ref>{{cite journal |last=Lovett |first=Richard |date=May 3, 2008 |title=Burying biomass to fight climate change |url=https://www.newscientist.com/article/mg19826542.400 |url-status=live |journal=New Scientist |issue=2654 |url-access=subscription |archive-url=https://web.archive.org/web/20090803044239/http://www.newscientist.com/article/mg19826542.400 |archive-date=August 3, 2009 |access-date=May 9, 2010}}</ref> The global potential for carbon sequestration using wood burial is estimated to be 10 ± 5 GtC/yr and largest rates in tropical forests (4.2 GtC/yr), followed by temperate (3.7 GtC/yr) and boreal forests (2.1 GtC/yr).<ref name=":10" /> In 2008, [[Ning Zeng]] of the University of Maryland estimated 65 GtC{{Update inline|date=May 2024|reason=any update?}} lying on the floor of the world's forests as coarse woody material which could be buried and costs for wood burial carbon sequestration run at US$50/tC which is much lower than carbon capture from e.g. power plant emissions.<ref name=":10" /> CO<sub>2</sub> fixation into woody biomass is a natural process carried out through [[photosynthesis]]. This is a nature-based solution and methods being trialled include the use of "wood vaults" to store the wood-containing carbon under oxygen-free conditions.<ref>{{Cite web |title=A stealth effort to bury wood for carbon removal has just raised millions |url=https://www.technologyreview.com/2022/12/15/1065016/a-stealth-effort-to-bury-wood-for-carbon-removal-has-just-raised-millions/ |access-date=2024-05-05 |website=MIT Technology Review |language=en}}</ref>

In 2022, a certification organization published methodologies for biomass burial.<ref>{{Cite web |title=A deceptively simple technology for carbon removal {{!}} GreenBiz |url=https://www.greenbiz.com/article/deceptively-simple-technology-carbon-removal |access-date=2023-09-19 |website=www.greenbiz.com |date=March 13, 2023 |language=en}}</ref> Other biomass storage proposals have included the burial of biomass deep underwater, including at the bottom of the [[Black Sea]].<ref>{{Cite web |date=2023-05-11 |title=Can we fight climate change by sinking carbon into the sea? |url=https://www.canarymedia.com/articles/carbon-capture/can-we-fight-climate-change-by-sinking-carbon-into-the-sea |access-date=2023-09-19 |website=Canary Media |language=en}}</ref>

== Geological carbon sequestration ==

=== Underground storage in suitable geologic formations ===
{{Main|Carbon capture and storage|Direct air capture}}
Geological sequestration refers to the storage of CO<sub>2</sub> underground in depleted oil and gas reservoirs, saline formations, or deep, coal beds unsuitable for mining.<ref>CO2 wettability of seal and reservoir rocks and the implications for carbon geo-sequestration - Iglauer - 2015 - Water Resources Research - Wiley Online Library</ref>

Once CO<sub>2</sub> is captured from a point source, such as a cement factory,<ref>{{Cite web|last=Morgan|first=Sam|date=2019-09-06|title=Norway's carbon storage project boosted by European industry|url=https://www.euractiv.com/section/energy-environment/news/norways-carbon-storage-project-boosted-by-european-industry/|access-date=2020-06-27|website=www.euractiv.com|language=en-GB|archive-date=June 27, 2020|archive-url=https://web.archive.org/web/20200627100100/https://www.euractiv.com/section/energy-environment/news/norways-carbon-storage-project-boosted-by-european-industry/|url-status=live}}</ref> it can be compressed to ≈100 bar into a [[supercritical fluid]]. In [[supercritical carbon dioxide|this form]], the CO<sub>2</sub> could be transported via pipeline to the place of storage. The CO<sub>2</sub> could then be injected deep underground, typically around {{Convert|1|km|abbr=on|sigfig=1}}, where it would be stable for hundreds to millions of years.<ref name=":0">{{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=June 11, 2020 |access-date=September 10, 2019 |s2cid=27994746}}</ref> Under these storage conditions, the density of [[Supercritical carbon dioxide|supercritical]] CO<sub>2</sub> is 600 to 800&nbsp;kg/m<sup>3</sup>.<ref name=":1">{{Cite journal|last1=Aydin|first1=Gokhan|last2=Karakurt|first2=Izzet|last3=Aydiner|first3=Kerim|date=2010-09-01|title=Evaluation of geologic storage options of CO<sub>2</sub>: Applicability, cost, storage capacity and safety|journal=Energy Policy|series=Special Section on Carbon Emissions and Carbon Management in Cities with Regular Papers|volume=38|issue=9|pages=5072–5080|doi=10.1016/j.enpol.2010.04.035|bibcode=2010EnPol..38.5072A }}</ref>

The important parameters in determining a good site for carbon storage are: rock porosity, rock permeability, absence of faults, and geometry of rock layers. The medium in which the CO<sub>2</sub> is to be stored ideally has a high porosity and permeability, such as sandstone or limestone. Sandstone can have a permeability ranging from 1 to 10<sup>−5</sup> [[Darcy (unit)|Darcy]], with a porosity as high as ≈30%. The porous rock must be capped by a layer of low permeability, which function as a seal, or caprock, for the CO<sub>2</sub>. Shale is an example of a very good caprock, with a permeability of 10<sup>−5</sup> to 10<sup>−9</sup> Darcy. Once injected, the CO<sub>2</sub> plume will rise via buoyant forces, since it is less dense than its surroundings. Once it encounters a caprock, it will spread laterally until it encounters a gap. If there are fault planes near the injection zone, there is a possibility the CO<sub>2</sub> could migrate along the fault to the surface, leaking into the atmosphere, which would be potentially dangerous to life in the surrounding area. Another risk related to carbon sequestration is induced seismicity. If the injection of CO<sub>2</sub> creates pressures underground that are too high, the formation will fracture, potentially causing an earthquake.<ref name=":2">Smit, Berend; Reimer, Jeffrey A.; Oldenburg, Curtis M.; Bourg, Ian C. (2014). ''Introduction to Carbon Capture and Sequestration''. London: Imperial College Press. {{ISBN|978-1-78326-328-8}}.</ref>

[[Trapping mechanisms for carbon geosequestration#Structural trapping|Structural trapping]] is considered the principal storage mechanism, impermeable or low permeability rocks such as [[mudstone]], [[anhydrite]], [[halite]], or tight carbonates{{Clarify|reason=tight?|date=May 2024}} act as a barrier to the upward buoyant migration of CO2, resulting in the retention of CO2 within a storage formation.<ref>{{Cite journal |last1=Iglauer |first1=Stefan |last2=Pentland |first2=C. H. |last3=Busch |first3=A. |date=January 2015 |title=CO<sub>2</sub> wettability of seal and reservoir rocks and the implications for carbon geo-sequestration |journal=Water Resources Research |language=en |volume=51 |issue=1 |pages=729–774 |doi=10.1002/2014WR015553|doi-access=free |bibcode=2015WRR....51..729I |hdl=20.500.11937/20032 |hdl-access=free }}</ref> While trapped in a rock formation, CO<sub>2</sub> can be in the supercritical fluid phase or dissolve in groundwater/brine. It can also react with minerals in the geologic formation to become carbonates.

=== Mineral sequestration ===
[[Trapping mechanisms for carbon geosequestration#Mineral trapping|Mineral sequestration]] aims to trap carbon in the form of solid [[carbonate]] salts. This process occurs slowly in nature and is responsible for the deposition and accumulation of [[limestone]] over geologic time. [[Carbonic acid]] in groundwater slowly reacts with complex [[silicate]]s to dissolve [[calcium]], [[magnesium]], [[alkali]]s and [[silica]] and leave a residue of [[clay minerals]]. The dissolved calcium and magnesium react with [[bicarbonate]] to precipitate calcium and magnesium carbonates, a process that organisms use to make shells. When the organisms die, their shells are deposited as sediment and eventually turn into limestone. Limestones have accumulated over billions of years of geologic time and contain much of Earth's carbon. Ongoing research aims to speed up similar reactions involving alkali carbonates.<ref>{{cite web |date=27 July 2007 |title=Carbon-capture Technology To Help UK Tackle Global Warming |url=https://www.sciencedaily.com/releases/2007/07/070727091001.htm |work=ScienceDaily |access-date=February 3, 2023 |archive-date=June 3, 2016 |archive-url=https://web.archive.org/web/20160603022452/https://www.sciencedaily.com/releases/2007/07/070727091001.htm |url-status=live }}</ref>

[[Zeolitic imidazolate framework]]s (ZIFs) are [[metal–organic framework]]s similar to [[zeolite]]s. Because of their porosity, chemical stability and thermal resistance, ZIFs are being examined for their capacity to capture carbon dioxide.<ref>{{Cite journal |last1=Phan |first1=Anh |last2=Doonan |first2=Christian J. |last3=Uribe-Romo |first3=Fernando J. |last4=Knobler |first4=Carolyn B. |last5=O'Keeffe |first5=Michael |last6=Yaghi |first6=Omar M. |date=2010-01-19 |title=Synthesis, Structure, and Carbon Dioxide Capture Properties of Zeolitic Imidazolate Frameworks |url=https://pubs.acs.org/doi/10.1021/ar900116g |journal=Accounts of Chemical Research |language=en |volume=43 |issue=1 |pages=58–67 |doi=10.1021/ar900116g |pmid=19877580 |issn=0001-4842 |access-date=February 22, 2023 |archive-date=February 22, 2023 |archive-url=https://web.archive.org/web/20230222234059/https://pubs.acs.org/doi/10.1021/ar900116g |url-status=live |url-access=subscription }}</ref>{{Update inline|date=May 2024|reason=what was result?}}

==== Mineral carbonation ====
{{update section|date=June 2019}}

CO<sub>2</sub> [[exothermic]]ally reacts with metal oxides, producing stable carbonates (e.g. [[calcite]], [[magnesite]]). This process (CO<sub>2</sub>-to-stone) occurs naturally over periods of years and is responsible for much surface [[limestone]]. [[Olivine]] is one such metal oxide.<ref name="Olivine weathering2">{{cite web |last=Schuiling |first=Olaf |title=Olaf Schuiling proposes olivine rock grinding |url=http://www.gather.com/viewArticle.action?articleId=281474979949059 |archive-url=https://archive.today/20130411003510/http://www.gather.com/viewArticle.action?articleId=281474979949059 |archive-date=11 April 2013 |access-date=23 December 2011}}</ref>{{self-published inline|date=March 2013}} Rocks rich in metal oxides that react with CO<sub>2</sub>, such as [[Magnesium oxide|MgO]] and [[Calcium oxide|CaO]] as contained in [[basalt]]s, have been proven as a viable means to achieve carbon-dioxide mineral storage.<ref>{{cite journal |last1=Snæbjörnsdóttir |first1=Sandra Ó. |last2=Sigfússon |first2=Bergur |last3=Marieni |first3=Chiara |last4=Goldberg |first4=David |last5=Gislason |first5=Sigurður R. |last6=Oelkers |first6=Eric H. |date=2020 |title=Carbon dioxide storage through mineral carbonation |url=https://hal.archives-ouvertes.fr/hal-03384454/file/Oelkers_%2520Mineral%2520Storage%2520of%2520Carbon%2520Dioxide_AAM-2.pdf |journal=Nature Reviews Earth & Environment |volume=1 |issue=2 |pages=90–102 |bibcode=2020NRvEE...1...90S |doi=10.1038/s43017-019-0011-8 |s2cid=210716072 |access-date=February 6, 2023 |archive-date=October 4, 2022 |archive-url=https://web.archive.org/web/20221004235808/https://hal.archives-ouvertes.fr/hal-03384454/file/Oelkers_%2520Mineral%2520Storage%2520of%2520Carbon%2520Dioxide_AAM-2.pdf |url-status=live }}</ref><ref>{{cite journal |last1=McGrail |first1=B. Peter |last2=Spane |first2=F.A. |last3=Amonette |first3=J.E. |last4=Thompson |first4=C.R. |display-authors=1 |date=2014 |title=Injection and Monitoring at the Wallula Basalt Pilot Project |journal=Energy Procedia |volume=63 |pages=2939–2948 |doi=10.1016/j.egypro.2014.11.316|doi-access=free |bibcode=2014EnPro..63.2939M }}</ref> The reaction rate can in principle be accelerated with a [[catalyst]]<ref>{{cite journal |last1=Bhaduri |first1=Gaurav A. |last2=Šiller |first2=Lidija |date=2013 |title=Nickel nanoparticles catalyse reversible hydration of CO<sub>2</sub> for mineralization carbon capture and storage |journal=Catalysis Science & Technology |volume=3 |issue=5 |page=1234 |doi=10.1039/C3CY20791A}}</ref> or by increasing pressures, or by mineral pre-treatment, although this method can require additional energy. 

[[Ultramafic rock|Ultramafic]] [[mine tailings]] are a readily available source of fine-grained metal oxides that could serve this purpose.<ref>{{cite journal |last1=Wilson |first1=Siobhan A. |last2=Dipple |first2=Gregory M. |last3=Power |first3=Ian M. |last4=Thom |first4=James M. |last5=Anderson |first5=Robert G. |last6=Raudsepp |first6=Mati |last7=Gabites |first7=Janet E. |last8=Southam |first8=Gordon |year=2009 |title=CO<sub>2</sub> Fixation within Mine Wastes of Ultramafic-Hosted Ore Deposits: Examples from the Clinton Creek and Cassiar Chrysotile Deposits, Canada |journal=Economic Geology |volume=104 |pages=95–112 |doi=10.2113/gsecongeo.104.1.95}}</ref> Accelerating passive CO<sub>2</sub> sequestration via mineral carbonation may be achieved through microbial processes that enhance mineral dissolution and carbonate precipitation.<ref>{{cite journal |last1=Power |first1=Ian M. |last2=Dipple |first2=Gregory M. |last3=Southam |first3=Gordon |year=2010 |title=Bioleaching of Ultramafic Tailings by ''Acidithiobacillus'' spp. For CO<sub>2</sub> Sequestration |journal=Environmental Science & Technology |volume=44 |issue=1 |pages=456–62 |bibcode=2010EnST...44..456P |doi=10.1021/es900986n |pmid=19950896}}</ref><ref>{{cite journal |last1=Power |first1=Ian M |last2=Wilson |first2=Siobhan A |last3=Thom |first3=James M |last4=Dipple |first4=Gregory M |last5=Southam |first5=Gordon |year=2007 |title=Biologically induced mineralization of dypingite by cyanobacteria from an alkaline wetland near Atlin, British Columbia, Canada |journal=Geochemical Transactions |volume=8 |issue=1 |page=13 |doi=10.1186/1467-4866-8-13 |pmc=2213640 |pmid=18053262|bibcode=2007GeoTr...8...13P |doi-access=free }}</ref><ref>{{cite journal |last1=Power |first1=Ian M. |last2=Wilson |first2=Siobhan A. |last3=Small |first3=Darcy P. |last4=Dipple |first4=Gregory M. |last5=Wan |first5=Wankei |last6=Southam |first6=Gordon |year=2011 |title=Microbially Mediated Mineral Carbonation: Roles of Phototrophy and Heterotrophy |journal=Environmental Science & Technology |volume=45 |issue=20 |pages=9061–8 |bibcode=2011EnST...45.9061P |doi=10.1021/es201648g |pmid=21879741}}</ref>

Carbon, in the form of {{chem|CO|2}} can be removed from the atmosphere by chemical processes, and stored in stable [[carbonate mineral]] forms. This process ({{chem|CO|2}}-to-stone) is known as "carbon sequestration by mineral [[carbonation]]" or mineral sequestration. The process involves reacting carbon dioxide with abundantly available metal oxides – either [[magnesium oxide]] (MgO) or [[calcium oxide]] (CaO) – to form stable carbonates. These reactions are [[exothermic]] and occur naturally (e.g., the [[weathering]] of rock over [[geologic time]] periods).<ref name="herzog" /><ref name="goldberg">{{Cite web|title=Conference Proceedings|url=http://www.netl.doe.gov/events/conference-proceedings|access-date=2021-12-30|website=netl.doe.gov|language=en|archive-date=February 17, 2017|archive-url=https://web.archive.org/web/20170217195605/https://www.netl.doe.gov/publications/proceedings/10/co2capture/presentations/thursday/Matt}}</ref>

:CaO + {{chem|CO|2}} → {{chem|CaCO|3}}

:MgO + {{chem|CO|2}} → {{chem|MgCO|3}}

Calcium and magnesium are found in nature typically as calcium and magnesium [[silicate minerals|silicates]] (such as [[forsterite]] and [[serpentinite]]) and not as binary oxides. For forsterite and serpentine the reactions are:

:{{chem|Mg|2|SiO|4}} + 2 {{chem|CO|2}} → 2 {{chem|MgCO|3}} + {{chem|SiO|2}}

:{{chem|Mg|3|Si|2|O|5|(OH)|4}}+ 3 {{chem|CO|2}} → 3 {{chem|MgCO|3}} + 2 {{chem|SiO|2}} + 2 {{chem|H|2|O}}

These reactions are slightly more favorable at low temperatures.<ref name="herzog">{{cite web |url= http://sequestration.mit.edu/pdf/carbonates.pdf |title= Carbon Sequestration via Mineral Carbonation: Overview and Assessment |last= Herzog |first= Howard |date= March 14, 2002 |website= Massachusetts Institute of Technology |access-date= March 5, 2009 |archive-date= May 17, 2008 |archive-url= https://web.archive.org/web/20080517134455/http://sequestration.mit.edu/pdf/carbonates.pdf |url-status= live }}</ref> This process occurs naturally over geologic time frames and is responsible for much of the Earth's surface [[limestone]]. The reaction rate can be made faster however, by reacting at higher temperatures and/or pressures, although this method requires some additional energy. Alternatively, the mineral could be milled to increase its surface area, and exposed to water and constant abrasion to remove the inert silica as could be achieved naturally by dumping olivine in the high energy surf of beaches.<ref>{{cite journal|journal=Earth System Dynamics Discussions|pages=551–568|volume=2|issue=2|date=2011|author1=Schuiling, R.D.|author2=Boer, de P.L.|title=Rolling stones; fast weathering of olivine in shallow seas for cost-effective CO<sub>2</sub> capture and mitigation of global warming and ocean acidification|url=http://www.earth-syst-dynam-discuss.net/2/551/2011/esdd-2-551-2011.pdf|doi=10.5194/esdd-2-551-2011|bibcode=2011ESDD....2..551S|hdl=1874/251745|access-date=December 19, 2016|archive-date=July 22, 2016|archive-url=https://web.archive.org/web/20160722083731/http://www.earth-syst-dynam-discuss.net/2/551/2011/esdd-2-551-2011.pdf|url-status=live |doi-access=free }}</ref>

When {{chem|CO|2}} is dissolved in water and injected into hot basaltic rocks underground it has been shown that the {{chem|CO|2}} reacts with the basalt to form solid carbonate minerals.<ref>{{Cite news|url=https://www.newscientist.com/article/2093272-co2-injected-deep-underground-turns-to-rock-and-stays-there/|title=CO<sub>2</sub> injected deep underground turns to rock – and stays there|last=Le Page|first=Michael|date=2016-06-19|work=New Scientist|access-date=2017-12-04|language=en-US|archive-date=December 5, 2017|archive-url=https://web.archive.org/web/20171205093039/https://www.newscientist.com/article/2093272-co2-injected-deep-underground-turns-to-rock-and-stays-there/|url-status=live}}</ref> A test plant in Iceland started up in October 2017, extracting up to 50 tons of CO<sub>2</sub> a year from the atmosphere and storing it underground in basaltic rock.<ref>{{Cite news|url=http://www.powermag.com/test-of-carbon-capture-technology-underway-at-iceland-geothermal-plant/?mypower|title=Test of Carbon Capture Technology Underway at Iceland Geothermal Plant|last=Proctor|first=Darrell|date=2017-12-01|work=POWER Magazine|access-date=2017-12-04|language=en-US|archive-date=December 5, 2017|archive-url=https://web.archive.org/web/20171205043332/http://www.powermag.com/test-of-carbon-capture-technology-underway-at-iceland-geothermal-plant/?mypower|url-status=live}}</ref>{{Update inline|date=May 2024}}

== Sequestration in oceans ==
Several start-ups are trying to do this at scale.<ref>{{Cite web |title=The controversial machine sending CO2 to the ocean and making hydrogen |url=https://www.bbc.com/future/article/20241217-the-controversial-machine-using-marine-carbon-removal-to-store-co2-in-the-ocean |access-date=2024-12-21 |website=www.bbc.com |date=December 18, 2024 |language=en-GB}}</ref>

=== Marine carbon pumps ===
{{further|Solubility pump|Biological pump}}
[[File:Oceanic Food Web.jpg|thumb|upright=2|{{center|The [[pelagic food web]], showing the central involvement of [[marine microorganism]]s in how the ocean imports carbon and then exports it back to the atmosphere and ocean floor}}]]
The ocean sequesters carbon through diverse processes.<ref>{{Cite web |date=2016-12-03 |title=The Ocean, a carbon sink - Ocean & Climate Platform |url=https://ocean-climate.org/en/awareness/the-ocean-a-carbon-sink/ |access-date=2024-05-21 |language=en-US}}</ref> The [[solubility pump]] moves carbon dioxide from the atmosphere into the surface ocean where it reacts with water molecules to form carbonic acid. The solubility of carbon dioxide increases with decreasing water temperatures. [[Thermohaline circulation]] moves dissolved carbon dioxide to cooler waters where it is more soluble, increasing carbon concentrations in the ocean interior. The [[biological pump]] moves dissolved carbon dioxide from the surface ocean to the ocean's interior through the conversion of inorganic carbon to organic carbon by photosynthesis. Organic matter that survives respiration and remineralization can be transported through sinking particles and organism migration to the deep ocean.{{citation needed|date=July 2023}}

The low temperatures, high pressure, and reduced oxygen levels in the deep sea slow down [[decomposition]] processes, preventing the rapid release of carbon back into the atmosphere and acting as a long-term storage reservoir.<ref>Heinze, C., Meyer, S., Goris, N., Anderson, L., Steinfeldt, R., Chang, N., ... & Bakker, D. C. (2015). The ocean carbon sink–impacts, vulnerabilities and challenges. Earth System Dynamics, 6(1), 327-358.</ref>

===Vegetated coastal ecosystems===
{{excerpt|Blue carbon|paragraphs=1|file=no}}

=== Seaweed farming and algae ===
{{Further|Seaweed farming#Climate change mitigation}}
[[File:Kelp_Forest_(12801115735).jpg|thumb|{{center|[[Kelp forest]]}}]]
[[File:Seagrass_at_Rapid_Bay_Jetty_P1262907.JPG|thumb|{{center|[[Seagrass meadow]]}}]]
[[Seaweed]] grows in shallow and coastal areas, and captures significant amounts of carbon that can be transported to the deep ocean by oceanic mechanisms; seaweed reaching the deep ocean sequester carbon and prevent it from exchanging with the atmosphere over millennia.<ref name="nature.com">{{Cite journal |last1=Ortega |first1=Alejandra |last2=Geraldi |first2=N.R. |last3=Alam |first3=I. |last4=Kamau |first4=A.A. |last5=Acinas |first5=S. |last6=Logares |first6=R. |last7=Gasol |first7=J. |last8=Massana |first8=R. |last9=Krause-Jensen |first9=D. |last10=Duarte |first10=C. |year=2019 |title=Important contribution of macroalgae to oceanic carbon sequestration |url=https://www.nature.com/articles/s41561%20019%200421%208 |url-status=live |journal=Nature Geoscience |language=en |volume=12 |issue=9 |pages=748–754 |bibcode=2019NatGe..12..748O |doi=10.1038/s41561-019-0421-8 |archive-url=https://web.archive.org/web/20210506142307/https://www.nature.com/articles/s41561%20019%200421%208 |archive-date=May 6, 2021 |access-date=July 18, 2020 |hdl-access=free |hdl=10754/656768 |s2cid=199448971|url-access=subscription }}</ref> Growing seaweed offshore with the purpose of sinking the seaweed in the depths of the sea to sequester carbon has been suggested.<ref>{{Cite web |last=Temple |first=James |date=2021-09-19 |title=Companies hoping to grow carbon-sucking kelp may be rushing ahead of the science |url=https://www.technologyreview.com/2021/09/19/1035889/kelp-carbon-removal-seaweed-sinking-climate-change/ |url-status=live |archive-url=https://web.archive.org/web/20210919212025/https://www.technologyreview.com/2021/09/19/1035889/kelp-carbon-removal-seaweed-sinking-climate-change/ |archive-date=September 19, 2021 |access-date=2021-11-25 |website=MIT Technology Review |language=en}}</ref> In addition, seaweed grows very fast and can theoretically be harvested and processed to generate [[biomethane]], via [[anaerobic digestion]] to generate electricity, via [[Cogeneration|cogeneration/CHP]] or as a replacement for [[natural gas]]. One study suggested that if seaweed farms covered 9% of the ocean they could produce enough biomethane to supply Earth's equivalent demand for fossil fuel energy, remove 53 [[gigatonnes]] of {{CO2|link=yes}} per year from the atmosphere and sustainably produce 200&nbsp;kg per year of fish, per person, for 10&nbsp;billion people.<ref>{{cite news |last1=Flannery |first1=Tim |author1-link=Tim Flannery |date=November 20, 2015 |title=Climate crisis: seaweed, coffee and cement could save the planet |work=[[The Guardian]] |url=https://www.theguardian.com/books/2015/nov/20/climate-crisis-future-brighter-tim-flannery |url-status=live |access-date=November 25, 2015 |archive-url=https://web.archive.org/web/20151124223820/http://www.theguardian.com/books/2015/nov/20/climate-crisis-future-brighter-tim-flannery |archive-date=November 24, 2015}}</ref>{{Obsolete source|date=May 2024}}Ideal species for such farming and conversion include ''[[Laminaria digitata]]'', ''[[Fucus serratus]]'' and ''[[Saccharina latissima]]''.<ref>{{cite journal |last1=Vanegasa |first1=C. H. |last2=Bartletta |first2=J. |date=February 11, 2013 |title=Green energy from marine algae: biogas production and composition from the anaerobic digestion of Irish seaweed species |journal=Environmental Technology |volume=34 |issue=15 |pages=2277–2283 |doi=10.1080/09593330.2013.765922 |pmid=24350482 |bibcode=2013EnvTe..34.2277V |s2cid=30863033}}<!--|access-date=November 25, 2015--></ref>

Both [[macroalgae]] and [[microalgae]] are being investigated as possible means of carbon sequestration.<ref name="Chung2011">{{cite journal |last1=Chung |first1=I. K. |last2=Beardall |first2=J. |last3=Mehta |first3=S. |last4=Sahoo |first4=D. |last5=Stojkovic |first5=S. |year=2011 |title=Using marine macroalgae for carbon sequestration: a critical appraisal |journal=Journal of Applied Phycology |volume=23 |issue=5 |pages=877–886 |doi=10.1007/s10811-010-9604-9 |bibcode=2011JAPco..23..877C |s2cid=45039472}}</ref><ref name=":03">{{Cite journal |last1=Duarte |first1=Carlos M. |last2=Wu |first2=Jiaping |last3=Xiao |first3=Xi |last4=Bruhn |first4=Annette |last5=Krause-Jensen |first5=Dorte |date=2017 |title=Can Seaweed Farming Play a Role in Climate Change Mitigation and Adaptation? |journal=Frontiers in Marine Science |volume=4 |page=100 |doi=10.3389/fmars.2017.00100 |issn=2296-7745 |doi-access=free|bibcode=2017FrMaS...4..100D |hdl=10754/623247 |hdl-access=free }}</ref> Marine [[phytoplankton]] perform half of the global photosynthetic CO<sub>2</sub> fixation (net global primary production of ~50&nbsp;Pg C per year) and half of the oxygen production despite amounting to only ~1% of global plant biomass.<ref name="Behrenfeld2014">{{cite journal |last1=Behrenfeld |first1=Michael J. |year=2014 |title=Climate-mediated dance of the plankton |journal=Nature Climate Change |volume=4 |issue=10 |pages=880–887 |bibcode=2014NatCC...4..880B |doi=10.1038/nclimate2349}}</ref>

Because [[algae]] lack the complex [[lignin]] associated with [[terrestrial plant]]s, the carbon in algae is released into the atmosphere more rapidly than carbon captured on land.<ref name="Chung2011" /><ref name="Mcleod2011">{{cite journal |last1=Mcleod |first1=E. |last2=Chmura |first2=G. L. |last3=Bouillon |first3=S. |last4=Salm |first4=R. |last5=Björk |first5=M. |last6=Duarte |first6=C. M. |last7=Silliman |first7=B. R. |year=2011 |title=A blueprint for blue carbon: toward an improved understanding of the role of vegetated coastal habitats in sequestering CO<sub>2</sub> |url=https://espace.library.uq.edu.au/view/UQ:251863/UQ251863_OA.pdf |url-status=live |journal=Frontiers in Ecology and the Environment |volume=9 |issue=10 |pages=552–560 |doi=10.1890/110004 |archive-url=https://web.archive.org/web/20161220195926/http://espace.library.uq.edu.au/view/UQ:251863/UQ251863_OA.pdf |archive-date=2016-12-20 |access-date=2019-09-30 |doi-access=free|bibcode=2011FrEE....9..552M }}</ref> Algae have been proposed as a short-term storage pool of carbon that can be used as a [[feedstock]] for the production of various [[biogenic]] fuels.<ref>{{Citation |last=Alam |first=Sahib |title=Chapter 9 - Algae: An emerging feedstock for biofuels production |date=2022-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780323904766000030 |work=Algal Biotechnology |pages=165–185 |editor-last=Ahmad |editor-first=Ashfaq |publisher=Elsevier |language=en |doi=10.1016/b978-0-323-90476-6.00003-0 |isbn=978-0-323-90476-6 |access-date=2023-02-26 |editor2-last=Banat |editor2-first=Fawzi |editor3-last=Taher |editor3-first=Hanifa |archive-date=February 26, 2023 |archive-url=https://web.archive.org/web/20230226231151/https://www.sciencedirect.com/science/article/pii/B9780323904766000030 |url-status=live |url-access=subscription }}</ref>

[[File:WomenWorking SeaweedZanzibar 2.jpg|thumb|Women working with seaweed]]
Large-scale seaweed farming could sequester significant amounts of carbon.<ref name=":152">{{Cite journal |last1=Duarte |first1=Carlos M. |last2=Wu |first2=Jiaping |last3=Xiao |first3=Xi |last4=Bruhn |first4=Annette |last5=Krause-Jensen |first5=Dorte |date=2017 |title=Can Seaweed Farming Play a Role in Climate Change Mitigation and Adaptation? |journal=Frontiers in Marine Science |language=en |volume=4 |doi=10.3389/fmars.2017.00100 |issn=2296-7745 |doi-access=free|bibcode=2017FrMaS...4..100D |hdl=10754/623247 |hdl-access=free }}</ref> Wild seaweed will sequester large amount of carbon through dissolved particles of organic matter being transported to deep ocean seafloors where it will become buried and remain for long periods of time.<ref name=":73">{{Cite journal |last1=Froehlich |first1=Halley E. |last2=Afflerbach |first2=Jamie C. |last3=Frazier |first3=Melanie |last4=Halpern |first4=Benjamin S. |date=2019-09-23 |title=Blue Growth Potential to Mitigate Climate Change through Seaweed Offsetting |journal=Current Biology |language=en |volume=29 |issue=18 |pages=3087–3093.e3 |doi=10.1016/j.cub.2019.07.041 |issn=0960-9822 |pmid=31474532 |doi-access=free|bibcode=2019CBio...29E3087F }}</ref> With respect to carbon farming, the potential growth of seaweed for carbon farming would see the harvested seaweed transported to the deep ocean for long-term burial.<ref name=":73" /> Seaweed farming occurs mostly in the Asian Pacific coastal areas where it has been a rapidly increasing market.<ref name=":73" /> The IPCC [[Special Report on the Ocean and Cryosphere in a Changing Climate]] recommends "further research attention" on seaweed farming as a mitigation tactic.<ref name=":242">{{Cite book |last1=Bindoff |first1=N. L. |title=IPCC Special Report on the Ocean and Cryosphere in a Changing Climate |last2=Cheung |first2=W. W. L. |last3=Kairo |first3=J. G. |last4=Arístegui |first4=J. |last5=Guinder |first5=V. A. |last6=Hallberg |first6=R. |last7=Hilmi |first7=N. J. M. |last8=Jiao |first8=N. |last9=Karim |first9=Md S. |year=2019 |pages=447–587 |chapter=Chapter 5: Changing Ocean, Marine Ecosystems, and Dependent Communities |ref={{harvid|IPCC SROCC Ch5|2019}} <!-- ipcc:20200202 --> |display-authors=4 |chapter-url=https://www.ipcc.ch/site/assets/uploads/sites/3/2019/11/09_SROCC_Ch05_FINAL.pdf |first15=A. |last13=Rinkevich |last10=Levin |first11=S. |last11=O'Donoghue |first13=B. |last15=Tagliabue |first12=S. R. |last14=Suga |first16=P. |last16=Williamson |first10=L. |last12=Purca Cuicapusa |first14=T. |access-date=February 9, 2023 |archive-date=May 28, 2020 |archive-url=https://web.archive.org/web/20200528000740/https://www.ipcc.ch/site/assets/uploads/sites/3/2019/11/09_SROCC_Ch05_FINAL.pdf |url-status=live }}</ref>

=== Ocean fertilization ===
[[Image:Phytoplankton SoAtlantic 20060215.jpg|thumb|upright|An oceanic [[Algal bloom|phytoplankton bloom]] in the [[South Atlantic Ocean]], off the coast of [[Argentina]]. Encouraging such blooms with [[iron fertilization]] could lock up carbon on the seabed. However, this approach is currently (2022) no longer being actively pursued.]]{{excerpt|ocean fertilization|paragraphs=1–3|file=no}}

=== Artificial upwelling ===
Artificial upwelling or downwelling is an approach that would change the mixing layers of the ocean. Encouraging various ocean layers to mix can move nutrients and dissolved gases around.<ref name="Lovelock07">{{cite journal |last1=Lovelock |first1=James E. |last2=Rapley |first2=Chris G. |author-link2=Chris Rapley |date=September 27, 2007 |title=Ocean pipes could help the earth to cure itself |journal=Nature |volume=449 |issue=7161 |page=403 |bibcode=2007Natur.449..403L |doi=10.1038/449403a |pmid=17898747 |doi-access=free}}</ref> Mixing may be achieved by placing large vertical pipes in the oceans to pump nutrient rich water to the surface, triggering [[algal blooms|blooms of algae]], which store carbon when they grow and export{{Clarify|reason=better word than 'export'?|date=May 2024}} carbon when they die.<ref name="Lovelock07" /><ref>{{cite journal |last=Pearce |first=Fred |date=September 26, 2007 |title=Ocean pumps could counter global warming |url=https://www.newscientist.com/article/dn12698 |url-status=live |journal=New Scientist |archive-url=https://web.archive.org/web/20090423004033/http://www.newscientist.com/article/dn12698 |archive-date=April 23, 2009 |access-date=May 9, 2010}}</ref><ref>{{cite journal |last=Duke |first=John H. |year=2008 |title=A proposal to force vertical mixing of the Pacific Equatorial Undercurrent to create a system of equatorially trapped coupled convection that counteracts global warming |url=http://www.johnduke.com/JDukeETCC09052007.pdf |url-status=live |journal=Geophysical Research Abstracts |archive-url=https://web.archive.org/web/20110713113313/http://www.johnduke.com/JDukeETCC09052007.pdf |archive-date=July 13, 2011 |access-date=May 9, 2010}}</ref> This produces results somewhat similar to iron fertilization. One side-effect is a short-term rise in {{chem|CO|2}}, which limits its attractiveness.<ref>{{cite journal |last1=Dutreuil |first1=S. |last2=Bopp |first2=L. |last3=Tagliabue |first3=A. |date=May 25, 2009 |title=Impact of enhanced vertical mixing on marine biogeochemistry: lessons for geo-engineering and natural variability |url=http://www.biogeosciences.net/6/901/2009/bg-6-901-2009.html |url-status=live |journal=Biogeosciences |volume=6 |issue=5 |pages=901–912 |bibcode=2009BGeo....6..901D |doi=10.5194/bg-6-901-2009 |archive-url=https://web.archive.org/web/20150923190148/http://www.biogeosciences.net/6/901/2009/bg-6-901-2009.html |archive-date=September 23, 2015 |access-date=August 21, 2015 |doi-access=free}}</ref>

Mixing layers involve transporting the denser and colder [[deep ocean water]] to the surface [[mixed layer]]. As the [[ocean temperature]] decreases with depth, more [[carbon dioxide]] and other compounds are able to dissolve in the deeper layers.<ref>{{Cite news |title=Ocean temperature |language=en |work=Science Learning Hub |url=https://www.sciencelearn.org.nz/resources/707-ocean-temperature |access-date=2018-11-28 |archive-date=December 1, 2022 |archive-url=https://web.archive.org/web/20221201140025/https://www.sciencelearn.org.nz/resources/707-ocean-temperature |url-status=live }}</ref> This can be induced by reversing the [[oceanic carbon cycle]] through the use of large vertical pipes serving as ocean pumps,<ref>{{Cite news |last=Pearce |first=Fred |title=Ocean pumps could counter global warming |language=en-US |work=New Scientist |url=https://www.newscientist.com/article/dn12698-ocean-pumps-could-counter-global-warming/ |access-date=2018-11-28 |archive-date=December 1, 2022 |archive-url=https://web.archive.org/web/20221201140025/https://www.newscientist.com/article/dn12698-ocean-pumps-could-counter-global-warming/ |url-status=live }}</ref> or a mixer array.<ref>{{Cite journal |last=Duke |first=John H. |date=2008 |title=A proposal to force vertical mixing of the Pacific Equatorial Undercurrent to create a system of equatorially trapped coupled convection that counteracts global warming |url=http://www.johnduke.com/JDukeETCC09052007.pdf |journal=Geophysical Research Abstracts |access-date=January 29, 2009 |archive-date=July 13, 2011 |archive-url=https://web.archive.org/web/20110713113313/http://www.johnduke.com/JDukeETCC09052007.pdf }}</ref> When the nutrient rich deep ocean water is moved to the surface, [[Algal bloom|algae bloom]] occurs, resulting in a decrease in carbon dioxide due to carbon intake from [[phytoplankton]] and other [[Photosynthesis|photosynthetic]] [[Eukaryote|eukaryotic]] [[organism]]s. The transfer of heat between the layers will also cause seawater from the mixed layer to sink and absorb more carbon dioxide. This method has not gained much traction as algae bloom harms [[marine ecosystem]]s by blocking sunlight and releasing harmful toxins into the ocean.<ref>{{Cite web |last=US EPA |first=OW |date=2013-06-03 |title=Harmful Algal Blooms {{!}} US EPA |url=https://www.epa.gov/nutrientpollution/harmful-algal-blooms |access-date=2018-11-28 |website=US EPA |language=en |archive-date=February 4, 2020 |archive-url=https://web.archive.org/web/20200204072812/https://www.epa.gov/nutrientpollution/harmful-algal-blooms |url-status=live }}</ref> The sudden increase in carbon dioxide on the surface level will also temporarily decrease the [[pH]] of the seawater, impairing the growth of [[coral reef]]s. The production of [[carbonic acid]] through the dissolution of carbon dioxide in seawater hinders [[marine biogenic calcification]] and causes major disruptions to the oceanic [[food chain]].<ref>{{Cite web |last=Shirley |first=Jolene S. |title=Discovering the Effects of Carbon Dioxide Levels on Marine Life and Global Climate |url=https://soundwaves.usgs.gov/2007/01/ |access-date=2018-11-28 |website=soundwaves.usgs.gov |archive-date=December 9, 2018 |archive-url=https://web.archive.org/web/20181209123525/https://soundwaves.usgs.gov/2007/01/ }}</ref>

=== Basalt storage ===
Carbon dioxide sequestration in [[basalt]] involves the injecting of {{chem|CO|2}} into deep-sea formations. The {{chem|CO|2}} first mixes with seawater and then reacts with the basalt, both of which are alkaline-rich elements. This reaction results in the release of {{chem|Ca<sup>2+</sup>}} and {{chem|Mg<sup>2+</sup>}} ions forming stable carbonate minerals.<ref>{{cite journal |author1=David S. Goldberg |author2=Taro Takahashi |author3=Angela L. Slagle |year=2008 |title=Carbon dioxide sequestration in deep-sea basalt |journal=Proc. Natl. Acad. Sci. USA |volume=105 |issue=29 |pages=9920–25 |bibcode=2008PNAS..105.9920G |doi=10.1073/pnas.0804397105 |pmc=2464617 |pmid=18626013 |doi-access=free}}</ref>

Underwater basalt offers a good alternative to other forms of oceanic carbon storage because it has a number of trapping measures to ensure added protection against leakage. These measures include "geochemical, sediment, gravitational and [[hydrate]] formation." Because {{chem|CO|2}} hydrate is denser than {{chem|CO|2}} in seawater, the risk of leakage is minimal. Injecting the {{chem|CO|2}} at depths greater than {{convert|2700|m|ft|sp=us}} ensures that the {{chem|CO|2}} has a greater density than seawater, causing it to sink.<ref name="environmentalresearchweb.org">{{cite web |date=July 15, 2008 |title=Carbon storage in undersea basalt offers extra security |url=http://environmentalresearchweb.org/cws/article/futures/35017 |archive-url=https://web.archive.org/web/20090802221558/http://environmentalresearchweb.org/cws/article/futures/35017 |archive-date=August 2, 2009 |access-date=May 9, 2010 |publisher=environmentalresearchweb}}</ref>

One possible injection site is [[Juan de Fuca Plate]]. Researchers at the [[Lamont–Doherty Earth Observatory]] found that this plate at the western coast of the United States has a possible storage capacity of 208 gigatons. This could cover the entire [[Greenhouse gas emissions by the United States|current U.S. carbon emissions]] for over 100&nbsp;years (as of 2009).<ref name="environmentalresearchweb.org" />

This process is undergoing tests as part of the [[CarbFix]] project, resulting in 95% of the injected 250 tonnes of CO<sub>2</sub> to solidify into [[calcite]] in two years, using 25 tonnes of water per tonne of CO<sub>2</sub>.<ref name="Matter">{{cite journal |last1=Matter |first1=Juerg M. |last2=Stute |first2=Martin |last3=Snæbjörnsdottir |first3=Sandra O. |last4=Oelkers |first4=Eric H. |last5=Gislason |first5=Sigurdur R. |last6=Aradottir |first6=Edda S. |last7=Sigfusson |first7=Bergur |last8=Gunnarsson |first8=Ingvi |last9=Sigurdardottir |first9=Holmfridur |last10=Gunlaugsson |first10=Einar |last11=Axelsson |first11=Gudni |last12=Alfredsson |first12=Helgi A. |last13=Wolff-Boenisch |first13=Domenik |last14=Mesfin |first14=Kiflom |last15=Fernandez de la Reguera Taya |first15=Diana |date=June 10, 2016 |title=Rapid carbon mineralization for permanent disposal of anthropogenic carbon dioxide emissions |journal=Science |volume=352 |issue=6291 |pages=1312–1314 |bibcode=2016Sci...352.1312M |doi=10.1126/science.aad8132 |pmid=27284192 |doi-access=free |last16=Hall |first16=Jennifer |last17=Dideriksen |first17=Knud |last18=Broecker |first18=Wallace S.}}</ref><ref>{{cite web |date=June 10, 2016 |title=Scientists turn carbon dioxide into stone to combat global warming |url=https://www.theverge.com/2016/6/10/11901368/carbon-dioxide-capture-storage-stone-climate-change-study |url-status=live |archive-url=https://web.archive.org/web/20160611024900/http://www.theverge.com/2016/6/10/11901368/carbon-dioxide-capture-storage-stone-climate-change-study |archive-date=June 11, 2016 |access-date=June 11, 2016 |work=The Verge |publisher=Vox Media}}</ref>{{Update inline|date=May 2024|reason=what was the result of the tests?}}<!--under ocean?-->

==== Mineralization and deep sea sediments ====
{{see also|Pelagic sediment|}}Similar to [[Mineralization (geology)|mineralization]] processes that take place within rocks, mineralization can also occur under the sea. The rate of dissolution of carbon dioxide from atmosphere to oceanic regions{{Clarify|reason=why 'oceanic regions' not just 'the ocean'?|date=May 2024}} is determined by the circulation period of the ocean and buffering ability of [[subducting]] surface water.<ref name=":62">{{Cite journal |last1=Goldthorpe |first1=Steve |date=2017-07-01 |title=Potential for Very Deep Ocean Storage of CO<sub>2</sub> Without Ocean Acidification: A Discussion Paper |journal=Energy Procedia |language=en |volume=114 |pages=5417–5429 |doi=10.1016/j.egypro.2017.03.1686 |issn=1876-6102 |doi-access=free|bibcode=2017EnPro.114.5417G }}</ref> Researchers have demonstrated that the carbon dioxide marine storage at several kilometers depth could be viable for up to 500 years, but is dependent on injection site and conditions. Several studies have shown that although it may fix carbon dioxide effectively, carbon dioxide may be released back to the atmosphere over time. However, this is unlikely for at least a few more centuries. The neutralization of [[Calcium carbonate|CaCO<sub>3</sub>]], or balancing the concentration of CaCO<sub>3</sub> on the seafloor, land and in the ocean, can be measured on a timescale of thousands of years. More specifically, the predicted time is 1700 years for ocean and approximately 5000 to 6000 years for land.<ref>{{Cite journal |last=House |first=Kurt |date=November 10, 2005 |title=Permanent carbon dioxide storage in deep-sea sediments |url=http://www.pnas.org/content/pnas/103/33/12291.full.pdf |journal=Proceedings of the National Academy of Sciences |volume=103 |issue=33 |pages=12291–12295 |bibcode=2006PNAS..10312291H |doi=10.1073/pnas.0605318103 |pmc=1567873 |pmid=16894174 |doi-access=free |access-date=November 30, 2022 |archive-date=March 6, 2021 |archive-url=https://web.archive.org/web/20210306111121/https://www.pnas.org/content/pnas/103/33/12291.full.pdf |url-status=live }}</ref><ref>{{Cite journal |last=RIDGWELL |first=ANDY |date=2007-01-13 |title=Regulation of atmospheric CO<sub>2</sub> by deep-sea sediments in an Earth System Model |url=http://www.ggy.bris.ac.uk/personal/AndyRidgwell/pubs/ridgwell_hargreaves_2007.pdf |journal=Global Biogeochemical Cycles |volume=21 |issue=2 |pages=GB2008 |bibcode=2007GBioC..21.2008R |doi=10.1029/2006GB002764 |s2cid=55985323 |access-date=November 30, 2022 |archive-date=March 4, 2021 |archive-url=https://web.archive.org/web/20210304085544/http://www.ggy.bris.ac.uk/personal/AndyRidgwell/pubs/ridgwell_hargreaves_2007.pdf |url-status=live }}</ref> Further, the dissolution time for CaCO<sub>3</sub> can be improved by injecting near or downstream of the storage site.<ref name=":52">{{Cite web |title=Archived copy |url=https://www.ipcc.ch/pdf/special-reports/srccs/srccs_chapter6.pdf |archive-url=https://web.archive.org/web/20180612233258/https://www.ipcc.ch/pdf/special-reports/srccs/srccs_chapter6.pdf |archive-date=2018-06-12 |access-date=2018-12-08}}</ref>

In addition to [[carbon mineralization]], another proposal is deep sea [[sediment]] injection. It injects liquid carbon dioxide at least {{Convert|3000|m|abbr=on}} below the surface directly into ocean sediments to generate carbon dioxide hydrate. Two regions are defined for exploration: 1) the negative buoyancy zone (NBZ), which is the region between liquid carbon dioxide denser than surrounding water and where liquid carbon dioxide has neutral buoyancy, and 2) the hydrate formation zone (HFZ), which typically has low temperatures and high pressures. Several research models have shown that the optimal depth of injection requires consideration of intrinsic permeability and any changes in liquid carbon dioxide permeability for optimal storage. The formation of hydrates decreases liquid carbon dioxide permeability, and injection below HFZ is more energetically favored than within the HFZ. If the NBZ is a greater column of water than the HFZ, the injection should happen below the HFZ and directly to the NBZ.<ref>Yogendra Kumar, Jitendra Sangwai, (2023) Environmentally Sustainable Large-Scale CO2 Sequestration through Hydrates in Offshore Basins: Ab Initio Comprehensive Analysis of Subsea Parameters and Economic Perspective, Energy & Fuels, doi=https://doi.org/10.1021/acs.energyfuels.3c00581</ref> In this case, liquid carbon dioxide will sink to the NBZ and be stored below the buoyancy and hydrate cap. Carbon dioxide leakage can occur if there is dissolution into [[pore fluid]]{{Clarify|reason=what is pore fluid?|date=May 2024}}or via [[molecular diffusion]]. However, this occurs over thousands of years.<ref name=":52" /><ref>{{Cite journal |last1=Qanbari |first1=Farhad |last2=Pooladi-Darvish |first2=Mehran |last3=Tabatabaie |first3=S. Hamed |last4=Gerami |first4=Shahab |date=2012-09-01 |title=CO<sub>2</sub> disposal as hydrate in ocean sediments |journal=Journal of Natural Gas Science and Engineering |language=en |volume=8 |pages=139–149 |doi=10.1016/j.jngse.2011.10.006 |bibcode=2012JNGSE...8..139Q |issn=1875-5100}}</ref><ref>{{Cite journal |last1=Zhang |first1=Dongxiao |last2=Teng |first2=Yihua |date=2018-07-01 |title=Long-term viability of carbon sequestration in deep-sea sediments |journal=Science Advances |language=en |volume=4 |issue=7 |pages=eaao6588 |doi=10.1126/sciadv.aao6588 |issn=2375-2548 |pmc=6031374 |pmid=29978037|bibcode=2018SciA....4.6588T }}</ref>

=== Adding bases to neutralize acids ===
{{Further|Ocean acidification#Carbon removal technologies which add alkalinity}}
Carbon dioxide forms [[carbonic acid]] when dissolved in water, making [[ocean acidification]] a significant consequence of elevated {{chem|CO|2}} levels. The acidification also limits the rate at which {{chem|CO|2}} can be absorbed by the ocean (through the [[solubility pump]]). Various [[base (chemistry)|bases]] have been suggested that could neutralize the ocean acidity and thereby enhance {{chem|CO|2}} absorption.<ref>{{cite journal |author=Kheshgi, H.S. |year=1995 |title=Sequestering atmospheric carbon dioxide by increasing ocean alkalinity |journal=Energy |volume=20 |issue=9 |pages=915–922 |doi=10.1016/0360-5442(95)00035-F|bibcode=1995Ene....20..915K }}</ref><ref>{{cite journal |author1=K.S. Lackner |author2=C.H. Wendt |author3=D.P. Butt |author4=E.L. Joyce |author5=D.H. Sharp |year=1995 |title=Carbon dioxide disposal in carbonate minerals |journal=Energy |volume=20 |issue=11 |pages=1153–70 |doi=10.1016/0360-5442(95)00071-N|bibcode=1995Ene....20.1153L }}
</ref><ref>{{cite journal |author1=K.S. Lackner |author2=D.P. Butt |author3=C.H. Wendt |year=1997 |title=Progress on binding {{chem|CO|2}} in mineral substrates |url=https://zenodo.org/record/1259949 |url-status=live |journal=Energy Conversion and Management |type=Submitted manuscript |volume=38 |pages=S259–S264 |doi=10.1016/S0196-8904(96)00279-8 |archive-url=https://web.archive.org/web/20190824214110/https://zenodo.org/record/1259949 |archive-date=August 24, 2019 |access-date=July 31, 2018}}</ref><ref>{{cite journal |last1=Rau |first1=Greg H. |last2=Caldeira |first2=Ken |date=November 1999 |title=Enhanced carbonate dissolution: A means of sequestering waste {{chem|CO|2}} as ocean bicarbonate |url=https://zenodo.org/record/1259951 |url-status=live |journal=Energy Conversion and Management |volume=40 |issue=17 |pages=1803–1813 |doi=10.1016/S0196-8904(99)00071-0 |archive-url=https://web.archive.org/web/20200610182433/https://zenodo.org/record/1259951 |archive-date=June 10, 2020 |access-date=March 7, 2020}}</ref><ref>{{cite journal |last1=Rau |first1=Greg H. |last2=Knauss |first2=Kevin G. |last3=Langer |first3=William H. |last4=Caldeira |first4=Ken |date=August 2007 |title=Reducing energy-related {{chem|CO|2}} emissions using accelerated weathering of limestone |journal=Energy |volume=32 |issue=8 |pages=1471–7 |doi=10.1016/j.energy.2006.10.011|bibcode=2007Ene....32.1471R }}</ref> For example, adding crushed [[limestone]] to oceans enhances the absorption of carbon dioxide.<ref>{{cite journal |author=Harvey, L.D.D. |year=2008 |title=Mitigating the atmospheric {{chem|CO|2}} increase and ocean acidification by adding limestone powder to upwelling regions |journal=[[Journal of Geophysical Research]] |volume=113 |pages=C04028 |doi=10.1029/2007JC004373 |s2cid=54827652|doi-access=free }}</ref> Another approach involves adding [[sodium hydroxide]], produced through [[electrolysis]] of saltwater or brine. The resulting [[hydrochloric acid]] byproduct can be neutralized by reacting it with volcanic silicate rocks, such as [[enstatite]]—effectively accelerating the natural weathering process to help restore ocean pH.<ref>{{cite web |date=November 7, 2007 |title=Scientists enhance Mother Nature's carbon handling mechanism |url=http://live.psu.edu/story/27135 |archive-url=https://web.archive.org/web/20100603155005/http://live.psu.edu/story/27135 |archive-date=June 3, 2010 |publisher=Penn State Live}}</ref><ref>{{cite journal |author1=Kurt Zenz House |author2=Christopher H. House |author3=Daniel P. Schrag |author4=Michael J. Aziz |year=2007 |title=Electrochemical Acceleration of Chemical Weathering as an Energetically Feasible Approach to Mitigating Anthropogenic Climate Change |journal=Environ. Sci. Technol. |volume=41 |issue=24 |pages=8464–8470 |bibcode=2007EnST...41.8464H |doi=10.1021/es0701816 |pmid=18200880}}</ref><ref>{{cite news |last=Clover |first=Charles |date=November 7, 2007 |title=Global warming 'cure' found by scientists |work=The Daily Telegraph |location=London |url=https://www.telegraph.co.uk/earth/earthnews/3313398/Global-warming-cure-found-by-scientists.html |access-date=April 3, 2010 |archive-url=https://web.archive.org/web/20090411215744/http://www.telegraph.co.uk/earth/earthnews/3313398/Global-warming-cure-found-by-scientists.html |archive-date=April 11, 2009}}</ref>

==== Single-step carbon sequestration and storage ====
Single-step carbon sequestration and storage is a saline water-based mineralization technology extracting carbon dioxide from seawater and storing it in the form of solid minerals.<ref>{{Cite journal |last1=La Plante |first1=Erika Callagon |last2=Simonetti |first2=Dante A. |last3=Wang |first3=Jingbo |last4=Al-Turki |first4=Abdulaziz |last5=Chen |first5=Xin |last6=Jassby |first6=David |last7=Sant |first7=Gaurav N. |date=2021-01-25 |title=Saline Water-Based Mineralization Pathway for Gigatonne-Scale CO<sub>2</sub> Management |journal=ACS Sustainable Chemistry & Engineering |volume=9 |issue=3 |pages=1073–1089 |doi=10.1021/acssuschemeng.0c08561 |s2cid=234293936|doi-access=free }}</ref>

=== Abandoned ideas ===

==== Direct deep-sea carbon dioxide injection ====
{{Main|Direct deep-sea carbon dioxide injection}}

It was once suggested that CO<sub>2</sub> could be stored in the oceans by direct injection into the deep ocean and storing it there for some centuries. At the time, this proposal was called "ocean storage" but more precisely it was known as "[[direct deep-sea carbon dioxide injection]]". However, the interest in this avenue of carbon storage has much reduced since about 2001 because of concerns about the unknown impacts on [[marine life]]<ref name=":02">IPCC, 2005: [https://www.ipcc.ch/report/carbon-dioxide-capture-and-storage/ IPCC Special Report on Carbon Dioxide Capture and Storage] {{Webarchive|url=https://web.archive.org/web/20221128120121/https://www.ipcc.ch/report/carbon-dioxide-capture-and-storage/ |date=November 28, 2022 }}. Prepared by Working Group III of the Intergovernmental Panel on Climate Change [Metz, B., O. Davidson, H. C. de Coninck, M. Loos, and L. A. Meyer (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, US, 442 pp.</ref>[[Marine life|{{rp|279}}]], high costs and concerns about its stability or permanence.<ref name=":0" /> The "IPCC Special Report on Carbon Dioxide Capture and Storage" in 2005 did include this technology as an option.<ref name=":02" />[[Marine life|{{rp|279}}]] However, the [[IPCC Fifth Assessment Report]] in 2014 no longer mentioned the term "ocean storage" in its report on climate change mitigation methods.<ref>IPCC, 2014: [https://www.ipcc.ch/report/ar5/wg3/ Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change] {{Webarchive|url=https://web.archive.org/web/20170126121016/http://www.ipcc.ch/report/ar5/wg3/ |date=January 26, 2017 }} [Edenhofer, O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. Savolainen, S. Schlömer, C. von Stechow, T. Zwickel and J.C. Minx (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, US.</ref> The 2022 [[IPCC Sixth Assessment Report]] does not mention "ocean storage" in its "Carbon Dioxide Removal taxonomy".<ref name="AR6 WGIII Ch 12">IPCC (2022) [https://www.ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6_WGIII_Chapter_12.pdf Chapter 12: Cross sectoral perspectives] {{Webarchive|url=https://web.archive.org/web/20221013122242/https://www.ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6_WGIII_Chapter_12.pdf|date=13 October 2022}} in [https://www.ipcc.ch/report/ar6/wg3/ Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change] {{Webarchive|url=https://web.archive.org/web/20220802125242/https://www.ipcc.ch/report/ar6/wg3/|date=2 August 2022}}, Cambridge University Press, Cambridge, United Kingdom and New York, NY, US</ref>{{rp|12–37}}

== Costs ==
Cost of carbon sequestration (not including capture and transport) varies but is below US$10 per tonne in some cases where onshore storage is available.<ref>{{Cite web |title=Is carbon capture too expensive? – Analysis |url=https://www.iea.org/commentaries/is-carbon-capture-too-expensive |url-status=live |archive-url=https://web.archive.org/web/20211024201314/https://www.iea.org/commentaries/is-carbon-capture-too-expensive |archive-date=October 24, 2021 |access-date=2021-11-30 |website=IEA |date=February 17, 2021 |language=en-GB}}</ref> For example [[Carbfix]] cost is around US$25 per tonne of CO<sub>2</sub>.<ref>{{Cite web |title=This startup has unlocked a novel way to capture carbon—by turning the dirty gas into rocks |url=https://fortune.com/2021/03/06/carbon-capture-storage-rocks-net-zero-carbfix-startup-iceland/ |url-status=live |archive-url=https://web.archive.org/web/20211121025918/https://fortune.com/2021/03/06/carbon-capture-storage-rocks-net-zero-carbfix-startup-iceland/ |archive-date=November 21, 2021 |access-date=2021-12-01 |website=Fortune |language=en}}</ref> A 2020 report estimated sequestration in forests (so including capture) at US$35 for small quantities to US$280 per tonne for 10% of the total required to keep to 1.5 C warming.<ref>{{Cite journal |last1=Austin |first1=K. G. |last2=Baker |first2=J. S. |last3=Sohngen |first3=B. L. |last4=Wade |first4=C. M. |last5=Daigneault |first5=A. |last6=Ohrel |first6=S. B. |last7=Ragnauth |first7=S. |last8=Bean |first8=A. |date=2020-12-01 |title=The economic costs of planting, preserving, and managing the world's forests to mitigate climate change |journal=Nature Communications |language=en |volume=11 |issue=1 |page=5946 |bibcode=2020NatCo..11.5946A |doi=10.1038/s41467-020-19578-z |issn=2041-1723 |pmc=7708837 |pmid=33262324}}</ref> But there is risk of forest fires releasing the carbon.<ref>{{Cite web |last=Woodward |first=Aylin |title=The world's biggest carbon-removal plant just opened. In a year, it'll negate just 3 seconds' worth of global emissions. |url=https://www.businessinsider.com/carbon-capture-storage-expensive-climate-change-2021-9 |url-status=live |archive-url=https://web.archive.org/web/20211130145042/https://www.businessinsider.com/carbon-capture-storage-expensive-climate-change-2021-9 |archive-date=November 30, 2021 |access-date=2021-11-30 |website=Business Insider |language=en-US}}</ref>

== See also ==
{{Portal|Ecology|Climate change}}
* [[Carbon budget]]
* [[Mycorrhizal fungi and soil carbon storage]]

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

{{wikiquote}}
{{Scholia}}

{{authority control}}
{{climate change}}

{{DEFAULTSORT:Carbon Sequestration}}
[[Category:Carbon capture and storage| ]]
[[Category:Carbon dioxide removal]]
[[Category:Emissions reduction]]
[[Category:Forestry and the environment]]
[[Category:Photosynthesis]]
[[Category:Reforestation]]
[[Category:Sustainable food system]]