Carbon dioxide removal

Summary

Planting trees is a means of carbon dioxide removal.

Carbon dioxide removal (CDR), also known as greenhouse gas removal, is a process in which carbon dioxide gas (CO
2
) is removed from the atmosphere and sequestered for long periods of time[1][2][3] – in the context of net zero greenhouse gas emissions targets,[4] CDR is increasingly integrated into climate policy, as a climate engineering option.[5] CDR methods are also known as negative emissions technologies, and may be cheaper than preventing some agricultural greenhouse gas emissions.[6]

CDR methods include afforestation, agricultural practices that sequester carbon in soils, bio-energy with carbon capture and storage, ocean fertilization, enhanced weathering, and direct air capture when combined with storage.[2][7][8] To assess whether net negative emissions are achieved by a particular process, comprehensive life cycle analysis of the process must be performed.

A 2019 consensus report by the US National Academies of Sciences, Engineering, and Medicine concluded that using existing CDR methods at scales that can be safely and economically deployed, there is potential to remove and sequester up to 10 gigatons of carbon dioxide per year.[6] This would offset greenhouse gas emissions at about a fifth of the rate at which they are being produced.

In 2021 the IPCC said that emission pathways that limit globally averaged warming to 1.5 °C or 2 °C by the year 2100 assume the use of CDR approaches in combination with emission reductions.[9][10]

Definitions

The Intergovernmental Panel on Climate Change defines CDR as:

Anthropogenic activities removing CO
2
from the atmosphere and durably storing it in geological, terrestrial, or ocean reservoirs, or in products. It includes existing and potential anthropogenic enhancement of biological or geochemical sinks and direct air capture and storage, but excludes natural CO
2
uptake not directly caused by human activities.[1]

The U.S.-based National Academies of Sciences, Engineering, and Medicine (NASEM) uses the term "negative emissions technology" with a similar definition.[6]

The concept of deliberately reducing the amount of CO
2
in the atmosphere is often mistakenly classified with solar radiation management as a form of climate engineering and assumed to be intrinsically risky.[6] In fact, CDR addresses the root cause of climate change and is part of strategies to reduce net emissions.[2]

Concepts using similar terminology

CDR can be confused with carbon capture and storage (CCS), a process in which carbon dioxide is collected from point-sources such as gas-fired power plants, whose smokestacks emit CO
2
in a concentrated stream. The CO
2
is then compressed and sequestered or utilized.[1] When used to sequester the carbon from a gas-fired power plant, CCS reduces emissions from continued use of the point source, but does not reduce the amount of carbon dioxide already in the atmosphere.

Potential for climate change mitigation

Using CDR in parallel with other efforts to reduce greenhouse gas emissions, such as deploying renewable energy, is likely to be less expensive and disruptive than using other efforts alone.[6] A 2019 consensus study report by NASEM assessed the potential of all forms of CDR other than ocean fertilization that could be deployed safely and economically using current technologies, and estimated that they could remove up to 10 gigatons of CO
2
per year if fully deployed worldwide.[6] This is one-fifth of the 50 gigatons of CO
2
emitted per year by human activities.[6] In the IPCC's 2018 analysis of ways to limit climate change, all analyzed mitigation pathways that would prevent more than 1.5 °C of warming included CDR measures.[11]

Some mitigation pathways propose achieving higher rates of CDR through massive deployment of one technology, however these pathways assume that hundreds of millions of hectares of cropland are converted to growing biofuel crops.[6] Further research in the areas of direct air capture, geologic sequestration of carbon dioxide, and carbon mineralization could potentially yield technological advancements that make higher rates of CDR economically feasible.[6]

The IPCC's 2018 report said that reliance on large-scale deployment of CDR would be a "major risk" to achieving the goal of less than 1.5 °C of warming, given the uncertainties in how quickly CDR can be deployed at scale.[11] Strategies for mitigating climate change that rely less on CDR and more on sustainable use of energy carry less of this risk.[11][12] The possibility of large-scale future CDR deployment has been described as a moral hazard, as it could lead to a reduction in near-term efforts to mitigate climate change.[13][6] The 2019 NASEM report concludes:

Any argument to delay mitigation efforts because NETs will provide a backstop drastically misrepresents their current capacities and the likely pace of research progress.[6]

Carbon sequestration

Forests, kelp beds, and other forms of plant life absorb carbon dioxide from the air as they grow, and bind it into biomass. As the use of plants as carbon sinks can be undone by events such as wildfires, the long-term reliability of these approaches has been questioned.

Carbon dioxide that has been removed from the atmosphere can also be stored in the Earth's crust by injecting it into the subsurface, or in the form of insoluble carbonate salts (mineral sequestration). This is because they are removing carbon from the atmosphere and sequestering it indefinitely and presumably for a considerable duration (thousands to millions of years).

Methods

Afforestation, reforestation, and forestry management

According to the International Union for Conservation of Nature: "Halting the loss and degradation of natural systems and promoting their restoration have the potential to contribute over one-third of the total climate change mitigation scientists say is required by 2030."[14]

Forests are vital for human society, animals and plant species. This is because trees keep our air clean, regulate the local climate and provide a habitat for numerous species. Trees and plants convert carbon dioxide back into oxygen, using photosynthesis. They are important for regulating CO
2
levels in the air, as they remove and store carbon from the air. Without them, the atmosphere would heat up quickly and destabilise the climate.[15]

Biosequestration

Biosequestration is the capture and storage of the atmospheric greenhouse gas carbon dioxide by continual or enhanced biological processes. This form of carbon sequestration occurs through increased rates of photosynthesis via land-use practices such as reforestation, sustainable forest management, and genetic engineering. The SALK Harnessing Plants Initiative led by Joanne Chory is an example of an enhanced photosynthesis initiative[16][17] Carbon sequestration through biological processes affects the global carbon cycle.

Agricultural practices

Measuring soil respiration on agricultural land.
Carbon farming is a name for a variety of agricultural methods aimed at sequestering atmospheric carbon into the soil and in crop roots, wood and leaves. The aim of carbon farming is to increase the rate at which carbon is sequestered into soil and plant material with the goal of creating a net loss of carbon from the atmosphere.[18] Increasing a soil's organic matter content can aid plant growth, increase total carbon content, improve soil water retention capacity[19] and reduce fertilizer use.[20][21] As of 2016, variants of carbon farming reached hundreds of millions of hectares globally, of the nearly 5 billion hectares (1.2×1010 acres) of world farmland.[22] [23] In addition to agricultural activities, forests management is also a tool that is used in carbon farming. [24] The practice of carbon farming is often done by individual land owners who are given incentive to use and to integrate methods that will sequester carbon through policies created by governments. [25] Carbon farming methods will typically have a cost, meaning farmers and land-owners typically need a way in which they can profit from the use of carbon farming and different governments will have different programs.[25] Potential sequestration alternatives to carbon farming include scrubbing CO2 from the air with machines (direct air capture); fertilizing the oceans to prompt algal blooms that after death carry carbon to the sea bottom[26];storing the carbon dioxide emitted by electricity generation; and crushing and spreading types of rock such as basalt that absorb atmospheric carbon.[21] Land management techniques that can be combined with farming include planting/restoring forests, burying biochar produced by anaerobically converted biomass and restoring wetlands. (Coal beds are the remains of marshes and peatlands.)[27]

Wetland restoration

Estimates of the economic value of blue carbon ecosystems per hectare. Based on 2009 data from UNEP/GRID-Arendal.[28][29]
Blue carbon is carbon sequestration (the removal of carbon dioxide from the earth's atmosphere) by the world's oceanic and coastal ecosystems, mostly by algae, seagrasses, macroalgae, mangroves, salt marshes and other plants in coastal wetlands. This occurs through plant growth and the accumulation and burial of organic matter in the soil. Because oceans cover 70% of the planet, ocean ecosystem restoration has the greatest blue carbon development potential. Research is ongoing, but in some cases it has been found that these types of ecosystems remove far more carbon than terrestrial forests, and store it for millennia.

Bioenergy with carbon capture & storage

Bioenergy with carbon capture and storage (BECCS) is the process of extracting bioenergy from biomass and capturing and storing the carbon, thereby removing it from the atmosphere.[30] The carbon in the biomass comes from the greenhouse gas carbon dioxide (CO2) which is extracted from the atmosphere by the biomass when it grows. Energy is extracted in useful forms (electricity, heat, biofuels, etc.) as the biomass is utilized through combustion, fermentation, pyrolysis or other conversion methods. Some of the carbon in the biomass is converted to CO2 or biochar which can then be stored by geologic sequestration or land application, respectively, enabling carbon dioxide removal and making BECCS a negative emissions technology.[31]

The IPCC Fifth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC), suggests a potential range of negative emissions from BECCS of 0 to 22 gigatonnes per year.[32] As of 2019, five facilities around the world were actively using BECCS technologies and were capturing approximately 1.5 million tonnes per year of CO2.[33] Wide deployment of BECCS is constrained by cost and availability of biomass.[34][35]

Biochar

Biochar is created by the pyrolysis of biomass, and is under investigation as a method of carbon sequestration. Biochar is a charcoal that is used for agricultural purposes which also aids in carbon sequestration, the capture or hold of carbon. It is created using a process called pyrolysis, which is basically the act of high temperature heating biomass in an environment with low oxygen levels. What remains is a material known as char, similar to charcoal but is made through a sustainable process, thus the use of biomass.[36] Biomass is organic matter produced by living organisms or recently living organisms, most commonly plants or plant based material.[37] A study done by the UK Biochar Research Center has stated that, on a conservative level, biochar can store 1 gigaton of carbon per year. With greater effort in marketing and acceptance of biochar, the benefit could be the storage of 5–9 gigatons per year of carbon in biochar soils.[38][better source needed]

Enhanced weathering

Enhanced weathering is a chemical approach to remove carbon dioxide involving land- or ocean-based techniques. One example of a land-based enhanced weathering technique is in-situ carbonation of silicates. Ultramafic rock, for example, has the potential to store from hundreds to thousands of years' worth of CO2 emissions, according to estimates.[39][40] Ocean-based techniques involve alkalinity enhancement, such as grinding, dispersing, and dissolving olivine, limestone, silicates, or calcium hydroxide to address ocean acidification and CO2 sequestration.[41] One example of a research project on the feasibility of enhanced weathering is the CarbFix project in Iceland.[42][43][44]

Direct air capture

Flow diagram of direct air capture process using sodium hydroxide as the absorbent and including solvent regeneration.
Flow diagram of direct air capture process using sodium hydroxide as the absorbent and including solvent regeneration.

Direct air capture (DAC) is a process of capturing carbon dioxide (CO
2
)
directly from the ambient air (as opposed to capturing from point sources, such as a cement factory or biomass power plant) and generating a concentrated stream of CO
2
for sequestration or utilization or production of carbon-neutral fuel and windgas. Carbon dioxide removal is achieved when ambient air makes contact with chemical media, typically an aqueous alkaline solvent[45] or functionalized sorbents.[46] These chemical media are subsequently stripped of CO2 through the application of energy (namely heat), resulting in a CO2 stream that can undergo dehydration and compression, while simultaneously regenerating the chemical media for reuse.

DAC was suggested in 1999 and is still in development,[47][48] though several commercial plants are in operation or planning across Europe and the US. Large-scale DAC deployment may be accelerated when connected with economical use cases, or policy incentives.

DAC is not an alternative to traditional, point-source carbon capture and storage (CCS), but can be used to manage emissions from distributed sources, like exhaust fumes from cars. When combined with long-term storage of CO
2
, DAC can act as a carbon dioxide removal tool, although as of 2021 it is not profitable because the cost per tonne of carbon dioxide is several times the carbon price.

Ocean fertilization

A visualization of bloom populations in the North Atlantic and North Pacific oceans from March 2003 to October 2006. The blue areas are nutrient deficient. Green to yellow show blooms fed by dust blown from nearby landmasses.[49]
Ocean fertilization or ocean nourishment is a type of climate engineering based on the purposeful introduction of nutrients to the upper ocean[50] to increase marine food production[51] and to remove carbon dioxide from the atmosphere. A number of techniques, including fertilization by iron, urea and phosphorus have been proposed. But research in the early 2020s suggested that it could only permanently sequester a small amount of carbon.[52]

Issues

Economic issues

A crucial issue for CDR is the cost, which differs substantially among the different methods: some of these are not sufficiently developed to perform cost assessments. In 2021 DAC cost from $250 to $600 per tonne, compared to less than $50 for most reforestation.[53] In early 2021 the EU carbon price was slightly over $50. However the value of BECCS and CDR generally in integrated assessment models in the long term is highly dependant on the discount rate.[54]

On 21 January 2021, Elon Musk announced he was donating $100m for a prize for best carbon capture technology.[55]

Other issues

CDR faces issues common to all forms of climate engineering, including moral hazard.

Removal of other greenhouse gases

Although some researchers have suggested methods for removing methane, others say that nitrous oxide would be a better subject for research due to its longer lifetime in the atmosphere.[56]

See also

Bibliography

  • IPCC, 2018: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [V. Masson-Delmotte, P. Zhai, H. O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J. B. R. Matthews, Y. Chen, X. Zhou, M. I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, T. Waterfield (eds.)].
    • Report website, chapters I–V
    • Summary for policymakers, 32 pp.
    • Headline statements, 2 pp.
    • Technical summary, 22 pp.
    • FAQ, 24 pp.
    • Glossary, 24 pp.

References

  1. ^ a b c Intergovernmental Panel on Climate Change. "Glossary — Global Warming of 1.5 ºC". Retrieved February 23, 2020.
  2. ^ a b c "Geoengineering the climate: science, governance and uncertainty". The Royal Society. 2009. Retrieved September 10, 2011.
  3. ^ Minx, Jan C; Lamb, William F; Callaghan, Max W; Fuss, Sabine; Hilaire, Jérôme; Creutzig, Felix; Amann, Thorben; Beringer, Tim; De Oliveira Garcia, Wagner; Hartmann, Jens; Khanna, Tarun; Lenzi, Dominic; Luderer, Gunnar; Nemet, Gregory F; Rogelj, Joeri; Smith, Pete; Vicente Vicente, Jose Luis; Wilcox, Jennifer; Del Mar Zamora Dominguez, Maria (2018). "Negative emissions: Part 1 – research landscape and synthesis" (PDF). Environmental Research Letters. 13 (6): 063001. Bibcode:2018ERL....13f3001M. doi:10.1088/1748-9326/aabf9b.
  4. ^ Geden, Oliver (May 2016). "An actionable climate target". Nature Geoscience. 9 (5): 340–342. Bibcode:2016NatGe...9..340G. doi:10.1038/ngeo2699. ISSN 1752-0908.
  5. ^ Schenuit, Felix; Colvin, Rebecca; Fridahl, Mathias; McMullin, Barry; Reisinger, Andy; Sanchez, Daniel L.; Smith, Stephen M.; Torvanger, Asbjørn; Wreford, Anita; Geden, Oliver (March 4, 2021). "Carbon Dioxide Removal Policy in the Making: Assessing Developments in 9 OECD Cases". Frontiers in Climate. 3: 638805. doi:10.3389/fclim.2021.638805. ISSN 2624-9553.
  6. ^ a b c d e f g h i j k National Academies of Sciences, Engineering (October 24, 2018). Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. ISBN 978-0-309-48452-7.
  7. ^ Vergragt, P.J.; Markusson, N.; Karlsson, H. (2011). "Carbon capture and storage, bio-energy with carbon capture and storage, and the escape from the fossil-fuel lock-in". Global Environmental Change. 21 (2): 282–92. doi:10.1016/j.gloenvcha.2011.01.020.
  8. ^ Azar, C.; Lindgren, K.; Larson, E.; Möllersten, K. (2006). "Carbon Capture and Storage from Fossil Fuels and Biomass – Costs and Potential Role in Stabilizing the Atmosphere". Climatic Change. 74 (1–3): 47–79. Bibcode:2006ClCh...74...47A. doi:10.1007/s10584-005-3484-7. S2CID 4850415.
  9. ^ Page 4-81, IPCC Sixth Assessment Report Working Group 1, 9/8/21, https://www.ipcc.ch/2021/08/09/ar6-wg1-20210809-pr/
  10. ^ IPCC15, Ch 2.
  11. ^ a b c "SR15 Technical Summary" (PDF). Retrieved July 25, 2019.
  12. ^ Anderson, K.; Peters, G. (October 14, 2016). "The trouble with negative emissions". Science. 354 (6309): 182–183. Bibcode:2016Sci...354..182A. doi:10.1126/science.aah4567. hdl:11250/2491451. ISSN 0036-8075. PMID 27738161. S2CID 44896189.
  13. ^ IPCC15 & Ch. 2 p. 124.
  14. ^ "Forests and climate change". IUCN. November 11, 2017. Retrieved October 7, 2020.
  15. ^ "Forest Protection & Climate Change: Why Is It Important?". Climate Transform. May 13, 2021. Retrieved May 31, 2021.
  16. ^ Beerling, David (2008). The Emerald Planet: How Plants Changed Earth's History. Oxford University Press. pp. 194–5. ISBN 978-0-19-954814-9.
  17. ^ National Academies Of Sciences, Engineering (2019). Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, D.C.: National Academies of Sciences, Engineering, and Medicine. pp. 45–136. doi:10.17226/25259. ISBN 978-0-309-48452-7. PMID 31120708.
  18. ^ Nath, Arun Jyoti; Lal, Rattan; Das, Ashesh Kumar (January 1, 2015). "Managing woody bamboos for carbon farming and carbon trading". Global Ecology and Conservation. 3: 654–663. doi:10.1016/j.gecco.2015.03.002. ISSN 2351-9894.
  19. ^ "Carbon Farming | Carbon Cycle Institute". www.carboncycle.org. Retrieved April 27, 2018.
  20. ^ "Carbon Farming: Hope for a Hot Planet – Modern Farmer". Modern Farmer. March 25, 2016. Retrieved April 25, 2018.
  21. ^ a b Velasquez-Manoff, Moises (April 18, 2018). "Can Dirt Save the Earth?". The New York Times. ISSN 0362-4331. Retrieved April 28, 2018.
  22. ^ "Excerpt | The Carbon Farming Solution". carbonfarmingsolution.com. Retrieved April 27, 2018.
  23. ^ Burton, David. "How carbon farming can help solve climate change". The Conversation. Retrieved April 27, 2018.
  24. ^ Jindal, Rohit; Swallow, Brent; Kerr, John (2008). "Forestry-based carbon sequestration projects in Africa: Potential benefits and challenges". Natural Resources Forum. 32 (2): 116–130. doi:10.1111/j.1477-8947.2008.00176.x. ISSN 1477-8947.
  25. ^ a b Tang, Kai; Kragt, Marit E.; Hailu, Atakelty; Ma, Chunbo (May 1, 2016). "Carbon farming economics: What have we learned?". Journal of Environmental Management. 172: 49–57. doi:10.1016/j.jenvman.2016.02.008. ISSN 0301-4797. PMID 26921565.
  26. ^ Ortega, Alejandra; Geraldi, N.R.; Alam, I.; Kamau, A.A.; Acinas, S.; Logares, R.; Gasol, J.; Massana, R.; Krause-Jensen, D.; Duarte, C. (2019). "Important contribution of macroalgae to oceanic carbon sequestration". Nature Geoscience. 12 (9): 748–754. Bibcode:2019NatGe..12..748O. doi:10.1038/s41561-019-0421-8. hdl:10754/656768. S2CID 199448971.
  27. ^ Lehmann, Johannes; Gaunt, John; Rondon, Marco (March 1, 2006). "Bio-char Sequestration in Terrestrial Ecosystems – A Review". Mitigation and Adaptation Strategies for Global Change. 11 (2): 403–427. CiteSeerX 10.1.1.183.1147. doi:10.1007/s11027-005-9006-5. ISSN 1381-2386. S2CID 4696862.
  28. ^ Nellemann, Christian et al. (2009): Blue Carbon. The Role of Healthy Oceans in Binding Carbon. A Rapid Response Assessment. Arendal, Norway: UNEP/GRID-Arendal
  29. ^ Macreadie, P.I., Anton, A., Raven, J.A., Beaumont, N., Connolly, R.M., Friess, D.A., Kelleway, J.J., Kennedy, H., Kuwae, T., Lavery, P.S. and Lovelock, C.E. (2019) "The future of Blue Carbon science". Nature communications, 10(1): 1–13. doi:10.1038/s41467-019-11693-w.
  30. ^ Obersteiner, M. (2001). "Managing Climate Risk". Science. 294 (5543): 786–7. doi:10.1126/science.294.5543.786b. PMID 11681318. S2CID 34722068.
  31. ^ National Academies of Sciences, Engineering (October 24, 2018). Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. doi:10.17226/25259. ISBN 978-0-309-48452-7. PMID 31120708.
  32. ^ Smith, Pete; Porter, John R. (July 2018). "Bioenergy in the IPCC Assessments". GCB Bioenergy. 10 (7): 428–431. doi:10.1111/gcbb.12514.
  33. ^ "BECCS 2019 perspective" (PDF).
  34. ^ Rhodes, James S.; Keith, David W. (2008). "Biomass with capture: Negative emissions within social and environmental constraints: An editorial comment". Climatic Change. 87 (3–4): 321–8. Bibcode:2008ClCh...87..321R. doi:10.1007/s10584-007-9387-4.
  35. ^ Grantham 2019, p. 10
  36. ^ "What is biochar?". UK Biochar research center. University of Edinburgh Kings Buildings Edinburgh. Retrieved April 25, 2016.
  37. ^ "What is Biomass?". Biomass Energy Center. Direct.gov.uk. Archived from the original on October 3, 2016. Retrieved April 25, 2016.
  38. ^ "Biochar reducing and removing CO2 while improving soils: A significant sustainable response to climate change" (PDF). UKBRC. UK Biochar research Center. Retrieved April 25, 2016.
  39. ^ "Maps show rocks ideal for sequestering carbon". The New York Times. Retrieved May 15, 2018.
  40. ^ U.S. Department of the Interior. "Mapping the Mineral Resource Base for Mineral Carbon-Dioxide Sequestration in the Conterminous United States" (PDF). U.S. Geological Survey. Data Series 414.
  41. ^ "Cloud spraying and hurricane slaying: how ocean geoengineering became the frontier of the climate crisis". The Guardian. June 23, 2021. Retrieved June 23, 2021.
  42. ^ "CarbFix Project | Global Carbon Capture and Storage Institute". www.globalccsinstitute.com. Archived from the original on July 3, 2018. Retrieved May 15, 2018.
  43. ^ "The CarbFix Project". www.or.is (in Icelandic). August 22, 2017. Archived from the original on May 16, 2018. Retrieved May 15, 2018.
  44. ^ "Turning Carbon Dioxide Into Rock, and Burying It". The New York Times. February 9, 2015. ISSN 0362-4331. Retrieved May 15, 2018.
  45. ^ Keith, David W.; Holmes, Geoffrey; St. Angelo, David; Heide, Kenton (June 7, 2018). "A Process for Capturing CO2 from the Atmosphere". Joule. 2 (8): 1573–1594. doi:10.1016/j.joule.2018.05.006.
  46. ^ Beuttler, Christoph; Charles, Louise; Wurzbacher, Jan (November 21, 2019). "The Role of Direct Air Capture in Mitigation of Anthropogenic Greenhouse Gas Emissions". Frontiers in Climate. 1: 10. doi:10.3389/fclim.2019.00010.
  47. ^ Sanz-Pérez, Eloy S.; Murdock, Christopher R.; Didas, Stephanie A.; Jones, Christopher W. (October 12, 2016). "Direct Capture of CO
    2
    from Ambient Air". Chemical Reviews. 116 (19): 11840–11876. doi:10.1021/acs.chemrev.6b00173. PMID 27560307.
  48. ^ "Direct Air Capture (Technology Factsheet)" (PDF). Geoengineering Monitor. May 24, 2018. Retrieved August 27, 2019.
  49. ^ NASA Goddard Multimedia Accessed June 2012
  50. ^ Matear, R. J. & B. Elliott (2004). "Enhancement of oceanic uptake of anthropogenic CO2 by macronutrient fertilization". J. Geophys. Res. 109 (C4): C04001. Bibcode:2004JGRC..10904001M. doi:10.1029/2000JC000321.
  51. ^ Jones, I.S.F. & Young, H.E. (1997). "Engineering a large sustainable world fishery". Environmental Conservation. 24 (2): 99–104. doi:10.1017/S0376892997000167.
  52. ^ "Cloud spraying and hurricane slaying: how ocean geoengineering became the frontier of the climate crisis". the Guardian. June 23, 2021. Retrieved June 23, 2021.
  53. ^ Lebling, Katie; McQueen, Noah; Pisciotta, Max; Wilcox, Jennifer (January 6, 2021). "Direct Air Capture: Resource Considerations and Costs for Carbon Removal". Cite journal requires |journal= (help)
  54. ^ Köberle, Alexandre C. (December 1, 2019). "The Value of BECCS in IAMs: a Review". Current Sustainable/Renewable Energy Reports. 6 (4): 107–115. doi:10.1007/s40518-019-00142-3. ISSN 2196-3010.
  55. ^ @elonmusk (January 21, 2021). "Am donating $100M towards a prize for best carbon capture technology" (Tweet) – via Twitter.
  56. ^ Lackner, Klaus S. (2020). "Practical constraints on atmospheric methane removal". Nature Sustainability. 3 (5): 357. doi:10.1038/s41893-020-0496-7. ISSN 2398-9629.

External links

  • Krupp, Fred; Keohane, Nathaniel; Pooley, Eric (September 25, 2019). "Less Than Zero; Can Carbon-Removal Technologies Curb Climate Change?". Foreign Affairs (March/April 2019): 142–152.
  • The Road to Ten Gigatons - Carbon Removal Scale Up Challenge Game.