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File:2007 Arctic Sea Ice.jpg|thumb|250px|right|Significant reduction in ice volume in the Arctic Ocean in the range between 1979 and 2007 years
 
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{{Short description|Deliberate and large-scale intervention in the Earth's climate system}}
{{Expand German|Geo-Engineering|date=August 2011}}
{{Redirect|Geoengineering}}
{{Expand Russian|Геоинженерия|date=August 2011}}
{{Distinguish|Geotechnical engineering}}
[[File:Phytoplankton SoAtlantic 20060215.jpg|right|thumb|An oceanic [[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.]]
The modern concept of '''geoengineering''' (or '''climate engineering''') describes deliberately manipulating the [[Earth]]'s climate to counteract the [[effects of global warming]] from [[greenhouse gas]] emissions. Other uses of the word sometimes occur.


'''Climate engineering''' (or '''geoengineering''') is an umbrella term for both [[carbon dioxide removal]] and [[solar radiation modification]], when applied at a planetary scale.<ref name="AR6 WGIII Ch 1">IPCC (2022) [https://www.ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6_WGIII_Chapter01.pdf Chapter 1: Introduction and Framing] 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|168}} However, these two processes have very different characteristics. For this reason, the [[Intergovernmental Panel on Climate Change]] no longer uses this overarching term.<ref name="AR6 WGIII Ch 1" />{{rp|168}}<ref name="IPCC AR6 WGI Glossary">IPCC, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf Annex VII: Glossary] [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C.&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] [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 2215–2256, {{doi|10.1017/9781009157896.022}}.</ref> Carbon dioxide removal approaches are part of [[climate change mitigation]]. Solar radiation modification is reflecting some [[Solar irradiance|sunlight (solar radiation)]] back to space.<ref name=":022">{{Cite book |last=National Academies of Sciences |first=Engineering |url=https://www.nap.edu/catalog/25762/reflecting-sunlight-recommendations-for-solar-geoengineering-research-and-research-governance |title=Reflecting Sunlight: Recommendations for Solar Geoengineering Research and Research Governance |date=2021-03-25 |isbn=978-0-309-67605-2 |language=en |doi=10.17226/25762 |access-date=2021-04-17 |archive-url=https://web.archive.org/web/20210417055338/https://www.nap.edu/catalog/25762/reflecting-sunlight-recommendations-for-solar-geoengineering-research-and-research-governance |archive-date=2021-04-17 |url-status=live |s2cid=234327299}}</ref> All forms of climate engineering cannot be standalone solutions to climate change, but need to be coupled with other forms of climate change mitigation.<ref name=":023">{{Cite journal |last=Munday |first=Jeremy |date=2019 |title=Tackling Climate Change through Radiative Cooling |journal=Joule |volume=3 |issue=9 |pages=2057–2060 |doi=10.1016/j.joule.2019.07.010 |s2cid=201590290 |quote=Further, radiative cooling cannot be a complete, standalone solution, but rather is part of a more comprehensive approach that must include CO2 reduction. Otherwise, the radiative balance will not last long, and the potential financial benefits of mitigation will not fully be realized because of continued ocean acidification, air pollution, and redistribution of biomass. |doi-access=free }}</ref> Some publications place [[Passive daytime radiative cooling|passive radiative cooling]] into the climate engineering category. This technology increases the Earth's thermal emittance.<ref name=":442">{{Cite journal |last1=Zevenhovena |first1=Ron |last2=Fält |first2=Martin |date=June 2018 |title=Radiative cooling through the atmospheric window: A third, less intrusive geoengineering approach |url=https://www.sciencedirect.com/science/article/abs/pii/S0360544218304936 |journal=Energy |volume=152 |quote=An alternative, third geoengineering approach would be enhanced cooling by thermal radiation from the Earth's surface into space. |via=Elsevier Science Direct}}</ref><ref name=":122222">{{Cite journal |last1=Wang |first1=Tong |last2=Wu |first2=Yi |last3=Shi |first3=Lan |last4=Hu |first4=Xinhua |last5=Chen |first5=Min |last6=Wu |first6=Limin |date=2021 |title=A structural polymer for highly efficient all-day passive radiative cooling |journal=Nature Communications |volume=12 |issue=365 |page=365 |doi=10.1038/s41467-020-20646-7 |pmc=7809060 |pmid=33446648 |quote=One possibly alternative approach is passive radiative cooling—a sky-facing surface on the Earth spontaneously cools by radiating heat to the ultracold outer space through the atmosphere’s longwave infrared (LWIR) transparency window (λ ~ 8–13 μm).}}</ref><ref name=":52">{{Cite journal |last1=Chen |first1=Meijie |last2=Pang |first2=Dan |last3=Chen |first3=Xingyu |last4=Yan |first4=Hongjie |last5=Yang |first5=Yuan |year=2022 |title=Passive daytime radiative cooling: Fundamentals, material designs, and applications |journal=EcoMat |volume=4 |doi=10.1002/eom2.12153 |quote=Passive daytime radiative cooling dissipates terrestrial heat to the extremely cold outer space without using any energy input or producing pollution. It has the potential to simultaneously alleviate the two major problems of energy crisis and global warming. |s2cid=240331557|doi-access=free }}</ref> The media tends to use ''climate engineering'' also for other technologies such as glacier stabilization, ocean liming, and [[iron fertilization]] of oceans. The latter would modify [[carbon sequestration]] processes that take place in oceans.
The [[United States National Academy of Sciences|National Academy of Sciences]] defined geoengineering as "options that would involve large-scale engineering of our environment in order to combat or counteract the effects of changes in atmospheric chemistry." <ref name="nas_policy_implications">[http://books.nap.edu/openbook.php?record_id=1605&page=433 Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base] (1992), [[Committee on Science, Engineering, and Public Policy]] (COSEPUP)</ref> The [[Intergovernmental Panel on Climate Change]] concluded in 2007 that geoengineering options, such as ocean fertilization to remove CO<sub>2</sub> from the [[atmosphere]], remained largely unproven.<ref name=ipcc>{{cite book
|year=2007
|contribution=C. Mitigation in the short and medium term (until 2030).
|title= Summary for Policymakers.
|series=Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change
|editor=B. Metz ''et al.''
|publisher=Print version: Cambridge University Press, Cambridge, U.K., and New York, N.Y., U.S.A.. This version: IPCC website
|isbn=9780521880114
|author=IPCC
|url=http://www.ipcc.ch/publications_and_data/ar4/wg3/en/spmsspm-c.html
|accessdate=2010-05-15}}</ref> It was judged that reliable cost estimates for geoengineering had not yet been published.


Some types of climate engineering are highly controversial due to the large uncertainties around effectiveness, [[side effect]]s and [[unforeseen consequences]].<ref name=":04">{{Cite book |author=Gernot Wagner |url=https://gwagner.com/books/geoengineering-the-gamble/ |title=Geoengineering: the Gamble |year=2021}}</ref> However, the risks of such interventions must be seen in the context of the trajectory of climate change without them.<ref name="perspectives2">{{cite book |author1=Matthias Honegger |url=https://www.fni.no/doc&pdf/FNI-Climate-Policy-Perspectives-5.pdf |title=Climate Engineering{{Snd}} Avoiding Pandora's Box through Research and Governance. |author2=Axel Michaelowa |author3=Sonja Butzengeiger-Geyer |publisher=Fridtjof Nansen Institute (FNI), Perspectives |year=2012 |series=FNI Climate Policy Perspectives |access-date=2018-10-09 |archive-url=https://web.archive.org/web/20150906055338/https://www.fni.no/doc%26pdf/FNI-Climate-Policy-Perspectives-5.pdf |archive-date=2015-09-06 |url-status=dead}}</ref><ref>{{cite web |author=Zahra Hirji |date=October 6, 2016 |title=Removing CO2 From the Air Only Hope for Fixing Climate Change, New Study Says; Without 'negative emissions' to help return atmospheric {{CO2}} to 350 ppm, future generations could face costs that 'may become too heavy to bear,' paper says. |url=https://insideclimatenews.org/news/04102016/climate-change-removing-carbon-dioxide-air-james-hansen-2-degrees-paris-climate-agreement-global-warming |url-status=live |archive-url=https://web.archive.org/web/20191117214634/https://insideclimatenews.org/news/04102016/climate-change-removing-carbon-dioxide-air-james-hansen-2-degrees-paris-climate-agreement-global-warming |archive-date=November 17, 2019 |access-date=October 7, 2016 |website=insideclimatenews.org |publisher=[[InsideClimate News]]}}</ref>
Geoengineering accompanies [[mitigation of global warming|mitigation]] and [[adaptation to global warming|adaptation]] to form a three-stranded 'MAG' approach to tackling [[global warming]], notably advocated by the [[Institution of Mechanical Engineers]].<ref>{{cite book
|year=2009 |month=November
|last=Fox |first=T
|title=Climate change have we lost the battle
|url=http://www.imeche.org/Libraries/Key_Themes/IMechE_MAG_Report.sflb.ashx
|format=pdf
|publisher=Institution of Mechanical Engineers
|accessdate=2011-06-14}}</ref> Some geoengineering techniques are based on [[carbon sequestration]]. These techniques seek to reduce greenhouse gases in the atmosphere directly. These include direct methods (e.g. [[carbon dioxide air capture]]) and indirect methods (e.g. [[ocean iron fertilization]]). These techniques can be regarded as [[mitigation of global warming]]. Alternatively, [[solar radiation management]] techniques do not reduce greenhouse gas concentrations, and can only address the warming effects of [[carbon dioxide]] and other gases; they cannot address problems such as [[ocean acidification]], which are expected as a result of rising carbon dioxide levels.
Examples of proposed solar radiation management techniques include the production of [[stratospheric sulfur aerosols (geoengineering)|stratospheric sulfur aerosols]], which was suggested by [[Paul Crutzen]],<ref>{{cite doi|10.1007/s10584-006-9101-y}}</ref> [[Space mirror (anti-global warming measure)|space mirrors]], and [[cloud reflectivity enhancement]]. Most techniques have at least some side effects.


According to climate economist [[Gernot Wagner]], the term ''geoengineering'' is "so vague and all-encompassing as to have lost much meaning".<ref name=":04" />{{Rp|page=14}}{{TOC limit|3}}
To date, no large-scale geoengineering projects have been undertaken. Some limited [[tree planting]]<ref>{{cite doi|10.1016/S0961-9534(98)00071-3}}</ref> and [[cool roof]]<ref>{{cite web|url=http://www.energy.ca.gov/title24/coolroofs/|title=Cool Roofs and Title 24|publisher=The California Energy Commission|accessdate=2009-02-25}}</ref> projects are already underway, and ocean [[iron fertilization]] is at an advanced stage of research, with small-scale research trials and global modelling having been completed.<ref>{{cite journal | last=Boyd | first=P.W. | coauthors=''et al.'' | title=Mesoscale Iron Enrichment Experiments 1993–2005: Synthesis and Future Directions | year=2007 | journal=[[Science (journal)|Science]] | volume=315 | pages=612–617 | doi=10.1126/science.1131669 | pmid=17272712 | issue=5812}}</ref> [[Field research]] into [[stratospheric sulphur aerosols (geoengineering)|sulfur aerosols]] has also started.<ref>{{cite doi|10.3103/S106837390905001X}}</ref> Some commentators have suggested that consideration of geoengineering presents a [[moral hazard]] because it threatens to reduce the political and popular pressure for emissions reduction.<ref>{{cite web | url=http://www.irgc.org/geoengineering | title=Geoengineering | publisher=[[International Risk Governance Council]] | accessdate=2009-10-07 | year=2009 }}</ref> Scientists do not typically suggest geoengineering as an alternative to [[emissions control]], but rather an accompanying strategy.<ref>{{cite doi|10.1126/science.1131728}}</ref> Reviews of geoengineering techniques have emphasised that they are not substitutes for emission controls and have identified potentially stronger and weaker schemes.<ref name="lenton09">{{cite journal | doi=10.5194/acp-9-5539-2009 | last=Lenton | first=T.M. | coauthors=Vaughan, N.E. | year=2009 | title=The radiative forcing potential of different climate geoengineering options | journal=Atmos. Chem. Phys. | volume=9 | issue=15 | pages=5539–5561 | url=http://www.atmos-chem-phys.net/9/5539/2009/acp-9-5539-2009.html }}</ref><ref name="imeche09">{{cite web|url=http://www.imeche.org/Libraries/Key_Themes/IMechEGeoengineeringReport.sflb.ashx|title=Geoengineering - Giving us time to act?|publisher=I Mech E|accessdate=2011-03-12}}</ref><ref name="roysoc09">{{cite web |url=http://royalsociety.org/WorkArea/DownloadAsset.aspx?id=10768
== Terminology ==
|title=Geoengineering the climate
Climate engineering (or geoengineering) has been used as an umbrella term for both carbon dioxide removal and [[Solar radiation modification|solar radiation management]], when applied at a planetary scale.<ref name="AR6 WGIII Ch 1" />{{rp|168}} However, these two methods have very different geophysical characteristics, which is why the [[Intergovernmental Panel on Climate Change]] no longer uses this term.<ref name="AR6 WGIII Ch 1" />{{rp|168}}<ref name="IPCC AR6 WGI Glossary" /> This decision was communicated in around 2018, see for example the "[[Special Report on Global Warming of 1.5 °C]]".<ref>{{Cite book |url=https://www.cambridge.org/core/product/identifier/9781009157940/type/book |title=Global Warming of 1.5°C: IPCC Special Report on impacts of global warming of 1.5°C above pre-industrial levels in context of strengthening response to climate change, sustainable development, and efforts to eradicate poverty |date=2022 |publisher=Cambridge University Press |isbn=978-1-009-15794-0 |edition=1 |doi=10.1017/9781009157940.008}}</ref>{{rp|550}} <noinclude>Specific technologies that fall into the "climate engineering" umbrella term include:<ref name=":13" />{{rp|30}}
|publisher=The Royal Society |year=2009
|accessdate=2009-09-02}} </ref>


* [[Carbon dioxide removal]]
==Definition==
** [[Biochar]]: Biochar is a high-carbon, fine-grained residue that is produced via [[pyrolysis]]<ref name="DOI10.1038/ncomms1053">{{cite journal |author=Dominic Woolf |author2=James E. Amonette |author3=F. Alayne Street-Perrott |author4=Johannes Lehmann |author5=Stephen Joseph |date=August 2010 |title=Sustainable biochar to mitigate global climate change |journal=Nature Communications |volume=1 |issue=5 |pages=56 |bibcode=2010NatCo...1...56W |doi=10.1038/ncomms1053 |issn=2041-1723 |pmc=2964457 |pmid=20975722}}</ref>
Geoengineering is the idea of applying [[planetary engineering]] to [[Earth]]. Geoengineering would involve the deliberate modification of Earth's [[natural environment|environment]] on a large scale "to suit human needs and promote habitability".<ref>"a controversial field known as geoengineering, which means rearranging the Earth's environment on a large scale to suit human needs and promote habitability" [http://www.nytimes.com/2006/06/27/science/earth/27cool.html?ex=1151985600&en=ca9e39a26d7e4ece&ei=5065&partner=MYWAY How to Cool a Planet (Maybe)] New York Times - June 27, 2006</ref> Typically, the term is used to describe proposals to counter the effects of human-induced [[climate change]]. However, others define it more narrowly as nature-integrated engineering projects.<ref>{{cite web| url=http://www.ce.berkeley.edu/geo/index.php| title=UC Berkeley Department of Civil and Environmental Engineering| accessdate=2007-05-05}}</ref> The term ''geoengineering'' is distinct from environmental damage and accidental [[anthropogenic]] climate change, which are side-effects of human activity, rather than an intended consequence. The global [[Natural resource extraction|extraction]] of [[hydrocarbon]]s from the subsurface using integrated geoscience and engineering technology has been termed 'petroleum geoengineering' as an activity with global impact.<ref>Corbett, P., 2009, Petroleum Geoengineering - Integration of Static and Dynamic models, [[Society of Exploration Geophysicists]]/European Association of Geoscientist and Engineers,100p, ISBN 978-1-56080-153-5</ref> Definitions of the term are not universally accepted.<ref>{{cite doi|10.1007/BF00142578}}</ref>
** [[Bioenergy with carbon capture and storage]] (BECCS): the process of extracting [[bioenergy]] from [[biomass]] and [[Carbon capture and storage|capturing and storing the carbon]], thereby [[Carbon dioxide removal|removing it from the atmosphere]].<ref name="Obersteiner2">{{cite journal |last1=Obersteiner |first1=M. |year=2001 |title=Managing Climate Risk |journal=Science |volume=294 |issue=5543 |pages=786–7 |doi=10.1126/science.294.5543.786b |pmid=11681318 |s2cid=34722068}}</ref>
** [[Direct air capture]] and carbon storage: a process of capturing carbon dioxide directly from the ambient air (as opposed to capturing from [[Point source pollution|point sources]], such as a [[cement]] factory or [[biomass]] [[Power station|power plant]]) and generating a concentrated stream of {{CO2}} for [[Carbon sequestration|sequestration]] or [[Carbon capture and utilization|utilization]] or production of [[carbon-neutral fuel]] and [[windgas]].
** [[Enhanced weathering]]: a process that aims to accelerate the natural [[weathering]] by spreading finely ground [[Silicate mineral|silicate]] rock, such as [[basalt]], onto surfaces which speeds up chemical reactions between rocks, water, and air. It also [[Carbon dioxide removal|removes carbon dioxide]] ({{CO2}}) from the atmosphere, permanently storing it in solid [[carbonate mineral]]s or ocean [[alkalinity]].<ref>{{Cite web |date=2018-02-19 |title=Guest post: How 'enhanced weathering' could slow climate change and boost crop yields |url=https://www.carbonbrief.org/guest-post-how-enhanced-weathering-could-slow-climate-change-and-boost-crop-yields |url-status=live |archive-url=https://web.archive.org/web/20210908204350/https://www.carbonbrief.org/guest-post-how-enhanced-weathering-could-slow-climate-change-and-boost-crop-yields |archive-date=2021-09-08 |access-date=2021-11-03 |website=Carbon Brief |language=en}}</ref> The latter also slows [[ocean acidification]].
* [[Solar geoengineering|Solar Radiation Management]]
** [[Marine cloud brightening]]: a proposed technique that would make [[cloud]]s brighter, reflecting a small fraction of [[Solar irradiance|incoming sunlight]] back into space in order to offset [[Global warming|anthropogenic global warming]].<ref name=":1">{{Cite book |author=Committee on Geoengineering Climate: Technical Evaluation and Discussion of Impacts |url=http://www.nap.edu/catalog.php?record_id=18988 |title=Climate Intervention: Reflecting Sunlight to Cool Earth |author2=Board on Atmospheric Sciences and Climate |author3=Ocean Studies Board |author4=Division on Earth and Life Studies |author5=National Research Council |publisher=National Academies Press |year=2015 |isbn=978-0-309-31482-4 |access-date=2016-10-21 |archive-url=https://web.archive.org/web/20191214192318/http://www.nap.edu/catalog.php?record_id=18988 |archive-date=2019-12-14 |url-status=live}}</ref>
** [[Space mirror (climate engineering)|Mirrors in space]] (MIS): satellites that are designed to change the amount of solar radiation that impacts the Earth as a form of climate engineering. Since the conception of the idea in 1923, 1929, 1957 and 1978 (Hermann Oberth) and also in the 1980s, space mirrors have mainly been theorized as a way to deflect sunlight to counter [[global warming]] and were seriously considered in the 2000s.<ref>{{Cite book |last=Oberth |first=Hermann |date=1984 |orig-date=1923 |title=[[Die Rakete zu den Planetenräumen]] |language=german |publisher=Michaels-Verlag Germany |pages=87–88}}</ref><ref>{{Cite book |last=Oberth |first=Hermann |title=ways to spaceflight |pages=177–506 |url=https://archive.org/details/nasa_techdoc_19720008133 |via=archiv.org |publisher=NASA |access-date=21 December 2017 |language=en |date=1970 |orig-year=1929}}</ref><ref>{{Cite book |last=Oberth |first=Hermann |date=1957 |title=Menschen im Weltraum |language=german |publisher=Econ Duesseldorf Germany |pages=125–182}}</ref><ref>{{Cite book |last=Oberth |first=Hermann |date=1978 |title=Der Weltraumspiegel |language=german |publisher=Kriterion Bucharest}}</ref><ref>{{Cite web |last=Kaufman |first=Rachel |date=August 8, 2012 |title=Could Space Mirrors Stop Global Warming? |url=https://www.livescience.com/22202-space-mirrors-global-warming.html |access-date=2019-11-08 |work=Live Science |language=en}}</ref><ref name=":3">{{Cite journal |last1=Sánchez |first1=Joan-Pau |last2=McInnes |first2=Colin R. |date=2015-08-26 |title=Optimal Sunshade Configurations for Space-Based Geoengineering near the Sun-Earth L1 Point |journal=PLOS ONE |volume=10 |issue=8 |pages=e0136648 |bibcode=2015PLoSO..1036648S |doi=10.1371/journal.pone.0136648 |issn=1932-6203 |pmc=4550401 |pmid=26309047 |doi-access=free}}</ref>
** [[Stratospheric aerosol injection]] (SAI): a proposed method to introduce [[aerosol]]s into the [[stratosphere]] to create a cooling effect via [[global dimming]] and increased [[albedo]], which occurs naturally from [[Volcano|volcanic eruptions]].<ref name="Crutzen062">{{Cite journal |last1=Crutzen |first1=P. J. |year=2006 |title=Albedo Enhancement by Stratospheric Sulfur Injections: A Contribution to Resolve a Policy Dilemma? |journal=Climatic Change |volume=77 |issue=3–4 |pages=211–220 |bibcode=2006ClCh...77..211C |doi=10.1007/s10584-006-9101-y |doi-access=free}}</ref>
The following methods are not termed ''climate engineering'' in the [[IPCC Sixth Assessment Report|latest IPCC assessment report]] in 2022<ref name="AR6 WGIII Ch 1" />{{rp|6–11}} but are included under this umbrella term by other publications on this topic:<ref>{{Cite web |title=Chapter 2 : Land–Climate interactions: Special Report on Climate Change and Land |url=https://www.ipcc.ch/srccl/chapter/chapter-2/ |access-date=2023-10-20}}</ref><ref name=":04" />
* [[Passive daytime radiative cooling]]
* Ground-level albedo modification: a process of increasing Earth's albedo through the means of altering things on the Earth's surface. Examples include [[Bio-geoengineering|planting light-colored plants]] to help with reflecting sunlight back into space.<ref>{{Cite journal |last1=Wang |first1=Zhuosen |last2=Schaaf |first2=Crystal B. |last3=Sun |first3=Qingsong |last4=Kim |first4=JiHyun |last5=Erb |first5=Angela M. |last6=Gao |first6=Feng |last7=Román |first7=Miguel O. |last8=Yang |first8=Yun |last9=Petroy |first9=Shelley |last10=Taylor |first10=Jeffrey R. |last11=Masek |first11=Jeffrey G. |last12=Morisette |first12=Jeffrey T. |last13=Zhang |first13=Xiaoyang |last14=Papuga |first14=Shirley A. |date=2017-07-01 |title=Monitoring land surface albedo and vegetation dynamics using high spatial and temporal resolution synthetic time series from Landsat and the MODIS BRDF/NBAR/albedo product |journal=International Journal of Applied Earth Observation and Geoinformation |language=en |volume=59 |pages=104–117 |doi=10.1016/j.jag.2017.03.008 |issn=1569-8432 |pmc=7641169 |pmid=33154713}}</ref>
* Glacier stabilization: proposals aiming to slow down or prevent [[sea level rise]] caused by the collapse of notable marine-terminating [[glacier]]s, such as [[Jakobshavn Glacier]] in [[Greenland]] or [[Thwaites Glacier]] and [[Pine Island Glacier]] in [[Antarctica]]. It may be possible to bolster some glaciers directly,<ref name="Wolovick2018">{{Cite journal |last1=Wolovick |first1=Michael J. |last2=Moore |first2=John C. |date=20 September 2018 |title=Stopping the flood: could we use targeted geoengineering to mitigate sea level rise? |url=https://tc.copernicus.org/articles/16/397/2022/ |journal=The Cryosphere |volume=12 |issue=9 |pages=2955–2967 |language=en |doi=10.5194/tc-12-2955-2018 |doi-access=free }}</ref> but blocking the flow of [[ocean heat content|ever-warming ocean water]] at a distance, allowing it more time to mix with the cooler water around the glacier, is likely to be far more effective.<ref name="Wolovick2023a">{{Cite journal |last1=Wolovick |first1=Michael |last2=Moore |first2=John |last3=Keefer |first3=Bowie |date=27 March 2023 |title=Feasibility of ice sheet conservation using seabed anchored curtains |url=https://academic.oup.com/pnasnexus/article/2/4/pgad103/7087219 |journal=PNAS Nexus |volume=2 |issue=3 |pages=pgad053 |language=en |doi=10.1093/pnasnexus/pgad053 |pmid=37007716 |pmc=10062297 }}</ref><ref name="Wolovick2023b">{{Cite journal |last1=Wolovick |first1=Michael |last2=Moore |first2=John |last3=Keefer |first3=Bowie |date=27 March 2023 |title=The potential for stabilizing Amundsen Sea glaciers via underwater curtains |url=https://academic.oup.com/pnasnexus/article/2/4/pgad103/7087219 |journal=PNAS Nexus |volume=2 |issue=4 |pages=pgad103 |language=en |doi=10.1093/pnasnexus/pgad103 |pmid=37091546 |pmc=10118300 }}</ref><ref name="MIT2022">{{Cite web|title=The radical intervention that might save the "doomsday" glacier|url=https://www.technologyreview.com/2022/01/14/1043523/save-doomsday-thwaites-glacier-antarctica/|access-date=2022-01-14|website=MIT Technology Review|language=en}}</ref>
* Ocean geoengineering<ref name=":0" /> (adding material such as lime or iron to the ocean to affect its ability to [[Carbon sequestration|sequester carbon dioxide]])</noinclude>


==Background==
== Technologies ==


=== Carbon dioxide removal ===
Several notable organisations have investigated geoengineering with a view to evaluating its potential, including, [[NASA]],<ref>{{cite web|url=http://event.arc.nasa.gov/main/home/reports/SolarRadiationCP.pdf|title=Workshop on managing solar radiation|date=April 2007|publisher=NASA|accessdate=2009-05-23}}</ref> the [[Royal Society]],<ref>{{cite press release
{{excerpt|carbon dioxide removal|paragraphs=1-2}}
|title=Stop emitting CO2 or geoengineering could be our only hope
|url=http://royalsociety.org/Stop-emitting-CO2-or-geoengineering-could-be-our-only-hope/
|date=28 August 2009
|publisher=The Royal Society
|accessdate=14 June 2011}}</ref> the [[Institute of Mechanical Engineers]],<ref>{{cite web|url=http://www.imeche.org/about/keythemes/environment/Climate+Change/Cooling+the+Planet+competition/Hot+Ideas+for+Cooling+the+Planet.htm|title=Hot ideas for cooling the planet|publisher=IMechE|accessdate=2009-05-23}} {{Dead link|date=September 2010|bot=H3llBot}}</ref><ref>{{cite web|url=http://www.imeche.org/about/keythemes/environment/Climate+Change/Cooling+the+Planet+competition/Geo-engineering+methods.htm|title=Example geoengineering methods|publisher=IMechE|accessdate=2009-05-23}} {{Dead link|date=September 2010|bot=H3llBot}}</ref> and the [[UK Parliament]],<ref>{{cite web|url=http://www.parliament.uk/documents/upload/postpn327.pdf|title=Geo-engineering research|date=March 2009|work=Postnote|publisher=Parliamentary Office of Science and Technology|accessdate=2009-05-23}}</ref>. The [[Asilomar International Conference on Climate Intervention Technologies]] was convened to identify and develop risk reduction guidelines for climate intervention experimentation.<ref>http://climateresponsefund.org/index.php?option=com_content&view=article&id=137&Itemid=81</ref>


=== Solar radiation modification ===
The major environmental organisations such as [[Friends of the Earth]]<ref name="Extreme action guardian">{{cite news |url=http://www.guardian.co.uk/environment/2008/sep/01/climatechange.scienceofclimatechange2 |title=Extreme and risky action the only way to tackle global warming, say scientists |last=Adam |first=David |date= 1 September 2008 |work=Guardian Newspaper |accessdate=2009-05-23 | location=London}}</ref> and [[Greenpeace]]<ref name="Geoengineering no solution">{{cite news|url=http://www.guardian.co.uk/environment/2008/sep/01/climatechange.scienceofclimatechange1|title=Geo-engineering is no solution to climate change|last=Parr|first=Doug|date=1/9/8|work=Guardian Newspaper|accessdate=2009-05-23 | location=London}}</ref> have typically been reluctant to endorse geoengineering. Some have argued that any public support for geoengineering may weaken the fragile political consensus to reduce [[greenhouse gas]] emissions.<ref>http://www.21stcenturychallenges.org/focus/geo-engineering/</ref>
[[File:SPICE_SRM_overview.jpg|alt=refer to caption and image description|right|thumb|320x320px|Proposed solar radiation modification using a tethered balloon to inject sulfate aerosols into the stratosphere]]
{{excerpt|Solar geoengineering|paragraphs=1-2|file=no}}


=== Passive daytime radiative cooling ===
==Proposed strategies==
Enhancing the [[Emissivity|thermal emissivity]] of Earth through passive daytime radiative cooling has been proposed as an alternative or "third approach" to climate engineering<ref name=":442"/><ref name=":12222">{{Cite journal |last1=Wang |first1=Tong |last2=Wu |first2=Yi |last3=Shi |first3=Lan |last4=Hu |first4=Xinhua |last5=Chen |first5=Min |last6=Wu |first6=Limin |date=2021 |title=A structural polymer for highly efficient all-day passive radiative cooling |journal=Nature Communications |volume=12 |issue=365 |page=365 |doi=10.1038/s41467-020-20646-7 |pmid=33446648 |pmc=7809060 |quote=One possibly alternative approach is passive radiative cooling—a sky-facing surface on the Earth spontaneously cools by radiating heat to the ultracold outer space through the atmosphere’s longwave infrared (LWIR) transparency window (λ ~ 8–13 μm). }}</ref> that is "less intrusive" and more predictable or reversible than stratospheric aerosol injection.<ref name=":042">{{Cite journal |last=Munday |first=Jeremy |date=2019 |title=Tackling Climate Change through Radiative Cooling |journal=Joule |volume=3 |issue=9 |pages=2057–2060 |doi=10.1016/j.joule.2019.07.010 |quote=A reduction in solar absorption is usually proposed through the injection of reflective aerosols into the atmosphere; however, serious concerns have been raised regarding side effects of these forms of geoengineering and our ability to undo any of the climatic changes we create. |s2cid=201590290|doi-access=free }}</ref>
Several geoengineering strategies have been proposed. IPCC documents detail several notable proposals.<ref>http://www.grida.no/publications/other/ipcc_tar/?src=/CLIMATE/IPCC_TAR/wg3/176.htm</ref> These fall into two main categories: [[solar radiation management]] and [[carbon dioxide removal]]. However, [[list of proposed geoengineering schemes|other proposals exist]].


{{excerpt|Passive daytime radiative cooling|paragraphs=1-2}}[[File:A technofix for the climate- Marine geoengineering.webm|thumb|Video to explain some of the marine geoengineering approaches with a focus on their risks, negative impacts and potential side-effects, as well as on the question of governance of these technologies.]]
===Solar radiation management===
{{Main|Solar radiation management}}
{{See also|Stratospheric sulfur aerosols (geoengineering)|Albedo}}
Solar radiation management<ref>http://thehardlook.typepad.com/thehardlook/files/schnare_supplemental_testimony_a_framework_for_geoengineering.pdf</ref> (SRM) projects seek to reduce the amount of sunlight heating the Earth and thus counteract global warming. They do not reduce [[greenhouse gas]] concentrations in the [[atmosphere]], and thus do not address problems such as [[ocean acidification]] caused by these gases. Solar radiation management projects often have the advantage of speed. While [[greenhouse gas remediation]] offers a comprehensive possible solution to climate change, it does not give instant results; for that, solar radiation management is required.


=== Ocean geoengineering ===
Techniques that fall into this category include:
{{Main|Carbon sequestration#Sequestration techniques in oceans}}
* Creating reflective [[aerosols]], such as [[stratospheric sulfur aerosols (geoengineering)|stratospheric sulfur aerosols]].
{{See also|Ocean fertilization}}
* Ocean foams<ref>{{cite doi|10.3354/cr00885}}</ref>
* [[Cool roof]]—using pale-coloured roofing and paving materials
* [[Cloud reflectivity enhancement]] – using fine [[sea water]] spray to whiten clouds and increase cloud reflectivity.
* [[Space sunshade]]—obstructing [[solar radiation]] with space-based mirrors or other structures


Ocean geoengineering involves adding material such as lime or iron to the ocean to affect its ability to support marine life and/or sequester {{Chem|CO|2}}. In 2021 the US [[National Academies of Sciences, Engineering, and Medicine]] (NASEM) requested $2.5 billion funds for research in the following decade, specifically including field tests.<ref name=":0">{{Cite web |last=Voosen |first=Paul |date=16 December 2022 |title=Ocean geoengineering scheme aces its first field test |url=https://www.science.org/content/article/ocean-geoengineering-scheme-aces-its-first-field-test |access-date=2022-12-19 |website=www.science.org |language=en}}</ref>
===Greenhouse gas remediation===
{{Main|Greenhouse gas remediation|Carbon sequestration}}
Greenhouse gas remediation projects seek to remove greenhouse gases from the atmosphere, and thus tackle the root cause of global warming. They either directly remove greenhouse gases, or alternatively seek to influence natural processes to remove greenhouse gases indirectly. These projects offer a comprehensive solution to the problem of excess greenhouse gases in the atmosphere, but they will take many years to work fully. Many projects overlap with [[carbon capture and storage]] and [[carbon sequestration]] projects, and may not be considered to be geoengineering by all commentators. Techniques in this category include:
* [[Ocean nourishment]] including [[Iron fertilisation]] of the oceans
* Creating [[biochar]] (anaerobic charcoal) and burying it to create [[terra preta]]
* [[Bio-energy with carbon capture and storage]]
* [[Carbon air capture]] to remove [[carbon dioxide]] from ambient air


===Arctic geoengineering===
==== Ocean liming ====
{{Main|Carbon sequestration#Adding bases to neutralize acids|Ocean acidification#Carbon removal technologies which add alkalinity}}
[[File:2007 Arctic Sea Ice.jpg|thumb|250px|right|Significant reduction in ice volume in the Arctic Ocean in the range between 1979 and 2007 years]]
Enriching seawater with calcium hydroxide ([[Lime (material)|lime]]) has been reported to lower [[Ocean acidification|ocean acidity]], which reduces pressure on [[marine life]] such as [[oysters]] and absorb {{Chem|CO|2}}. The added lime raised the water's [[pH]], capturing {{Chem|CO|2}} in the form of [[calcium bicarbonate]] or as [[carbonate]] deposited in [[mollusk]] shells. Lime is produced in volume for the cement industry.<ref name=":0" /> This was assessed in 2022 in an experiment in [[Apalachicola, Florida]] in an attempt to halt declining oyster populations. pH levels increased modestly, as {{Chem|CO|2}} was reduced by 70 ppm.<ref name=":0" />
{{Main|Arctic geoengineering}}
Various hydrological geoengineering projects aim to change the climate without directly or indirectly removing greenhouse gases, or directly influencing [[solar radiation]]. These principally act by limiting [[Arctic shrinkage|Arctic sea ice loss]]. Keeping the Arctic ice is seen by many commentators as vital,<ref>http://www.cleverclimate.org/climate/25/motivation/</ref> due to its role in the planet's [[albedo]] and in keeping [[methane]], which is an important greenhouse gas, locked up in [[permafrost]].<ref>Zimov, S. A., et al. (2006), CLIMATE CHANGE: Permafrost and the Global Carbon Budget, Science, 312(5780), 1612-1613.</ref>


A 2014 experiment added [[sodium hydroxide]] (lye) to part of Australia's [[Great Barrier Reef]]. It raised pH levels to nearly preindustrial levels.<ref name=":0" />
===Heat transport===
The use of vertical ocean pipes to mix cooler deep water and warmer surface water has been proposed. This technology has also been suggested for the disruption of [[hurricanes]] by [[Bill Gates]] and others in a recent [[patent application]].<ref>
US Patent Application No. 20090177569, titled: “Water alteration structure risk management or ecological alteration management systems and methods”
US Patent Application No. 20090175685, titled: “Water alteration structure movement method and system”
US Patent Application No. 20090173801, titled: “Water alteration structure and system having below surface valves or wave reflectors”
US Patent Application No. 20090173404, titled: “Water alteration structure and system”
US Patent Application No. 20090173386</ref><ref>{{cite news|url=http://www.usatoday.com/weather/research/2009-07-15-gates-hurricanes_N.htm|title=Hurricane-calming technology? Bill Gates has a plan |date=2009-07-15|accessdate=2009-07-23 | work=USA Today | first=Dan | last=Vergano}}</ref> Modification of hurricanes may be considered [[weather modification]] rather than geoengineering, depending on the definition used.


However, producing alkaline materials typically releases large amounts of {{Chem|CO|2}}, partially offsetting the sequestration. Alkaline additives become diluted and dispersed in one month, without durable effects, such that if necessary, the program could be ended without leaving long-term effects.<ref name=":0" />
==Justification==


==== Iron fertilization ====
===Tipping points and positive feedback===
{{excerpt|Iron fertilization|paragraphs=1|file=no}}
[[File:65 Myr Climate Change.png|thumb|300px|right|Climate change during the last 65 million years. The Paleocene–Eocene Thermal Maximum is labelled PETM.]]
It is argued that [[climate change]] has already, or is soon to have passed one or more [[tipping point (climatology)|tipping point]]s<ref name="ReferenceA">{{cite doi|10.1073/pnas.0705414105}}</ref> where aspects of the climate system may 'tip' from one stable state to another stable state, much like a glass tipping over. When the new stable state is reached, it may trigger or accelerate warming [[positive feedback]] effects,<ref>http://www.energybulletin.net/node/10322</ref> such as the collapse of Arctic sea ice triggering the release of [[methane]] from [[permafrost]] in [[Siberia]].<ref>{{cite news| url=http://www.independent.co.uk/environment/climate-change/exclusive-the-methane-time-bomb-938932.html | work=The Independent | location=London | title=The methane time bomb | first=Steve | last=Connor | date=2008-09-23 | accessdate=2010-03-30}}</ref><ref>{{cite news| url=http://www.telegraph.co.uk/scienceandtechnology/science/sciencenews/3352065/Arctic-ice-hits-'tipping-point'.html | work=[[The Daily Telegraph]] | location=London | title=Arctic ice hits 'tipping point' | first=Roger | last=Highfield | date=2007-03-16 | accessdate=2010-03-30}}</ref> The "nightmare scenario" is that a [[domino effect]] will occur, with successive parts of the climate system tipping one after the other, with each change being caused by the previous one and causing the next one. Such a situation will lead to spiralling and potentially sudden climate change.


==== Submarine forest ====
The precise identity of such "tipping points" is not clear, with scientists taking differing views on whether specific systems are capable of "tipping" and the point at which this "tipping" will occur.<ref>http://researchpages.net/ESMG/people/tim-lenton/tipping-points/</ref> An example of a previous tipping point is that which preceded the rapid warming leading up to the [[Paleocene–Eocene Thermal Maximum]]. Once the tipping point is reached, cuts in greenhouse gas emissions will not be able to reverse the change. Depending on the precise nature of the individual system that "tips", [[positive feedback]]s may occur, with warming causing more warming, which causes yet more warming—a runaway global warming event.<ref>{{cite news| url=http://www.guardian.co.uk/environment/2006/sep/04/greenpolitics.science | work=The Guardian | location=London | title=Energy review ignores climate change 'tipping point' | first=Alok | last=Jha | date=2006-09-04 | accessdate=2010-03-30}}</ref> Therefore, some commentators suggest that more conservative use of resources is not enough to [[mitigation of global warming|mitigate global warming]]. Even if all greenhouse emissions suddenly came to a complete halt, the world would continue to be affected for centuries,<ref>http://cbs2.com/national/Global.Warming.Paris.2.279083.html</ref> and further warming may occur due to positive feedback. Conservation of resources and reduction of greenhouse emissions, used in conjunction with geoengineering, are therefore considered a viable option.<ref>{{cite news| url=http://www.guardian.co.uk/environment/2006/oct/18/bookextracts.books | work=The Guardian | location=London | title=How close is runaway climate change? | first=Paul | last=Brown | date=2006-10-18 | accessdate=2010-03-30}}</ref><ref>http://ipsnews.net/news.asp?idnews=42662</ref><ref>{{cite news| url=http://www.independent.co.uk/news/science/global-warming-now-unstoppable-scientists-warn-702979.html | work=[[The Independent]] | location=London | title=Global warming now 'unstoppable', scientists warn | first=Charles | last=Arthur | date=2001-01-23 | accessdate=2010-03-30}}</ref> Geoengineering offers the hope of temporarily reversing some aspects of climate change and allowing the natural climate to be substantially preserved whilst greenhouse gas emissions are brought under control and removed from the [[atmosphere]] by natural or artificial processes.
Another 2022 experiment attempted to sequester carbon using [[giant kelp]] planted off the [[Namibia]]n coast.<ref name=":0" /> Whilst this approach has been called ''ocean geoengineering'' by the researchers it is just another form of carbon dioxide removal via sequestration. Another term that is used to describe this process is ''[[blue carbon]] management'' and also ''marine geoengineering''.


=== Glacier stabilization ===
===Precautionary principle===
[[File:Wolovick2018_Thwaites_sill_timelines.png|thumb|left|A proposed "underwater sill" blocking 50% of warm water flows heading for the glacier could have the potential to delay its collapse and the resultant sea level rise by many centuries.<ref name="Wolovick2018" />]]
{{Main|Precautionary principle}}
{{excerpt|Thwaites Glacier#Engineering options for stabilization|paragraphs=1,2|file=no}}
Bearing in mind the threats from climate change, it can be argued that attempting geoengineering represents a lesser risk than not pursuing such strategies. While the understanding of geoengineering techniques is limited, the risks of global warming are at least partially understood, and are severe.<ref>http://unfccc.int/resource/conv/conv_005.html</ref>


===Costs===
==Problems==
Interventions at large scale run a greater risk of unintended disruptions of natural systems, resulting in a dilemma that such disruptions might be more damaging than the climate damage that they offset.<ref name="perspectives2" />


According to climate economist [[Gernot Wagner]] the term ''geoengineering'' is "largely an artefact and a result of the terms frequent use in popular discourse" and "so vague and all-encompassing as to have lost much meaning".<ref name=":04" />{{Rp|page=14}}
Some geoengineering techniques, such as [[cool roof]] techniques, can be achieved at little or no cost, and may even offer a financial payback.<ref>http://www.ornl.gov/sci/roofs+walls/facts/CoolCalcEnergy.htm</ref> IPCC (2007) concluded that reliable cost estimates for geoengineering options had not been published.<ref name=ipcc/> In general, solar radiation management techniques are substantially cheaper than are carbon dioxide removal techniques.{{Citation needed|date=August 2011}}


=== Ethical aspects ===
===Ethics and Responsibility===
Climate engineering may reduce the urgency of reducing carbon emissions, a form of [[moral hazard]].<ref name="Extreme action guardian2">{{cite news |last=Adam |first=David |date=1 September 2008 |title=Extreme and risky action the only way to tackle global warming, say scientists |work=The Guardian |url=https://www.theguardian.com/environment/2008/sep/01/climatechange.scienceofclimatechange2 |url-status=live |access-date=2009-05-23 |archive-url=https://web.archive.org/web/20190806230902/https://www.theguardian.com/environment/2008/sep/01/climatechange.scienceofclimatechange2 |archive-date=2019-08-06}}</ref> Also, most efforts have only temporary effects, which implies rapid rebound if they are not sustained.<ref name=":4">{{cite web |year=2009 |title=Geoengineering |url=http://www.irgc.org/geoengineering |url-status=dead |archive-url=https://web.archive.org/web/20091203132630/http://www.irgc.org/geoengineering |archive-date=2009-12-03 |access-date=2009-10-07 |publisher=[[International Risk Governance Council]]}}</ref> The Union of Concerned Scientists points to the danger that the technology will become an excuse not to address the root causes of climate change, slow our emissions reductions and start moving toward a low-carbon economy.<ref>{{Cite web |date=Dec 4, 2020 |title=What Is Solar Geoengineering? |url=https://www.ucsusa.org/resources/what-solar-geoengineering |website=The Union of Concerned Scientists}}</ref> However, several public opinion surveys and focus groups reported either a desire to increase emission cuts in the presence of climate engineering, or no effect.<ref>{{Cite journal |last1=Kahan |first1=Dan M. |last2=Jenkins-Smith |first2=Hank |last3=Tarantola |first3=Tor |last4=Silva |first4=Carol L. |last5=Braman |first5=Donald |date=2015-03-01 |title=Geoengineering and Climate Change Polarization Testing a Two-Channel Model of Science Communication |journal=The Annals of the American Academy of Political and Social Science |volume=658 |issue=1 |pages=192–222 |doi=10.1177/0002716214559002 |issn=0002-7162 |s2cid=149147565}}</ref><ref>{{Cite journal |last1=Wibeck |first1=Victoria |last2=Hansson |first2=Anders |last3=Anshelm |first3=Jonas |date=2015-05-01 |title=Questioning the technological fix to climate change{{Snd}} Lay sense-making of geoengineering in Sweden |url=http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-119732 |journal=Energy Research & Social Science |volume=7 |pages=23–30 |doi=10.1016/j.erss.2015.03.001}}</ref><ref>{{Cite journal |last1=Merk |first1=Christine |last2=Pönitzsch |first2=Gert |last3=Kniebes |first3=Carola |last4=Rehdanz |first4=Katrin |last5=Schmidt |first5=Ulrich |date=2015-02-10 |title=Exploring public perceptions of stratospheric sulfate injection |journal=Climatic Change |volume=130 |issue=2 |pages=299–312 |bibcode=2015ClCh..130..299M |doi=10.1007/s10584-014-1317-7 |issn=0165-0009 |s2cid=154196324}}</ref> Other modelling work suggests that the prospect of climate engineering may in fact increase the likelihood of emissions reduction.<ref>{{Cite journal |last=Reynolds |first=Jesse |date=2015-08-01 |title=A critical examination of the climate engineering moral hazard and risk compensation concern |journal=The Anthropocene Review |volume=2 |issue=2 |pages=174–191 |doi=10.1177/2053019614554304 |issn=2053-0196 |s2cid=59407485}}</ref><ref>{{Cite journal |last=Morrow |first=David R. |date=2014-12-28 |title=Ethical aspects of the mitigation obstruction argument against climate engineering research |journal=Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences |volume=372 |issue=2031 |pages=20140062 |bibcode=2014RSPTA.37240062M |doi=10.1098/rsta.2014.0062 |issn=1364-503X |pmid=25404676 |doi-access=free}}</ref><ref>{{Cite journal |last=Urpelainen |first=Johannes |date=2012-02-10 |title=Geoengineering and global warming: a strategic perspective |journal=International Environmental Agreements: Politics, Law and Economics |volume=12 |issue=4 |pages=375–389 |doi=10.1007/s10784-012-9167-0 |issn=1567-9764 |s2cid=154422202}}</ref><ref>{{Cite journal |last=Moreno-Cruz |first=Juan B. |date=2015-08-01 |title=Mitigation and the geoengineering threat |journal=Resource and Energy Economics |volume=41 |pages=248–263 |doi=10.1016/j.reseneeco.2015.06.001|hdl=1853/44254 |hdl-access=free }}</ref>
Climate engineering would represent a large-scale, intentional effort to modify the environment, which differ from inadvertent climate change through activities such as burning fossil fuels. Intentional climate change is viewed very differently from a moral standpoint.<ref>Bodansky, D. (1996) May we engineer the climate? [[Climatic Change]] 33: 309-321</ref> This raises questions of whether we as humans have the right to change the climate. The selection of a globally-agreed target temperature is a significant problem in any geoengineering [[governance]] regime, as different countries or interest groups may seek different global temperatures<ref name = geoengineering_option>Victor, D. G., M. G. Morgan, J. Apt, J. Steinbruner, K. Ricke (2009) The Geoengineering Option: A last resort against global warming? Foreign Affairs March/April 2009</ref>


If climate engineering can alter the climate, then this raises questions whether humans have the right to deliberately change the climate, and under what conditions. For example, using climate engineering to stabilize temperatures is not the same as doing so to optimize the climate for some other purpose. Some religious traditions express views on the relationship between humans and their surroundings that encourage (to conduct responsible stewardship) or discourage (to avoid hubris) explicit actions to affect climate.<ref>{{cite journal |last1=Clingerman |first1=F. |last2=O'Brien |first2=K. |year=2014 |title=Playing God: why religion belongs in the climate engineering debate |journal=[[Bulletin of the Atomic Scientists]] |volume=70 |issue=3 |pages=27–37 |bibcode=2014BuAtS..70c..27C |doi=10.1177/0096340214531181 |s2cid=143742343}}</ref>
Solar radiation management is an incomplete solution to global warming.<ref>Michaelson, J. (1998) ‘Geoengineering: a climate change Manhattan project’. [[Stanford University|Stanford]] Environmental Law Journal, Stanford CA, January 1998</ref> The possible option of geoengineering may reduce incentives to reduce emissions of greenhouse gases. It is argued that geoengineering could be used to ‘buy time’ before drastic climate change happens, allowing [[Climate change mitigation|mitigation]] and adaptation measures more time to be implemented and work.<ref>Gardiner, S. M. Is “Arming the Future” with geoengineering really the lesser evil? Some doubts about the ethics of intentionally manipulating the climate system in Gardiner, S., S. Caney, D. Jamieson & H. Shue (eds) Climate Ethics: Essential Readings. Oxford University Press, 2010, 284-314</ref> But the opposition points out that there are issues regarding the interference this causes with actual efforts for climate change, creating an unnecessary distraction.
== Society and culture ==


===Political viability===
=== Public perception ===
A large 2018 study used an online survey to investigate public perceptions of six climate engineering methods in the United States, United Kingdom, Australia, and New Zealand.<ref name=":13">{{Cite journal |last1=Carlisle |first1=Daniel P. |last2=Feetham |first2=Pamela M. |last3=Wright |first3=Malcolm J. |last4=Teagle |first4=Damon A. H. |date=2020-04-12 |title=The public remain uninformed and wary of climate engineering |url=https://eprints.soton.ac.uk/440717/1/Thepublic_remain_uninformed.pdf |url-status=live |journal=Climatic Change |language=en |volume=160 |issue=2 |pages=303–322 |bibcode=2020ClCh..160..303C |doi=10.1007/s10584-020-02706-5 |issn=1573-1480 |archive-url=https://web.archive.org/web/20210614062101/https://eprints.soton.ac.uk/440717/1/Thepublic_remain_uninformed.pdf |archive-date=2021-06-14 |access-date=2021-05-18 |s2cid=215731777}}</ref> Public awareness of climate engineering was low; less than a fifth of respondents reported prior knowledge. Perceptions of the six climate engineering methods proposed (three from the carbon dioxide removal group and three from the solar radiation modification group) were largely negative and frequently associated with attributes like 'risky', 'artificial' and 'unknown effects'. Carbon dioxide removal methods were preferred over solar radiation modification. Public perceptions were remarkably stable with only minor differences between the different countries in the surveys.<ref name=":13" /><ref name=":22">{{Cite journal |last1=Wright |first1=Malcolm J. |last2=Teagle |first2=Damon A. H. |last3=Feetham |first3=Pamela M. |date=February 2014 |title=A quantitative evaluation of the public response to climate engineering |url=https://www.nature.com/articles/nclimate2087 |url-status=live |journal=Nature Climate Change |language=en |volume=4 |issue=2 |pages=106–110 |bibcode=2014NatCC...4..106W |doi=10.1038/nclimate2087 |issn=1758-6798 |archive-url=https://web.archive.org/web/20200728153000/https://www.nature.com/articles/nclimate2087 |archive-date=2020-07-28 |access-date=2020-05-22}}</ref>
It has been argued that regardless of the economic, scientific and technical aspects, the difficulty of achieving concerted political action on climate change requires other approaches.<ref>{{cite news| url=http://www.guardian.co.uk/commentisfree/cifamerica/2008/dec/12/environment-climate-change-poznan | work=The Guardian | location=London | title=Let's get real on the environment | date=2008-12-12 | accessdate=2010-03-30 | first=David | last=Appell}}</ref> Those arguing political expediency say the difficulty of achieving meaningful emissions cuts <ref>{{cite news| url=http://www.nytimes.com/2007/10/24/opinion/24caldiera.html?_r=2&ref=opinion&oref=slogin | work=The New York Times | title=How to Cool the Globe | first=Ken | last=Caldeira | date=2007-10-24 | accessdate=2010-03-30}}</ref> and the effective failure of the [[Kyoto Protocol]] demonstrate the practical difficulties of achieving carbon dioxide [[emissions reduction]] by the agreement of the [[international community]].<ref>{{cite news| url=http://www.guardian.co.uk/environment/2008/sep/01/climatechange.scienceofclimatechange2 | work=The Guardian | location=London | title=Extreme and risky action the only way to tackle global warming, say scientists | first=David | last=Adam | date=2008-09-01 | accessdate=2010-03-30}}</ref> However, others point to support for geoengineering proposals among think tanks with a history of climate change skepticism and opposition to emissions reductions as evidence that the prospect of geoengineering is itself already politicized and being promoted as part of an argument against the need for (and viability of) emissions reductions; that, rather than geoengineering being a solution to the difficulties of emissions reductions, the prospect of geoengineering is being used as part of an argument to stall emissions reductions in the first place.<ref>http://www.worldchanging.com/archives/009784.html</ref>


Some environmental organizations (such as [[Friends of the Earth]] and [[Greenpeace]]) have been reluctant to endorse or oppose solar radiation modification, but are often more supportive of nature-based carbon dioxide removal projects, such as [[afforestation]] and [[peatland restoration]].<ref name="Extreme action guardian2" /><ref name="Geoengineering no solution2">{{cite news |last=Parr |first=Doug |date=1 September 2008 |title=Geo-engineering is no solution to climate change |work=Guardian Newspaper |location=London |url=https://www.theguardian.com/environment/2008/sep/01/climatechange.scienceofclimatechange1 |url-status=live |access-date=2009-05-23 |archive-url=https://web.archive.org/web/20180820234933/https://www.theguardian.com/environment/2008/sep/01/climatechange.scienceofclimatechange1 |archive-date=2018-08-20}}</ref>
Geoenginering poses several challenges in the context of governance because of issues of power and jurisdiction.<ref name = benefits_risks_costs>[[Alan Robock|Robock, A.]], A. Marquardt, B. Kravitz, and G. Stenchikov (2009). Benefits, Risks, and costs of stratospheric geoengineering, Geophysical Research Letters, 36, D19703, doi:10.1029/2009GL039209</ref> Geoengineering as a climate change solution differs from other mitigation and adaptation strategies. Unlike a carbon trading system that would be focused on participation from multiple parties along with transparency, monitoring measures and compliance procedures; this is not necessarily required by geoengineering. Bengtsson<ref>Bengtsson, L. (2006) ‘Geo-engineering to confine climate change: is it at all feasible?’ Climatic Change 77: 229-234</ref> (2006) argues that “the artificial release of sulphate aerosols is a commitment of at least several hundred years”. This highlights the importance for a political framework that is sustainable enough to contain a multilateral commitment over such a long period and yet is flexible as the techniques innovate through time. There are many controversies surrounding this topic and hence, geoengineering has been made into a very political issue. Most discussions and debates are not about which geoengineering technique is better than the other, or which one is more economically and socially feasible. Discussions are broadly on who will have control over the deployment of geoengineering and under what governance regime the deployment can be monitored and supervised. This is especially important due to the regional variability of the effects of many geoengineering techniques, benefiting some countries while damaging others. The challenge posed by geoengineering is not how to get countries to do it. It is to address the fundamental question of who should decide whether and how geoengineering should be attempted – a problem of governance.<ref>Barrett, S (2007) Why cooperate? The incentive to supply global public goods. Oxford University Press, Oxford</ref>


==History ==
==Risks and criticisms==
Several organizations have investigated climate engineering with a view to evaluating its potential, including the [[US Congress]],<ref name="Bullis2">{{cite web |last=Bullis |first=Kevin |title=U.S. Congress Considers Geoengineering |url=http://www.technologyreview.com/view/416187/us-congress-considers-geoengineering/ |url-status=live |archive-url=https://web.archive.org/web/20130126213315/http://www.technologyreview.com/view/416187/us-congress-considers-geoengineering/ |archive-date=26 January 2013 |access-date=26 December 2012 |work=MIT Technology Review}}</ref> the US National Academy of Sciences, Engineering, and Medicine,<ref>{{Cite web |title=Climate Intervention Reports » Climate Change at the National Academies of Sciences, Engineering, and Medicine |url=https://nas-sites.org/americasclimatechoices/other-reports-on-climate-change/2015-2/climate-intervention-reports/ |url-status=live |archive-url=https://web.archive.org/web/20160729015758/http://nas-sites.org/americasclimatechoices/other-reports-on-climate-change/2015-2/climate-intervention-reports/ |archive-date=2016-07-29 |access-date=2015-11-02 |website=nas-sites.org}}</ref> the [[Royal Society]],<ref>{{cite press release |title=Stop emitting CO2 or geoengineering could be our only hope |url=http://royalsociety.org/Stop-emitting-CO2-or-geoengineering-could-be-our-only-hope/ |date=28 August 2009 |publisher=The Royal Society |access-date=14 June 2011 |archive-date=24 June 2011 |archive-url=https://web.archive.org/web/20110624054716/http://royalsociety.org/Stop-emitting-CO2-or-geoengineering-could-be-our-only-hope/ |url-status=live}}</ref> the [[UK Parliament]],<ref>{{cite web |date=March 2009 |title=Geo-engineering research |url=https://researchbriefings.files.parliament.uk/documents/POST-PN-327/POST-PN-327.pdf |access-date=2022-09-11 |work=Postnote |publisher=Parliamentary Office of Science and Technology}}</ref> the [[Institution of Mechanical Engineers]],<ref name="imeche092">{{cite web |title=Geo-engineering{{Snd}} Giving us the time to act? |url=http://www.imeche.org/Libraries/Key_Themes/IMechEGeoengineeringReport.sflb.ashx |url-status=dead |archive-url=https://web.archive.org/web/20110722191723/http://www.imeche.org/Libraries/Key_Themes/IMechEGeoengineeringReport.sflb.ashx |archive-date=2011-07-22 |access-date=2011-03-12 |publisher=I Mech E}}</ref> and the [[Intergovernmental Panel on Climate Change]]. The IMechE report examined a small subset of proposed methods (air capture, urban albedo and algal-based {{co2}} capture techniques), and its main conclusions were that climate engineering should be researched and trialed at the small scale alongside a wider [[decarbonization]] of the economy.<ref name="imeche092" />
Various criticisms have been made of geoengineering.<ref>{{cite web|url=http://www.ametsoc.org/policy/2009geoengineeringclimate_amsstatement.pdf|title=AMS Policy Statement on Geoengineering the Climate System|publisher=American Meteorological Society|accessdate=2009-07-22}}</ref> Some commentators appear fundamentally opposed. Groups such as [[ETC Group]]<ref name=ETC>{{cite web|title=ETC website|url=http://www.etcgroup.org/en/issues/geoengineering}}</ref> and individuals such as [[Raymond Pierrehumbert]] have called for a moratorium on geoengineering techniques.<ref>http://www.worldchanging.com/archives/008091.html</ref><ref>http://features.csmonitor.com/environment/2008/07/16/can-we-engineer-a-cooler-earth/</ref>


The Royal Society review examined a wide range of proposed climate engineering methods and evaluated them in terms of effectiveness, affordability, timeliness, and safety (assigning [[Qualitative data|qualitative]] estimates in each assessment). The key recommendations reports were that "Parties to the [[UNFCCC]] should make increased efforts towards mitigating and adapting to climate change, and in particular to agreeing to global emissions reductions", and that "[nothing] now known about geoengineering options gives any reason to diminish these efforts".<ref name="Royal Society Policy Document2">{{cite report |url=http://royalsociety.org/uploadedFiles/Royal_Society_Content/policy/publications/2009/8693.pdf |title=Geoengineering the Climate: Science, Governance and Uncertainty |author=Working group |date=2009 |publisher=The Royal Society |location=London |page=1 |isbn=978-0-85403-773-5 |id=RS1636 |access-date=2011-12-01 |archive-url=https://web.archive.org/web/20140312031514/http://royalsociety.org/uploadedfiles/royal_society_content/policy/publications/2009/8693.pdf |archive-date=2014-03-12 |url-status=live}}</ref> Nonetheless, the report also recommended that "research and development of climate engineering options should be undertaken to investigate whether low-risk methods can be made available if it becomes necessary to reduce the rate of warming this century".<ref name="Royal Society Policy Document2" />
===Ineffectiveness===
The effectiveness of the schemes proposed may fall short of predictions. In ocean [[iron fertilization]], for example, the amount of carbon dioxide removed from the [[atmosphere]] may be much lower than predicted, as carbon taken up by [[plankton]] may be released back into the atmosphere from dead plankton, rather than being carried to the bottom of the sea and sequestered.<ref>Seasonal rhythms of net primary production and particulate organic carbon flux to depth describe the efficiency of biological pump in the global ocean", Journal of Geophysical Research, vol. 112, C10011, doi:10.1029/2006JC003706</ref>


In 2009, a review examined the scientific plausibility of proposed methods rather than the practical considerations such as engineering feasibility or economic cost. The authors found that "[air] capture and storage shows the greatest potential, combined with [[afforestation]], reforestation and bio-char production", and noted that "other suggestions that have received considerable media attention, in particular, "ocean pipes" appear to be ineffective".<ref name="lenton092">{{cite journal |last=Lenton |first=T.M. |author2=Vaughan, N.E. |year=2009 |title=The radiative forcing potential of different climate geoengineering options |url=http://www.atmos-chem-phys.net/9/5539/2009/acp-9-5539-2009.html |url-status=live |journal=[[Atmospheric Chemistry and Physics]] |volume=9 |issue=15 |pages=5539–5561 |bibcode=2009ACP.....9.5539L |doi=10.5194/acp-9-5539-2009 |archive-url=https://web.archive.org/web/20191214043800/https://www.atmos-chem-phys.net/9/5539/2009/acp-9-5539-2009.html |archive-date=2019-12-14 |access-date=2009-09-04 |doi-access=free}}</ref> They concluded that "[climate] geoengineering is best considered as a potential complement to the mitigation of {{co2}} emissions, rather than as an alternative to it".<ref name="lenton092" />
[[File:WOA05 GLODAP del pH AYool.png|thumb|right|300px|Change in sea surface [[pH]] caused by [[anthropogenic]] [[carbon dioxide|CO<sub>2</sub>]] between the 1700s and the 1990s. This [[ocean acidification]] will still be a major problem unless [[atmosphere|atmospheric]] CO<sub>2</sub> is reduced.]]


In 2015, the US National Academy of Sciences, Engineering, and Medicine concluded a 21-month project to study the potential impacts, benefits, and costs of climate engineering. The differences between these two classes of climate engineering "led the committee to evaluate the two types of approaches separately in companion reports, a distinction it hopes carries over to future scientific and policy discussions."<ref name="www8.nationalacademies.org2">{{Cite press release |title=Climate Intervention Is Not a Replacement for Reducing Carbon Emissions; Proposed Intervention Techniques Not Ready for Wide-Scale Deployment |url=http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=02102015 |website=NEWS from the national academies |date=Feb 10, 2015 |access-date=2015-11-24 |archive-date=2015-11-17 |archive-url=https://web.archive.org/web/20151117032144/http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=02102015 |url-status=live}}</ref><ref name="Climate Intervention2">{{Cite book |author=National Research Council<!--|last2 = Impacts|first2 = Committee on Geoengineering Climate: Technical Evaluation Discussion of|last3 = Division On Earth And Life Studies|first3 = National Research Council (U.S.)|last4 = Ocean Studies Board|first4 = National Research Council (U.S.)|last5 = Climate|first5 = Board on Atmospheric Sciences--> |title=Climate Intervention: Reflecting Sunlight to Cool Earth |date=2017 |publisher=The National Academies Press |isbn=978-0-309-31482-4 |doi=10.17226/18988}} Ebook: {{ISBN|978-0-309-31485-5}}.</ref><ref>{{Cite book |author=National Research Council |url=https://www.nap.edu/catalog/18805/climate-intervention-carbon-dioxide-removal-and-reliable-sequestration |title=Climate Intervention: Carbon Dioxide Removal and Reliable Sequestration |date=2015 |isbn=978-0-309-30529-7 |language=en |doi=10.17226/18805 |access-date=2018-08-20 |archive-url=https://web.archive.org/web/20180821031740/https://www.nap.edu/catalog/18805/climate-intervention-carbon-dioxide-removal-and-reliable-sequestration |archive-date=2018-08-21 |url-status=live}}</ref> The resulting study titled ''Climate Intervention'' was released in February 2015 and consists of two volumes: ''Reflecting Sunlight to Cool Earth''<ref name="Council2">{{Cite book |author=National Research Council |url=https://www.nap.edu/catalog/18988/climate-intervention-reflecting-sunlight-to-cool-earth |title=Climate Intervention: Reflecting Sunlight to Cool Earth |year=2015 |publisher=National Academies Press |isbn=978-0-309-31482-4 |language=en |access-date=2018-08-20 |archive-url=https://web.archive.org/web/20191214192318/http://www.nap.edu/catalog.php?record_id=18988 |archive-date=2019-12-14 |url-status=live}}</ref> and ''Carbon Dioxide Removal and Reliable Sequestration''.<ref>{{Cite book |author=National Research Council |url=https://www.nap.edu/catalog/18805/climate-intervention-carbon-dioxide-removal-and-reliable-sequestration |title=Climate Intervention: Carbon Dioxide Removal and Reliable Sequestration |year=2015 |publisher=National Academies Press |isbn=978-0-309-30529-7 |language=en |access-date=2018-08-20 |archive-url=https://web.archive.org/web/20180821031740/https://www.nap.edu/catalog/18805/climate-intervention-carbon-dioxide-removal-and-reliable-sequestration |archive-date=2018-08-21 |url-status=live}}</ref>
=== Incomplete solution to CO<sub>2</sub> emissions ===
Techniques that do not remove [[greenhouse gases]] from the [[atmosphere]] may control [[global warming]], but do not reduce other effects from these gases, such as [[ocean acidification]].<ref>http://infohost.nmt.edu/~chem/wingenter/Wingenter_PeECE_III_GRL_2007.pdf</ref> While not an argument against geoengineering ''per se'', this is an argument against reliance on geoengineering to the exclusion of greenhouse gas reduction.


In June 2023 the US government released a report that recommended conducting research on stratospheric aerosol injection and marine cloud brightening.<ref>{{Cite web |last=Hanley |first=Steve |date=2023-07-03 |title=US & EU Quietly Begin To Discuss Geoengineering |url=https://cleantechnica.com/2023/07/03/us-eu-quietly-begin-to-discuss-geoengineering/ |access-date=2023-07-06 |website=CleanTechnica |language=en-US}}</ref>
===Control and predictability problems===
The full effects of various geoengineering schemes are not well understood.<ref>http://news.mongabay.com/2007/0627-planktos.html</ref> Matthews et al.<ref>{{cite doi|10.1088/1748-9326/4/4/045105}}</ref> compared geoengineering to a number of previous environmental interventions and concluded that "Given our current level of understanding of the climate system, it is likely that the result of at least some geoengineering efforts would follow previous ecological examples where increased human intervention has led to an overall increase in negative environmental consequences."


As of 2024 the Coastal Atmospheric Aerosol Research and Engagement (CAARE) project was launching [[sea salt]] into the marine sky in an effort to increase cloud "brightness" (reflective capacity). The sea salt is launched from the [[USS Hornet Sea, Air & Space Museum]] (based on the project's regulatory filings).<ref>{{Cite web |title=Marine Cloud Brightening Program studies clouds, aerosols and pathways to reduce climate risks |url=https://environment.uw.edu/news/2024/04/marine-cloud-brightening-program-studies-clouds-aerosols-and-pathways-to-reduce-climate-risks |access-date=2024-04-08 |website=College of the Environment |language=en-US}}</ref>
Performance of the systems may become ineffective, unpredictable or unstable as a result of external events, such as [[volcanic eruptions]], [[phytoplankton]] blooms, [[El Niño]], [[solar flares]], etc., potentially leading to profound and unpredictable disruption to the climate system.

It may be difficult to predict the effectiveness of projects,<ref>Keith Bower et al., 2006 Computational assessment of a proposed technique for global warming mitigation via albedo-enhancement of marine stratocumulus clouds. Atmos. Res., vol. 82, no. 1-2, 2006, pp. 328-336</ref> with models of techniques giving widely varying results.<ref>http://royalsociety.org/page.asp?tip=1&id=6232</ref> In the instances of systems which involve [[tipping point]]s, this may result in irreversible effects. [[Climate modelling]] is far from an exact science even when applied to comparatively well-understood natural climate systems, and it is made more complex by the need to understand novel and unnatural processes which by definition lack relevant observation data.<ref>{{cite news| url=http://news.bbc.co.uk/1/hi/sci/tech/4762720.stm | work=BBC News | title=Guns and sunshades to rescue climate | date=2006-03-02 | accessdate=2010-03-30 | first=Molly | last=Bentley}}</ref>

===Side effects===
The techniques themselves may cause significant foreseen or unforeseen harm. For example, the use of reflective [[balloons]] may result in significant [[litter]],<ref>http://books.nap.edu/openbook.php?record_id=1605&page=824</ref> which may be harmful to [[wildlife]].

[[Ozone depletion]] is a risk of some geoengineering techniques, notably those involving [[sulfur]] delivery into the [[stratosphere]].<ref>The Sensitivity of Polar Ozone Depletion to Proposed Geoengineering
Schemes", Science, vol. 320, no. 5880, 30 May 2008, pp. 1201-1204, doi:10.1126/science.1153966</ref>

The active nature of geoengineering may in some cases create a clear division between winners and losers. Most of the proposed interventions are regional, such as albedo modification in the [[Arctic]]. Necessarily, such interventions compel those in the affected regions to tolerate the effects of geoengineering for the supposed benefit of the global climate.<ref>http://www.newscientist.com/article/dn12397</ref>

There may be unintended climatic consequences, such as changes to the [[hydrological cycle]]<ref>http://www.sciencedaily.com/releases/2008/05/080527155519.htm</ref> including [[droughts]]<ref>I. M. Held et al., "Simulation of Sahel drought in the 20th and 21st centuries", Proceedings of the National Academy of Sciences, vol. 102, no. 50, pp. 17891–17896, doi:10.1073/pnas.0509057102. Available online at: http://climate.envsci.rutgers.edu/pdf/2008JD010050small.pdf</ref> or [[floods]], caused by the geoengineering techniques, but possibly not predicted by the [[climate modelling|models]] used to plan them.<ref>Keith Bower et al., 2006 Computational assessment of a proposed technique for global warming
mitigation via albedo-enhancement of marine stratocumulus clouds. Atmos. Res., vol. 82, no. 1-2, 2006, pp. 328–336</ref> Such effects may be cumulative or [[chaos theory|chaotic]] in nature, making prediction and control very difficult.<ref>{{cite web
| last = Robock
| first = Alan
| title = ''20 reasons why geoengineering may be a bad idea ''
| publisher = ''[http://www.thebulletin.org "Bulletin of the Atomic Scientists"]''
| date = May / June 2008
| url = http://thebulletin.metapress.com/content/r567g4063g1h562l/?p=a537203c8e7b4be3b0cd5cd51fa30b61&pi=5
| doi= 10.2968/064002006
| accessdate = 2009-08-04 }}</ref>

===Unreliable systems===
The performance of the interventions may be inconsistent due to mechanical failure, non-availability of consumables or funding problems.

The geoengineering techniques would, in many instances, be vulnerable to being switched off or deliberately destroyed. As examples, cloud making ships could be switched off or sunk and space mirrors could be tilted to make them useless. Anyone capable of exerting such power may seek to abuse it for commercial gain, military advantage or simple terrorism.

===Weaponisation===
Geoengineering research began as a war tactic in the 1940s for the US and the Soviet Union during the Cold War.<ref name = geoengineering_option/> During the Vietnam War, the US used geoengineering to flood certain areas. Then in 1976, 85 countries signed the U.N. Convention on the Prohibition of Military of Any Other Hostile Use of Environmental Modification Techniques.<ref name = benefits_risks_costs/>

The [[Environmental Modification Convention]] generally prohibits weaponising geoengineering techniques. However, this does not eliminate the risk. Geoengineering techniques may serve as [[weapon of mass destruction|weapons of mass destruction]], creating droughts or famines designed to destroy or disable an enemy.<ref>http://www.foreignpolicy.com/story/cms.php?story_id=4146</ref> They could also be used simply to make battlefield conditions more favourable to one side or the other in a war<ref>http://www.fas.org/spp/military/docops/usaf/2025/v3c15/v3c15-1.htm
</ref> (such as in [[Operation Popeye]]). For example, [[laser-guided]] weapons are confounded by clouds, and thus switching off cloud machines would favour forces using such weapons, and switching them on would favour ground forces defending against them.<ref>http://www.fas.org/man/dod-101/sys/smart/lgb.htm</ref>

Whilst laws or treaties may prevent the manipulation of the climate as a weapon of war,<ref>http://www.state.gov/t/ac/trt/4783.htm</ref> it could be argued that geoengineering is itself a manipulation, and thus destroying or disabling the geoengineering structures is not prohibited. A new legal framework may be necessary in the event that large-scale geoengineering becomes established.{{Or|date=November 2010}}

[[Carnegie]]’s [[Ken Caldeira]] said, "It will make it harder to achieve broad consensus on developing and governing these technologies if there is suspicion that gaining military advantage is an underlying motivation for its development..."<ref>
{{cite web|url=http://groups.google.com/group/climateintervention/browse_thread/thread/60f448608e209134?pli=1|title=DARPA and Geoengineering|last=Caldiera|first=Ken|coauthors=Various|date=March 18, 2009|work=Geoengineering Google group|accessdate=2009-03-21}}</ref>

===Effect on sunlight, sky and clouds===
Managing solar radiation using aerosols or cloud cover will change the ratio between direct and indirect solar radiation. This may affect plant life<ref>L. Gu et al., "Responses of Net Ecosystem Exchanges
of Carbon Dioxide to Changes in Cloudiness: Results from Two North American Deciduous Forests", Journal of Geophysical Research, vol. 104, no. 31, pp. 421–31, 434 (1999); L. Gu et al., "Advantages of Diffuse Radiation for Terrestrial Ecosystem Productivity", Journal of Geophysical Research, vol. 107, (2002); L. Gu et al., "Response of a Deciduous Forest to the Mount Pinatubo Eruption: Enhanced Photosynthesis", Science, vol. 299, pp. 2,035–38 (2003)</ref> and [[solar energy]].<ref>Balan Govindasamy and Ken Caldeira, "Geoengineering Earth's Radiation Balance to Mitigate CO2-Induced Climate Change", Geophysical Research Letters, vol. 27, pp. 2,141–44 (2000). For the response of solar power systems, see Michael C. MacCracken, "Geoengineering: Worthy of Cautious Evaluation?" Climatic Change, vol. 77, pp. 235–43 (2006)</ref> There will be a significant effect on the appearance of the [[sky]] from [[aerosol]] projects, notably a hazing of blue skies and a change in the appearance of [[sunset]]s.<ref>http://www.nasa.gov/centers/langley/news/researchernews/rn_robockfeature.html</ref> Aerosols may affect the formation of clouds, especially [[cirrus cloud]]s.<ref>K. Sassen et al., ";The 5–6 December 1991 FIRE IFO II Jet Stream Cirrus Case Study: Possible Influences of Volcanic Aerosols", Journal of Atmospheric Science, vol. 52, pp. 97–123 (1993)</ref>

===Moral hazard===
The existence of such techniques may reduce the political and social impetus to reduce carbon emissions.<ref>David Adam, "Extreme and risky action the only way to tackle global warming, say scientists",
Guardian, 1 September 2008. Available online at: http://www.guardian.co.uk/environment/
2008/sep/01/climatechange.scienceofclimatechange2</ref>. The issue of [[moral hazard]] means that many environmental groups and campaigners are reluctant to advocate geoengineering for fear of reducing the imperative to cut [[greenhouse gas]] emissions.<ref name="Moral hazard">{{cite web|url=http://www.celsias.com/article/geo-engineering-a-moral-hazard/|title=Geo-Engineering - a Moral Hazard|date=14 November 2007|publisher=celsias.com|accessdate=9 September 2010}}</ref>

Other criticism comes from those who see geoengineering projects as reacting to the symptoms of global warming rather than addressing the [[Attribution of recent climate change|real causes of climate change]]. Because geoengineering is a form of controlling the risks associated with global warming, it leads to a [[moral hazard]] problem. The problem is that knowledge that geoengineering is possible could lead to climate impacts seeming less fearsome, which could in turn lead to a weaker commitment to reducing greenhouse gas emissions.<ref>{{cite web|url=http://www.ted.com/index.php/talks/view/id/192|title=A surprising idea for solving climate change (lecture at TED conference)|author=David Keith|accessdate=2008-04-06}}</ref>

===Lack of global control===
Geoengineering opens up various political and economic issues. [[David Keith (scientist)|David Keith]] argues that the cost of geoengineering the Earth is within the realm of small countries, large corporations, or even very wealthy individuals.<ref name=Keith2 /> Steve Rayner agrees that not all geoengineering possibilities are expensive, and that some, such as ocean iron fertilisation, are within the reach of very wealthy individuals, calling them a "Greenfinger" (after the fictional [[Auric Goldfinger|Goldfinger]]).<ref name="news.bbc.co.uk">{{cite news| url=http://news.bbc.co.uk/nol/shared/spl/hi/programmes/analysis/transcripts/31_07_08.txt | work=BBC News | accessdate=2010-03-30}}</ref><ref name=Randerson>{{cite news|url=http://www.guardian.co.uk/environment/2008/nov/18/climatechange-greentech|title=Geoengineering 'no substitute' for climate targets, UK minister warns|date=2008-11-18|work=[[The Guardian]]|author=James Randerson|publisher=Guardian News and Media Limited | location=London}}</ref> David Victor suggests that geoengineering is within the reach of any individual who has a small fraction of the bank account of [[Bill Gates]], who takes it upon him or her self to be the "self-appointed protector of the planet".<ref>{{cite journal|journal=[[Oxford Review of Economic Policy]]|year=2008|volume=24|issue=2|pages=322–336|doi=10.1093/oxrep/grn018|publisher=Oxford University Press|title=On the regulation of geoengineering|author=David G. Victor}}</ref>

This effectively eliminates any control over who gets to decide when to cool the Earth and how often this should be done.<ref name=Keith2>{{cite web|url=http://www.ucalgary.ca/~keith/papers/89.Keith.EngineeringThePlanet.p.pdf|format=PDF|title=Engineering the Planet|author=David Keith|accessdate=2008-04-08|pages="3–4,8"}}</ref> The resulting power would be enormous, and could not necessarily be readily controlled by legal, political or regulatory systems.<ref name="news.bbc.co.uk"/> These legal and regulatory systems may themselves be far less powerful than the geoengineers controlling the climate become.

It is quite feasible for [[carbon offsetting]] firms to set up unregulated, unsupervised and dangerous geoengineering projects. This may be done in order to sell [[carbon credits]] to individuals and firms.

Geoengineering schemes have the potential to cause significant environmental damage, and may even end up releasing further [[greenhouse gases]] into the [[atmosphere]].<ref>http://www.abc.net.au/science/articles/2007/11/09/2085584.htm</ref> Opposition to some early schemes has been intense, with respected environmental groups campaigning against them.<ref>http://www.worldwildlife.org/who/media/press/2007/WWFPresitem973.html</ref>

===Rapid warming if stopped===

If [[solar radiation management]] were to abruptly stop, the climate would rapidly warm.<ref name="ReferenceB">{{cite doi|10.1088/1748-9326/4/4/045103}}</ref> This would cause a sudden rise in global temperatures towards levels which would have existed without the use of the geoengineering technique. The rapid rise in temperature may lead to more severe consequences than a gradual rise of the same magnitude.<ref name="ReferenceB"/>

==Implementation issues==
There is no general consensus that geoengineering is safe, appropriate or effective, for the reasons listed above. Other environmentalists see calls for geoengineering as part of an explicit strategy to delay emissions reductions on the part of those with connections to [[coal]] and [[petroleum|oil]] industries.<ref>http://www.worldchanging.com/archives//009753.html</ref>{{syn|date=April 2011}}

All proposed geoengineering techniques require implementation on a relatively large scale, in order to make a significant difference to the Earth's climate. The least costly schemes are budgeted at a cost of millions,<ref>http://docs.google.com/gview?attid=0.1&thid=11e473ed2477ae05&a=v&pli=1</ref> with many more complex schemes such as [[space sunshade]] costing far more.

Many techniques, again such as space sunshade, require a complex technical development process before they are ready to be implemented. There is no clear institutional mechanism for handling this [[research and development]] process. As a result, many promising techniques do not have the engineering development or experimental evidence to determine their feasibility or efficacy at present.

Once a technique has been developed and tested, its implementation is still likely to be difficult. Climate change is by nature a global problem, and therefore no one institution, company or government is responsible for it. The substantial costs of most geoengineering techniques therefore cannot currently be apportioned. Roll-out of such technologies is therefore likely to be delayed until these issues can be resolved. A notable exception is the use of small [[albedo]] manipulation projects, known as ''cool roof'', in which the colour of roofing or paving surfaces can be manipulated to reflect solar radiation back into space. These can be, and are, implemented by individuals, companies and governments without controversy.<ref>http://www.consumerenergycenter.org/coolroof/</ref>

Due to the radical changes caused by geoengineering interventions, legal issues are also an impediment to implementation. The changes resulting from geoengineering necessarily benefit some people and disadvantage others. There may therefore be legal challenges to the implementation of geoengineering techniques by those adversely affected by them.<ref>http://ieet.org/index.php/IEET/more/2094/</ref>

==Evaluation of geoengineering==
Most of what is known about the suggested techniques is based on laboratory experiments, observations of natural phenomena and on [[computer modelling]] techniques. Some geoengineering schemes employ methods that have analogues in natural phenomena such as [[stratospheric sulfur aerosols]] and [[cloud condensation nuclei]]. As such, studies about the efficacy of these schemes can draw on information already available from other research, such as that following the 1991 [[volcanic eruption|eruption]] of [[Mount Pinatubo]]. However, comparative evaluation of the relative merits of each technology is complicated, especially given modelling uncertainties and the early stage of engineering development of many geoengineering schemes.<ref>http://www.imeche.org/media/Public+Affairs/geoenginq.htm</ref>

Reports into geoengineering have also been published in the [[United Kingdom]] by the [[Institution of Mechanical Engineers]]<ref name="imeche09"/> and the [[Royal Society]].<ref name="roysoc09"/> The IMechE report examined a small subset of proposed schemes (air capture, urban albedo and algal-based {{co2}} capture schemes), and its main conclusions were that geoengineering should be researched and trialled at the small scale alongside a wider [[decarbonisation]] of the economy.<ref name="imeche09"/>

The Royal Society review examined a wide range of geoengineering schemes and evaluated them in terms of effectiveness, affordability, timeliness and safety (assigning [[qualitative data|qualitative]] estimates in each assessment). Similarly to Lenton and Vaughan,<ref name="lenton09"/> the report divided schemes into "carbon dioxide removal" (CDR) and "solar radiation management" (SRM) approaches that respectively address longwave and shortwave radiation. The key recommendations of the report were that "Parties to the [[UNFCCC]] should make increased efforts towards mitigating and adapting to climate change, and in particular to agreeing to global emissions reductions", and that "[nothing] now known about geoengineering options gives any reason to diminish these efforts".<ref name="roysoc09"/> Nonetheless, the report also recommended that "research and development of geoengineering options should be undertaken to investigate whether low risk methods can be made available if it becomes necessary to reduce the rate of warming this century".<ref name="roysoc09"/>

In a 2009 review study, Lenton and Vaughan evaluated a range of geoengineering schemes from those that sequester {{co2}} from the atmosphere and decrease [[longwave radiation]] trapping, to those that decrease the Earth's receipt of [[shortwave radiation]].<ref name="lenton09"/> In order to permit a comparison of disparate techniques, they used a common evaluation for each scheme based on its effect on net radiative forcing. As such, the review examined the scientific plausibility of schemes rather than the practical considerations such as engineering feasibility or economic cost. Lenton and Vaughan found that "[air] capture and storage shows the greatest potential, combined with afforestation, reforestation and bio-char production", and noted that "other suggestions that have received considerable media attention, in particular “ocean pipes” appear to be ineffective".<ref name="lenton09"/> They concluded that "[climate] geoengineering is best considered as a potential complement to the mitigation of {{co2}} emissions, rather than as an alternative to it".<ref name="lenton09"/>


==See also==
==See also==
{{Portal box|Environment|Sustainable development}}
{{Portal|Environment|Weather|Global warming}}
{{Div col}}
* [[Arctic geoengineering]]
* [[Climate justice]]
* [[Earth systems engineering and management]]
* [[Land surface effects on climate]]
* [[List of geoengineering topics]]
* [[List of geoengineering topics]]
* [[Weather modification]]
* [[List of proposed geoengineering projects]]
{{Div col end}}
* [[Convention on Biological Diversity]]
{{Clear}}
* [[ETC Group]]

* [[Arctic geoengineering]]
==Further reading==
* [[Terraforming]]
* [[Liao, S. Matthew]]; [[Sandberg, Anders]]; [[Roache, Rebecca]] (2012). "[https://derkamerad.com/wp-content/uploads/2022/12/Ethics-Policy-And-Environment-June-2012-%E2%80%93-Human-Engineering-And-Climate-Change.pdf Human Engineering and Climate Change]." ''Ethics, Policy & Environment'', 15(2), 206–221. doi:10.1080/21550085.2012.685574
* [[Virgin Earth Challenge]]
* Döbler, Niklas A.; Carbón, Claude (2023). "[https://link.springer.com/content/pdf/10.1007/s12124-023-09797-6.pdf Adapting Ourselves, Instead of the Environment: An Inquiry into Human Enhancement for Function and Beyond.]" ''Integrative Psychological & Behavioral Science'', 58, 589-637. doi:10.1007/s12124-023-09797-6
* [[Planetary Engineering]]
* [[Weather control]]
* [[Carbon sink]]


==References==
==References==
{{Reflist|2}}
{{Reflist}}


{{Climate change}}
==Further reading==
{{Human impact on the environment}}
* {{cite book|title=Geo-Engineering Climate Change: Environmental Necessity or Pandora’s Box?|
{{Engineering fields}}
editor1-first=Brian|editor1-last=[[Brian Launder|Launder]]|editor2-first=J. Michael T. |editor2-last=Thompson|publisher=[[Cambridge University Press]]|date=December 2009|isbn=978-0-521-198035}}
{{Population}}
*{{cite book|author=[[Eli Kintisch]]|year=2010|title=Hack the Planet: Science's Best Hope, or Worst Nightmare, for Averting Climate Catastrophe|isbn=978-0470524268}}
{{Authority control}}
*{{cite book|author=Jeff Goodell|authorlink=Jeff Goodell|year=2010|title=How to Cool the Planet: Geoengineering and the Audacious Quest to Fix Earth’s Climate|isbn=978-0618990610}}
* {{cite journal| journal= Nature| volume= 447| pages= 132–136| date=May 10, 2007 | doi=10.1038/447132a| title=Climate change: Is this what it takes to save the world?| first=Oliver| last= Morton| pmid= 17495899| issue= 7141}} --Abstract only, full article requires payment.
*{{cite book|author=[[James Rodger Fleming]]|publisher=[[Columbia University Press]]|date=September 15, 2010|title=Fixing the Sky: The Checkered History of Weather and Climate Control|isbn=978-0231144124}}


[[Category:Climate engineering| ]]
==External links==
[[Category:Climate change|Engineering]]
* [http://www.newscientist.com/article/dn19660-what-the-un-ban-on-geoengineering-really-means.html What the UN ban on geoengineering really means] November 1, 2010 by [[Fred Pearce]] of [[New Scientist]]
[[Category:Climate change policy|Engineering]]
* [http://www.washingtonpost.com/wp-dyn/content/article/2010/10/29/AR2010102906361.html Geoengineering sparks international ban, first-ever congressional report] Juliet Eilperin [[Washington Post]] October 30, 2010
[[Category:Emissions reduction]]
* [http://www.washingtonpost.com/wp-srv/nation/pdfs/Geongineeringreport.pdf Engineering the Climate : Research Needs and Strategies for International Coordination October 2010 report] from the [[U.S. House of Representatives]]
[[Category:Engineering disciplines]]
* [http://www.washingtonpost.com/wp-dyn/content/article/2010/10/03/AR2010100303437.html Threat of global warming sparks U.S. interest in geoengineering] by Juliet Eilperin of the [[Washington Post]] October 3, 2010
* [http://www.theatlantic.com/magazine/archive/2009/07/re-engineering-the-earth/7552/ Re-Engineering the Earth] by Graeme Wood of [[The Atlantic]] , July 2009
* [http://www.worldchanging.com/archives/008364.html Geoengineering Retrospective] Overview of articles on geoengineering by Julia Levitt, [[Worldchanging]], August 2008
* [http://geo-engineering.blogspot.com/ Geo-engineering website, describing current methods/proposals done to revert climate change by geo-engineering], by Sam Carana
* [http://www.geocrisis.com/cpe_geoengineering_menu.htm Geoengineering links], [[GeoCrisis]] annotated list, 2006?
*[http://www.technologyreview.com/energy/24157/ "The Geoengineering Gambit"], [[Technology Review]], Jan. 2010
* [http://www.time.com/time/specials/2007/article/0,28804,1720049_1720050_1721653,00.html 10 Ideas That Are Changing The World: 6.Geoengineering] [[Time (magazine)]], March 2008
* [http://orgprints.org/15528/01/15528.pdf Geo-engineering in the Southern Ocean], by John Paull, [[Australian National University]], 2009
* [http://news.bbc.co.uk/1/hi/programmes/6298507.stm 5 ways to save the earth], BBC documentary about geo-engineering, 20 February 2007
* [http://www.wired.com/science/planetearth/news/2007/07/geoengineering Climate Engineering Is Doable, as Long as We Never Stop] [[Wired (magazine)]], July 2007
* [http://www.metatronics.net/lit/geo2.html "Geoengineering: A Climate Change Manhattan Project"] by Jay Michaelson, Stanford Environmental Law Journal, 1998
* [http://www.openthefuture.com/wcarchive/2005/08/terraforming_earth_iv_the_ques.html Terraforming Earth IV: The Question of Methane] August 11, 2005
* [http://news.bbc.co.uk/2/hi/programmes/6354759.stm "Futuristic fleet of 'cloudseeders'"] John Latham BBC News. Feb. 15, 2007
* [http://www.democracynow.org/2010/7/8/a_debate_on_geoengineering_vandana_shiva A Debate on Geoengineering: Vandana Shiva vs. Gwynne Dyer] - video report by ''[[Democracy Now!]]''
* [http://www.npr.org/templates/story/story.php?storyId=127245606 Geoengineering: 'A Bad Idea Whose Time Has Come'] discussion on [[NPR]]
* [http://www.guardian.co.uk/environment/2010/apr/06/geoengineering-carbon-emissions We need birth control, not geoengineering] April 6, 2010
* [http://www.guardian.co.uk/environment/2010/may/14/bill-gates-cloud-whitening-dangerous Bill Gates' cloud-whitening trials 'a dangerous experiment'] May 14, 2010 regarding [[Bill Gates]]
* [http://www.guardian.co.uk/environment/2010/sep/13/geoengineering-coalition-world-climate The powerful coalition that wants to engineer the world's climate: Businessmen, scientists and right-wing thinktanks are joining forces to promote 'geo-engineering' ideas to cool the planet's climate] September 13, 2010 [[Clive Hamilton]]

[[Category:Global warming]]
[[Category:Planetary engineering]]
[[Category:Planetary engineering]]
[[Category:Emissions reduction]]
[[Category:Geoengineering| ]]

[[bg:Геоинженерство]]
[[da:Geo-engineering]]
[[de:Geo-Engineering]]
[[es:Geoingeniería]]
[[fr:Géo-ingénierie]]
[[id:Teknik kebumian]]
[[it:Geoingegneria]]
[[hu:Geomérnökség]]
[[nl:Geo-engineering]]
[[ja:地球工学]]
[[pl:Inżynieria pogody i klimatu]]
[[ru:Геоинженерия]]

Latest revision as of 15:01, 25 June 2024

Climate engineering (or geoengineering) is an umbrella term for both carbon dioxide removal and solar radiation modification, when applied at a planetary scale.[1]: 168  However, these two processes have very different characteristics. For this reason, the Intergovernmental Panel on Climate Change no longer uses this overarching term.[1]: 168 [2] Carbon dioxide removal approaches are part of climate change mitigation. Solar radiation modification is reflecting some sunlight (solar radiation) back to space.[3] All forms of climate engineering cannot be standalone solutions to climate change, but need to be coupled with other forms of climate change mitigation.[4] Some publications place passive radiative cooling into the climate engineering category. This technology increases the Earth's thermal emittance.[5][6][7] The media tends to use climate engineering also for other technologies such as glacier stabilization, ocean liming, and iron fertilization of oceans. The latter would modify carbon sequestration processes that take place in oceans.

Some types of climate engineering are highly controversial due to the large uncertainties around effectiveness, side effects and unforeseen consequences.[8] However, the risks of such interventions must be seen in the context of the trajectory of climate change without them.[9][10]

According to climate economist Gernot Wagner, the term geoengineering is "so vague and all-encompassing as to have lost much meaning".[8]: 14 

Terminology[edit]

Climate engineering (or geoengineering) has been used as an umbrella term for both carbon dioxide removal and solar radiation management, when applied at a planetary scale.[1]: 168  However, these two methods have very different geophysical characteristics, which is why the Intergovernmental Panel on Climate Change no longer uses this term.[1]: 168 [2] This decision was communicated in around 2018, see for example the "Special Report on Global Warming of 1.5 °C".[11]: 550  Specific technologies that fall into the "climate engineering" umbrella term include:[12]: 30 

The following methods are not termed climate engineering in the latest IPCC assessment report in 2022[1]: 6–11  but are included under this umbrella term by other publications on this topic:[24][8]

Technologies[edit]

Carbon dioxide removal[edit]

Planting trees is a nature-based way to remove carbon dioxide from the atmosphere, however the effect may only be temporary in some cases.[31][32]

Carbon dioxide removal (CDR) is a process in which carbon dioxide (CO2) is removed from the atmosphere by deliberate human activities and durably stored in geological, terrestrial, or ocean reservoirs, or in products.[33]: 2221  This process is also known as carbon removal, greenhouse gas removal or negative emissions. CDR is more and more often integrated into climate policy, as an element of climate change mitigation strategies.[34][35] Achieving net zero emissions will require first and foremost deep and sustained cuts in emissions, and then—in addition—the use of CDR ("CDR is what puts the net into net zero emissions"[36]). In the future, CDR may be able to counterbalance emissions that are technically difficult to eliminate, such as some agricultural and industrial emissions.[37]: 114 

CDR includes methods that are implemented on land or in aquatic systems. Land-based methods include afforestation, reforestation, agricultural practices that sequester carbon in soils (carbon farming), bioenergy with carbon capture and storage (BECCS), and direct air capture combined with storage.[37]: 115  There are also CDR methods that use oceans and other water bodies. Those are called ocean fertilization, ocean alkalinity enhancement,[38] wetland restoration and blue carbon approaches.[37]: 115  A detailed analysis needs to be performed to assess how much negative emissions a particular process achieves. This analysis includes life cycle analysis and "monitoring, reporting, and verification" (MRV) of the entire process.[39] Carbon capture and storage (CCS) are not regarded as CDR because CCS does not reduce the amount of carbon dioxide already in the atmosphere.

Solar radiation modification[edit]

refer to caption and image description
Proposed solar radiation modification using a tethered balloon to inject sulfate aerosols into the stratosphere

Solar radiation modification (SRM), or solar geoengineering, is a type of climate engineering (or geoengineering) in which sunlight (solar radiation) would be reflected back to outer space to offset human-caused global warming. There are multiple potential approaches, with stratospheric aerosol injection being the most-studied, followed by marine cloud brightening. SRM could be a temporary measure to limit climate-change impacts while greenhouse gas emissions are reduced and carbon dioxide is removed,[40] but would not be a substitute for reducing emissions.

Multiple authoritative international scientific assessments, based on evidence from climate models and natural analogues, have generally shown that some forms of SRM could reduce global warming and many adverse effects of climate change.[41][42][43] Specifically, controlled stratospheric aerosol injection appears able to greatly moderate most environmental impacts—especially warming—and consequently most ecological, economic, and other impacts of climate change across most regions. However, because warming from greenhouse gases and cooling from SRM would operate differently across latitudes and seasons, a world where global warming would be offset by SRM would have a different climate from one where this warming did not occur in the first place. Furthermore, confidence in the current projections of how SRM would affect regional climate and ecosystems is low.[40]

Passive daytime radiative cooling[edit]

Enhancing the thermal emissivity of Earth through passive daytime radiative cooling has been proposed as an alternative or "third approach" to climate engineering[5][44] that is "less intrusive" and more predictable or reversible than stratospheric aerosol injection.[45]

Passive daytime radiative cooling (PDRC) can lower temperatures with zero energy consumption or pollution by radiating heat into outer space. Widespread application has been proposed as a solution to global warming.[46]

Passive daytime radiative cooling (PDRC) is a zero-energy building cooling method proposed as a solution to reduce air conditioning, lower urban heat island effect, cool human body temperatures in extreme heat, move toward carbon neutrality and control global warming by enhancing terrestrial heat flow to outer space through the installation of thermally-emissive surfaces on Earth that require zero energy consumption or pollution.[47][48][49][50][51][46][52][53][54] In contrast to compression-based cooling systems that are prevalently used (e.g., air conditioners), consume substantial amounts of energy, have a net heating effect, require ready access to electricity and often require coolants that are ozone-depleting or have a strong greenhouse effect,[55][56] application of PDRCs may also increase the efficiency of systems benefiting from a better cooling, such like photovoltaic systems, dew collection techniques, and thermoelectric generators.[57][58]

PDRC surfaces are designed to be high in solar reflectance (to minimize heat gain) and strong in longwave infrared (LWIR) thermal radiation heat transfer through the atmosphere's infrared window (8–13 μm) to cool temperatures even during the daytime.[59][60][61] It is also referred to as passive radiative cooling, daytime passive radiative cooling, radiative sky cooling, photonic radiative cooling, and terrestrial radiative cooling.[60][61][57][62] PDRC differs from solar radiation management because it increases radiative heat emission rather than merely reflecting the absorption of solar radiation.[63]
Video to explain some of the marine geoengineering approaches with a focus on their risks, negative impacts and potential side-effects, as well as on the question of governance of these technologies.

Ocean geoengineering[edit]

Ocean geoengineering involves adding material such as lime or iron to the ocean to affect its ability to support marine life and/or sequester CO
2
. In 2021 the US National Academies of Sciences, Engineering, and Medicine (NASEM) requested $2.5 billion funds for research in the following decade, specifically including field tests.[30]

Ocean liming[edit]

Enriching seawater with calcium hydroxide (lime) has been reported to lower ocean acidity, which reduces pressure on marine life such as oysters and absorb CO
2
. The added lime raised the water's pH, capturing CO
2
in the form of calcium bicarbonate or as carbonate deposited in mollusk shells. Lime is produced in volume for the cement industry.[30] This was assessed in 2022 in an experiment in Apalachicola, Florida in an attempt to halt declining oyster populations. pH levels increased modestly, as CO
2
was reduced by 70 ppm.[30]

A 2014 experiment added sodium hydroxide (lye) to part of Australia's Great Barrier Reef. It raised pH levels to nearly preindustrial levels.[30]

However, producing alkaline materials typically releases large amounts of CO
2
, partially offsetting the sequestration. Alkaline additives become diluted and dispersed in one month, without durable effects, such that if necessary, the program could be ended without leaving long-term effects.[30]

Iron fertilization[edit]

Iron fertilization is the intentional introduction of iron-containing compounds (like iron sulfate) to iron-poor areas of the ocean surface to stimulate phytoplankton production. This is intended to enhance biological productivity and/or accelerate carbon dioxide (CO2) sequestration from the atmosphere. Iron is a trace element necessary for photosynthesis in plants. It is highly insoluble in sea water and in a variety of locations is the limiting nutrient for phytoplankton growth. Large algal blooms can be created by supplying iron to iron-deficient ocean waters. These blooms can nourish other organisms.

Submarine forest[edit]

Another 2022 experiment attempted to sequester carbon using giant kelp planted off the Namibian coast.[30] Whilst this approach has been called ocean geoengineering by the researchers it is just another form of carbon dioxide removal via sequestration. Another term that is used to describe this process is blue carbon management and also marine geoengineering.

Glacier stabilization[edit]

A proposed "underwater sill" blocking 50% of warm water flows heading for the glacier could have the potential to delay its collapse and the resultant sea level rise by many centuries.[26]

Some engineering interventions have been proposed for Thwaites Glacier and the nearby Pine Island Glacier to physically stabilize its ice, or to preserve it by blocking the flow of warm ocean water, which currently renders the collapse of these two glaciers practically inevitable even without further warming.[64][65] A proposal from 2018 included building sills at the Thwaites' grounding line to either physically reinforce it, or to block some fraction of warm water flow. The former would be the simplest intervention, yet equivalent to "the largest civil engineering projects that humanity has ever attempted": it is also only 30% likely to work. Constructions blocking even 50% of the warm water flow are expected to be far more effective, yet far more difficult as well.[66] Further, some researchers argued that this proposal could be ineffective, or even accelerate sea level rise.[67] The original authors suggested attempting this intervention on smaller sites, like the Jakobshavn Glacier in Greenland, as a test,[66][65] as well as acknowledging that this intervention cannot prevent sea level rise from the increased ocean heat content, and would be ineffective in the long run without greenhouse gas emission reductions.[66]

In 2023, a modified proposal was tabled. It was proposed that an installation of underwater "curtains", made of a flexible material and anchored to the Amundsen Sea floor would be able to interrupt warm water flow while reducing costs and increasing their longevity (conservatively estimated at 25 years for curtain elements and up to 100 years for the foundations) relative to more rigid structures. With them in place, Thwaites Ice Shelf and Pine Island Ice Shelf would presumably regrow to a state they last had a century ago, thus stabilizing these glaciers.[68][69][65] To achieve this, the curtains would have to be placed at a depth of around 600 metres (0.37 miles) (to avoid damage from icebergs which would be regularly drifting above) and be 80 km (50 mi) long. The authors acknowledged that while work on this scale would be unprecedented and face many challenges in the Antarctic (including polar night and the currently insufficient numbers of specialized polar ships and underwater vessels), it would also not require any new technology and there is already experience of laying down pipelines at such depths.[68][69]

Problems[edit]

Interventions at large scale run a greater risk of unintended disruptions of natural systems, resulting in a dilemma that such disruptions might be more damaging than the climate damage that they offset.[9]

According to climate economist Gernot Wagner the term geoengineering is "largely an artefact and a result of the terms frequent use in popular discourse" and "so vague and all-encompassing as to have lost much meaning".[8]: 14 

Ethical aspects[edit]

Climate engineering may reduce the urgency of reducing carbon emissions, a form of moral hazard.[70] Also, most efforts have only temporary effects, which implies rapid rebound if they are not sustained.[71] The Union of Concerned Scientists points to the danger that the technology will become an excuse not to address the root causes of climate change, slow our emissions reductions and start moving toward a low-carbon economy.[72] However, several public opinion surveys and focus groups reported either a desire to increase emission cuts in the presence of climate engineering, or no effect.[73][74][75] Other modelling work suggests that the prospect of climate engineering may in fact increase the likelihood of emissions reduction.[76][77][78][79]

If climate engineering can alter the climate, then this raises questions whether humans have the right to deliberately change the climate, and under what conditions. For example, using climate engineering to stabilize temperatures is not the same as doing so to optimize the climate for some other purpose. Some religious traditions express views on the relationship between humans and their surroundings that encourage (to conduct responsible stewardship) or discourage (to avoid hubris) explicit actions to affect climate.[80]

Society and culture[edit]

Public perception[edit]

A large 2018 study used an online survey to investigate public perceptions of six climate engineering methods in the United States, United Kingdom, Australia, and New Zealand.[12] Public awareness of climate engineering was low; less than a fifth of respondents reported prior knowledge. Perceptions of the six climate engineering methods proposed (three from the carbon dioxide removal group and three from the solar radiation modification group) were largely negative and frequently associated with attributes like 'risky', 'artificial' and 'unknown effects'. Carbon dioxide removal methods were preferred over solar radiation modification. Public perceptions were remarkably stable with only minor differences between the different countries in the surveys.[12][81]

Some environmental organizations (such as Friends of the Earth and Greenpeace) have been reluctant to endorse or oppose solar radiation modification, but are often more supportive of nature-based carbon dioxide removal projects, such as afforestation and peatland restoration.[70][82]

History[edit]

Several organizations have investigated climate engineering with a view to evaluating its potential, including the US Congress,[83] the US National Academy of Sciences, Engineering, and Medicine,[84] the Royal Society,[85] the UK Parliament,[86] the Institution of Mechanical Engineers,[87] and the Intergovernmental Panel on Climate Change. The IMechE report examined a small subset of proposed methods (air capture, urban albedo and algal-based CO2 capture techniques), and its main conclusions were that climate engineering should be researched and trialed at the small scale alongside a wider decarbonization of the economy.[87]

The Royal Society review examined a wide range of proposed climate engineering methods and evaluated them in terms of effectiveness, affordability, timeliness, and safety (assigning qualitative estimates in each assessment). The key recommendations reports were that "Parties to the UNFCCC should make increased efforts towards mitigating and adapting to climate change, and in particular to agreeing to global emissions reductions", and that "[nothing] now known about geoengineering options gives any reason to diminish these efforts".[88] Nonetheless, the report also recommended that "research and development of climate engineering options should be undertaken to investigate whether low-risk methods can be made available if it becomes necessary to reduce the rate of warming this century".[88]

In 2009, a review examined the scientific plausibility of proposed methods rather than the practical considerations such as engineering feasibility or economic cost. The authors found that "[air] capture and storage shows the greatest potential, combined with afforestation, reforestation and bio-char production", and noted that "other suggestions that have received considerable media attention, in particular, "ocean pipes" appear to be ineffective".[89] They concluded that "[climate] geoengineering is best considered as a potential complement to the mitigation of CO2 emissions, rather than as an alternative to it".[89]

In 2015, the US National Academy of Sciences, Engineering, and Medicine concluded a 21-month project to study the potential impacts, benefits, and costs of climate engineering. The differences between these two classes of climate engineering "led the committee to evaluate the two types of approaches separately in companion reports, a distinction it hopes carries over to future scientific and policy discussions."[90][91][92] The resulting study titled Climate Intervention was released in February 2015 and consists of two volumes: Reflecting Sunlight to Cool Earth[93] and Carbon Dioxide Removal and Reliable Sequestration.[94]

In June 2023 the US government released a report that recommended conducting research on stratospheric aerosol injection and marine cloud brightening.[95]

As of 2024 the Coastal Atmospheric Aerosol Research and Engagement (CAARE) project was launching sea salt into the marine sky in an effort to increase cloud "brightness" (reflective capacity). The sea salt is launched from the USS Hornet Sea, Air & Space Museum (based on the project's regulatory filings).[96]

See also[edit]

Further reading[edit]

References[edit]

  1. ^ a b c d e IPCC (2022) Chapter 1: Introduction and Framing in 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
  2. ^ a b IPCC, 2021: Annex VII: Glossary [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C.  Méndez, S. Semenov, A. Reisinger (eds.)]. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 2215–2256, doi:10.1017/9781009157896.022.
  3. ^ National Academies of Sciences, Engineering (2021-03-25). Reflecting Sunlight: Recommendations for Solar Geoengineering Research and Research Governance. doi:10.17226/25762. ISBN 978-0-309-67605-2. S2CID 234327299. Archived from the original on 2021-04-17. Retrieved 2021-04-17.
  4. ^ Munday, Jeremy (2019). "Tackling Climate Change through Radiative Cooling". Joule. 3 (9): 2057–2060. doi:10.1016/j.joule.2019.07.010. S2CID 201590290. Further, radiative cooling cannot be a complete, standalone solution, but rather is part of a more comprehensive approach that must include CO2 reduction. Otherwise, the radiative balance will not last long, and the potential financial benefits of mitigation will not fully be realized because of continued ocean acidification, air pollution, and redistribution of biomass.
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