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Geoengineering (also known asclimate engineering orclimate intervention) is the deliberate large-scale interventions in the Earth’s climate system intended to counteract human-causedclimate change.[1] The term commonly encompasses two broad categories: large-scalecarbon dioxide removal (CDR) andsolar radiation modification (SRM). CDR involves techniques to removecarbon dioxide from the atmosphere and is generally considered a form ofclimate change mitigation. SRM aims to reduce global warming by reflecting a small portion ofsunlight (solar radiation) away from Earth and back into space. Although historically grouped together, these approaches differ substantially in mechanisms, timelines, and risk profiles, and are now typically discussed separately.[2]: 168 [3] Some other large-scale engineering proposals—such as interventions to slow the melting of polar and alpine ice—are also sometimes classified as forms of geoengineering.
Some types of geoengineering present political, social and ethical issues. One common objection is that focusing on these technologies could undermine efforts to reduce greenhouse gas emissions. Effective governance and international oversight are widely regarded as essential.
Major scientific organizations have examined the potential, risks, and governance needs of geoengineering, including theUS National Academies of Sciences, Engineering, and Medicine,[4][5][6] theRoyal Society,[7] the UN Educational, Scientific and Cultural Organization (UNESCO),[8] and theWorld Climate Research Programme.[1]
Carbon dioxide removal (CDR) is a process in whichcarbon dioxide (CO2) is removed fromEarth's atmosphere by deliberatehuman activities and durably stored in geological, terrestrial, or marine reservoirs, or in products.[11]: 2221 This process is also known as carbon removal, greenhouse gas removal or negative emissions. CDR is more and more often integrated intoclimate policy, as an element ofclimate change mitigation strategies.[12][13] Achievingnet 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 thenet intonet zero emissions"[14]). In the future, CDR may be able to counterbalance emissions that are technically difficult to eliminate, such as some agricultural and industrial emissions.[15]: 114
CDR includes methods that are implemented on land or in aquatic systems. Land-based methods includeafforestation,reforestation, agricultural practices that sequester carbon in soils (carbon farming),bioenergy with carbon capture and storage (BECCS), anddirect air capture combined with storage.[15][16] There are also CDR methods that use oceans and other water bodies. Those are calledocean fertilization,ocean alkalinity enhancement,[17]wetland restoration andblue carbon approaches.[15] A detailed analysis needs to be performed to assess how much negative emissions a particular process achieves. This analysis includeslife cycle analysis and "monitoring, reporting, and verification" (MRV) of the entire process.[18]Carbon capture and storage (CCS) are not regarded as CDR because CCS does not reduce the amount ofcarbon dioxide already in the atmosphere.
Solar radiation modification (SRM), also called solar geoengineering, is a group of large-scale approaches to reduceglobal warming by increasing the amount ofsunlight that is reflected away fromEarth and back toouter space. It is not intended to replaceefforts to reducegreenhouse gas emissions,[19] but rather to complement them as a potential way to limit global warming.[20]: 1489 SRM is a form of geoengineering.
The most-researched SRM method isstratospheric aerosol injection (SAI), in which small reflective particles would be introduced into the upper atmosphere to reflect sunlight.[21]: 350 Other approaches includemarine cloud brightening (MCB), which would increase the reflectivity of clouds over the oceans, or constructing aspace sunshade or aspace mirror, to reduce the amount of sunlight reaching earth.[22][23]
Glacial geoengineering is a set of proposed geoengineering approaches that focus on slowing the loss ofglaciers,ice sheets, andsea ice inpolar regions and, in some cases, alpine areas. Proposals are motivated by concerns that feedback loops—such as ice-albedo loss, accelerated glacier flow, and permafrost methane release—could amplifyclimate change and triggerclimate tipping points.[24][25]
Proposed glacial geoengineering methods include regional or localsolar radiation management, thinningcirrus clouds to allow more heat to escape, and deploying mechanical or engineering structures to stabilize ice. Specific strategies under investigation arestratospheric aerosol injection focused on polar regions,[24]marine cloud brightening,[26] surfacealbedo modification with reflective materials,[27] basal interventions such as draining subglacial water or promoting basal freezing,[25] andice shelf protection measures including seabed curtains.[28]
Glacial geoengineering is in the early research stage and many proposals face major technical, environmental, and governance challenges.[26] Supporters argue that targeted interventions could help stabilize ice sheets, slow sea-level rise, and reduce the risk of passing irreversible thresholds in theclimate system. At the same time, experts caution that the effectiveness of these methods remains highly uncertain and that interventions could produce unintended side effects.[25] Glacial geoengineering is generally considered a possible complement to, not a replacement for, efforts to reduce greenhouse gas emissions.[24][26]
Most governance issues relating to geoengineering are specific to the category or the specific method. Nevertheless, a couple of international governance instruments have addressed geoengineering collectively.
The Conference of Parties to theConvention on Biological Diversity have made several decisions regarding "climate related geoengineering." That of 2010 established "a comprehensive non-binding normative framework"[29]: 106 for "climate-related geoengineering activities that may affect biodiversity," requesting that such activities be justified by the need to gather specific scientific data, undergo prior environmental assessment, be subject to effective regulatory oversight.[30]: 96–97 [31]: 161–162 The Parties' 2016 decision called for "more transdisciplinary research and sharing of knowledge... in order to better understand the impacts of climate-related geoengineering."[31]: 161–162 [32]
The parties to theLondon Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter and its associated London Protocol have addressed "marine geoengineering." In 2013, the parties to the London Protocol adopted an amendment to establish a legally binding framework for regulating marine geoengineering, initially limited to ocean fertilization and requiring assessment and permitting before any activity proceeds. This amendment has not yet entered into force due to insufficient ratifications. In 2022, the parties to both agreements acknowledged growing interest in marine geoengineering, identified four techniques for priority review, and encouraged careful assessment of proposed projects under existing guidelines while considering options for further regulation. In 2023, they cautioned that these techniques could pose serious environmental risks, highlighted scientific uncertainty about their effects, urged strict application of assessment frameworks, and called for broader international cooperation.[33] Their work is supported by the Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection of theInternational Maritime Organization.[citation needed]
{{cite book}}: CS1 maint: location missing publisher (link)even if successful, SRM can not replace but only complement CO2 abatement.
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