Climate engineering
Climate engineering (or geoengineering) is an umbrella term for both carbon dioxide removal and solar radiation modification, when applied at a planetary scale.[1]: 6–11 However, these two processes have very different characteristics. For this reason, the Intergovernmental Panel on Climate Change no longer uses this overarching term.[1]: 6–11 [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,
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
Terminology
Climate engineering (or geoengineering) has been used as an umbrella term for both carbon dioxide removal and solar radiation management (or
- Carbon dioxide removal
- Biochar - Biochar is a high-carbon, fine-grained residue that is produced via pyrolysis[13]
- Bioenergy with carbon capture and storage (BECCS) - the process of extracting bioenergy from biomass and capturing and storing the carbon, thereby removing it from the atmosphere.[14]
- windgas.
- Enhanced weathering - a process that aims to accelerate the natural weathering by spreading finely ground silicate rock, such as basalt, onto surfaces which speeds up chemical reactions between rocks, water, and air. It also removes carbon dioxide (CO2) from the atmosphere, permanently storing it in solid carbonate minerals or ocean alkalinity.[15] The latter also slows ocean acidification.
- Solar Radiation Management
- anthropogenic global warming.[16]
- Stratospheric aerosol injection (SAI) - a proposed method to introduce aerosols into the stratosphere to create a cooling effect via global dimming and increased albedo, which occurs naturally from volcanic eruptions.[23]
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]
- 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 planting light-colored plants to help with reflecting sunlight back into space.[25]
- Glacier stabilization - proposals aiming to slow down or prevent sea level rise caused by the collapse of notable marine-terminating glaciers, such as Jakobshavn Glacier in Greenland or Thwaites Glacier and Pine Island Glacier in Antarctica. It may be possible to bolster some glaciers directly,[26] but blocking the flow of 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.[27][28][29]
- Ocean geoengineering[30] (adding material such as lime or iron to the ocean to affect its ability to sequester carbon dioxide)
Technologies
Carbon dioxide removal
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 includeSolar geoengineering
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 climate change. 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.
Studies usingPassive daytime radiative cooling
Enhancing the thermal emissivity of Earth through passive daytime radiative cooling has been proposed as an alternative or "third approach" to climate engineering[5][41] that is "less intrusive" and more predictable or reversible than stratospheric aerosol injection.[42]
Ocean geoengineering
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
Enriching seawater with calcium hydroxide (
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
Submarine forest
Another 2022 experiment attempted to sequester carbon using
Glacier stabilization
Some engineering interventions have been proposed for Thwaites Glacier and the nearby
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.[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
Climate engineering may reduce the urgency of reducing carbon emissions, a form of moral hazard.[67] Also, most efforts have only temporary effects, which implies rapid rebound if they are not sustained.[68] 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.[69] 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.[70][71][72] Other modelling work suggests that the prospect of climate engineering may in fact increase the likelihood of emissions reduction.[73][74][75][76]
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.[77]
Society and culture
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.[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][78]
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.[67][79]
History
Several organizations have investigated climate engineering with a view to evaluating its potential, including the
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
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".[86] 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".[86]
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."[87][88][89] The resulting study titled Climate Intervention was released in February 2015 and consists of two volumes: Reflecting Sunlight to Cool Earth[90] and Carbon Dioxide Removal and Reliable Sequestration.[91]
In June 2023 the US government released a report that recommended conducting research on stratospheric aerosol injection and marine cloud brightening.[92]
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).[93]
See also
- Arctic geoengineering
- Climate justice
- Earth systems engineering and management
- Land surface effects on climate
- List of geoengineering topics
- Weather modification
References
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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.
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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.
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