Climate engineering

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Climate engineering (also called geoengineering) is a term used for both carbon dioxide removal (CDR) and solar radiation management (SRM), also called solar geoengineering, when applied at a planetary scale.[1]: 6–11  However, they have very different geophysical characteristics which is why the IPCC (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 geoengineering involves reflecting some sunlight (solar radiation) back to space.[3] All forms of geoengineering are not a standalone solution to climate change, but need to be coupled with other forms of climate change mitigation.[4] Another approach to geoengineering is to increase the Earth's thermal emittance through passive radiative cooling.[5][6][7]

Carbon dioxide removal (CDR) is defined as "Anthropogenic activities removing carbon dioxide (CO2) from the atmosphere and durably storing it in geological, terrestrial, or ocean reservoirs, or in products. It includes existing and potential anthropogenic enhancement of biological or geochemical CO2 sinks and direct air carbon dioxide capture and storage (DACCS), but excludes natural CO2 uptake not directly caused by human activities."[2]

Some types of climate engineering is 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]

Definition[edit]

As of 2018 the terms "climate engineering" and "geoengineering" are not used by the Intergovernmental Panel on Climate Change (IPCC).[11]: 550  Climate engineering (or geoengineering) is used in the literature as a term for both CDR (carbon dioxide removal) or SRM (Solar radiation management or solar geoengineering) when applied at a planetary scale.[1]: 6–11  However, they have very different geophysical characteristic which is why the IPCC no longer uses this term.[1]: 6–11 [2]

Methods[edit]

Overview[edit]

The following list is an incomplete list of example technologies that have been called climate engineering approaches:[12]: 30 

Carbon dioxide removal[edit]

Planting trees is a means of carbon dioxide removal.

Carbon dioxide removal (CDR), also known as negative CO2 emissions, is a process in which carbon dioxide gas (CO2) is removed from the atmosphere and sequestered for long periods of time.[20][21][22] Similarly, greenhouse gas removal (GGR) or negative greenhouse gas emissions is the removal of greenhouse gases (GHGs) from the atmosphere by deliberate human activities, i.e., in addition to the removal that would occur via natural carbon cycle or atmospheric chemistry processes.[23] In the context of net zero greenhouse gas emissions targets,[24] CDR is increasingly integrated into climate policy, as a new element of mitigation strategies.[25] CDR and GGR methods are also known as negative emissions technologies (NET), and may be cheaper than preventing some agricultural greenhouse gas emissions.[26]

CDR methods include afforestation, agricultural practices that sequester carbon in soils, bio-energy with carbon capture and storage, ocean fertilization, enhanced weathering, and direct air capture when combined with storage.[21][27][28] To assess whether net negative emissions are achieved by a particular process, comprehensive life cycle analysis of the process must be performed.

Solar geoengineering[edit]

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

Solar geoengineering, or solar radiation modification (SRM), is a type of climate engineering in which sunlight (solar radiation) would be reflected back to outer space to limit or reverse human-caused climate change. It is not a substitute for reducing greenhouse gas emissions, but would act as a temporary measure to limit warming while emissions of greenhouse gases are reduced and carbon dioxide is removed. The most studied methods of SRM are stratospheric aerosol injection and marine cloud brightening.[29]

Solar geoengineering appears able to prevent some or much of climate change temperature increases.[30][31] Climate models consistently indicate that it is capable of returning global, regional, and local temperatures and precipitation closer to pre-industrial levels. Solar geoengineering's principal advantages are the speed with which it could be deployed and become active and the reversibility of its direct climatic effects,[32] although the latter varies depending on method, with some concerns raised over stratospheric aerosol injection.[33][34]

Proposed methods of solar geoengineering may be atmospheric, terrestrial, or space-based. Stratospheric aerosol injection appears technically feasible and inexpensive in terms of direct financial costs, though still out of reach for individuals, small states, or other non-state rogue actors; it would instead be the exclusive domain of large national economies or coalitions including at least one such economy.[32] Space-based propositions are only theoretical, being too expensive and infeasible to implement.[35]

Solar geoengineering would not directly reduce carbon dioxide concentrations in the atmosphere, and thus does not address ocean acidification or air pollution caused by high levels of atmospheric CO2.[31] Solar geoengineering's excessive and/or poorly distributed use, or sudden and sustained termination, could pose serious environmental risks. Other negative impacts are possible and more research is required to thoroughly address such impacts.[36] Governing solar geoengineering is challenging for multiple reasons, including that few countries would likely be capable of doing it alone.[36]

Passive daytime radiative cooling[edit]

Enhancing the thermal emissivity of Earth through passive daytime radiative cooling (PDRC) has been proposed as an alternative or "third approach" to geoengineering[37][38] that is "less intrusive" and more predictable or reversible than stratospheric aerosol injection.[39]

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.[40]

Passive daytime radiative cooling (PDRC) is a renewable cooling method proposed as a solution to global warming of enhancing terrestrial heat flow to outer space through the installation of thermally-emissive surfaces on Earth that require zero energy consumption or pollution.[40][41][42][43] Because all materials in nature absorb more heat during the day than at night, 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 during the daytime.[44][45][46] It is also referred to as passive radiative cooling (PRC), daytime passive radiative cooling (DPRC), radiative sky cooling (RSC), photonic radiative cooling, and terrestrial radiative cooling.[45][46][47][48] PDRC differs from solar radiation management because it increases radiative heat emission rather than merely reflecting the absorption of solar radiation.[49]

Some estimates propose that if 1-2% of the Earth's surface area were dedicated to PDRC that warming would cease and temperature increases would be rebalanced to survivable levels.[50][51] Regional variations provide different cooling potentials with desert and temperate climates benefiting more from application than tropical climates, attributed to the effects of humidity and cloud cover on reducing the effectiveness of PDRCs.[52][53][54] Low-cost scalable PDRC materials feasible for mass production have been developed, such as coatings, thin films, metafabrics, aerogels, and biodegradable surfaces, to reduce air conditioning, lower urban heat island effect, cool human body temperatures in extreme heat, and move toward carbon neutrality as a zero-energy cooling method.[55][56][57][58][59]

Application of PDRCs may also increase the efficiency of solar energy systems, dew collection techniques, and thermoelectric generation.[60][61] PDRCs can be modified to be self-adaptive if necessary, 'switching' from passive cooling to heating to mitigate any potential "overcooling" effects in urban environments.[56][62] They have also been developed in colors other than white, although there is generally a tradeoff in cooling potential, since darker color surfaces are less reflective.[63][64] Research, development, and interest in PDRCs has grown rapidly since the 2010s, which has been attributed to a scientific breakthrough in the use of photonic metamaterials to achieve daytime cooling in 2014,[65][66] along with growing concerns over energy use and global warming.[67][68]

Issues[edit]

Artefact[edit]

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 

Moral hazard and ethics[edit]

Climate engineering may reduce the urgency of reducing carbon emissions,[69] a form of moral hazard. However, several public opinion surveys and focus groups reported either desire to increase emission cuts in the presence of climate engineering, or of 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]

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 stablize 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.[75]

Opponents offer several objections:[76] Climate engineering could reduce pressure for emissions reductions, which could exacerbate overall climate risks. Also, most efforts have only temporary effects, requiring ever-increasing interventions which imply rapid rebound if they are not sustained. Others assert that the threat of climate engineering could spur emissions cuts.[76][77][78]

Hesitation[edit]

Some environmental organizations (such as Friends of the Earth and Greenpeace) have been reluctant to endorse or oppose solar geoengineering, but are often more supportive of nature-based carbon dioxide removal projects, such as afforestation and peatland restoration.[69][79]

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

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 geoengineering group) were largely negative and frequently associated with attributes like 'risky', 'artificial' and 'unknown effects'. Carbon dioxide removal methods were preferred over solar geoengineering. Public perceptions were remarkably stable with only minor differences between the different countries in the surveys.[12][80]

History[edit]

Several organizations have investigated climate engineering with a view to evaluating its potential, including the US Congress,[81] the US National Academy of Sciences, Engineering, and Medicine,[82] the Royal Society,[83] the UK Parliament,[84] the Institution of Mechanical Engineers,[85] 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.[85]

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".[86] 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".[86]

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".[87] 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".[87]

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."[88][89][90] The resulting study titled Climate Intervention was released in February 2015 and consists of two volumes: Reflecting Sunlight to Cool Earth[91] and Carbon Dioxide Removal and Reliable Sequestration.[92] According to their brief about the study:[93][91]

Climate intervention is no substitute for reductions in carbon dioxide emissions and adaptation efforts aimed at reducing the negative consequences of climate change. However, as our planet enters a period of changing climate never before experienced in recorded human history, interest is growing in the potential for deliberate intervention in the climate system to counter climate change... Carbon dioxide removal strategies address a key driver of climate change, but research is needed to fully assess if any of these technologies could be appropriate for large-scale deployment. Albedo modification strategies could rapidly cool the planet's surface but pose environmental and other risks that are not well understood and therefore should not be deployed at climate-altering scales; more research is needed to determine if albedo modification approaches could be viable in the future.

See also[edit]

References[edit]

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  41. ^ Munday, Jeremy (2019). "Tackling Climate Change through Radiative Cooling". Joule. 3 (9): 2057–2060. doi:10.1016/j.joule.2019.07.010. S2CID 201590290. Archived from the original on 2022-02-22. Retrieved 2022-09-27 – via ScienceDirect. By covering the Earth with a small fraction of thermally emitting materials, the heat flow away from the Earth can be increased, and the net radiative flux can be reduced to zero (or even made negative), thus stabilizing (or cooling) the Earth.
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