Climate engineering
Climate engineering, or commonly geoengineering, is deliberate and large-scale intervention in the Earth's climate system. The main category of climate engineering is solar geoengineering or solar radiation management. Solar geoengineering, or solar radiation modification, would reflect some sunlight (solar radiation) back to space to limit or reverse human-caused climate change. Carbon dioxide removal (CDR), the practice of deliberately reducing the amount of in the atmosphere, is often mistakenly classified with solar geoengineering as a form of climate engineering and assumed to be intrinsically risky. In fact, CDR addresses the root cause of climate change and  is part of strategies to reduce net emissions. The Intergovernmental Panel on Climate Change (IPCC) no longer refers to CDR as a subgroup of climate engineering, but uses the terms "solar radiation management" and "carbon dioxide removal" separately. Climate engineering approaches are sometimes viewed as potential complementary options for limiting climate change or its impacts, alongside reducing greenhouse gas emissions and adaptation. Scientists agree that solar geoengineering and carbon dioxide removal cannot substitute for reducing emissions. Given that all types of measures for addressing climate change have economic, political, or physical limitations, some climate engineering approaches might eventually be  used as part of an ensemble of responses, which could have the objective of climate restoration. Because of insufficient research there are large uncertainties regarding the effectiveness, side effects and potential unforeseen consequences. Most experts argue that the risks of such interventions must be seen in the context of the risks of dangerous climate change. Interventions at large scale may run a greater risk of disrupting natural systems, resulting in a dilemma that those approaches that could prove highly cost-effective in addressing extreme climate risk, might themselves cause substantial risk. Some have suggested that the concept of engineering the  climate could reduce political and public pressure for emissions reduction, which could exacerbate overall climate risks; others assert that the threat of climate engineering could spur emissions cuts. Definition. As of 2018 the terms "climate engineering" and "geoengineering" are not used by the Intergovernmental Panel on Climate Change. 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". Solar geoengineering. Solar geoengineering would deflect sunlight away from the Earth, or by increasing the reflectivity  (albedo) of the atmosphere or the Earth's surface. These methods are not a substitute for climate change mitigation because they would not reduce greenhouse gas concentrations in the atmosphere, and thus would not address ocean acidification caused by carbon dioxide. In general, solar geoengineering projects presently appear able to take effect rapidly and reversible in their direct climatic effects. The US National Academy of Sciences, Engineering, and Medicine states in a 2021 report: "The available research indicates that SG could reduce surface temperatures and potentially ameliorate some risks posed by climate change (e.g., to avoid crossing critical climate “tipping  points”; to reduce harmful impacts of weather extremes)." Solar geoengineering methods may include: Solar geoengineering requires relatively large scale implementation in order to impact the Earth's climate. The least costly proposals are estimated at tens of billions of US dollars annually in direct deployment costs. This is low enough that it might be in the interests of several single countries to implement them unilaterally. Solar geoengineering may pose novel significant risks such as regional climate disruptions. Issues. Moral hazard or risk compensation. The existence of such techniques may reduce the political and social impetus to reduce carbon emissions. This  has generally been called a potential moral hazard, although risk compensation may be a more accurate term. This concern causes many environmental groups and campaigners to be reluctant to advocate or discuss climate engineering for fear of reducing the imperative to cut greenhouse gas emissions. However, several public opinion surveys and focus groups have found evidence of either assertions of a desire to increase emission cuts in the face of climate engineering, or of no effect. Other modelling work suggests that the prospect of climate engineering may in fact increase the likelihood of emissions reduction.<ref name="doi10.1007/s10584-011-0102-0"></ref > Politics. 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 some nature-based carbon dioxide removal projects, such as afforestation and peatland restoration. Some commentators appear fundamentally opposed. The ETC Group has called for a moratorium on climate engineering techniques. It has been argued that regardless of the economic, scientific, and technical aspects, the difficulty of achieving concerted political action on global warming requires other approaches. Those arguing political expediency say the difficulty of achieving meaningful emissions cuts 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. However, others point to support for climate engineering proposals among think tanks with a history of opposition to emissions reductions as evidence that, rather than climate engineering being a solution to the difficulties of emissions reductions, the prospect of climate engineering is being used as part of an argument to stall emissions reductions in the first place. Ethics and responsibility. Climate engineering would represent a large-scale, intentional effort to modify the climate. It would differ from activities such  as burning fossil fuels, as those change the climate inadvertently. Intentional climate change is often viewed differently from a moral standpoint. It raises questions of whether humans have the right to change the climate deliberately, and under what conditions. For example, there may be an ethical distinction between climate engineering to minimize global warming and doing so to optimize the climate. Furthermore, ethical arguments often confront larger considerations of worldview, including individual and social-religious commitments. This may imply that discussions of climate engineering should reflect on how religious commitments might influence the discourse. For many people, religious beliefs are  pivotal in defining the role of human beings in the wider world. Some religious communities might claim that humans have no responsibility in managing the climate, instead of seeing such world systems as the exclusive domain of a Creator. In contrast, other religious communities might see the human role as one of "stewardship" or benevolent management of the world. The question of ethics also relates to issues of policy decision-making. For example, the selection of a globally agreed target temperature is a significant problem in any climate engineering governance regime, as different countries or interest groups may seek different  global temperatures. One of the lesser focused aspects of climate engineering is the role it can play in global inequality (Environmental Justice). Emissions are largely concentrated in a relatively few companies. In not addressing the issue or changing practices to emit less, they directly receive benefit from the damage they cause to the climate. In a similar way, wealthier nations have far greater emissions than their poorer counterparts. However, it is poorer nations who will be unable to pay the costly fees for the adaptation and mitigation needed to meet the challenges of climate change. Simply put, wealthy nations have  the most to give and poorer nations have the most to lose. Climate engineering has the potential to address inequality by putting the burden on those who benefit from the emissions rather than sharing the burden with those who have little responsibility and who are doomed to suffer the most. Governance. Climate engineering opens up various political and economic issues. The governance issues characterizing carbon dioxide removal compared to solar geoengineering are largely distinct. As a result of these differing characteristics, the key governance problem for carbon dioxide removal (as with emissions reductions) is making sure actors do enough of  it (the so-called "free rider problem"), whereas the key governance issue for solar geoengineering is making sure actors do not do it too early or too much (sometimes called the "free driver" problem). Domestic and international governance vary by the proposed climate engineering method. There is presently a lack of a universally agreed framework for the regulation of climate engineering activity or research. Scholars at the Oxford Martin School at Oxford University proposed a set of voluntary principles, which may guide climate engineering research and use. The short version of the 'Oxford Principles' is: These principles have been endorsed  by the House of Commons of the United Kingdom Science and Technology Select Committee on "The Regulation of Geoengineering", and have been referred to by authors discussing the issue of governance. The Asilomar International Conference on Climate Intervention Technologies was convened to identify and develop risk reduction guidelines for climate intervention experimentation. The Parties to the Convention on Biological Diversity have made three decisions on what they call "climate-related geo-engineering." A decision in 2010 called on countries to refrain from "climate-related geo-engineering activities that may affect biodiversity" until these are governed, they are scientifically justified, and  associated risks have been considered. Some critics of climate engineering call this a "de facto moratorium," but the Secretariat of the Convention on Biological Diversity calls it a “non-binding normative framework.” Many legal scholars reject this characterization. The 2016 decision called for "more transdisciplinary research and sharing of knowledge among appropriate institutions is needed in order to better understand the impacts." Public perception. A large 2018 study investigated public perceptions of six climate engineering methods, with an online survey in the United States, United Kingdom, Australia, and New Zealand. The findings were also compared against similar 2012 survey in  Australia and New Zealand. Public awareness of climate engineering was low with less than a fifth of respondents reporting prior knowledge. Perceptions of the six climate engineering methods 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 2018 and 2012 surveys. In a 2017 focus group study conducted by the Cooperative Institute for Research in Environmental Sciences (CIRES) in the United States, Japan, New Zealand, and Sweden, participants were asked about  carbon sequestration options, reflection proposals such as with space mirrors, or brightening of clouds, and their majority responses could be summed up as follows: Moderators floated then the idea of a future "climate emergency" such as rapid environmental change. The participants felt that mitigation and adaptation to climate change were strongly preferred options in such a situation, and climate engineering was seen as a last resort. Evaluations of climate engineering. Most of what is known about the suggested techniques are based on laboratory experiments, observations of natural phenomena, and computer modeling techniques. Some proposed climate engineering methods employ methods that  have analogs in natural phenomena such as stratospheric sulfur aerosols and cloud condensation nuclei. As such, studies about the efficacy of these methods can draw on information already available from other research, such as that following the 1991 eruption of Mount Pinatubo. However, comparative evaluation of the relative merits of each technology is complicated, especially given modeling uncertainties and the early stage of engineering development of many proposed climate engineering methods. Several organizations have investigated climate engineering with a view to evaluating its potential, including the US Congress, the US National Academy of Sciences, Engineering, and Medicine, the Royal Society , the UK Parliament, the Institution of Mechanical Engineers, and the Intergovernmental Panel on Climate Change. The IMechE report examined a small subset of proposed methods (air capture, urban albedo and algal-based 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. 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". 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". In a 2009 review study, Lenton and Vaughan evaluated a range of proposed climate engineering techniques. In order to permit a comparison of disparate techniques, they used a common  evaluation for each technique based on its effect on net radiative forcing. As such, the review examined the scientific plausibility of proposed methods 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". They concluded that "[climate] geoengineering is best considered as a potential complement to the mitigation of emissions, rather than as an alternative to it". In  October 2011, a Bipartisan Policy Center panel issued a report urging immediate researching and testing in case "the climate system reaches a 'tipping point' and swift remedial action is required." The US National Academy of Sciences, Engineering, and Medicine conducted 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." The resulting study titled "Climate Intervention" was released in February  2015 and consists of two volumes: "Reflecting Sunlight to Cool Earth" and "Carbon Dioxide Removal and Reliable Sequestration". According to their brief about the study: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.