Reflecting Sunlight Recommendations for Solar Geoengineering Research and Research Governance (2021) / Chapter Skim
Currently Skimming:
2 Assessment of the Current Solar Geoengineering Research and Research Governance Landscape
2 Assessment of the Current Solar Geoengineering Research and Research Governance Landscape
Pages 31-110
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There are two main approaches considered herein for increasing how much incoming solar energy is reflected back to space: stratospheric aerosol injection (SAI) and marine cloud brightening (MCB)
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SUN STRATOSPHERIC Increased scattering by AEROSOL Stratospheric Aerosols ~16-25 KM Thinning high clouds to allow more heat to escape CIRRUS CLOUDS ~6-13 KM Increased scattering by brightened clouds MARINE CLOUDS ~0-3 KM FIGURE 2.1a Illustration of the basic mechanisms involved in Stratospheric Aerosol Injection (SAI) , Marine Cloud Brightening (MCB)
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; C: typical cirrus clouds.
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The Mt. Pinatubo eruption is estimated to have cooled global mean temperatures by approximately 0.5°C for 1 year or more (IPCC, 2013)
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2.1c Cirrus Cloud Thinning Cirrus clouds -- thin wispy clouds composed primarily of ice crystals that form in the upper troposphere -- warm the planet (particularly at higher latitudes) because they reduce outgoing longwave radiation more than they reflect incoming sunlight.
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For any of these SG methods, the climate response will depend on the specific method of forcing, as well as the spatial distribution of that forcing. This reality, together with existing uncertainties in climate modeling more generally, means that our ability to estimate climate responses and the downstream impacts of those responses is currently very limited.
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. Moreover, building more proportional representation in geoengineering research from women and scientists from underrepresented populations is important for reasons of fairness and balance, especially given expectations that women and people from the Global South will receive the brunt of damages from climate change and that the possible distribution of benefits and damages from climate intervention strategies are as yet unknown (Buck et al., 2014)
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Stratospheric Aerosol Injection As reviewed extensively in NRC (2015) , evidence from large volcanic eruptions serves as the essential demonstration that it is possible to reduce solar (shortwave)
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Aerosols such as sulfate also absorb longwave (IR) radiation, causing heating of the lower tropical stratosphere; this both influences stratospheric circulation and results in increased water vapor in the stratosphere, the radiative effects of which 39
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with varying degrees of complexity in global climate models. This subsection summarizes current knowledge focused on these small scales, while the next subsection addresses the resulting larger-scale climate response.
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More observations of volcanic eruption impacts would thus be extremely valuable, but they may still be insufficient to constrain some processes. Stratospheric heating.
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Stratospheric aerosols may also affect upper cirrus cloud cover, either through the stratospheric heating modifying vertical velocities (Kuebbeler et al., 2012) or possibly through the aerosols themselves (Cirisan et al., 2013)
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. Changes in the dominant ozone loss cycles are shown in blue if decreasing (net chemical production is increasing)
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. Finally, in addition to the SAI impacts discussed above (i.e., stratospheric heating and stratospheric ozone loss)
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of a global climate model, and hence these processes are all parameterized. As a result, climate model simulations are not a useful tool for better resolving process uncertainties except insofar as overall constraints can be imposed.
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. Since the addition of particles brightens clouds by changing the sizes of droplets in clouds, other cloud properties may also be changed (Boucher et al., 2014; Sherwood et al., 2015)
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. Smaller-scale regional and LES models that do represent the microscale have produced results that span the range of AIEs represented by climate models, but they also yield results with higher and lower sensitivities and stronger, nonlinear feedbacks (sometimes outweighing the cloud formation processes; see Ackerman et al., 2004; Bretherton et al., 2007; Feingold et al., 2002; Lebo and Feingold, 2014; Lu and Seinfeld, 2005; Stevens et al., 1998; Witte et al., 2019; Xue et al., 2008)
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Existing observa tional networks of atmospheric measurements were designed for predicting weather and monitoring air quality and impacts of stratospheric ozone loss, not for quantifying AIEs (for either background emissions or deliberate injections)
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Cirrus Cloud Thinning The efficacy of CCT is currently highly uncertain. Unlike low clouds, cirrus clouds in the upper troposphere warm the planet by reducing outgoing longwave radiation more than they reflect incoming shortwave.
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It is first important to recognize that no SG approach can simply reverse the climate effects of increased atmospheric GHG concentrations. While SG interventions could reduce global mean temperature, this would not restore the same climate as one without the increased GHGs.
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. Many solar-reduction simulations suggest that the climate resulting from an increase in GHGs offset by SG intervention is likely to be closer in many places to the original climate than one with the same increased GHG but without SG -- not just in global mean temperature but regionally and for hydrological variables and extremes as well (e.g., Irvine et al., 2019; Kravitz et al., 2014)
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Temperature Responses Existing research suggests that SG intervention would lead to a reduction in global mean temperature relative to scenarios of climate change without any intervention but with residual regional variations in climate relative to that which would have occurred without SG. These variations depend on assumptions made in creating the 52
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are not yet studied, which underscores both the nascent state of impacts research and the challenges of assessing impacts when SG does not simply restore the climate back to a previous state. Precipitation Responses Aside from direct temperature impacts, one of the primary climate responses and risks associated with SG are regional hydrological cycle changes.
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. Over Europe and Eurasia, the stratospheric heating caused by SAI produces a stronger polar vortex, which lowers Arctic sea level pressure and increases the zonal wind over the North Atlantic, leading to a shift in storm tracks that result in widespread warming with wetting over northern Europe and drying over southern Europe -- these changes are small however, compared to a scenario with increased GHGs but no SAI (e.g., Simpson et al., 2019)
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, "Climate emulators…are trained based on a limited number of simulations with GCMs and allow for prediction of climate response for a much broader set of trajectories, trading the fidelity of a GCM simulation for computational efficiency." 55
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. While choices such as latitudes or seasons to inject aerosols affect the spatial response, choices regarding how much to inject in any given year are ultimately iterative and would likely be adjusted in response to changing circumstances and observed climate responses.
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The Complexities of Assessing SG Impacts The types of SG approaches discussed herein will alter numerous environmental conditions that natural and human systems depend upon (Irvine et al., 2016) -- not only temperature and precipitation patterns but also many other factors (e.g., solar radiation levels and the ratio of direct to diffuse light, sea level rise, carbon cycle dynamics, ocean biogeochemistry, and extreme weather events)
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, how that approach is deployed, and how much cooling is pursued. Many of these details will be highly contingent on the socioeconomic and geopolitical background conditions and decision-making framework through which different types of interventions are implemented.
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There has not been any comparable level of work of SG impacts research, and it is not possible to make sound decisions about relative benefits and harms in the presence of such information asymmetry. Thus, for some potential impacts, it is illadvised to interpret these limited studies as indicating any real confidence in scientific understanding.
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One can confidently assume the overall sign of the effect of SG cooling effects on sea level rise, but the details are highly uncertain because (i) ice sheet loss depends not only on changes in air surface temperature but also on changes in precipitation and cloud cover as well as temperatures of the surrounding ocean water (e.g., Irvine et al., 2016; Moore et al., 2019)
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SG-driven changes in global temperature and hydrological cycle intensity can affect the ocean in many ways -- for instance, by altering the loss of sea ice and the stratification of the water column -- with consequences on ocean biogeochemistry, nutrient mixing and distributions, and oxygen concentration. Global ocean modeling experiments suggest that SG interventions could lead to a global decrease in ocean net primary production (NPP)
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MCB interventions in particular are being actively explored as mechanisms for targeted cooling of waters around coral reefs.6 However, even with cooler water temperatures, coral reefs will still be vulnerable to biogeochemical changes such as ocean acidification, although reducing heat stress could also reduce the sensitivity of corals to these biogeochemical changes. 6 See Marine Cloud Brightening for the Great Barrier Reef, savingthegreatbarrierreef.org.
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It was found that the global cooling resulting from rapid SG implementation results in temperature velocity vectors with the opposite direction of current warming; this rapid switch could halt or even reverse current climate-driven migration pressures on many species. Sudden termination of SG was found to cause extremely rapid temperature velocities for both land and ocean environments (far exceeding the values pre 63
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. While agricultural yields are clearly an important impact to assess, there are a wide variety of conclusions reached from these modeling studies, with unclear dependency on the specific scenario, the details of the SG approach simulated, and the specific climate model and crop model employed.
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This is in part because the responses of stratospheric ozone to SG interventions remain uncertain and in part because population exposure to these UV hazards can be affected by complex atmospheric processes, by changing human practices (e.g., occupational exposure interventions) , and by other factors (Nowack et al., 2016)
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At low latitudes, lofting material to ~20 km would be sufficient to achieve cooling, but injection at higher altitudes would increase efficiency and reduce the amount of material that would need to be added to achieve a given cooling, thus reducing some potential unwanted side effects. This efficiency benefit is a result of both longer aerosol lifetime and -- at least with sulfate aerosols -- reduced stratospheric heating, which in turn means smaller increases in stratospheric water vapor that counteract some of the cooling (Krishnamohan et al., 2019; Tilmes et al., 2018a)
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; unlike SAI, however, it may be possible using MCB to obtain local and regional climate effects with much smaller-scale efforts. There are as of yet no published cost estimates for such actions.
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• If interventions were deployed, how would we assess whether they are hav ing the intended effects? Could we confidently attribute specific climate outcomes -- including extreme weather events -- to the SG intervention versus natural (unforced)
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It would be straightforward to rapidly detect whether SG was working in the sense of having a lower global mean temperature than would have occurred without SG. But if the question is whether SG is affecting the climate differently from how GHGs affect the climate, one may need to identify differences between the "1.5°C climate" produced by GHG forcing offset by stratospheric aerosols and the "1.5°C climate" that would have occurred with the hypothetical world of lower GHG levels.
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Aura is projected to keep operating until roughly 2023. • The ALTIUS mission, scheduled for launch in 2023, will measure the vertical profile of NO2, H2O, CH4, and a few other trace gases; however, no space program to date includes the capabilities for limb emission and IR solar occultation profiling that are needed to continue the monitoring of key ozone-related species (HCl, ClO, HNO3, CCl4, etc.)
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This includes consideration of ethical issues (2.3a) , public perception (2.3b)
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Some scholars have argued against further research on geoengineering on grounds that SG will distract from the critical work of mitigation (e.g., Cairns section of Long 9 Thisdiscussion, which focuses on normative issues, connects with issues raised in Sections 2.3b, c, and d, because public perception research can clarify how various publics view ethical and justice issues in relation to SG research and development (2.3b) ; research on economic and political incentives can show how these incentives may align or conflict with ethical conduct and governance of SG research and possible deployment (2.3c)
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" While the thermostat metaphor may be overly simplistic, it does capture the general concerns about what goals to aim for and how they would be determined. The Paris Agreement goals for limiting global mean temperature increase may provide one obvious reference point, but this does not necessarily capture all of the specific climate outcomes one must consider for geoengineering implementation.
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What would count as fair opportunities to participate in decisions about geoengineering research, development, and deployment? How should disagreements be addressed?
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. But intergenerational equity might also support drastic and immediate mitigation of GHG emissions that would obviate the need for SG, and it might also counsel against any SG deployment that potentially commits future generations to prolonged deployment.
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. Whether and to what extent geoengineering research, development, and possible deployment pose a moral hazard is to some extent an empirical question, but it is in practice difficult to assess.
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. Regardless of whether SG is likely to deter mitigation and adaptation, SG will need to be considered in relation to other climate responses and as part of a broader set of possible strategies for addressing global climate change (Preston, 2016)
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. Ethical issues also arise in relation to the structure of SG research processes more broadly, and existing ethics literature has suggested that SG research should be inclusive (both geographically and demographically)
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. Research on public perception of SG is valuable both to assess the state of public understanding and opinion regarding SG as a potential climate response and to inform measures to engage public and stakeholder input in decision making over SG research and research governance (see Chapter 5)
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It can be said that SG research is a socio technical system, with research and public opinion of research co-constructing each other. Caveats aside, existing research on public perception of SG does provide some consistent messages overall and reveals gaps that will need to be addressed if a fuller picture is desired.
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. This conditional support depended on participants' views on factors such as the seriousness of climate change as a problem, the ways that the research is conducted, the scientific robustness of the project, the "foreseeability" or the efficacy of the research, the existence of effective governance mechanisms, and the presence of democratic conditions in society (MacNaghten and Szerszynski, 2013)
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. Moral Hazard Concerns The concept of "moral hazard" (also discussed in Chapter 3) has also been explored in public perception studies.
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. Empirical public perception framing research thus far has revealed concerns that SG can evoke a frame of "messing with nature" (Corner et al., 2013)
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Descriptive Analysis: How Could Solar Geoengineering Affect Economic Outcomes? Chronologically, the economics literature initially focused on questions about how SG would alter the international politics of climate change.
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The general approach of IAMs is to link an economic module and a climate module -- via GHG emissions and via a climate damage function that attempts to capture how climate change impacts will alter aggregate economic outcomes. Introducing SG in these models requires adjustment in the RF equation that drives changes in temperature and introduction of a damage function to represent new adverse impacts created by SG.
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. This literature, which focuses primarily on environmental law, but also discusses human rights and intellectual property law, generally has concluded that SG lacks coordinated and systematic governance (Flegal et al., 2019; Long, 2013)
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Technologies, publics, political regimes, and climate targets are co-produced and co-evolve, multiplying the challenges of responsible SG research and necessitating an examination of how beliefs, judgments, and practices during the research process may have influenced the research (see, e.g., McLaren and Markusson, 2020)
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• For intervention strategies such as SAI, these factors in turn will influence how the injected material scatters and absorbs incident radiation; changes in RF cause thermodynamic and dynamic changes in climate at a range of scales. This can affect other Earth systems, such as ice sheets and sea levels -- pro cesses that will require investigation of climatologists and other earth scientists.
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For some knowledge gaps, relatively modest investment in geoengineering-specific research could provide significant additional knowledge. For other topics, (e.g., understanding the response of regional precipitation to SG radiative forcing)
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Studies published to date do not provide a sufficient basis for supporting informed decisions. 2.5 CURRENT MECHANISMS FOR RESEARCH GOVERNANCE This section assesses existing governance structures that are relevant to SG research, encompassing several dimensions of hard governance (i.e., derived from domestic and international laws, treaties, and regulations; customary international legal principles; and human rights, liability, and environmental law)
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. Small-scale field experiments with minimal physical effects are not likely to trigger the obligation to prepare an EIS and may not even require preparation of an environmental assessment if they fall within a "categorical exclusion," which refers to categories of actions that an agency has previously determined not to have significant impacts (40 C.F.R.
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Although field experimentation per se is unlikely to require a state or local permit, state permitting requirements for weather modification operations (see below) may in turn trigger state environmental policy act review.
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Although the broad definitions of weather modification under state weather modification laws may encompass SG field experiments, these laws may not apply to field experiments with limited effects. Some jurisdictions explicitly exempt research activities from permit and license requirements.
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. Although SG field experiments might result in the release of material into ocean waters, ODA permitting requirements would not apply unless the material is transported for the purpose of ocean disposal.
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Field experiments that harm persons or property could lead to liability under several tort law theories, including negligence, strict liability, and nuisance (Hester, 2018)
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However, various components of international law define the space in which such research might occur and express norms relevant to such research. Two treaty regimes -- the United Nations (UN)
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. The amendments define marine geoengineering as "a deliberate intervention in the marine environment to manipulate natural processes, including to counteract anthropogenic climate change and/or its impacts, and that has the potential to result in deleterious effects, especially where those effects may be widespread, long lasting or severe" (Resolution LP.4(8)
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, the Vienna Convention for the Protection of the Ozone Layer ("Vienna Convention") and Montreal Protocol, the Convention on Long-Range Transboundary Air Pollution (CLRTAP)
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The Vienna Convention and Montreal Protocol, which almost all nations have ratified, aim to avoid adverse modification of the stratospheric ozone layer. The Vienna Convention requires parties to "take appropriate measures .
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. hostile use of environmental modification techniques" and explicitly states that it "shall not hinder the use of environmental modification techniques for peaceful purposes and shall be without prejudice to the generally recognized principles and applicable rules of international law concerning such use" (ENMOD, arts.
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UNCLOS establishes a governance regime for the oceans that largely codifies customary international law. Ratified by more than 160 nations, but not the United States, the treaty establishes various obligations potentially relevant to marine-based SG.
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. This central obligation of customary international law does not establish an absolute duty to avoid transboundary harm, however (Hunter et al., 2015)
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Applying the principle of intergenerational equity to SG may require a complex weighing of different risks, costs, and benefits. One could contend that preservation of the planet for future generations calls for immediate reductions in GHG emissions so that SG deployment (and research)
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However, current mechanisms and principles of liability under international law are not likely to play a significant role in SG research governance. In theory, states are generally responsible for breaches of international law, and a state may be held strictly liable for transboundary harm caused by activities within its jurisdiction or control (Sands and Peel, 2012)
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. Human Rights and Environmental Law Finally, international law on human rights also may be relevant to SG research.
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. The preamble to the Paris Agreement encourages parties to "respect, promote and consider their respective obligations to human rights" when taking actions to address climate change, but neither it nor the main text of the agreement specifies how to implement this direction (Paris preamble recital 11)
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. Although participants in the project are involved in stakeholder engagement, commentators have raised questions regarding the ability of existing regulations to adequately govern these experiments (Fidelman et al., 2019; McDonald et al., 2019)
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• The Council of Europe produced a Convention for the Protection of Human Rights and Dignity of the Human Being with regard to the Application of Biol ogy and Medicine (the "Oviedo Convention")
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In 2003, the U.S. National Academies appointed a committee to propose ethical guidelines for human embryonic stem cell research.
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Timely creation of a legally binding international governance regime for SG seems unlikely, except perhaps in the context of a perceived crisis stemming from the lack of such a governance regime. Customary international law also seems highly unlikely to evolve, and to be accepted, to include any nuanced governance rules.
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