Two strategies proposed for SRM involve adding dust or chemicals to the Earth's atmosphere to increase the reflected fraction of sunlight (6–8)
SRM attempts to modify the amount of solar energy that reaches the Earth's surface, effectively offsetting some of the warming effects of greenhouse gasses.
He has contributed and contributes to several government-funded Australian research projects: Reef Restoration and Adaptation Program; Monitoring collective capacity and effectiveness of implementation of the Great Barrier Reef 2050 Plan; Review and synthesis of existing partnerships in the Great Barrier Reef; and the National Environmental Science Program. He is Director of the World Health Organization Collaborating Centre on Health in Impact Assessments and an Extraordinary Professor at the Research Unit for Environmental Sciences and Management, Faculty of Natural and Agricultural Sciences, North West University, South Africa. **Sovacool, B.K.** is Director of the Boston University Institute for Global Sustainability and Professor in the Department of Earth & Environment; Professor of Energy Policy at the Science Policy Research Unit at the University of Sussex Business School in the United Kingdom; and University Distinguished Professor in the Department of Business Development and Technology at University of Aarhus, Denmark.
**Solar Radiation Modification (SRM) refers to deliberate, large-scale actions intended to decrease global average surface temperatures by increasing the reflection of sunlight away from the Earth.** Proposed SRM methods involve the use of aerosols (small particles) or other materials to increase the reflectivity of the atmosphere, clouds, or Earth’s surface. **Long-term protection of Earth’s climate and oceans requires substantial reductions in emissions and atmospheric concentrations of CO2 and other GHGs. SRM is not considered a substitute for climate mitigation efforts, which include decarbonization and GHG emission cuts.** SRM research is being conducted as a response to growing concerns that the pace of CO2 emissions reductions and CDR technology development is not sufficient to avoid severe impacts of climate change in the next decades. **Many of the processes most important for understanding SRM approaches—such as those that control the formation of clouds and aerosols—are among the most uncertain components of the climate system.** Climate models differ in simulating large-scale aerosol climate effects, including on surface temperatures, due to variations in how aerosol processes, atmospheric transport and mixing, and physics are represented.
In this chapter, we briefly review what is known about proposed solar radiation management (SRM) approaches and related governance and ethical issues and conclude with a discussion of the research needed to better understand SRM. For use of SRM as a potential “backstop option” in the case of an emerging “climate emergency,” improved observations and understanding of climate system thresholds, reversibility, and abrupt changes (see Chapter 6)—for example, observations to let us know when an ice sheet or methane hydrate field may become unstable (e.g., Khvorostyanov et al., 2008; Shakhova et al., 2010)—could inform societal debate and decision making about needs for deployment of a climate intervention system. There is, however, additional research that would be needed to support full evaluation of SRM approaches (just as there is with other options for limiting the magnitude of future climate change), including a variety of social, ecological, and physical sciences (see Chapter 4).
Other approaches include marine cloud brightening (MCB), which would increase the reflectivity of clouds over the oceans, or constructing a space sunshade or a
Volcanic stratospheric clouds are produced by injections of SO2, so that might be the gas of choice, but some have suggested H2SO4 to reduce growth of aerosol particles (e.g., Pierce et al. Outdoor research, which involves injecting salt particles into marine clouds or various substances into the stratosphere, requires governance, including review of potential environmental impacts, monitoring of the experiments, and sanctions if the researchers break the rules (e.g., Shepherd et al. It includes the Geoengineering Model Inter-comparison Project (GeoMIP), in which 19 climate modeling groups have simulated how the climate would respond to reduced insolation, creation of a stratospheric aerosol cloud, or brightened marine clouds to reduce climate change from various global warming scenarios. Future research is planned with scenarios that might involve credible deployments, such as balancing overshoot scenarios to keep global warming at less than 1.5–2.0 K above preindustrial temperatures (e.g., Tilmes et al. Research shows that it may be possible to control regional climates (e.g., Tilmes et al.
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