Solar Geoengineering: A Solution Without a Plan Peter Lorenz E-103:The Challenge of Human Induced Climate Change May 8, 2020 Abstract Solar Geoengineering refers to a set of technologies that seek to alter Earth's natural reflective balance as a means to mitigate the warming impact of greenhouse gases. Since this novel intervention does not require a dramatic decrease in greenhouse gas emissions, Solar radiation management (SRM), will likely become a possible intervention to fight climate change and its effects. Therefore, this paper will outline current research on sulfuric aerosol injections as a specific type of solar geoengineering, discuss externalities and implementation pathways, and outline a plan to promote sound governance with this emerging pathway. I. Introduction Climate Change and global warming represent direct threats to human and other life on Earth (Robock, 2014). A 2015 US National Research Council Report on climate intervention recommended the primary course of action to be mitigation (e.g. ceasing fossil fuel extraction), adaptation and carbon dioxide removal. Therefore, current solutions or interventions rely on individuals acting sustainably and reconsidering their environmental priorities, as policy makers and governments attempt to enact subsequent global policy. However ideal this may be, the current mitigation plans are not anticipated to meet the benchmark of maintaining warming to only two degrees celsius above the pre industrial global average (Aengenheyster, Feng, Ploeg, & Dijkstra, 2018). Alternatively, solar radiation management (SRM), a type of geoengineering, does not rely on reducing emissions to decrease climate change impacts. Instead of addressing the root causes, SRM looks to delay effects of climate change by altering the constraints of the Earth. This may be possible through the introduction of chemicals (e.g sulfur dioxide) into the atmosphere to mitigate anthropogenic climate change (SRMGI, 2020). Additionally, its effects are thought to be quicker and would not require a change in human behavior in the way other climate change interventions work to promote sustainable societies (Aengenheyster, Feng, Ploeg, & Dijkstra, 2018). This paper does not purport to encourage a move away from addressing the root causes of climate change and the importance of sustainable living. Instead this author looks into the possibility of SRM as an innovative means of overcoming climate change and its current obstacles including political support and enforcement, fossil fuel industry interests, and individual’s inability to reduce activities of daily living that contribute to greenhouse gas emission. This approach understands the real possibility that geoengineering interventions are likely to be an increased consideration amongst policy makers in the future (Stephens and Surprise, 2020). However, the outcomes of such chemical interventions are still largely unknown (Smith and Wagner, 2018). It is imperative that the enticing potential of solar geoengineering not be explored without understanding its possibilities, limits, and consequences. The current technologies of solar radiation management (SRM) lack a global policy framework and, most importantly, implementation of SRM technologies carries a broad risk to the entire global community. The paper seeks to better understand SRM on both the scientific and policy level. It will discuss the atmospheric understanding by which SRM affects the environment, current research, and future concerns regarding deployment scenarios and global policies governing implementation. II. Specification of Geoengineering Geoengineering is a general term that encompasses an assortment of technologies to address climate change through the implementation of technology based solutions. Two main forms of geoengineering are Solar Geoengineering and Greenhouse Gas Removal (SRMGI, 2020). Solar geoengineering or solar radiation management (SRM), looks to reflect a portion of the sun’s energy back into space to counteract the temperature rise associated with increased levels of GHG in the atmosphere (Robock, 2014; Smith and Wagner, 2018; SRMGI, 2020). GHG absorb energy through solar radiation reflected off the Earth’s surface and trap the excess heat energy, which causes a global rise in temperature (Robock, 2014). Greenhouse Gas Removal aims to remove carbon dioxide and other GHG from the atmosphere to lessen the negative impacts (e.g. warming) of the greenhouse effect and ocean acidification (SRMGI, 2020). Figure 1. Select Types of Geoengineering Interventions (Lorenz, 2020) One type of SRM technology includes the deployment of sulfur oxide into the stratosphere, known as stratospheric aerosol injections (SAI). These particles circulate the planet via stratospheric winds and reflect portions of the inbound solar radiation as a means to cool the planet (Robock, 2014). Due to the global impact of implementation, feasibility and probability of implementation, this paper will focus on SAI. III. Stratospheric Sulfur Aerosols Stratospheric sulfur aerosols are a naturally occurring concentration in the atmosphere that results from the photochemical decomposition of atmospheric gases containing sulfur (USGS, 2019). Sulfur aerosols are a mixture of sulfuric acid and water that are located in the “Junge Layer” of the earth’s atmosphere (Junge et al., 1961). The Junge Layer, discovered in 1960, is a layer of microscopic aerosol particles between the tropopause and upper stratosphere and located at approximately 18 miles (30 km) altitude (Junge et al., 1961). Figure 1 illustrates the layers of the Earth's atmosphere and the approximate altitude of each layer. (Figure 2: University of Georgia, 2017) The natural occurrence of sulfur aerosols can be traced back to sulfur dispersions in the stratosphere which occur as a result of the eruptions of volcanoes on Earth’s surface (USGS, 2019). When an eruption of 4 or greater on the Volcanic Explosivity Index occurs, sulfur aerosols form as a result of the eruption force, causing an injection of sulfur dioxide into the stratosphere (USGS, 2019). Figure 2 depicts the eruption of a volcano and the dispersal of erupted materials and gases into the stratosphere (University of Georgia, 2017). The dispersion of sulfur dioxide (SO2) and subsequent conversion into sulfuric acid (H2SO4) has numerous ​ ​ ​ ​ ​ ​ effects on the climate and the earth's environment (USGS, 2019). Upon the conversion of sulfur dioxide (SO2 ) into sulfuric acid (H2SO4), the sulfuric acid condenses in the stratosphere and ​ ​ ​ ​ ​ ​ ​ forms sulfate aerosols. While the dispersion of carbon dioxide (CO2), ash, HCl and HF cause a ​ ​ variety of human health and environmental impacts however the purpose of this paper this author elicits to restrict the scope to the sulfur aerosols. (Figure 3: USGS, 2019) The key property of sulfur aerosols is its ability to reflect sunlight (Robock, 2014) (SRMGI, 2020). As a result of the reflective properties, there is a reduction in the amount of sunlight reaching the Earth's surface once the aerosols reach a critical mass in the stratosphere. Figure 3 illustrates the observed change in solar radiation transmitted to Mauna Loa Observatory following major volcanic eruptions. (Figure 4, NOAA 2019) The presence of aerosols in the stratosphere causes an increase in the amount of solar radiation reflected back into space, which results in a cooling of the Earth's troposphere (Robock, 2014) (SRMGI, 2020). This reduction in the amount of sunlight reaching the Earth’s surface is also known as the cooling effect (National Academy of Sciences,1992). Such a cooling effect ​ ​ can be observed following major volcanic eruptions (Newhall, Hendley, & Stauffer, 1997). For ​ ​ example, the 1991 eruption of Mount Pinatubo in the Philippines caused an estimated 20 million ​ tons of sulfur dioxide (SO2) to be collected in the stratosphere (Newhall, Hendley, & Stauffer, ​ ​ 1997). The Mount Pinatubo eruption was the second-largest terrestrial eruption of the 20th ​ century and led to a 0.5 Celsus decrease in the global temperature between 1991 and 1993 as a ​ result of the material dispersed during the eruption (Newhall, Hendley, & Stauffer, 1997). IV. Research and Current Experiments As detailed above, the interaction of sulfuric aerosols and solar radiation has the potential to reduce total solar radiation entering the Earth’s atmosphere and thereby reduce the global temperature. However, currently the technology required to implement a full scale anthropogenic SRM project does not exist (Smith and Wagner, 2018). These projects aim to replicate the natural occurrence of large volcanic eruptions in a variety of ways, yet/and the foundation for each technology is based on emulating the cooling effect of sulfur aerosols in the stratosphere (Smith and Wagner, 2018). The most well researched and most probable implementation for solar radiation management is the injection of sulfur dioxide into the stratosphere via airplane or high altitude balloons. The original idea to inject sulfur in the stratosphere as a means to modify the climate and artificially cool the earth originates from Russian climatologist Mikhail Budyko in 1974 (Robock, 2014). Dr. Budyko estimated that the dispersion of 200,000 tons of sulfur in the stratosphere would offset the warming that occurred between 1920 and 1940 (Robock, 2014) . By 1992, geoengineering was a focus area for the US National Research Council which produced a comprehensive list of implementation options. These options form the foundation