Potential impacts of stratospheric aerosol injection on drought risk managements over major river basins in Africa

Most socio-economic activities in Africa depend on the continent’s river basins, but effectively managing drought risks over the basins in response to climate change remains a big challenge. While studies have shown that the stratospheric aerosol injection (SAI) intervention could mitigate temperature-related climate change impacts over Africa, there is a dearth of information on how the SAI intervention could influence drought characteristics and drought risk managements over the river basins. The present study thus examines the potential impacts of climate change and the SAI intervention on droughts and drought management over the major river basins in Africa. Multi-ensemble climate simulation datasets from the Stratospheric Aerosol Geoengineering Large Ensemble (GLENS) Project were analysed for the study. The Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI) were used to characterize the upper and lower limits of future drought severity, respectively, over the basins. The SPEI is a function of rainfall and potential evapotranspiration, whereas the SPI is only a function of rainfall, so the difference between the two indices is influenced by atmospheric evaporative demand. The results of the study show that, while the SAI intervention, as simulated in GLENS, may offset the impacts of climate change on temperature and atmospheric evaporative demand, the level of SAI that compensates for temperature change would overcompensate for the impacts on precipitation and therefore impose a climate water balance deficit in the tropics. SAI would narrow the gaps between SPEI and SPI projections over the basins by reducing SPEI drought frequency through reduced temperature and atmospheric evaporative demand while increasing SPI drought frequency through reduced rainfall. The narrowing of this gap lowers the level of uncertainty regarding future changes in drought frequency, but nonetheless has implications for future drought management in the basins, because while SAI lowers the upper limit of the future drought stress, it also raises the lower limit of the drought stress.

A Fate Worse Than Warming? Stratospheric Aerosol Injection and Global Catastrophic Risk

Injecting particles into atmosphere to reflect sunlight, stratospheric aerosol injection (SAI), represents a potential technological solution to the threat of climate change. But could the cure be worse than the disease? Understanding low probability, yet plausible, high-impact cases is critical to prudent climate risk management and SAI deliberation. But analyses of such high impact outcomes are lacking in SAI research. This paper helps resolve this gap by investigating SAI's contributions to global catastrophic risk. We split SAI's contributions to catastrophic risk into four interrelated dimensions:1. Acting as a direct catastrophic risk through potentially unforeseen ecological blowback.2. Interacting with other globally catastrophic hazards like nuclear war.3. Exacerbating systemic risk (risks that cascade and amplify across different systems);4. Acting as a latent risk (risk that is dormant but can later be triggered).The potential for major unforeseen environmental consequences seems highly unlikely but is ultimately unknown. SAI plausibly interacts with other catastrophic calamities, most notably by potentially exacerbating the impacts of nuclear war or an extreme space weather event. SAI could contribute to systemic risk by introducing stressors into critical systems such as agriculture. SAI's systemic stressors, and risks of systemic cascades and synchronous failures, are highly understudied. SAI deployment more tightly couples different ecological, economic, and political systems. This creates a precarious condition of latent risk, the largest cause for concern. Thicker SAI masking extreme warming could create a planetary Sword of Damocles. That is, if SAI were removed but underlying greenhouse gas concentrations not reduced, there would be extreme warming in a very short timeframe. Sufficiently large global shocks could force SAI termination and trigger SAI's latent risk, compounding disasters and catastrophic risks. Across all these dimensions, the specific SAI deployment, and associated governance, is critical. A well-coordinated use of a small amount of SAI would incur negligible risks, but this is an optimistic scenario. Conversely, larger use of SAI used in an uncoordinated manner poses many potential dangers. We cannot equivocally determine whether SAI will be worse than warming. For now, a heavy reliance on SAI seems an imprudent policy response.

Methods for Dispersal of Precipitated Calcium Carbonate for Stratospheric Aerosol Injection

Two methods for the laboratory-scale formation of aerosols of nanosized particles of precipitated calcium carbonate (PCC), for potential use in Stratospheric Aerosol Injection (SAI), a Solar Radiation Management (SRM) technique, are described. The first uses the coarse fluidization of bulk PCC in a simple vessel, followed by dispersal using a commercially available two-fluid nozzle. The manufacturer’s measured particle mass distribution for the bulk material, and sprayed aerosol particle mass distributions are compared, indicating that the sprayed particles are well separated in spite of a notoriously problematic agglomeration tendency. The method is suitable for scale-up. A second dispersal method, useful for small laboratory experiments, using liquid carbon dioxide as a dispersant as well as spray propellant gave similar results. The mass mode diameters measured here (0.89 to 1.4 μm) differ from that stated by the manufacturer (0.7 μm), but the distributions are consistent in showing complete separation of the particles.

Legitimacy and procedural justice: how might stratospheric aerosol injection function in the public interest?

The success of stratospheric aerosol injection (SAI) in limiting global heating requires the inclusion and maintenance of the political ideals of legitimacy and procedural justice. Without them, the prospects are slim that this institution can be developed and operated in the public interest in such a way that it will protect and promote social well-being by minimising climate-related harm. Long term legitimacy and procedural justice are crucial to several sensitive features of SAI. They relate to openness, inclusivity and independence, in dealing both with external issues of concern to stakeholders representing the general public and with internal issues concerning agents directly involved in SAI. This article begins by outlining notions of legitimacy and procedural justice, and the criteria appropriate for SAI. Then it investigates how the moral indications provided by the related standards might ensure that SAI is not distorted in such ways that it serves the selfish interests of private parties. Finally, the article outlines two governance recommendations for ensuring that legitimacy and procedural justice in SAI are achieved and maintained over time, so that it can work continuously in the public interest.

Toward practical stratospheric aerosol albedo modification: Solar-powered lofting

Many climate intervention (CI) methods have been proposed to offset greenhouse gas–induced global warming, but the practicalities regarding implementation have not received sufficient attention. Stratospheric aerosol injection (SAI) involves introducing large amounts of CI material well within the stratosphere to enhance the aerosol loading, thereby increasing reflection of solar radiation. We explore a delivery method termed solar-powered lofting (SPL) that uses solar energy to loft CI material injected at lower altitudes accessible by conventional aircraft. Particles that absorb solar radiation are dispersed with the CI material and heat the surrounding air. The heated air rises, carrying the CI material to the stratosphere. Global model simulations show that black carbon aerosol (10 microgram per cubic meter) is sufficient to quickly loft CI material well into the stratosphere. SPL could make SAI viable at present, is also more energy efficient, and disperses CI material faster than direct stratospheric injection.

Updated and outdated reservations about research into stratospheric aerosol injection

In this paper, we seek to ground discussions of the governance of stratospheric aerosol injection research in recent literature about the field including an updated understanding of the technology’s deployment logistics and scale, pattern of effects, and research pathways. Relying upon this literature, we evaluate several common reservations regarding the governance of pre-deployment research and testing including covert deployment, technological lock-in, weaponization, slippery slope, and the blurry line between research and deployment. We conclude that these reservations are no longer supported by literature. However, we do not argue that there is no reason for concern. Instead, we enumerate alternative bases for caution about research into stratospheric aerosol injection which are supported by an up-to-date understanding of the literature. We conclude that in order to establish the correct degree and type of governance for stratospheric aerosol injection research, the research community must focus its attention on these well-grounded reservations. However, while these reservations are supported and warrant further attention, we conclude that none currently justifies restrictive governance of early-stage stratospheric aerosol injection research.

Effects of opinion statements on laypeople's acceptance of a climate engineering technology. Comparing the source credibility of researchers, politicians and a citizens' jury

To examine the influence of different actors' fictitious statements about research and deployment of stratospheric aerosol injection (SAI), we conducted an online survey in Germany. Participants assess researchers and a citizens' jury to be more credible than politicians. Credibility has a strong positive effect on SAI acceptance in both pro-SAI and contra-SAI conditions. Reading the statement against SAI-deployment led to significantly lower acceptance scores compared to reading the pro-statement. However, the difference between messages was unexpectedly small, indicating that the message content was not fully adopted while underlying traits and attitudes mainly shaped acceptance even despite, or because of, low levels of knowledge.