Abstract
Stratospheric aerosol injection (SAI) might counter a portion of human-caused climate change by reflecting sunlight into space. Uncertainties abound, for example about SAI’s effects on the atmosphere, on intended cooling, and on incentives for reducing emissions, among others. We construct a dataset of proposed SAI activities and find that the range of mass released to the atmosphere spans ten orders of magnitude and observe a gap of seven orders of magnitude between the largest proposed experiments and plans for early deployment. While introducing their own risks, testing activities in this gap might allow society to better understand atmospheric processes; build infrastructure and technical capabilities for deployment; and develop capabilities for governance of deployment, at a manageable scale, at which unanticipated outcomes are less consequential. We thus see high value in a well-resourced effort to situate the scale more precisely at which tests could provide useful information in reducing key uncertainties. However, there is a possibility that tests themselves make deployment more likely regardless of what is learned from them. We conclude that a crucial direction for governance of SAI tests is mitigating this slippery slope risk by building robust ex ante exit ramps, which specify conditions under which testing programs should not proceed, e.g. through the identification of a variety of unacceptable risks. Design and implementation of exit ramp mechanisms will be important to navigate a tradeoff between flexibility to accommodate new conditions and robustness to slippery slope pressures to evade them.
- Series: La Follette School Working Paper No. 2026-001
- Author: Gregory Nemet