Solar climate engineering (SCE) can be defined as a deliberate effort to cool Earth’s climate by reflecting additional solar radiation in order to compensate for global warming due to increasing greenhouse gas concentrations. Current SCE efforts are focused on one of two approaches: creating a layer of small particles in the stratosphere to mimic the effects of volcanic eruptions or adding particles to the marine boundary layer to increase the brightness (reflectivity) of marine boundary layer clouds. These efforts, both of which will be discussed, have been investigated in computer simulations but as yet have not been tested experimentally. Equally importantly, SCE presents serious issues of ethics and potential governance. Ethical issues include variants of arguments about the lesser of two evils, moral hazard, intra- and inter-generational justice, and hubris. SCE raises questions, among others, about the role of global governance and compensation for unexpected outcomes. Assessment of these issues changes as one moves from considering research to atmospheric testing and, ultimately, to deployment. The fundamental question, then, is whether there is a path forward through these intertwined issues of science, ethics and governance.
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