In recent years, some scientists have called for research into and potential development of ‘solar geoengineering’ technologies as an option to counter global warming. Solar geoengineering refers to a set of speculative techniques to reflect some incoming sunlight back into space, for example, by continuously spraying reflective sulphur aerosols into the stratosphere over several generations. Because of the significant ecological, social, and political risks posed by such technologies, many scholars and civil society organizations have urged governments to take action to prohibit the development and deployment of solar geoengineering techniques. In this article we take such calls for a prohibitory or a non-use regime on solar geoengineering as a starting point to examine existing international law and governance precedents that could guide the development of such a regime. The precedents we examine include international prohibitory and restrictive regimes that impose bans or restrictions on chemical weapons, biological weapons, weather modification technologies, anti-personnel landmines, substances that deplete the ozone layer, trade in hazardous wastes, deep seabed mining, and mining in Antarctica. We also assess emerging norms and soft law in anticipatory governance of novel technologies, such as human cloning and gene editing. While there is no blueprint for a solar geoengineering non-use regime in international law, our analysis points to numerous specific elements on which governments could draw to constrain or impose an outright prohibition on the development of technologies for solar geoengineering, should they opt to do so.

Stratospheric Aerosol Injection (SAI), is often referred to as a ‘Plan B’ if mitigation strategies to reduce emissions fail and the need to rapidly reduce global temperatures becomes urgent. In theory, SAI would help buy more time to bring carbon and other emissions down while also cooling or keeping the planet below the threshold for dangerous warming, though it is not a solution to the problem of climate change in itself. What little attention it has received in International Relations (IR) is usually focused on the need for governance of the technology and assumes that development and use of the technology will be driven primarily by vulnerability to climate impacts. Through an analysis of common security assumptions and preemptive security framings the article shows that while current assessments of SAI focus on the technology’s environmental impact, broader political and security dynamics, particularly the desire to render climate change more intelligible as a security problem with a solution may have substantial influence on how the technology is used and by whom.

What is a Classical Realist analysis of climate ethics and politics? Classical Realist ethical analysis differs from ideal normative theory in that it addresses state decision-makers rather than individuals, assumes highly imperfect compliance with the demands of justice, and is concerned with feasibility and transition rather than end-states. Classical Realists urge leaders to prioritise state security over private moral concerns, to assess rival policies against their likely consequences and to seek the ‘lesser evil’ among feasible choices. But how does Realism respond when the prudent pursuit of state security risks rendering much of the planet uninhabitable? In the 1950s, the development of the hydrogen bomb created just such a dilemma as status quo politics now carried a significant risk of thermonuclear omnicide. In response, Hans Morgenthau argued that states should manage systemic risk by working in concert to safeguard expanded, collective national interests. The Classical Realist mode of thought suggests an analogous response to systemic climate risks: states’ conceptions of national interest must expand to include cooperative system-preservation alongside traditional security concerns. Classical Realist arguments might then be mobilised to overcome resistance from vested interests and to support state-directed low carbon innovation, adaptation and mitigation agreements that prioritise ambition over distributional justice.