The role of the no-harm rule in governing solar radiation management geoengineering

Scientists propose developing solar radiation management (SRM) geoengineering to offset rising global mean surface temperatures associated with anthropogenic climate change. The most prominent proposal is stratospheric aerosol injection (SAI). SAI involves creating aerosol particles in the stratosphere to reflect some incoming solar radiation and thereby reduce global temperature increase. SAI poses risks of transboundary harm and/or harm to the atmosphere, such as regional drought and further depletion of the stratospheric ozone layer. It is therefore important that SAI is governed at an international level. However, presently there are no international agreements that specifically govern SAI, or SRM more generally. This thesis asks what role the 'no-harm' rule might play in the international governance of SAI. The no-harm rule is a longstanding principle of customary international law. It provides that states have an obligation to prevent significant transboundary harm and harm to the global commons. Legal scholarship has considered the potential of the no-harm rule as a basis of a claim for state responsibility should a state attempt SAI and cause significant transboundary harm. However, there has been no detailed consideration of the potential of the no-harm rule to respond prospectively to the risks of transboundary harm and/or harm to the atmosphere posed by SAI. This thesis examines the content of the no-harm rule and considers its likely influence on the behaviour of states in future attempts at SAI. Using doctrinal legal analysis, this thesis establishes that states have a duty to take positive action to prevent activities under their jurisdiction and control from causing significant transboundary harm and/or harm to the global commons. This includes conducting an environmental impact assessment and notifying and consulting with potentially affected states. In the context of SAI, states may also be held strictly responsible should significant harm nevertheless result. However, the meaning of 'significant' harm is ambiguous, and it is unclear how this should be interpreted to determine when SAI will give rise to obligations under the no-harm rule. This thesis applies Brunnee and Toope's theory of interactional international law to analyse the no-harm rule's capacity to promote compliance through as sense of legal obligation and legitimacy. This capacity appears strongest regarding the prevention of transboundary harm and weakest for the prevention of harm to the global commons. Given the risks of harm to the atmosphere posed by SAI, it should be a priority for the international community to develop the no-harm rule for application to global commons areas. This thesis recommends developing a set of objective criteria to reduce doctrinal ambiguity for determining if a proposed activity poses a risk of significant harm to the global commons. It also recommends creating greater opportunities for mutual engagement between state and non-state actors to enhance shared understandings and practices to strengthen the likelihood of compliance with the no-harm rule in this context. The results of this thesis provide a deeper understanding of the capacity of the no-harm rule to respond to the risks of SAI and how it might be developed to better contribute to international environmental governance.