War & Strategy

Autonomous Weapons Systems and Proportionality – New Article

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Published a new law review article, “Autonomous Weapons Systems and Proportionality: The Need for Regulation,” in the Case Western Reserve Journal of International Law, Vol. 57:1 (2025). The full text is available for download at SSRN here, and the abstract is below:

This article examines the question of whether International Humanitarian Law (IHL) requires modification to effectively govern autonomous weapons systems (AWS). While extensive scholarly discourse has focused on whether AWS can comply with existing IHL principles, and whether the development and deployment of AWS should be constrained through weapons treaties, insufficient attention has been paid to why and how IHL itself might need adaptation to regulate AWS as a method of warfare. Given that the imminent development and deployment is unlikely to be prohibited, and that AWS may not comply with IHL in certain circumstances, the question of why and how IHL needs to be adjusted is important. The analysis focuses on the principle of proportionality as a means of exploring and illustrating the issue.

The article first traces the evolution of AWS governance debates, highlighting the impasse at the Convention on Certain Conventional Weapons (CCW) regarding constraints on AWS development. It then conducts a detailed examination of the distinct elements and operation of the principle of proportionality, a principle whose implementation demands complex, contextual, and sophisticated judgment.

The article examines the evidence of certain weaknesses of AI-operated AWS, explains why the operationalization of the principle of proportionality would present challenges for such systems, and argues that AWS would likely struggle to implement the principle reliably and predictably in certain operational contexts. The final section supports and defends proposals for the certain adjustments or modifications of IHL to better regulate AWS, thereby ensuring AWS operations remain constrained by the core principles of IHL. It ends by briefly exploring the mechanisms that might be available for developing such constraints.

Geoengineering Wars and Atmospheric Governance

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Published my latest article, written with Scott Moore of UPenn, “Geoengineering Wars and Atmospheric Governance,” in the The Harvard International Law Journal. A copy can be downloaded from SSRN here. Here is the abstract:

The increasingly harsh and unevenly distributed heat-related harms caused by climate change, together with frustration over the collective inability to respond to the crisis, are likely to make unilateral geoengineering efforts increasingly attractive. Stratospheric aerosol injection (“SAI”) is a form of solar radiation modification that is effective, technically feasible, and within the financial means of many states and even non-state actors. Yet, there are virtually no global governance structures in place to specifically regulate such activity, and existing international law would provide only weak constraints on unilateral SAI efforts. These features create incentives for unilateral action in what is known as a “free driver” problem: few constraints on a unilateral action that has low direct cost combined with immediate direct individual benefit despite widely distributed risks and indirect costs.

There would be significant collateral environmental and climatic harms associated with SAI. That, coupled with the high risk of unilateral action, is reason enough for both caution and stronger governance. But another risk posed by any unilateral SAI effort—one that is underappreciated and under-theorized—is that of armed conflict. We explore how and why states would likely perceive the potential risks associated with unilateral SAI effort as constituting a threat to national security, and in the absence of adequate legal and institutional mechanisms to constrain such unilateral action, might well contemplate the use of force to defend against the perceived threat. The Article explores and explains how and why the jus ad bellum regime is unlikely to prevent states from engaging in unauthorized use of force against unilateral SAI actors. (click “read more” below for full abstract).

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Discussing Kursk on Asymmetrical Haircuts: The International Justice Podcast

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It was a pleasure to be a guest on Asymmetrical Haircuts: The International Justice Podcast, to discuss the legal issues implicated by the Ukrainian incursion into the Kursk region of Russia in August of 2024, in the episode “Justice Update – Ukraine (Almost) Joins the ICC, and Invades Russia,” Sept. 6, 2024.

Foreign Affairs Essay – The Battle Over Blocking the Sun

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My colleague Scott Moore and I published an essay in Foreign Affairs that summarized some of the arguments that we make in our forthcoming law review article in the Harvard International Law Journal. The essay (with a title we did not love) is “The Battle Over Blocking the Sun: Why the World Needs Rules for Solar Geoengineering,” Foreign Affairs, Aug. 14, 2024. The argument is captured in the abstract to our much longer law review article, “Geoengineering Wars and Atmospheric Governance,” Harvard International Law Journal (forthcoming, 2025), which is here:

The increasingly harsh and unevenly distributed heat-related harms caused by climate change, together with the frustration over the collective inability to respond to the crisis, are likely to make unilateral geoengineering efforts increasingly attractive. Stratospheric aerosol injection (SAI) is a form of solar radiation modification that is effective, technically feasible, and within the financial means of many states and even non-state actors. Yet there are virtually no global governance structures in place to specifically regulate such activity, and existing international law would provide only weak constraints on unilateral SAI efforts. These features create incentives for unilateral action in what is known as “free driver” problem —few constraints on unilateral action that has low direct cost combined with immediate direct individual benefit and widely distributed risks and indirect costs.

There would be significant collateral environmental and climatic harms associated with SAI. That, coupled with the high risk of unilateral action, is reason enough for both caution and stronger governance. But another risk posed by any unilateral SAI effort—one that is underappreciated and under-theorized—is that of armed conflict. We explore how and why states would likely perceive the potential risks associated with unilateral SAI effort as constituting a threat to national security, and in the absence of adequate legal and institutional mechanisms to constrain such unilateral action, might well contemplate the use of force to defend against the perceived threat. The article explores and explains how and why the jus ad bellum regime is unlikely to prevent states from engaging in unauthorized use of force against unilateral SAI actors.

Read more