Joint Symposium: Chatham House Paper on Proportionality in the Conduct of Hostilities

This is the final post in our joint symposium arising out of the publication of the Chatham House report, Proportionality in the Conduct of Hostilities: The Incidental Harm Side of the Assessment.

The new research paper published by Chatham House on Proportionality in the Conduct of Hostilities is a rigorous and thoughtful exposition of the civilian side of the notion of proportionality under international humanitarian law (IHL). This brief post focuses on three points that are raised by the paper: first, the way in which certain difficult questions concerning the reach of proportionality considerations are addressed; second, the question of the status of the natural environment; and third, the potential impact of the paper.

The proportionality calculus calls for a comparison of the expected incidental harm to civilians caused by an attack and the concrete and direct military advantage anticipated. Amongst the many difficult questions that arise from this formulation is the reach of the test, e.g. what type of harm is included, psychological or only physical harm? When might harm be considered as having been ‘caused’ by an attack? Does it include so-called ‘reverberating’ harm, manifesting sometime after an attack (as in the case with unexploded cluster sub-munitions)?

The research paper addresses this question of the reach of the proportionality analysis through the dual test of admissibility and weight. This has the significant advantage of offering a more nuanced way of dealing with some of these complicated questions concerning the scope of the proportionality analysis. For example, on the question of reverberating harm, the paper takes the position that ‘the geographic or temporal proximity of the harm to the attack is not determinative’ and should not affect the admissibility of reverberating harm (para 63). Instead, ‘[f]actors such as the passage of time between the attack and the injury, or the number of causal steps between one and the other, may affect the likelihood of the harm occurring and thus the weight to be assigned to it’ (para 64). That reverberating harm, manifesting sometime after an attack rather than at the time of the attack, must be taken into account in assessing proportionality must be right – there is nothing in the Additional Protocol I (API) formulation of the proportionality test that suggests excluding such types of harm. The reference in API is simply to an ‘attack which may be expected to cause incidental’ civilian harm – as the paper states, harm is caused by an attack if, ‘but for’ the attack, the harm would not occur (para 45), regardless of any proximity considerations. Instead, the proximity of expected harm to the attack might be relevant to the weight to be given to that potential harm.

This dual admissibility/weight test thus allows for a more nuanced consideration of different factors. Importantly, however, the test must be applied only where it facilitates application of the proportionality rule itself – that is, the validity of the test is dependent on its reflection of the proportionality rule as it appears in API. For example, in stating that temporally distant potential harm must be taken into account but that the weight of that harm may be affected by its proximity to the attack, it is important that considerations of weight not be used in a way that effectively excludes such harm from the proportionality analysis. The ‘weight’ assigned to potential harm may be reduced on the basis of proximity factors only insofar as such factors affect the extent to which such harm may be ‘expected’ to occur (the API test).

With respect to the natural environment, the research paper (in section 4.4.1.2) notes the divergent views of commentators as to whether elements of the natural environment are protected by IHL only insofar as harm thereto might in turn harm humans, or whether the natural environment is itself treated as a civilian object to be factored into the proportionality analysis. The paper (at para 136) supports the latter view, drawing on some State and judicial practice, as well as some soft law instruments. Once again, the paper proposes that the admissibility/weight model might be useful here:

Some damage to elements of the natural environment is inevitable in most attacks. But this is not a ground for excluding it from the assessment. Instead, the extent of the damage is something that is addressed by means of the weight assigned to it. (para 138)

This is a welcome conclusion. Not only does the treaty text itself not exclude elements of the natural environment from the category of civilian objects, but it is also clear that there is a trend in practice to recognise that the natural environment should be included in the proportionality calculus. Indeed, the negative definition of civilian objects under IHL is a clear indication that the category was meant to be broad and evolutive.

Overall, the research paper makes an important contribution to this complex and rather opaque field. Indeed, the traditional tools that we would use to interpret treaty provisions often are not at our disposal in IHL, where State practice is either unhelpful (as in the case of military manuals, which often simply reiterate treaty rules without elaborating) or confidential (as in the case of military doctrine). Actual operational practice is often also difficult to come by in the context of IHL. The Chatham House paper, and other similar initiatives (such as the expert meeting report from the ICRC and Université Laval), thus provide an important insight that can potentially help to fill this lacuna. Importantly, the paper was preceded by a number of consultations between academics and practitioners. There is, of course, always a risk with such endeavours – that the interpretation of treaty texts becomes dominated by a small number of individuals and that formalised treaty rules become conditioned by unrepresentative interpretations. However, the Chatham House paper appears to have traversed this difficult field well, basing itself not on the consultations as such, but rather the extensive research into doctrine and practice by the author.

The question that follows is what impact this document is likely to have. It is clear throughout that the document is not intended solely as a codification of State practice that might aid the interpretation of the proportionality rule (as noted, such practice often is not broadly available). Indeed, many of the positions taken in the paper, such as the admissibility/weight approach, are methods of applying the treaty rules in practice, rather than interpretations of those rules as such. And this appears to be the goal of the paper overall – a clarification of the principle of proportionality so as to operationalise it. This publication reflects perfectly the divergence between a heavily traditional understanding of the processes and actors involved in law creation and interpretation and a broader account of the myriad ways in which norms arise and evolve in international law (on this, see Anthea Roberts and Sandesh Sivakumaran, ‘The Theories and Realities of the Sources of International Law’ in Malcolm Evans (ed), International Law (5^th edn, Oxford, OUP)). Thus, military legal advisors may well be a key audience for this paper, though other actors, particularly courts (both domestic and international) that face litigation implicating the rule on proportionality, will also benefit. The heavy reliance on jurisprudence throughout the paper will likely make it relatively uncontroversial for such courts at least to refer to the paper. And the engagement of different State institutions, whether courts or executives, with the approaches taken in this paper could form the seeds of new rules or new legal interpretations.