1 Protocol Additional (I) to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of International Armed Conflicts, 1125 UNTS 3, 8 June 1977 (entered into force 7 December 1978), Art. 51(5)(b). Proportionality is also a customary IHL rule. See Jean-Marie Henckaerts and Louise Doswald-Beck (eds), Customary International Humanitarian Law, Vol. 2: Practice, Cambridge University Press, Cambridge, 2005, Rule 14, available at: https://ihl-databases.icrc.org/customary-ihl/eng/docs/v2_rul_rule14 (all internet references were accessed in October 2021).

2 Emanuela-Chiara Gillard, Proportionality in the Conduct of Hostilities: The Incidental Harm Side of the Assessment, Chatham House, December 2018, pp. 47–48.

3 The absolute amount of information is not the only important factor, however, as too much information can be detrimental and inhibit decision-making. Information needs to be relevant, accurate and timely.

4 E.-C. Gillard, above note 2, p. 47.

5 Ibid., p. 26.

6 Brown, Bernard L., “The Proportionality Principle in the Humanitarian Law of Warfare: Recent Efforts at Codification”, Cornell International Law Journal, Vol. 10, No.1, 1976, p. 145Google Scholar.

7 Arthur C. Clarke predicted a GPS-like technology in a letter he wrote in August 1956: “My general conclusions are that perhaps in 30 years the orbital relay system may take over all the functions of existing surface networks and provide others quite impossible today. For example, the three stations in the 24-hour orbit could provide not only an interference- and censorship-free global TV service for the same power as a single modern transmitter, but could also make possible a position-finding grid whereby anyone on earth could locate himself by means of a couple of dials on an instrument about the size of a watch.” See “Did Arthur C. Clarke Predict GPS?”, Technovelgy, available at: www.technovelgy.com/ct/Science-Fiction-News.asp?NewsNum=2967.

8 National Research Council, The Global Positioning System: A Shared National Asset, National Academies Press, Washington, DC, 1995, p. 146.

9 At an international expert meeting on proportionality, however, experts unanimously agreed that commanders have an obligation to proactively seek out and collect relevant and reasonably available information. See Laurent Gisel (ed.), International Expert Meeting: The Principle of Proportionality in the Rules Governing the Conduct of Hostilities under International Humanitarian Law, ICRC and University of Laval, June 2016, p. 48.

10 AP I, Art. 57 (emphasis added).

11 E.-C. Gillard, above note 2, p. 43.

12 Ibid., p. 16.

13 Ibid.

14 Whereas in the case of international armed conflicts, NSAGs would be bound by the four Geneva Conventions, AP I and the customary IHL of international armed conflicts.

15 For the various perspectives on this issue, see Sassòli, Marco, “Taking Armed Groups Seriously: Ways to Improve Their Compliance with International Humanitarian Law”, Journal of International Humanitarian Legal Studies, Vol. 1, No.1, 2020, p. 12Google Scholar.

16 Zegveld, Liesbeth, Accountability of Armed Opposition Groups in International Law, Cambridge University Press, Cambridge, 2009, p. 9Google Scholar.

17 M. Sassòli, above note 15, p. 13.

18 Article 57(2)(a)(iii) of AP I notes that “those who plan or decide upon an attack” are obligated to refrain from deciding to launch any attack that might be disproportionate. This suggests that the onus is on those who have the authority to plan or decide upon an attack, which in most cases would be military commanders, to refrain from disproportionate attacks. However, regarding Article 57(2)(b) on the cancelation and suspension of disproportionate attacks, it has been noted that the rule applies not only to those planning and deciding upon attacks, but also, and primarily, to those executing them. See Yves Sandoz, Christophe Swinarski and Bruno Zimmermann (eds), Commentary on the Additional Protocols, International Committee of the Red Cross (ICRC), Geneva, 1987, p. 686.

19 See Annyssa Bellal, “Welcome on Board: Improving Respect for International Humanitarian Law through the Engagement of Armed Non-State Actors”, in Terry D. Gill (ed.), Yearbook of International Humanitarian Law 2016, Vol. 19, T. M. C. Asser Press, The Hague, 2018, pp. 44; ICRC, Allies, Partners and Proxies: Managing Support Relationships in Armed Conflict to Reduce the Human Cost of War, Geneva, April 2021, p. 39; Geneva Call, “Garance Talks: Armed non-State Actors and Experts Gathered in Geneva to Discuss the Conduct of Hostilities in Armed Conflict”, 10 March 2020, available at: www.genevacall.org/garance-talks-armed-groups-and-experts-gathered-in-geneva-to-discuss-the-conduct-of-hostilities-in-armed-conflict/.

20 A. Bellal, above note 19, p. 44.

21 That being said, NSAGs are very diverse depending on the context in which they operate, including the level to which they maintain close links with the civilian population. See Médecins Sans Frontières, “The Practical Guide to Humanitarian Law: Nonstate Armed Groups”, available at: https://guide-humanitarian-law.org/content/article/3/non-state-armed-groups/. NSAGs that maintain close links are likely to have a considerable amount of information about the civilian population that does not require technology or material investments to collect – information that can be used for proportionality assessments.

22 Shue, Henry and Wippman, David, “Limiting Attacks on Dual-Use Facilities Performing Indispensable Civilian Functions”, Cornell International Law Journal, Vol. 35. No.3, 2002, p. 562Google Scholar.

23 Geneva Water Hub, The Geneva List of Principles on the Protection of Water Infrastructure, Geneva, August 2019, p. 28.

24 E.-C. Gillard, above note 2, p. 35.

25 Ibid.

26 Ibid. The types of incidental harm that are recognized by AP I are death and injury to civilians and damage to civilian objects. The Gillard paper does not define what is meant by “adverse effects” not recognized by AP I, but it can be assumed to include environmental damage, spread of disease etc.

27 Ibid.

28 Sassòli, Marco, International Humanitarian Law: Rules, Controversies, and Solutions to Problems Arising in Warfare, Edward Elgar, Cheltenham, 2019, p. 521CrossRefGoogle Scholar.

29 Clarke, Ben, “Proportionality in Armed Conflicts: A Principle in Need of Clarification?”, International Humanitarian Legal Studies, Vol. 3, No. 1, 2012, p. 75Google Scholar.

30 Ibid., p. 121.

31 Shamash, Hamutal Esther, “How Much is Too Much? An Examination of the Principle of Jus in Bello Proportionality”, Israel Defense Forces Law Review, Vol. 2, 2005–06, p. 18Google Scholar.

32 Janina Dill, Applying the Principle of Proportionality in Combat Operations, policy briefing, Oxford Institute for Ethics, Law, and Armed Conflict, December 2010, p. 4.

33 M. Sassòli, above note 28, p. 522. By “excessive”, Sassòli seems to be referring to the point at which the risk of losing one civilian life is excessively larger than the military advantage to be gained from the attack.

34 Ibid.

35 H. E. Shamash, above note 31, p. 14.

36 M. Sassòli, above note 28, p. 363.

37 “Equation”, Oxford Learner's Dictionary, available at: www.oxfordlearnersdictionaries.com/definition/english/equation.

38 E.-C. Gillard, above note 2, p. 47.

39 L. Gisel (ed.), above note 9, pp. 12–19, 17.

40 See, for example, the discussions in L. Gisel (ed.), above note 9, pp. 12–13; and Sigrid Redse Johansen, The Military Commander's Necessity: The Law of Armed Conflict and Its Limits, Cambridge University Press, Cambridge, September 2019, pp. 288–298.

41 L. Gisel (ed.), above note 9, pp. 62–63.

42 Ibid., p. 35.

43 However, the 2016 ICRC Commentary on Geneva Convention I states that the High Contracting Parties must also ensure respect for the rules applicable in non-international armed conflict, including by non-State armed groups (para. 125), and that this obligation is not limited to the Geneva Conventions but applies to the entire body of IHL binding upon a particular State (para. 126), which would include the rule of proportionality. See ICRC, Commentary on the First Geneva Convention: Convention (I) for the Amelioration of the Condition of the Wounded and Sick in Armed Forces in the Field, 2nd ed., Geneva, 2016.

44 See A. Bellal, above note 19; Hyeran Jo, “Compliance with International Humanitarian Law by Non-State Armed Groups: How Can It Be Improved?”, in T. D. Gill (ed.), above note 19; McLeod, Andrew, “Engaging Non-State Armed Groups for Humanitarian Purposes: Experience, Constraints and Ways Forward”, in Humanitarian Engagement with Non-State Armed Groups, Chatham House, London, April 2016Google Scholar.

45 At the same time, stronger command lines can be used to communicate and enforce restraints on military action. For instance, dissemination of the Taliban's code of conduct, known as the Layeha, would be easier and more effective if the Taliban was able to unify its command and control structure and resolve the difficulties that the top leadership face in coordinating fighters at the district and provincial levels. The Taliban attempted to find solutions to such challenges when it revised the Layeha in 2010. See Johnson, Thomas H. and DuPee, Matthew C., “Analysing the New Taliban Code of Conduct (Layeha): An Assessment of Changing Perspectives and Strategies of the Afghan Taliban”, Central Asian Survey, Vol. 31, No. 1, 2012, p. 87CrossRefGoogle Scholar.

46 Out of the 150 NSAGs that Geneva Call have engaged, more than half have signed one or more Deeds of Commitment or made similar pledges. See Geneva Call, The Garance Series, No. 3: Conduct of Hostilities by Armed Non-State Actors: Report from the 2020 Garance Talks, Geneva, 2020.

47 One of the very few NSAGs that has formally committed to the rule of proportionality is the Popular Mobilization Forces (PMF) of Iraq, which stated in its Unilateral Declaration in 2018 that it would “commit before the military attack and military operations to consider the anticipated military advantage in comparison with the expected collateral damages”. See PMF, “Declaration on the Commitment to Respect Humanitarian Norms during and in the Aftermath of Armed Conflict or Military Operations”, Geneva Call: Their Words, 2018, available at: https://tinyurl.com/yhwkwx2x.

48 M. Sassòli, above note 15, p. 41.

49 See Luciana Vosniak, “How the UN Can Help Ensure Non-State Armed Groups Protect Civilians”, International Peace Institute Global Observatory, 16 April 2021, available at: https://theglobalobservatory.org/2021/04/how-un-can-help-ensure-non-state-armed-groups-protect-civilians/. According to Vosniak, there are precedents for the UN to engage with NSAGs in order to achieve humanitarian objectives. For instance, UNSC Res. 1539 and 1612 established a framework for monitoring and reporting grave violations against children's rights in armed conflict. UN country teams and peacekeeping missions engage in dialogue with NSAGs in order to develop action plans outlining commitments to cease practices that violate children's rights. Similar resolutions and mechanisms can be used by the UN to engage NSAGs in capacity-building for assessing proportionality.

50 L. Gisel (ed.), above note 9, p. 64.

51 Juliane Garcia Ravel and Madalena Vasconcelos Rosa, “IHL in Action: Seven Patterns of Respect”, Humanitarian Law and Policy Blog, 19 November 2020, available at: https://blogs.icrc.org/law-and-policy/2020/11/19/ihl-in-action-seven-patterns-respect/.

52 See L. Gisel (ed.), above note 9, which makes ample use of hypothetical scenarios to facilitate discussions on the application of IHL.

53 Ibid., p. 47.

54 See E.-C. Gillard, above note 2, p. 41. While mental harm is not one of the previously described elements of COPAF, it can be included as an Optional Standard. As Gillard asserts, there is no reason in principle to exclude mental harm from the scope of proportionality assessments. Again, the more elements COPAF adds, the more rigorous the assessment becomes.

55 ICRC, above note 19, p. 38.

56 ICRC, Engagement with Non-State Armed Groups: Why, How, for What Purpose, and Other Salient Issues, position paper, Geneva, March 2021, p. 2.

57 ICRC, above note 19, p. 38.

58 Ibid., p. 39.

59 In 2020, 432 out of 1,734 civilian deaths in Syria were caused by the Syrian regime, which includes the Syrian army, security, local militias and Shiite foreign militias. On the other hand, NSAGs killed far fewer civilians – twenty-one civilians were killed by ISIS and twenty-six by Hay'at Tahrir Al-Sham. See Syrian Network for Human Rights, Extrajudicial Killing Claims the Lives of 1,734 Civilians in Syria in 2020, 1 January 2021, p. 9.

60 For instance, the UN Human Rights Council's report on IHL violations in Syria specifically singled out a Syrian Air Force attack on Al-Feijeh spring, which provides 70% of all of Damascus's water, in 22 December 2016. The report stated that “[t]he attack amounts to the war crime of attacking objects indispensable for the survival of the civilian population, and further violated the principle of proportionality in attacks”. See Human Rights Council, Human Rights Abuses and International Humanitarian Law Violations in the Syrian Arab Republic, 21 July 2016–28 February 2017, UN Doc. A/HRC/34/CRP.3, 10 March 2017, paras 32, 37.

61 Ezequiel Heffes and Jonathan Somer, Inviting Non-State Armed Groups to the Table: Inclusive Strategies towards a More Fit for Purpose International Humanitarian Law, briefing note, Overseas Development Institute, Centre for the Study of Armed Groups, December 2020, p. 2.

62 Ibid.