1 William A. Buckingham Jr, Operation Ranch Hand: The Air Force and Herbicides in Southeast Asia, 1961–1971, Office of the Air Force History, United States Air Force, Washington, DC, 1982, p. 21.

2 Andrew Glass, “U.S. Launches Spraying of Agent Orange, Jan. 18, 1962”, Politico, 18 January 2019, available at: www.politico.com/story/2019/01/18/us-launches-operation-ranch-hand-jan-18-1962-1102346 (all internet references were accessed in October 2023).

3 Ibid.

4 Schmitt, Michael N., “Green War: An Assessment of the Environmental Law of International Armed Conflict”, Yale Journal of International Law, Vol. 22, 1997, p. 10Google Scholar.

5 See US District Court for the Eastern District of New York, Vietnam Association for Victims of Agent Orange v. Dow Chemical Co. (in re Agent Orange Product Liability Litigation), MDL No. 381, 04-CV-400, Statement of Interest of the United States, 12 January 2005, pp. 4–13.

6 By “special”, we refer to instruments or provisions that pertain to the natural environment itself as the protected entity, regardless of whether parts thereof constitute civilian objects, in contrast to those general protections that focus on, for example, protected persons or objects. With respect to the latter, protections may be direct, contingent upon the environmental component in question qualifying as a civilian object, or merely incidental.

7 See e.g. International Law Commission (ILC), Principles on the Protection of the Environment in Armed Conflict, 2022 (PERAC Principles), Principle 13. See also the earlier draft of the PERAC Principles: ILC, Draft Principles on Protection of the Environment in Relation to Armed Conflicts, with Commentaries, in Yearbook of the International Law Commission, Vol. 2, Part 2, 2022 (ILC Draft Principles). Note that the commentary to Principle 13(2) indicates that the phrase “subject to applicable international law” is meant to “recognize[] that there are still different views regarding the customary status of both the duty of care and the prohibition as enshrined in Additional Protocol I”. See also Jean-Marie Henckaerts and Louise Doswald-Beck (eds), Customary International Humanitarian Law, Vol. 1: Rules, Cambridge University Press, Cambridge, 2005 (ICRC Customary Law Study), Rule 45, as well as the associated practice collected by the ICRC at: https://ihl-databases.icrc.org/en/customary-ihl/v2.

8 The fact that our analysis is limited to the environmental obligations pertaining to international armed conflicts does not imply that we believe certain protections addressed herein would not apply to non-international armed conflicts, which are simply beyond the scope of this article.

9 For a summary of other relevant treaties not addressed by this article, see, for example, Schmitt, Michael N., “Humanitarian Law and the Environment”, Denver Journal of International Law and Policy, Vol. 28, No. 3, 2000Google Scholar.

10 Regulations Concerning the Laws and Customs of War on Land, Annexed to Convention (IV) Respecting the Laws and Customs of War on Land, 36 Stat. 2227, TS No. 539, 18 October 1907 (entered into force 26 January 1910), Art. 23(g).

11 Rome Statute of the International Criminal Court, UN Doc. A/CONF.183/9, 17 July 1998 (entered into force 1 July 2002) (Rome Statute), Art. 8(2)(b)(xiii).

12 Project of an International Declaration Concerning the Laws and Customs of War, Brussels, 27 August 1874 (Brussels Declaration), Art. 13(g); Francis Lieber, Instructions for the Government of Armies of the United States in the Field, General Order No. 100, US Department of War, 24 April 1863 (Lieber Code), Art. 44. Both instruments were non-binding as a matter of international law. See also US Department of Defense (DoD), Law of War Manual, Office of the General Counsel, July 2023 (US Law of War Manual), sec. 2.3.1 and accompanying footnotes; Program on Humanitarian Policy and Conflict Research at Harvard University, Manual on International Law Applicable to Air and Missile Warfare, 2009, Rule 88.

13 ICJ, Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, ICJ Reports 1996 (Nuclear Weapons Advisory Opinion), paras 79–82, citing Trial of the Major War Criminals, 14 November 1945–1 October 1946, Vol. 1, Nuremberg, 1947, p. 254, and Report of the Secretary-General Pursuant to Paragraph 2 of Security Council Resolution 808 (1993), UN Doc. S/25704, 3 May 1993, introducing the Statute of the International Criminal Tribunal for the former Yugoslavia (ICTY), unanimously approved by the UN Security Council in UNSC Res. 827, 25 May 1993.

14 Geneva Convention (IV) relative to the Protection of Civilian Persons in Time of War of 12 August 1949, 75 UNTS 287 (entered into force 21 October 1950) (GC IV), Art. 53.

15 Ibid., Art. 147; Rome Statute, above note 11, Art. 8(2)(a)(iv). For an examination of how the ICTY has interpreted “extensive” in this context, see ICTY, The Prosecutor v. Tihomir Blaškić, Case No. IT-95-14-T, Judgment (Trial Chamber), 3 March 2000, para. 157.

16 Jean Pictet (ed.), Commentary on the Geneva Conventions of 12 August 1949, Vol. 4: Geneva Convention relative to the Protection of Civilian Persons in Time of War, ICRC, Geneva, 1958 (ICRC Commentary on GC IV), pp. 301, 601.

17 Nuclear Weapons Advisory Opinion, above note 13, paras 79–82.

18 GC IV, Art. 53; ICRC Commentary on GC IV, above note 16, p. 301. For the ICRC's most recent position on the matter, see ICRC, Guidelines on the Protection of the Natural Environment in Armed Conflict: Rules and Recommendations Relating to the Protection of the Natural Environment under International Humanitarian Law, with Commentary, Geneva, 2020 (ICRC Guidelines), paras 175–179. See also US Law of War Manual, above note 12, sec. 5.17.1 (“All property located in enemy territory is regarded as enemy property regardless of its ownership”); Yoram Dinstein and Arne Willy Dahl (eds), Oslo Manual on Select Topics of the Law of Armed Conflict: Rules and Commentary, Springer, Cham, 2020 (Oslo Manual), commentary accompanying Rule 97, para. 4 (“The notion of property is not defined by applicable treaties. The notion of property must therefore be understood in light of its ordinary (dictionary) meaning. All tangible, movable or immovable items as well as real property fall within the notion of ‘property’”).

19 Protection of the Environment in Relation to Armed Conflicts: Comments and Observations Received From Governments, International Organizations and Others, UN Doc. A/CN.4/749, 17 January 2022 (State Comments to ILC Draft Principles), p. 77; see also Bellinger, John B. III and Haynes, William J. Jr, “A US Government Response to the International Committee of the Red Cross Study Customary International Humanitarian Law”, International Review of the Red Cross, Vol. 89, No. 866, 2007, p. 455Google Scholar (stating that “parts of the natural environment may not be destroyed unless required by military necessity”).

20 US Department of the Army, The Commander's Handbook on the Law of Land Warfare, FM 6-27/MCTP 11-10C, August 2019 (US Land Handbook), para. 2-135.

21 The Oslo Manual notes that due regard for the environment should be given when planning military operations, explaining that the rule extends to belligerent States; neutral States; international sea areas; and outer space, the Moon and other celestial bodies. Oslo Manual, above note 18, Rules 138–139. It further notes that the question of whether the environment encompasses outer space, the Moon and celestial bodies for IHL purposes is “controversial”. Ibid., commentary accompanying Rule 139, para. 3.

22 Accord FM 6-27, above note 20, para. 2-135 (“Wanton destruction of the environment is prohibited”); UNGA Res. 47/37, “Protection of the Environment in Times of Armed Conflict”, 9 February 1993 (“Stressing that destruction of the environment, not justified by military necessity and carried out wantonly, is clearly contrary to existing international law”).

23 DoD, Conduct of the Persian Gulf War: Final Report to Congress, Appendix O: “The Role of the Law of War”, April 1992 (Final Report to Congress), p. 624. See also ibid., p. 621; Remarks by the United States of America before the Sixth Committee, UN Doc. A/C.6/46/SR.18, 22 October 1991, para. 37.

24 Final Report to Congress, above note 23, p. 606. See also “Letter From the Permanent Missions of the Hashemite Kingdom of Jordan and of the United States of America Addressed to the Chairman of the Sixth Committee”, UN Doc. A/C.6/47/3, 28 September 1992 (Letter from US and Jordan), p. 2.

25 Final Report to Congress, above note 23, p. 625.

26 Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques, 1108 UNTS 151, 18 May 1977 (entered into force 5 October 1978) (ENMOD Convention), Art. 1.

27 Ibid., Art. 1(1).

28 US Law of War Manual, above note 12, sec. 6.10.3.

29 Ibid., sec. 6.10.2; see also State Comments to ILC Draft Principles, above note 19, p. 104. A variation of the phrase also appears in Articles 35 and 55 of AP I: 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) (AP I), Arts 35(3), 55(1).

30 ENMOD Convention, above note 26, Art. 2. A well-known example of such a technique is the US cloud seeding programme employed in Vietnam to disrupt enemy supply lines and other operations: see M. N. Schmitt, above note 9, pp. 268–269, 278.

31 Report of the Conference of the Committee on Disarmament, Vol. 1: Understanding Relating to Article II, UN Doc. A/31/27, 1976, p. 92.

32 Ibid.

33 Ibid.; see M. N. Schmitt, above note 9, p. 279.

34 US Law of War Manual, above note 12, sec. 6.10.2 (emphasis added).

35 AP I, Art. 52. Or consider Article 54(2), according to which aspects of the environment would receive enhanced protection as “objects indispensable to the survival of the civilian population”: ibid., Art. 54(2). Relevant components of the environment qualifying as such would include “agricultural areas for the production of foodstuffs, crops, [and] livestock”, and bodies of water required for drinking water and irrigation.

36 Ibid., Arts 35, 55.

37 United States, “Statement on Ratification of the Convention on Prohibitions or Restrictions on the Use of Certain Conventional Weapons Which May Be Deemed to Be Excessively Injurious or to Have Indiscriminate Effects, Accepting Protocols I & II”, 1861 UNTS 482, 24 March 1995, p. 483 (“The United States considers that the fourth paragraph of the preamble to the Convention, which refers to the substance of provisions of article 35 (3) and article 55 (1) of additional Protocol I to the Geneva Conventions for the Protection of War Victims of August 12, 1949, applies only to States which have accepted those provisions”).

38 See ICRC Customary Law Study, above note 7, Rule 45; ILC Draft Principles, above note 7, Draft Principle 13. See also Solf, Waldemar A., “Protection of Civilians against the Effects of Hostilities under Customary International Law and under Protocol I”, American University International Law Review, Vol. 1, No. 1, 1986, p. 134Google Scholar.

39 ICRC Customary Law Study, above note 7, Rule 43.

40 On wanton destruction, see text accompanying above notes 19–25. On proportionality, see US Law of War Manual, above note 12, sec. 5.12; Letter from US and Jordan, above note 24, p. 3.

41 To the extent that paragraphs A and C apply, their treaty equivalents are Articles 52 (attacking civilian objects, military objectives) and 57 (proportionality) of AP I.

42 AP I, Art. 52(1). This is a definitional approach that the United States generally supports: US Law of War Manual, above note 12, secs 5.6.1.1, 5.6.3.

43 AP I, Art. 52(2). The United States likewise generally supports this definition, although it interprets it in ways that do not always mirror those of other States. US Law of War Manual, above note 12, sec. 5.6.3; Matheson, Michael J., “Remarks on the United States Position on the Relation of Customary International Law to the 1977 Protocols Additional to the 1949 Geneva Conventions at the Sixth Annual American Red Cross–Washington School of Law Conference on International Humanitarian Law, 22 January 1987”, American University Journal of International Law and Policy, Vol. 2, 1987, p. 436Google Scholar. The most prominent example of a US interpretation of the rule that diverges from the mainstream is the treatment of so-called “war-sustaining” objects as military objectives. U.S. Law of War Manual, above note 12, sec. 5.6.8.5; and see, generally, Ryan Goodman, “The Obama Administration and Targeting ‘War-Sustaining’ Objects in Noninternational Armed Conflict”, American Journal of International Law, Vol. 110, No. 4, October 2016.

44 ICRC Guidelines, above note 18, para. 18.

45 ICRC Customary Law Study, above note 7, pp. 143–144.

46 ICRC Guidelines, above note 18, paras 18, 95; PERAC Principles, above note 7, Principle 13.

47 PERAC Principles, above note 7, Principle 13(3).

48 ILC Draft Principles, above note 7, commentary accompanying Principle 13, para. 10; see also commentary accompanying Principle 14, para. 3.

49 ICRC Guidelines, above note 18, para. 19.

50 US Law of War Manual, above note 12, secs 5.6.1.1, 5.6.3.

51 State Comments to ILC Draft Principles, above note 19, p. 79 (emphasis added).

52 Ibid., p. 82.

53 Ibid., p. 79; see also J. B. Bellinger III and W. J. Haynes Jr, above note 19, p. 455 (noting that only “parts of the natural environment cannot be made the object of attack unless they constitute military objectives, as traditionally defined”).

54 See DoD, Report to Senate and House Appropriations Committees on International Policies and Procedures Regarding the Protection of Natural and Cultural Resources during Times of War, 19 January 1993, reprinted as Appendix VIII in Patrick J. Boylan, Review of the Convention for the Protection of Cultural Property in the Event of Armed Conflict, UNESCO, 1993, p. 202.

55 Israel follows a similar “anthropocentric” approach: “[A]n element of the natural environment constitutes a civilian object only when it is used or relied upon by civilians for their health or survival. It follows that there are elements of the natural environment which will constitute neither civilian objects (where such elements are not used by civilians or relied upon by them for their health or survival) nor military objectives (where such elements do not qualify as such under the law of armed conflict).” State Comments to ILC Draft Principles, above note 19, p. 17; see also ICRC Guidelines, above note 18, para. 19.

56 See, generally, M. N. Schmitt, above note 4, p. 6.

57 ICRC Customary Law Study, above note 7, Rule 44.

58 Ibid., commentary accompanying Rule 44, p. 147.

59 See US Navy, US Marine Corps and US Coast Guard, The Commander's Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-12/COMDTPUB P5800.7A, March 2022 (US Naval Handbook), sec. 8.4; Chairman of the Joint Chiefs of Staff, Joint Targeting, Joint Publication 3-60, 31 January 2013, Appendix A, para. 8(b).

60 ICRC Guidelines, above note 18, Rule 1.

61 ICRC Customary Law Study, above note 7, p. 147; ICRC Guidelines, above note 18, commentary accompanying Rule 1, para. 42. The ICRC's contention is contested, however: see e.g. Oslo Manual, above note 18, commentary accompanying Rule 138, para. 3.

62 ICRC Guidelines, above note 18, para. 44.

63 There is disagreement over whether the constant care requirement establishes a duty of care beyond the obligations to take feasible precautions in attack. See Schmitt, Michael N. and Shauss, Michael, “Uncertainty in the Law of Targeting: Towards a Cognitive Framework”, Harvard National Security Journal, Vol. 10, 2019, pp. 178–181Google Scholar.

64 M. J. Matheson, above note 43, pp. 426–427; see also FM 6-27, above note 20, para. 2-137 (“Routine conventional military operations involving the employment of air, ground, and naval forces that may cause damage to the environment are not activities prohibited by [the law of armed conflict]”).

65 AP I, Arts 35(3), 55(1)–(2); see also Dinstein, Yoram, The Conduct of Hostilities under the Law of International Armed Conflict, 4th ed., Cambridge University Press, Cambridge, 2022, para. 816CrossRefGoogle Scholar (“Neither provision of AP/I offers a definition of the phrase ‘natural environment’. The ICRC Commentary suggests that it ‘should be understood in the widest sense to cover the biological environment in which a population is living’ – i.e. the fauna and flora – as well as ‘climatic elements’”). Yves Sandoz, Christophe Swinarski and Bruno Zimmermann (eds), Commentary on the Additional Protocols, ICRC Geneva, 1987 (ICRC Commentary on the APs), para. 2126.

66 See e.g. Mark Simonoff, “Remarks at the 70th UN General Assembly Sixth Committee on Agenda Item 83: Report of the International Law Commission on the Work of its 67th Session, 11 November 2015”, in Office of the Legal Advisor, US Department of State, Digest of United States Practice in International Law, 2015, p. 287 (“Relatedly, we are troubled by the presence among the principles of rules extracted from certain treaties that we do not believe reflect customary law. For example, draft principle II-4 repeats a prohibition in Additional Protocol I … on attacks against the natural environment by way of reprisals that we do not believe exists as a matter of customary international law. To the extent the rule is offered to encourage normative development, we remain in disagreement with it, consistent with the objections we have stated on other occasions”).

67 US Law of War Manual, above note 12, sec. 6.10.3.1; FM 6-27, above note 20, para. 2-143.

68 M. J. Matheson, above note 43, p. 424; see also Oslo Manual, above note 18, commentary accompanying Rule 139, para. 4; Program on Humanitarian Policy and Conflict Research at Harvard University, Commentary on the HPCR Manual on International Law Applicable to Air and Missile Warfare, 2010 (AMW Manual Commentary), commentary accompanying Section M, para. 5.

69 Herbert J. Hansell, “Circular 175: Request for Authorization to Sign Two Protocols to the Geneva Conventions of 1949 for the Protection of Victims of War”, Memorandum to the Secretary of State, 11 October 1977, Tab E, p. I-35-4. The Joint Chiefs incorporated these comments by reference into their advice respecting Article 55: ibid., p. I-55-2.

70 Ibid., p. I-35-4; James E. Dalton, “JCS Review of the 1977 Protocols Additional to the 1949 Geneva Conventions”, Memorandum to the Secretary of Defense, 1 October 1982, Appendix A (citing no relevant proposed understandings or reservations with respect to Articles 35 or 55).

71 John W. Vessey Jr, “Review of the 1977 First Additional Protocol to the Geneva Conventions of 1949”, Memorandum to the Secretary of Defense, 3 May 1985, Appendix, pp. 24–25. The review recommended reserving the words “or may be expected” from Article 35 “[i]n light of the uncertainty surrounding the meaning of paragraph 3”, which “would eliminate the problem of collateral ecological damage from conventional weapons and methods of warfare, including herbicides and riot control agents, and would limit the obligations imposed to essentially those already established by the ENMOD Convention”. Ibid., Appendix, p. 25.

72 Ibid., Appendix, p. 57; see also ibid., Appendix, p. 25.

73 Ronald Reagan, “Message to the Senate Transmitting a Protocol to the 1949 Geneva Conventions”, 29 January 1987, available at: www.reaganlibrary.gov/archives/speech/message-senate-transmitting-protocol-1949-geneva-conventions.

74 His presentation remains the touchstone for the United States’ views on AP I.

75 M. J. Matheson, above note 43, p. 424; see also US Land Handbook, above note 20, para. 2-143 (“The United States has not accepted these provisions and repeatedly expressed the view that they are overly broad and ambiguous and do not constitute customary international law”).

76 ICRC Customary Law Study, above note 7, commentary accompanying Rule 45, p. 151. On persistent objectors, see the below section entitled “Persistent Objector Status”.

77 J. B. Bellinger III and W. J. Haynes Jr, above note 19, p. 455.

78 ICJ, Continental Shelf (Libyan Arab Jamahiriya/Malta), Judgment, ICJ Reports 1985, para. 27. See also Statute of the International Court of Justice, 59 Stat. 1055, 26 June 1945, Art. 38(1)(2); ICJ, Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States of America), Merits, Judgment, ICJ Reports 1986, para. 183.

79 ILC, Draft Conclusions on Identification of Customary International Law, with Commentaries, 2018 (ILC Draft Conclusions), commentary accompanying Conclusion 2, para. 2. It should be noted that in many cases a singular act may constitute evidence of both; for instance, an official statement concerning a rule or purported rule would likely constitute both verbal practice and an expression of opinio juris. Ibid., commentary accompanying Conclusion 3, para. 8; J. B. Bellinger III and W. J. Haynes Jr, above note 19, p. 446; Henckaerts, Jean-Marie, “Study on Customary International Humanitarian Law: A Contribution to the Understanding and Respect for the Rule of Law in Armed Conflict”, International Review of the Red Cross, Vol. 87, No. 857, 2005, p. 182CrossRefGoogle Scholar.

80 ICJ, North Sea Continental Shelf, Judgment, ICJ Reports 1969, para. 73. Note that, in addition to being “very widespread and representative”, the Court also characterized the requisite standard for State practice as being “extensive and virtually uniform”: ibid., para. 74. These two phrases arguably articulate different thresholds for State practice to qualify as “general”. See Identification of Customary International Law: Comments and Observations Received from Governments, UN Doc. A/CN.4/716, 14 February 2018 (State Comments to ILC Draft Conclusions), pp. 32, 34. In our assessment, the evidence of State practice under review does not satisfy either standard; thus, determining which is correct as a matter of law is immaterial to our analysis and, accordingly, beyond the scope of this article.

81 ILC Draft Conclusions, above note 79, Conclusion 6(1).

82 Henckaerts, Jean-Marie, “Customary International Humanitarian Law: A Response to U.S. Comments”, International Review of the Red Cross, Vol. 89, No. 866, 2007, p. 482CrossRefGoogle Scholar.

83 Permanent Court of International Justice, The Case of the S. S. “Lotus” (France v. Turkey), Judgment, 1927, p. 28; ILC Draft Conclusions, above note 79, commentary accompanying Conclusion 6, para. 3; State Comments to ILC Draft Conclusions, above note 80, p. 28.

84 ICRC Customary Law Study, above note 7, pp. xxxix–xl (“If the practice largely consists of abstention combined with silence, there will need to be some indication that the abstention is based on a legitimate expectation to that effect from the international community”).

85 See Nuclear Weapons Advisory Opinion, above note 13, para. 66 (contrasting the policy of deterrence with legal obligations).

86 Official Records of the Diplomatic Conference on the Reaffirmation and Development of International Humanitarian Law Applicable in Armed Conflicts, Geneva, 1974–1977, Vol. 15, CDDH/215/Rev.1, Federal Political Department, Bern, 1978, para. 27.

87 See e.g. State Comments to ILC Draft Principles, above note 19, pp. 71 (Israel) (“It is the position of Israel that under customary international law, the ‘natural environment’ in the abstract is not the subject of protection under the law of armed conflict, and treating it as such will be incorrect both legally and practically. As several members of the Commission have also pointed out, it is specific elements of the environment that may be the subject of protection. The protection afforded to these elements depends on the applicable rule concerned”), 79 (United States) (“[T]he natural environment is not always a “civilian object” but receives the protection afforded civilian objects insofar as it constitutes a civilian object”).

88 Ibid., p. 17.

89 ICJ, Nicaragua, above note 78, para. 186. Complete or perfect consistency, therefore, may not be required, so long as the practice is, as the ILC's commentary to its 2018 Draft Conclusions on Identification of Customary International Law suggests, “virtually or substantially uniform”. ILC Draft Conclusions, above note 79, commentary accompanying Conclusion 8, para. 7.

90 ILC Draft Conclusions, above note 79, commentary accompanying Conclusion 8, para. 4; J. B. Bellinger III and W. J. Haynes Jr, above note 19, p. 445 and fn. 4.

91 J.-M. Henckaerts, above note 82, p. 481.

92 ILC Draft Conclusions, above note 79, commentary accompanying Conclusion 3, para. 2.

93 ICRC Customary Law Study, above note 7, pp. xliv–xlv.

94 Ibid., p. xlv. Yet, the ICRC would presumably assert that, as regards the environment, it can be said that all States nonetheless have an interest in environmental protection: ibid., p. xlv (“Notwithstanding the fact that there are specially affected States in certain areas of international humanitarian law, it is also true that all States have a legal interest in requiring respect for international humanitarian law by other States, even if they are not a party to the conflict”). As further support, it would likely cite the “transnational importance” of the environment that is highlighted in the commentary to Article 35 of AP I: see ICRC Commentary on the APs, above note 65, paras 1441, 1462.

95 J. B. Bellinger III and W. J. Haynes Jr, above note 19, pp. 445–446.

96 ICJ, North Sea Continental Shelf, above note 80, paras 73–74.

97 See Dinstein, Yoram, “The ICRC Customary International Humanitarian Law Study”, International Law Studies, Vol. 82, 2006, p. 109Google Scholar (“If several ‘States whose interests are specially affected’ object to the formation of a custom, no custom can emerge”).

98 ILC Draft Conclusions, above note 79, Conclusions 2, 9.

99 ICJ, North Sea Continental Shelf, above note 80, para. 77; see also ICJ, Nicaragua, above note 78, para. 184.

100 See ICJ, Asylum Case (Colombia v. Peru), Judgment, ICJ Reports 1950, p. 286; ICJ, North Sea Continental Shelf, above note 80, para. 77; ICJ, S. S. “Lotus”, above note 83, p. 28. See also ILC Draft Conclusions, above note 79, commentary accompanying Conclusion 9, para. 3. For instance, concerning the use of nuclear weapons, a general practice of refraining from the use of such weapons, even over the course of several decades, would not indicate that the practice is accepted as law if done so simply “because the circumstances that might justify their use have fortunately not arisen”. Nuclear Weapons Advisory Opinion, above note 13, para. 66.

101 See e.g. J. B. Bellinger III and W. J. Haynes Jr, above note 19, pp. 455–456; State Comments to ILC Draft Principles, above note 19, pp. 68 (Canada), 70 (France), 71 (Israel), 77 (United States); M. J. Matheson, above note 43, p. 424.

102 ICRC Customary Law Study, above note 7, p. 148.

103 For example, the study cites as support the US Commander's Handbook on the Law of Naval Operations, which provides that “[a] commander has an affirmative obligation to avoid unnecessary damage to the environment to the extent that it is practicable to do so consistent with mission accomplishment. To that end, and as far as military requirements permit, methods or means of warfare should be employed with due regard to the protection and preservation of the natural environment.” US Naval Handbook, above note 59, sec. 8.4. That the ICRC could construe such language broadly is self-evident, but that passage, and similar provisions in other US manuals, must be interpreted within the context of and in deference to clear expressions of US opinio juris which unequivocally state that parts of the environment are only protected insofar as they constitute civilian objects. Moreover, that the exhortation reflects policy or military expediency is indicated by usage of the generally hortatory term “should”, rather than the binding terms “must” or “shall”.

104 Mark Simonoff, “Remarks at a UN General Assembly Sixth Committee Session on Agenda Item 81: Report of the International Law Commission on the Work of its 63rd and 65th Sessions, 4 November 2013”, in Office of the Legal Advisor, US Department of State, Digest of United States Practice in International Law, 2013, p. 234; J. B. Bellinger III and W. J. Haynes Jr, above note 19, p. 455; see also Stephen Townley, “Remarks at the 69th General Assembly Sixth Committee on the Work of the International Law Commission During its 66th Session, 5 November 2014”, in Office of the Legal Advisor, US Department of State, Digest of United States Practice in International Law, 2014, p. 299.

105 State Comments to ILC Draft Principles, above note 19, pp. 28–29. In another example, the Civilian Harm Mitigation and Response Action Plan recently promulgated by the US DoD states that “[h]ard-earned tactical and operational successes may ultimately end in strategic failure if care is not taken to protect the civilian environment as much as the situation allows – including the civilian population and the personnel, organizations, resources, infrastructure, essential services, and systems on which civilian life depends”. DoD, Civilian Harm Mitigation and Response Action Plan (CHMR-AP), 25 August 2022, p. 1, available at: https://media.defense.gov/2022/Aug/25/2003064740/-1/-1/1/CIVILIAN-HARM-MITIGATION-AND-RESPONSE-ACTION-PLAN.PDF. There is little doubt that the “civilian environment” referred to includes certain parts of the natural environment, but that policy does not alter the United States’ long-standing position with respect to the protections afforded to the environment as a matter of law. As it makes clear, “[n]othing in [the] plan is intended to suggest that existing DoD policies or practices are legally deficient or that the actions to be implemented pursuant to this plan are legally required, including under the law of war. The U.S. military routinely implements heightened policy standards and processes that are more protective of civilians than, and supplementary to, law of war requirements, without such standards and processes modifying or creating new legal requirements.” Ibid., p. 3 fn. 1.

106 ICJ, North Sea Continental Shelf, above note 80, paras 77–78.

107 Nuclear Weapons Advisory Opinion, above note 13, para. 31; ILC Draft Conclusions, above note 79, commentary accompanying Conclusion 9, para. 4.

108 ILC Draft Conclusions, above note 79, Conclusion 11; State Comments to ILC Draft Conclusions, above note 80, p. 45 (concurring in the Conclusion's text).

109 State Comments to ILC Draft Principles, above note 19, pp. 68 (Canada), 70 (France), 71 (Israel), 77 (United States).

110 While we see no reason to doubt the US position that the relevant rules do not qualify as customary law, our analysis that follows assumes they do solely for the purpose of illustration.

111 ILC Draft Conclusions, above note 79, commentary accompanying Conclusion 15, para. 1 (emphasis in original); see Y. Dinstein, above note 96, p. 109.

112 See ILC Draft Conclusions, above note 79, Conclusion 15(3) and accompanying commentary, para. 10. A peremptory norm is “a norm accepted and recognized by the international community of States as a whole as a norm from which no derogation is permitted and which can be modified only by a subsequent norm of general international law having the same character”. Vienna Convention on the Law of Treaties, 1155 UNTS 331, 23 May 1969 (entered into force 27 January 1980), Art. 53.

113 ICRC Customary Law Study, above note 7, p. xlv.

114 ICRC Customary Law Study, above note 7, commentary accompanying Rule 45, p. 151.

115 See e.g. State Comments to ILC Draft Principles, above note 19; J. B. Bellinger III and W. J. Haynes Jr, above note 19, p. 455 (noting that only “parts of the natural environment cannot be made the object of attack unless they constitute military objectives, as traditionally defined”); M. Simonoff, above note 66, p. 2 (“We also recommend that principle II-3 be eliminated or revised – perhaps with the addition of a caveat such as ‘where appropriate – in that environmental considerations will not in all cases be relevant in applying ‘the principle of proportionality and the rules on military necessity’ in the context of jus in bello’”).

116 M. Simonoff, above note 66, p. 18.

117 See AMW Manual Commentary, above note 68, commentary accompanying Section M, para. 5.

118 See ibid., commentary accompanying Rule 88, para. 1.