Related Rule
United States of America
Practice Relating to Rule 45. Causing Serious Damage to the Natural Environment
The US Air Force Commander’s Handbook (1980) states:
Weapons that may be expected to cause widespread, long-term, and severe damage to the natural environment are prohibited. This is a new principle, established by [the 1977 Additional Protocol I]. Its exact scope is not yet clear, though the United States does not regard it as applying to nuclear weapons. It is not believed that any presently employed conventional weapon would violate this rule. 
United States, Air Force Pamphlet 110-34, Commander’s Handbook on the Law of Armed Conflict, Judge Advocate General, US Department of the Air Force, 25 July 1980, § 6-2(c).
The US Operational Law Handbook (1993) states: “The following measures are expressly prohibited by the law of war and are not excusable on the basis of military necessity: … (i) using weapons which cause … prolonged damage to the natural environment”. 
United States, Operational Law Handbook, JA 422, Center for Law and Military Operations and International Law Division, The Judge Advocate General’s School, United States Army, Charlottesville, Virginia 22903-1781, 1993, p. Q-182, § (i).
In 1987, the Deputy Legal Adviser of the US Department of State stated:
We, however, consider that another principle in article 35, which also appears later in the Protocol, namely that the prohibition of methods or means of warfare intended or expected to cause widespread, long-term and severe damage to the environment, is too broad and ambiguous and is not a part of customary law.
The United States, however, considers the rule on the protection of the environment contained in article 55 of Protocol I as too broad and too ambiguous for effective use in military operations … Means and methods of warfare that have such a severe effect on the natural environment so as to endanger the civilian population may be inconsistent with the other general principles, such as the rule of proportionality. 
United States, Remarks of Michael J. Matheson, Deputy Legal Adviser, US Department of State, The Sixth Annual American Red Cross-Washington College of Law Conference on International Humanitarian Law: A Workshop on Customary International Law and the 1977 Protocols Additional to the 1949 Geneva Conventions, American University Journal of International Law and Policy, Vol. 2, 1987, pp. 424 and 436.
In 1991, in response to an ICRC memorandum on the applicability of IHL in the Gulf region, the US Department of the Army stated: “U.S. practice does not involve methods of warfare that would constitute widespread, long-term and severe damage to the environment.” 
United States, Letter from the Department of the Army to the legal adviser of the US Army forces deployed in the Gulf region, 11 January 1991, § 8(P), Report on US Practice, 1997, Chapter 4.4.
In 1991, in a report submitted to the UN Security Council on operations in the Gulf War, the United States stated:
In a development with potential devastating consequences for the environment of the Gulf, we would like to report that a vast oil slick occurred in the northern Gulf this week. Iraqi occupation forces created this slick by opening the Sea Island terminal pipelines and an oiling buoy on approximately 19 January, allowing oil to flow directly into the northern Gulf. We have evidence that Iraqi forces simultaneously emptied five oil tankers moored at piers at the Mina al-Ahmadi oil field. As of 28 January the resulting oil slick was at least 35 miles long and 10 miles wide. This is the largest oil slick in history.
On 26 January after full consultation with oil and environmental experts and the Governments of Kuwait and Saudi Arabia, United States aircraft destroyed two manifold areas used for pumping oil along pipelines. We believe this action has halted the discharge of oil into the Gulf. At the request of the Government of Saudi Arabia, the United States dispatched expert personnel and specific equipment to help contain the slick and minimize its environmental impact. Several other countries have also sent teams to provide assistance. 
United States, Letter dated 30 January 1991 to the President of the UN Security Council, UN Doc. S/22173, 30 January 1991, pp. 2–3.
In 1991, in a report submitted to the UN Security Council on operations in the Gulf War, the United States stated: “Iraqi authorities have deliberately caused serious damage to the natural environment of the region.” 
United States, Letter dated 13 February 1991 to the President of the UN Security Council, UN Doc. S/22216, 13 February 1991, p. 2.
In 1992, in its final report to Congress on the conduct of hostilities in the Gulf War, the US Department of Defence declared, with particular reference to the applicability of Articles 35 and 55 of the 1977 Additional Protocol I:
Even had Protocol I been in force, there were questions as to whether the Iraqi actions would have violated its environmental provisions. During that treaty’s negotiation, there was general agreement that one of its criteria for determining whether a violation had taken place (“long term”) was measured in decades. It is not clear the damage Iraq caused, while severe in a layman’s sense of the term, would meet the technical-legal use of that term in Protocol I. The prohibitions on damage to the environment contained in Protocol I were not intended to prohibit battlefield damage caused by conventional operations and, in all likelihood, would not apply to Iraq’s actions in the Persian Gulf War. 
United States, Department of Defence, Final Report to Congress on the Conduct of the Persian Gulf War, 10 April 1992, Appendix O, The Role of the Law of War, ILM, Vol. 31, pp. 636–637.
In 1992, in a memorandum annexed to a letter to the Chairman of the Sixth Committee of the UN General Assembly, Jordan and the United States noted that for those States party to the 1977 Additional Protocol I, the following principles of international law provide additional protection for the environment in times of armed conflict: “a) Article 55 of [the 1977 Additional Protocol I] requires States parties to take care in warfare to protect the natural environment against widespread, long-term and severe damage.” 
United States, International Law Providing Protection to the Environment in Times of Armed Conflict, annexed to Letter dated 28 September 1992 to the Chairman of the Sixth Committee of the UN General Assembly, UN Doc. A/C.6/47/3, 28 September 1992, § 2(a).
In 1994, in a memorandum on a depleted uranium tank round, the US Department of the Army stated that Articles 35(3) and 55 of the 1977 Additional Protocol I “do not codify customary international law, but nonetheless are obligations the United States has respected in its conduct of military operations since promulgation of the 1977 Additional Protocol I”. 
United States, Department of the Army, Memorandum on M829A2 Cartridge, 120mm, APFSDS-T, 27 December 1994, p. 5.
Upon ratification of the 1980 Convention on Certain Conventional Weapons, the United States stated:
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 Convention for the Protection of War Victims of August 12, 1949, applies only to States which have accepted those provisions. 
United States, Statements of understanding made upon ratification of the Convention on Certain Conventional Weapons, 24 March 1995.
In its written statement submitted to the ICJ in the Nuclear Weapons case in 1995, the United States stated, with respect to the prohibition on the use of “methods or means of warfare which are intended, or may be expected, to cause widespread, long-term and severe damage to the natural environment” as embodied in Articles 35(3) and 55 of the 1977 Additional Protocol I: “This is one of the new rules established by [the 1977 Additional Protocol I] that … do not apply to nuclear weapons.” 
United States, Written statement submitted to the ICJ, Nuclear Weapons case, 20 June 1995, pp. 29–30, § 8; see also Written statement submitted to the ICJ, Nuclear Weapons (WHO) case, 10 June 1994, pp. 30–31, § 8.
In November 2006, the US Departments of State and Defense released the details of a joint letter forwarded by those departments to the ICRC President regarding US Initial Reactions to the ICRC Study on Customary International Humanitarian Law. This letter stated, in part:
Protection of the environment during armed conflict obviously is desirable as a matter of policy, for reasons that include issues of civilian health, economic welfare, and ecology. The following discussion should not be interpreted as opposing general consideration, when appropriate and as a matter of policy, of the possible environmental implications of an attack. Additionally, it is clear under the principle of discrimination that parts of the natural environment cannot be made the object of attack unless they constitute military objectives, as traditionally defined, and that parts of the natural environment may not be destroyed unless required by military necessity.
Nevertheless, the Study fails to demonstrate that rule 45, as stated, constitutes customary international law in international or non-international armed conflicts, either with regard to conventional weapons or nuclear weapons. First, the Study fails to assess accurately the practice of specially affected States, which clearly have expressed their view that any obligations akin to those contained in rule 45 flow from treaty commitments, not from customary international law … Second, the Study misconstrues or overstates some of the State practice it cites. Third, the Study examines only limited operational practice in this area and draws flawed conclusions from it.
Summary. States have many reasons to condemn environmental destruction, and many reasons to take environmental considerations into account when determining which military objectives to pursue. For the reasons stated, however, the Study has offered insufficient support for the conclusion that rule 45 is a rule of customary international law with regard to conventional or nuclear weapons, in either international or non-international armed conflict. 
United States, Joint letter to the ICRC President, Dr Jakob Kellenberger, from US Department of State Legal Adviser, John B. Bellinger, and US Department of Defense General Counsel, William J. Haynes, on US Initial Reactions to the ICRC Study on Customary International Humanitarian Law, 3 November 2006.
In 2008, the US Senate approved the ratification of the 1954 Hague Convention for the Protection of Cultural Property, subject to certain understandings and a declaration:
Section 1. Senate Advice and Consent Subject to Understandings and a Declaration.
The Senate advises and consents to the ratification of the Hague Convention for the Protection of Cultural Property in the Event of Armed Conflict, concluded on May 14, 1954 (Treaty Doc. 106–1(A)), subject to the understandings of section 2 and the declaration of section 3.
Section 2. Understandings.
The advice and consent of the Senate under section 1 is subject to the following understandings, which shall be included in the instrument of ratification:
(3) It is the understanding of the United States of America that the rules established by the Convention apply only to conventional weapons, and are without prejudice to the rules of international law governing other types of weapons, including nuclear weapons.
Section 3. Declaration.
The advice and consent of the Senate under section 1 is subject to the following declaration:
With the exception of the provisions that obligate the United States to impose sanctions on persons who commit or order to be committed a breach of the Convention, this Convention is self-executing. This Convention does not confer private rights enforceable in United States courts. 
United States, Advice and Consent to Ratification of the 1954 Hague Convention for the Protection of Cultural Property, 2008, Sections 1–3.
In 1992, in a statement at the Second ENMOD Review Conference, the United States expressed the view that:
The [1976 ENMOD] Convention is not an Environmental Protection Treaty; it is not a treaty to prohibit damage to the environment resulting from armed conflict. Rather, the [1976 ENMOD] Convention fills a special, but important niche reflecting the international community’s consensus that the environment itself should not be used as an instrument of war. 
United States, Statement of 15 September 1992 at the Second ENMOD Review Conference, Geneva, 14–21 September 1992.
In 1992, in a memorandum annexed to a letter to the Chairman of the Sixth Committee of the UN General Assembly, Jordan and the United States noted that for those States party to the 1976 ENMOD Convention, the following principles of international law provide additional protection for the environment in times of armed conflict:
The 1977 Convention (ENMOD) prohibits States parties from engaging in military or any other hostile use of environmental modification techniques (i.e., any techniques for changing – through the deliberate manipulation of natural processes – the dynamics, composition or structure of earth, its biota, lithosphere, hydrosphere and atmosphere, or of outer space) having widespread, long-lasting or severe effects as the means of destruction, damage or injury to any other State party. 
United States, International Law Providing Protection to the Environment in Times of Armed Conflict, annexed to Letter dated 28 September 1992 to the Chairman of the Sixth Committee of the UN General Assembly, UN Doc. A/C.6/47/3, 28 September 1992, § 2(e).