Related Rule
Australia
Practice Relating to Rule 43. Application of General Principles on the Conduct of Hostilities to the Natural Environment
Australia’s Defence Force Manual (1994) states:
The natural environment is not a legitimate object of attack. Destruction of the environment, not justified by military necessity, is punishable as a violation of international law … The general prohibition on destroying civilian objects, unless justified by military necessity, also protects the environment. 
Australia, Manual on Law of Armed Conflict, Australian Defence Force Publication, Operations Series, ADFP 37 – Interim Edition, 1994, § 545(a) and (c).
Australia’s LOAC Manual (2006) states:
The natural environment is not a legitimate object of attack. Destruction of the environment, not justified by military necessity, is punishable as a violation of international law … The general prohibition on destroying civilian objects, unless justified by military necessity, also protects the environment … In the event of breaches to the rules protecting the environment, commanders are required to stop the violations, take action to prevent further breaches and report violations to higher authority so further action can be taken. 
Australia, The Manual of the Law of Armed Conflict, Australian Defence Doctrine Publication 06.4, Australian Defence Headquarters, 11 May 2006, § 5.50.
The LOAC Manual (2006) replaces both the Defence Force Manual (1994) and the Commanders’ Guide (1994).
Australia’s ICC (Consequential Amendments) Act (2002) incorporates in the Criminal Code the war crimes defined in the 1998 ICC Statute, including launching an attack in the knowledge that such attack will cause “widespread, long-term and severe damage to the natural environment … of such an extent as to be excessive in relation to the concrete and direct military advantage anticipated” in international armed conflicts. 
Australia, ICC (Consequential Amendments) Act, 2002, Schedule 1, § 268.38(2).
In 1991, during a debate in the UN General Assembly on the environmental impact of the Gulf War, Australia insisted that “what had been done in Kuwait was clearly illegal under the customary rules of warfare and the traditional concepts of proportionality and military necessity”. 
Australia, Statement before the Sixth Committee of the UN General Assembly, UN Doc. A/C.6/46/SR.20, 22 October 1991, § 7.
In a briefing note in 1992, the Australian Department of Foreign Affairs and Trade stated that the Gulf War had underlined “the continuing need for the extension of principles of humanitarian law in cases of armed conflict”, and referred to “the environmental devastation caused by the deliberate creation of oil slicks by Iraqi forces”. 
Australia, Department of Foreign Affairs and Trade, DFAT-92/013031 Pt 8, 13 February 1991, p. 2, § 5.
In its oral pleadings before the ICJ in the Nuclear Weapons case in 1995, Australia stated: “In recent times the issue of the protection of the environment in armed conflict has been a particular international concern.” It referred to a number of international treaties, including the relevant provisions of the 1976 ENMOD Convention, the 1977 Additional Protocol I and the 1993 Chemical Weapons Convention. It stated that these instruments provided “cumulative evidence that weapons having … potentially disastrous effects on the environment, and on civilians and civilian targets, are no longer compatible with the dictates of public conscience” reflected in the general principles of humanity. Australia added that “consideration of lethal effects of radiation over time provides a link between the principle which provides for the protection of civilian populations and the principle which provides for protection of the environment”. 
Australia, Oral pleadings before the ICJ, Nuclear Weapons case, 30 October 1995, Verbatim Record CR 95/22, p. 47, § 31.