International law of war and armed conflict and general rules of environmental protection
The starting point is that the natural environment is a civilian object under international humanitarian law. Unless otherwise provided, inhabitants and belligerents are "under the protection and the rule of the principles of the law
of nations, as they result from the usages established among
civilised peoples, from the laws of humanity and the dictates of
public conscience": 'Martens Clause' (Preamble, 1907 Hague Convention IV Respecting the Laws and Customs of War on Land). Art. 22 limits the right of belligerents to adopt means of injuring the enemy.
Arts. 35(3) (prohibition of methods) and 55 (due care) of 1977 Additional Protocol I to the Geneva Conventions (wide but not universal ratification) provide additional protection for the environment. "Taken together, these provisions embody a general obligation to protect the natural environment against widespread, long-term and severe environmental damage; the prohibition of methods and means of warfare which are intended, or may be expected, to cause such damage; and the prohibition of attacks against the natural environment by way of reprisals": para 31, ICJ Advisory Opinion on Nuclear Weapons 1996; see also ICJ applications Yugoslavia v UK 1999, DR Congo v Rwanda 2002.
"Uganda, by acts of looting, plundering and
exploitation of Congolese natural resources committed by members of
the Ugandan armed forces in the territory of the Democratic Republic of the Congo and by its failure to comply with its obligations as an occupying Power in Ituri district to prevent acts of looting, plundering and
exploitation of Congolese natural resources, violated obligations owed to
the Democratic Republic of the Congo under international law": ICJ judgment DR Congo v Uganda (Armed Activities on the Territory of the Congo) 2005.
"Works or installations containing dangerous forces, namely dams, dykes and nuclear electrical generating stations, shall not be made the object of attack, even where these objects are military objectives, if such attack may cause the release of dangerous forces and consequent severe losses among the civilian population.": art. 15 of the 1977 Additional Protocol II (non-international armed conflicts, less widely ratified than AP I); similarly art. 56(1) of the 1977 Additional Protocol I for international armed conflicts.
"Intentionally launching an attack in the knowledge that such attack will cause incidental loss of life or injury to civilians or damage to civilian objects or widespread, long-term and severe damage to the natural environment which would be clearly excessive in relation to the concrete and direct overall military advantage anticipated" is a war crime, being a "serious violations of the laws and customs applicable in international armed conflict, within the established framework of international law": art. 8(2)(b)(iv) Rome Statute of the International Criminal Court.
To summarize: "The general principles on the conduct of hostilities apply to the natural environment: A. No part of the natural environment may be attacked, unless it is a military objective. B. Destruction of any part of the natural environment is prohibited, unless required by imperative military necessity. C. Launching an attack against a military objective which may be expected to cause incidental damage to the environment which would be excessive in relation to the concrete and direct military advantage anticipated is prohibited": ICRC Customary IHL Rule 43 (Application of General Principles on the Conduct of Hostilities to the Natural Environment). Some states insist such rules (incl. Additional Protocol I) only apply to conventional weapons and do not apply to nuclear weapons. See also Rules 44 (due regard) and 45 (serious damage).
ILC Draft Principles on protection of the environment in relation to armed conflicts: Special Rapporteur Marie G. Jacobsson considered from 2013 to 2015 obligations before, during, and after an armed conflict and proposed 5 draft jus in bello principles (proportionality, distinction, precaution, no reprisal, protected zones) among others.
Special Rapporteur Marja Lehto continued in 2018 with some 21 draft principles covering all 3 phases plus occupation. As of mid-2019, some 28 principles (incl. re non-state actors) have been provisionally adopted by the Drafting Committee with the following parts: Introduction – Principles of general application – Principles applicable during armed conflict – Principles applicable in situations of occupation – Principles applicable after armed conflict.