Proportionality in attacks (under IHL)

Thus, even if a target in the conduct of hostilities is a lawful military objective under international humanitarian law (IHL), the rule of proportionality may either affect the means and methods of warfare that may lawfully be used, or even effectively prohibit an attack from being launched. Violating the rule of proportionality is an indiscriminate attack (in an international armed conflict) according to 1977 Additional Protocol I.See Arts. 51(5)(b) and 57(2)(a)(iii), 1977 Additional Protocol I. The rule is not codified in general IHL treaty provisions regulating non-international armed conflicts, either in Common Article 3 to the 1949 Geneva ConventionsThe provision, according to general agreement, does not regulate the conduct of hostilities. or 1977 Additional Protocol II, but is deemed by the International Committee of the Red Cross (ICRC) to be a customary rule of IHL applicable not only in international armed conflicts but also in non-international armed conflicts.Such a formal treaty prohibition does, though, exist with respect to the use of landmines. See Protocol on Prohibitions or Restrictions on the Use of Mines, Booby-Traps and Other Devices as amended on 3 May 1996 (Protocol II to the 1980 CCW Convention as amended on 3 May 1996). According to Rule 14 of the ICRC’s 2005 study of customary international humanitarian law:

Launching an attack which may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated, is prohibited. 

The question, of course, is what is ‘excessive’? In the ICRC's commentary on Article 51(5) of 1977 Additional Protocol I, from where the text originates, it is stated that:

Of course, the disproportion between losses and damages caused and the military advantages anticipated raises a delicate problem; in some situations there will be no room for doubt, while in other situations there may be reason for hesitation. In such situations the interests of the civilian population should prevail….Yves Sandoz, Christophe Swinarski and Bruno Zimmermann (eds.), Commentary on the Additional Protocols, ICRC, Geneva, 1987, §§1979–80.

In its 2005 study of customary IHL, the ICRC affirms that "launching an attack in the knowledge that such attack will cause incidental loss of civilian life, injury to civilians or damage to civilian objects which would be clearly excessive in relation to the concrete and direct military advantage anticipated" constitutes a war crime (our emphasis).

Last updated on: 30 November 2013