The controversy around nuclear weapons
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Authors: PILPG, Charline Yim, and Marryum Kahloon
As of December 2022, 92 states have signed the Treaty on the Prohibition of Nuclear Weapons (“TPNW”), in which state parties affirm that they “never under any circumstances” will “[u]se or threaten to use nuclear weapons or other nuclear explosive devices.” The treaty came into force in January 2021 when 50 states ratified it. In June 2022, the state parties to the TPNW convened their first meeting. Following that meeting, state parties to the TPNW adopted a declaration in which they confirmed that “[n]uclear weapons are now explicitly and comprehensively prohibited by international law,” and “any use or threat of use of nuclear weapons is a violation of international law, including the Charter of the United Nations.”
However, none of the states with nuclear weapons or nuclear weapons capabilities (the United States, United Kingdom, France, Russia, China, Pakistan, India, North Korea, and Israel) have ratified the TPNW. Indeed, as recently as January 2022, the United States, the United Kingdom, France, Russia, and China issued a joint declaration “affirm[ing] that nuclear weapons—for as long as they continue to exist—should serve defensive purposes, deter aggression, and prevent war.” Thus, while the TPNW is an important step to an international law principle of an absolute prohibition on the threat or use of nuclear weapons, the absence of endorsement by those states that have nuclear capabilities continues to create ambiguity as to whether this is in fact a principle under international law.
The 1996 advisory opinion issued by the International Court of Justice (“ICJ”) in response to the United Nations General Assembly’s request for an advisory opinion on the question remains the most authoritative statement on the legal status of nuclear weapons under customary international law.
In its advisory opinion, the ICJ concluded that “in neither customary nor conventional international law” was there “any specific authorization” or conversely “any comprehensive and universal prohibition” on the threat and/or use of nuclear weapons. The ICJ analyzed the question within the framework generally applicable to the use of force under international law, as codified in Articles 2(4) and 51 of the United Nations Charter. Accordingly, pursuant to Article 2(4) of the Charter, states have a baseline obligation to refrain from using force or the threat of force—including nuclear weapons—against other states. However, this prohibition is conditioned on the right to act in individual or collective self-defense under Article 51 of the Charter if an armed attack occurs. Thus, a state may use force or threaten the use of force as an act of self-defense in response to an armed attack.
The right to act in self-defense, however, is not limitless and is restricted by certain principles including necessity, proportionality, distinction, and minimization of suffering. The principles of necessity and proportionality provide that “self-defence would warrant only measures which are proportional to the armed attack and necessary to respond to it.” While the ICJ did not say that the use of nuclear weapons would never be a proportional act of self-defense (despite submissions to this effect by some states), it “note[d] that the very nature of all nuclear weapons and the profound risks associated therewith are further considerations to be borne in mind by states believing they can exercise a nuclear response in self-defence in accordance with the requirements of proportionality.”
The ICJ also confirmed that rules of international humanitarian law, including distinction and minimization of suffering, apply to the threat and/or use of nuclear weapons. The principle of distinction requires that “States must never make civilians the object of attack and must consequently never use weapons that are incapable of distinguishing between civilian and military targets.” In the case of nuclear weapons, some states argued that “nuclear weapons would in all circumstances be unable to draw any distinction between the civilian population and combatants, or between civilian objects and military objectives.” In addition, the principle of minimizing suffering prohibits states from “caus[ing] unnecessary suffering to combatants” and “us[ing] weapons causing them such harm or uselessly aggravating their suffering.” Any use of nuclear weapons arguably would result in an “enormous” number of casualties “on account of the blast, heat and radiation.”
However, in response, some states objected to the argument that, because they are subject to the law of armed conflict, recourse to the use of nuclear weapons is prohibited. The United Kingdom, in fact, argued that nuclear weapons could be utilized in a manner compatible with the rules of international humanitarian law:
“The reality . . . is that nuclear weapons might be used in a wide variety of circumstances with very different results in terms of likely civilian casualties. In some cases, such as the use of a low yield nuclear weapon against warships on the High Seas or troops in sparsely populated areas, it is possible to envisage a nuclear attack which caused comparatively few civilian casualties. It is by no means the case that every use of nuclear weapons against a military objective would inevitably cause very great collateral civilian casualties.”
The United States has similarly concluded that “there is no general prohibition in conventional or customary international law on the use of nuclear weapons, and there is no basis for speculation by the [ICJ] as to the manner in which the law of armed conflict might apply to the use of nuclear weapons in hypothetical future situations.”
Nevertheless, given the nature and effect of nuclear weapons, the ICJ determined that “the use of such weapons in fact seems scarcely reconcilable with respect for” the rules of international humanitarian law. It, however, ultimately stated that it could not “reach a definitive conclusion as to the legality or illegality of the use of nuclear weapons by a State in an extreme circumstance of self-defence, in which its very survival would be at stake.” Accordingly, the ICJ appears to have left open the possibility that nuclear weapons could lawfully be used in self-defense, but in extremely narrowly prescribed circumstances.
In sum, the question of the legal status of nuclear weapons under international law remains unclear and subject to many opposing views. The ICJ did help to clarify that nuclear weapons may only be legitimately utilized in self-defense and in extremely narrowly prescribed circumstances. Yet many unanswered questions remain. In fact, one may find it difficult to imagine the narrowly prescribed circumstances where a state could employ nuclear weapons in self-defense without violating the principles of necessity, proportionality, distinction, and minimization of suffering. Moreover, in the event a state is found to have violated international law by resorting to the use of nuclear weapons, it is unclear what remedies may be available. For example, seeking the enforcement of an ICJ judgment if the state refuses to comply pursuant to Article 94 of the UN Charter may be futile. The five permanent members of the Security Council (the United States, United Kingdom, France, Russia, China—i.e., five of the nuclear weapon states) would effectively be immune from enforcement as the permanent members have the
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