The legality of nuclear weapons under international law remains hotly contested.
In fact, the 1996 Advisory Opinion by the International Court of Justice (ICJ) on the legality of the threat or use of nuclear weapons raised as many questions as it answered, while in some respects the state of relevant international law has evolved since 1996.
Primary among the rules of international humanitarian law (IHL) is distinction in attacks, which requires parties to any conflict–international or non-international–to direct attacks only against lawful military objectives, whether persons or objects.
However, even if an attack is so directed, the rule of proportionality dictates that civilian harm (deaths, injuries, damage to civilian objects, or a combination thereof) may not be expected to be excessive when compared with the direct and concrete military advantage anticipated.
Arguably, expected environmental damage must also be assessed as part of the proportionality rule.
Broadly speaking, three scenarios have frequently been advanced for a lawful use of nuclear weapons:
The first of these scenarios is use against a nuclear-armed submarine on the high seas about to fire its missiles. While the high seas might suffer from environmental damage, a case can be made that the attack does not violate primary IHL rules.
Second, a mass gathering of armed forces in the desert far away from populated areas has been advanced as a possible lawful target for a nuclear strike.
Third, the potential use of nuclear weapons could be claimed to not violate IHL where it fulfilled the criteria for a belligerent reprisal. However, it is a huge challenge to envisage circumstances where use of nuclear weapons against civilians could hope to meet the stringent requirements of a lawful reprisal in practice.
Where use of nuclear weapons occurred by one state on the territory or against the armed forces of another (not the only possible scenario involving use, but arguably the most probable), then the requirements of jus ad bellum would also need to be satisfied. This body of law, which regulates the interstate use of force, would allow weapons, potentially including nuclear weapons, to be used in self-defense against an armed attack.
To do so, the law would judge the necessity for the use of force and whether the force that was used was proportionate to the aim of repelling the attack. Perhaps a surprise to some, the law would not impose particular restrictions on nuclear weapons as a weapon type, but merely consider their use as one element in the use of force equations. Arguably, the same formula also applies to threats (ad bellum): threatening use of force by nuclear weapons is governed by the same legal framework as threats of the use of force in general.
Only nine states possess nuclear weapons, but these states represent almost half the world’s population and more than one quarter of the earth’s land area. These nine states are currently not covered by the 1968 Nuclear Non-Proliferation Treaty (NPT)’s comprehensive prohibition on non-nuclear weapons states producing or otherwise acquiring nuclear weapons.
These states include the five permanent members of the United Nations Security Council, which are recognized nuclear weapon states under the NPT, as well as the Democratic People’s Republic of Korea, India, Israel, and Pakistan, which are not party to the NPT.
These states are not bound by multilateral treaty obligations that prohibit the acquisition and production of nuclear weapons; this does not mean that environmental law is irrelevant to these states’ activities involving nuclear weapons.
Types of nuclear weapons
A nuclear weapon is an explosive device whose destructive force results from either nuclear fission chain reactions or combined nuclear fission and fusion reactions.
Nuclear weapons whose explosive force results exclusively from fission reactions are commonly referred to as atomic bombs, while those that derive much or most of their energy in nuclear fusion reactions are termed thermonuclear weapons (or hydrogen bombs).
In fission weapons, a mass of fissile material is turned into a supercritical mass, producing explosive yields ranging from the equivalent of around one to five hundred kilotons of TNT. The detonation of any nuclear weapon is accompanied by a blast of radiation. Fission also produces radioactive debris, more commonly known as fallout. A thermonuclear weapon uses the heat generated by a fission bomb to compress and ignite a nuclear fusion stage. Thermonuclear weapons typically have a far higher explosive yield than do fission weapons, in the range of megatons rather than kilotons. Fusion reactions do not create fission products, but because all thermonuclear weapons contain at least one fission stage, thermonuclear weapons can generate at least as much nuclear fallout as fission-only weapons.
History
The world’s first detonation of a nuclear weapon, the result of the Project’s work, occurred just before 5.30am on 16 July 1945 at a site in New Mexico. The first nuclear weapon attack occurred on 6 August 1945 over the city of Hiroshima in Japan.
The second state after the US to test a nuclear bomb successfully was Russia, which in 1949 detonated an atomic bomb, made with plutonium as its nuclear material. ‘Greenhouse George’, a US test fire in Nevada in May 1951, was the first fusion nuclear weapon to be detonated.
Other nuclear weapon states are India, Israel, and Pakistan as well as the Democratic People’s Republic of Korea (DPR Korea) which conducted an underground test of a low-yield nuclear device in October 2006.
Use of Nuclear Weapons under International law
Any future use of a nuclear weapon, should one occur, is likely to be in the conduct of hostilities within an international armed conflict.5 Accordingly, any such use of a nuclear weapon would be judged under the applicable international laws, jus ad bellum (international law governing the interstate use of force) and jus in Bello (international law applicable in armed conflict).
The primary rules under jus in Bello are found in the law of armed conflict, which today is widely termed international humanitarian law (IHL).
Under IHL, while states ‘do not have unlimited freedom of choice of means in the weapons they use’, there is no requirement that each weapon be specifically ‘authorized’ for its use to be lawful; use of any given weapon will only be unlawful when, and to the extent that, it is prohibited by an applicable conventional or customary rule.
A fundamental rule of IHL stipulates that parties to a conflict must direct attacks only against lawful military objectives (whether military personnel or objects of concrete military value). The rule of distinction in attacks is a norm of customary international law, applicable in non-international armed conflicts as it is in international armed conflicts.
Accordingly, any weapon that is incapable of distinguishing between civilians/civilian objects and military targets is considered inherently indiscriminate and its use is always unlawful.
A supporting rule, that of proportionality in attacks, holds that even if an attack is effectively directed against military objectives, civilian harm (deaths, injuries, damage to civilian objects, or a combination thereof) it must not be launched if it may be expected to be excessive when compared with the direct and concrete military advantage anticipated. Arguably, environmental damage must also be assessed as part of the proportionality rule.
In his separate opinion in relation to the International Court of Justice (ICJ)’s 1996 Advisory Opinion on the Legality of the Threat or Use of Nuclear Weapons (the Nuclear Weapons Advisory Opinion), Judge Schwebel speculated on different types of uses of nuclear weapons and which of these might be lawful or not. He referred to the regularly projected scenario of use of tactical nuclear weapons against submarines that are themselves equipped with nuclear weapons as ‘discrete military or naval targets so situated that substantial civilian casualties would not ensue’.
A second oft-cited scenario concerns use of a nuclear weapon to destroy an enemy army situated in a desert.
What is unique about nuclear weapons is the radiation, which occurs at different times. ‘Prompt’ radiation comes first, soon after the explosion, consisting of neutrons, gamma rays, and electrons. Neutron radiation is an especially hazardous form of radiation to humans. In the explosion of a nuclear weapon, the fireball rises, sucking the cooler air below as well as radioactive debris up from the ground. Water drops are extracted from the cooler air to form clouds. Fallout begins one to two hours afterwards and lasts for a day or so.
In addition to a purely IHL analysis, however, international human rights law is also relevant to a determination of the legality of use of nuclear weapons. In the context of the right to life, international human rights courts primarily analyses whether sufficient effort was made to avoid or limit loss of life in cases where potentially lethal force cannot be avoided.
In parallel, and distinct from, determinations under IHL and human rights law of the legality of any future use of nuclear weapons, if use by a state were to occur on the territory or against the armed forces of another,25 the requirements of jus ad bellum would also need to be satisfied. This body of law, which regulates the interstate use of force, would allow for weapons, potentially including nuclear weapons, to be used in self-defense against an armed attack. To do so, the law would judge the necessity for use of force and whether the force that was actually used was proportionate to the aim of repelling the attack.
With respect to the proportionality calculation, there are two requirements. First, force used in self-defense should be assessed in light of the fulfillment of defensive purposes. Second, the amount of force used in self-defense should not be obviously excessive; it does not, though, need to be strictly proportionate to the offensive force. Perhaps a surprise to some, the law would not impose particular restrictions on nuclear weapons as a weapon type, but merely consider their use as one element in the use of force equations. Arguably, the same formula also applies to threats ad bellum: threatening use of force by nuclear weapons is governed by the same legal framework as threats of the use of force in general.
- Disarmament law obligations
The centerpiece of the disarmament regime relating to nuclear weapons is the 1968 Nuclear Non-Proliferation Treaty (NPT), which entered into force in 1970, and which has since gained near universal adherence. The Treaty has been termed a ‘grand bargain’ in which the non-nuclear weapon states (NNWS) forsake the nuclear option in exchange for a legal obligation on the part of the nuclear weapon states (NWS) to refrain from transferring the weapons to any other states, and to disarm and eventually eliminate their arsenals. In addition to the non-proliferation elements in Article I31 and Article II, the Treaty guarantees all parties the ‘inalienable right’ to peaceful uses of nuclear technology in Article IV, and, in Article VI, also requires the NWS to ‘pursue negotiations in good faith’ towards the reduction and eventual elimination of nuclear arsenals.
Since the primary purpose of the Treaty was to prevent further proliferation of nuclear weapons, the NPT has played and continues to play a crucial role in limiting nuclear arsenals in the world, and to limiting the number of states with access to nuclear weapons.
2. Nuclear-weapons-free zones
Article VII of the NPT supports the establishment of nuclear-weapons-free zones (NWFZs) as a regional component of the non-proliferation regime. According to the UN General Assembly, an NWFZ has two essential components: the total absence of nuclear weapons within the zone and the presence of an international verification and control machinery.
Beyond these broader disarmament obligations, arguably a ban on atmospheric testing of nuclear weapons has now crystallized into customary international law.
The same cannot, though, be said so easily with respect to underground testing. But the Rarotonga, Bangkok, Pelindaba and Semipalatinsk Treaties (discussed further below) obligate states parties not to conduct nuclear tests and require them to prevent such tests in their territories. They do so regardless of test yield, and whether tests are conducted in the atmosphere or underground.43 Moreover, already under the 1959 Antarctic Treaty any activity involving nuclear weapons, such as their testing, stockpiling, deployment, or launching in or from Antarctica is prohibited;44 similar prohibitions apply by treaty to nuclear weapons in outer space45 and on the sea bed.
