Illegality of nuclear weapons under international law, and its relevance for the divestment debate

Daniel Rietiker

This is a presentation delivered at the conference “Move the Nuclear Weapons Money”, Basel 12 April 2019.

Dear colleagues, ladies and gentlemen,

I thank Alyn Ware and Andi Niedecker very much for inviting me to this very promissing and important event.

I was proposed the title “Illegality of nuclear weapons under international law”. At first glance, I was surprised and asked myself how this topic might fit into the rest of the conference, dealing with divestment related to nuclear weapons. I did not ask the organisers what they had exactly in mind but I came to the conclusion that this topic does probably make sense, insofar as the legal dimension of the problem of nuclear weapons can add another important layer to the debate.

In other words, apart from moral, ethical, phisophical and other aspects, the legal argument can be an additional, powerful tool in the campaining efforts of civil society in the fight against nuclear weapons and, in particular with a view to divesting from those weapons. Indeed, there might be an added value in arguing that the use of nuclear weapon in inhabited area does not only kill thousands of innocent people, including children and women, but that such an odious act in the same time constitutes a breach of the Geneva Conventions and Protocols, violations of human rights and environmental law, as well as possible war crimes and crimes against humanity.

But unfortunately, it is not that easy to prove that nuclear weapons are absolutely illegal under international law. You might be convinced by this and me too, but this case is not easy to make. Certain behaviors and acts are prohibited by specific treaties, such as testing, transfert or acquisition of nuclear weapons, but quite surprisingly and contrary to other categories of weapons, such as anti-personnel mines or cluster munitions, which are today prohibited by the Ottawa and Oslo conventions, this same goal has not been reached yet in the field of nuclear weapons, the most inhumane weapon of all.

However, by the adoption of the Treaty on the Prohibition of Nuclear Weapons (TPNW) in New York in July 2017, the international community came a big step closer to a world free of nuclear weapons. This convention has been adopted by 122 votes in favor (with 1 abstention and 1 vote against), and so far 70 States have signed and 22 have ratified it. It needs 50 ratifications to enter into force.

It is maybe not a perfect instrument but it nevertheless constitutes a paradigm shift insofar as, once entered into force, it will prohibit the entire category of nuclear weapons, by banning very different behaviours and acts, such as developing, testing, producing, manufacturing, acquiring, possessing, stockpiling, transferring, or using or threatening to use such weapons. One of the distinctive features of the treaty is that it places the human being at the centre of attention. It reflects a human- and victim-centred approach to nuclear weapons, which is new in this field, expressed for instance by a clause on assistance to victims of use and testing of nuclear weapons. For those reasons, it is extremely important that civil society works together in order to push States to ratify this instrument swiftly.

What is important to understand is the fact that, once many States have ratified a certain treaty and comply with its provisions, a conventional prohibition can be doubled by customary prohibitions. This is extremely relevant because customary international law deriving from a treaty binds also States that have not ratified this instrument. This is sometimes called the “norm-building capacity” of international treaties. The conditions for this is a sufficiently high number of ratifications and a coherent and uniform application of the treaty.

But unfortunately, we are not there yet. The TPNW has not yet entered into force and is therefore not yet binding on States. As a result, it is difficult to argue that there is a general norm prohibiting nuclear weapons under international law.

In other words, we have to be more modest, identifying what we already have and use it. We have to identify the behaviors that are already illegal under international law. The most obvious argument in a campaign for divestment would be to prove that financing of nuclear weapons is contrary to international law. But it is doubtful whether this is the case today. A proposal by civil society to include such a prohibition into the TPNW was finally rejected. But it can be argued that “financing” is covered implicitly by the prohibition on “assisting, encouraging and inducing” in the sense of subparagraph e) of article 1 TPNW.

A second useful tool in the fight for divestment would be to argue that “developing, producing or manufacturing” nuclear weapons is illegal. Such prohibitions will be imposed on States Parties to the TPNW (article 1 a) TPNW). The same already applies for States not possessing nuclear weapons (NNWS) by virtue of article 2 NPT, but is harder to argue for States possessing nuclear weapons (NWS). From my point of view, such a case could be made for the NWS, indirectly, based on the duty of the NWS to negotiate in good faith in view of nuclear disarmament (article 6 NPT), since it cannot be claimed, in good faith, that manufacturing or modernizing nuclear weapons is compatible with that disarmament obligation.

Third, probably the most convincing argument against investment in nuclear weapons is, for the time being, to prove the illegality of their potential use. For people with normal common sense, investing in something that you won’t be able to use from a legal point of view is not logical. In other words, who would today buy a Diesel car in Europe, knowing that in a couple of years their use might be forbidden… Therefore, for NGOs fighting against investments in nuclear weapons, it would be important and relevant to explain that actual use of nuclear weapons is contrary to international law.

Again, this is not as simple as that. Contrary, inter alia, to certain gases, which had already been banned by a Geneva Protocol of 1925, the actual use of nuclear weapons has not yet been prohibited on the universal level by a treaty.

Moreover, in 1996, the International Court of Justice adopted a rather ambiguous and highly controversial advisory opinion on the Legality of the threat or use of nuclear weapons, in which it came to the unanimous conclusion that

the threat or use of nuclear weapons would “generally” be contrary to the rules of international law applicable in armed conflict, and in particular to those of humanitarian law.

But the court, in one of the most discussed and critiziced paragraph, went on to say that …

however, in view of the current state of international law, and of the elements of fact at its disposal, the Court cannot conclude definitively whether the threat or use of nuclear weapons would be lawful or unlawful in an extreme circumstance of self-defence, in which the very survival of a State would be at stake.

This statement is not very helpful, since it leaves a door open for those who plead in favor of the legality of threat or use of nuclear weapons. But to those, I would reply that, since 1996, not only 23 years have elapsed, but also a couple of significant developments have happened and new arguments and evidence in favor of the illegality of the use of nuclear weapons, in particular under IHL and human rights law, have been presented. To name just a few:

1) It may sound pathetic, but President Obama’s famous Prague speech on 5 April 2009, using surprisingly humanitarian language, coincides with the starting point for those developments. It followed an initiative of Henry Kissinger, William Perry, George Schultz and Sam Nunn, published in the Wall Street Journal, 4 January 2007.

2) Only one year after the Prague speech, at the 2010 NPT Review Conference, an instrument that does not as such prohibit the use of these weapons, States Parties expressed, for the first time ever, their reservations against a possible use of nuclear weapons.

3) The position of the ICRC, the most prominent organization assisting the victims of armed conflicts, has also become tougher on nuclear weapons. In November 2011, the Movement adopted a resolution entitled “Working towards the elimination of nuclear weapons”, which illustrates the new humanitarian trend particularly well:

The Council of Delegates,
emphasizes the incalculable human suffering that can be expected to result from any use of nuclear weapons, the lack of any adequate humanitarian response capacity and the absolute imperative to prevent such use,

finds it difficult to envisage how any use of nuclear weapons could be compatible with the rules of international humanitarian law, in particular the rules of distinction, precaution and proportionality (…)

4) This new spirit in favour of the elimination of nuclear weapons for the sake of the potential victims also triggered what is often referred to as the “humanitarian initiative”, including three conferences on the “humanitarian impact” of nuclear weapons (Oslo, Nayarit, and Vienna) and leading to the decision of the UNGA to establish, in 2013, an open-ended working group (OEWG) to develop proposals for multilateral nuclear disarmament negotiations. As a result of its work, the UNGA adopted, in October 2016, a resolution calling on Member States to launch negotiations in 2017 on a treaty banning nuclear weapons, which was finally adopted in New York on 7 July 2017.

5) This human or victim-centred approach to nuclear weapons did not only affect IHL, but also penetrated into other branches of international law, in particular human rights law. On 30 October 2018, the UN Human Rights Committee (HRC), which is in charge of the implementation of the 1966 International Covenant on Civil and Political Rights (ICCPR), has adopted its General Comment (GC) no. 36 relating to the right to life (Article 6 ICCPR). It is in many respects a remarkable document, of which para 66 reads as follows:

The threat or use of weapons of mass destruction, in particular nuclear weapons, which are indiscriminate in effect and are of a nature to cause destruction of human life on a catastrophic scale, is incompatible with respect for the right to life and may amount to a crime under international law. (…)

It is important to underline that General Comment Nr. 36 has been adopted by an international body (HRC), composed of independent members from NNWS as well as from NWS (in particular form France, UK, USA, and Israel).

The adoption of this General Comment is a proof for the awareness that nuclear weapons are indeed also – or maybe above all – a human rights issue and that their use would not be compatible with fundamental rights, such as the right to life, which cannot be derogated from, not even in times of emergency.


For the time being, the TPNW has not entered into force yet. Therefore, the illegality of nuclear weapons under international law, as such, is not as straightforward as the title of my speech might suggest. As a result, that treaty deserves our full support and civil society should engage in campaigning in favor of an early entry-into-force.

I am however firmly convinced that there is a lot of convincing evidence for the illegality, at least, of the use or threat of nuclear weapons, in particular under humanitarian and human rights law, which is already a very relevant and useful statement in the fight against investments into nuclear weapons.

I thank you very much for your kind attention.

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