5. NATO and the TPNW: Legal Issues
For a NATO member, joining the TPNW would pose considerable political problems for its membership of the Alliance, as it would challenge the political obligations of the latter. Such an act would likely be seen as tantamount, in Matthew Harries’ view, to a denuclearization of extended deterrence, entailing reliance only on a conventional umbrella rather than a nuclear one.94 Relying on a conventional umbrella may not unite the Allies as does the nuclear umbrella, as nuclear weapons have provided a powerful symbolic value to the Alliance – more so than their actual use. In other words, for the foreseeable future, practical regional political difficulties with the TPNW are likely to trump perceived legal ones.
Even so, legal complications of the TPNW for military alliances, as well as its shortcomings as perceived by its opponents, have been the subject of much discussion and examination95 – including by government inquiries such as those of Sweden, Norway, France and Switzerland.96 Some of those inquiries have drawn rebuttals, several quite detailed, such as by the Norwegian Academy of International Law. Comments on criticisms of the TPNW will be discussed in four specific respects: the TPNW’s relationship with the NPT; safeguards for non-proliferation verification; verification of nuclear disarmament; and military assistance and cooperation.97
The TPNW’s relationship with the NPT
As no NATO members have signed or ratified the TPNW, its prohibitions and obligations do not in a legal sense apply to them. But there has been particular questioning about the language of Article 18 of the TPNW, and its description of the relationship between the prohibition treaty and other agreements.98 The suggestion that Article 18 might enable parties to the TPNW to choose to forgo their obligations under other treaties, including the NPT, does not stand up to close scrutiny. It overlooks existing tenets of international law, including Article 30 of the Vienna Convention on the Law of Treaties, governing successive agreements dealing with the same subject matter, and pacta sunt servanda – i.e. every treaty in force is binding on the parties to it. It also overlooks the fact that, as a practical matter, the obligations undertaken by states parties to the TPNW are similar to – and reinforce – the obligations set out in the NPT itself. Criticism directed, for example, at the new treaty’s failure to permit reservations, and at its inclusion of a withdrawal clause, fail to appreciate that these provisions essentially follow the approach adopted by the NPT.99
In addition, in its 1996 advisory opinion, the ICJ has established that: ‘A weapon that is already unlawful per se, whether by treaty or custom, does not become lawful by reason of its being used for a legitimate purpose under the Charter.’100 While the advisory opinion does not classify nuclear weapons as unlawful per se, one current concern nuclear weapon states may have is the possibility of a prohibition on nuclear weapons becoming customary in international law. Other than conventional treaty law, international legal norms are also composed of customary international law, a body of rules that find their source from the ‘evidence of a general practice accepted as law’,101 and that must be respected by all subjects of international law. The US, the UK and France issued a joint statement immediately following the adoption of the TPNW, rejecting ‘any claim that this treaty reflects or in any way contributes to the development of customary international law’.102 This move, along with their persistent rejection of the TPNW, can have two implications:
- Preventing the actual development of a customary international law prohibiting nuclear weapons;103 and
- Treating them as ‘persistent objectors’, which may render a customary prohibition on nuclear weapons inapplicable to these nuclear weapon states.104
Safeguards for non-proliferation verification
Efforts in the TPNW negotiations to promote stronger safeguards (i.e. the IAEA’s Additional Protocol105) unfortunately fell short, just as they have for many years in the NPT. Indeed, it will be a challenge for the NPT Review Conference to achieve something that its predecessors have so far failed to do – to strengthen the NPT by requiring parties to go beyond the Article III baseline obligation of negotiating and concluding comprehensive safeguards agreements with the IAEA. The TPNW does, however, specifically adopt the NPT’s current safeguards,106 and exceeds the NPT by requiring – as a legal obligation under Article 3.1 of the prohibition treaty – that those of its parties with an IAEA Additional Protocol retain that protocol in place as their minimum baseline.107
Verification of nuclear disarmament
In the TPNW, verification of disarmament efforts is confined, for the time being, to a limited outline. In their paper for the Norwegian Academy of International Law, Gro Nystuen et al. note that negotiating detailed verification provisions without the participation of the nuclear weapon states was ‘deemed impractical’:108 the architects of the prohibition treaty consciously deferred the essential aspect of how the elimination of nuclear weapon programmes should be verified, organized and resourced. Those details were left to development at the point at which Article 4 of the TPNW would be invoked on the accession to the prohibition treaty of a nuclear weapon-possessing state, or one that has declared that it has disarmed prior to acceding. TPNW parties are required under paragraph 6 of Article 4 to designate a competent international authority or authorities to ‘negotiate and verify the irreversible elimination of nuclear weapon programmes, including the elimination or irreversible conversion of all nuclear weapons-related facilities’.109
As mentioned earlier, the Netherlands – the sole NATO member present throughout the negotiation of the treaty – based its vote against the adoption of the TPNW on the grounds that the new treaty was ‘not verifiable’.110 It is too early to predict the shape of the necessary verification mechanisms under a prohibition regime that has still to convene its first formal meeting of states parties (MSP)111 to determine how best to implement the Treaty. But in the meantime, the development of robust mechanisms for the verification of nuclear disarmament in TPNW MSPs, as in NPT review cycles, remains to be tested.
Military assistance and cooperation
Becoming party to the TPNW would not curtail military cooperation among non-nuclear weapon NATO members, their nuclear weapon partners, or NATO’s PfP partners, except in one specific respect. Article 1.1 (g) prohibits any stationing, installation or deployment of any nuclear weapons or other nuclear explosive devices in each state party’s territory or at any place under its jurisdiction or control. This reflects the situation that arises for the five NATO members that currently host US nuclear weapons. But these are matters of national choice, not NATO obligation. For instance, by analogy to other arms control prohibitions, a number of NATO members that possessed weapon systems prohibited by the Anti-Personnel Mine Ban Convention (APMBC) and the Convention on Cluster Munitions (CCM) were able to become party to those conventions once they met the required conditions of the conventions – i.e. destruction of the prohibited weapons within stipulated timelines. They were able to do without compromising their status in NATO vis-à-vis NATO non-parties to those agreements. For instance, the CCM allows (in Article 21) for military cooperation and operations to continue with non-party allies despite the risk that CCM parties may, due to their role in such operations, be associated with the use, stockpiling and transfer of cluster munitions. However, there is no equivalent in the TPNW to Article 21 of the CCM.112 Parties to the TPNW could participate in joint military operations with a nuclear weapon state without contravening the treaty, provided there is no nexus between a particular task and an activity prohibited by the TPNW such as the stationing one just mentioned.113
Observing TPNW meetings, however, could be a positive step. Article 8.5 of the TPNW provides that: ‘States not party to this Treaty, as well as the relevant entities of the United Nations system, other relevant international organizations or institutions, regional organizations, the International Committee of the Red Cross, the International Federation of Red Cross and Red Crescent Societies and relevant non-governmental organizations, shall be invited to attend the meetings of States Parties and the review conferences as observers.’ Switzerland, for one, is aware of this opportunity.114 Participation in treaty meetings by non-parties as observers is not uncommon in international law. For example, Israel observed the NPT Review Conference in 2015: seeking observer status in such circumstances does not create any commitment in terms of signature or ratification by a non-party. But availing itself of the opportunity to monitor directly meetings of states parties implies a state’s serious interest in those proceedings.