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The NPT and the TPNW: Compatible or conflicting nuclear weapons treaties?

The NPT and the TPNW: Compatible or conflicting nuclear weapons treaties?
Signing ceremony for Treaty on Prohibition of Nuclear Weapons. The Treaty, which was adopted on 7 July 2017 by 122 States, opened for signature on 20 September, on the sidelines of the annual general debate of the General Assembly. Photo: Flickr/UN Photo/Kim Haughton.
Dr Tytti Erästö

The 2017 Treaty on the Prohibition of Nuclear Weapons (TPNW) was negotiated with the purpose of strengthening the largely unimplemented disarmament pillar of the 1968 Treaty on the Non-Proliferation of Nuclear Weapons (NPT). Yet, one of the main criticisms against the Treaty has been its alleged incompatibility with the NPT.

What is one to make of these conflicting claims? And should the increasing number of TPNW ratifications be seen as good or bad news for the international nuclear order?


References to the NPT in the TPNW

The drafters of the TPNW took great care to avoid any conflict with the NPT. This intention is reflected in their repeated statements highlighting the mutually reinforcing nature of the two treaties, as well as in the TPNW text.  

The NPT is explicitly mentioned in the TPNW preamble, which reaffirms that ‘the full and effective implementation of the [NPT], which serves as the cornerstone of the nuclear disarmament and non-proliferation regime, has a vital role to play in promoting international peace and security’. Another, more implicit reference to the NPT is in Article 18, which states that ‘The implementation of this Treaty shall not prejudice obligations undertaken by States Parties with regard to existing international agreements, to which they are party, where those obligations are consistent with the Treaty.'

Some argue that the latter part of the above formulation ‘subordinates the NPT to the ban treaty’. However, this concern is based on the premise that there is an inconsistency between the obligations of the two treaties. But is there such inconsistency?


Legal compatibility of the treaties

Article 1 of the TPNW prohibits the development, deployment, possession, use and the threat of use of nuclear weapons. Its key prohibitions also include the stationing of nuclear weapons on states parties’ territory, as well as the assistance, encouragement or inducement of any activity prohibited by the treaty. These obligations apply equally to all states parties, but they do not bind countries that are outside the treaty. Although none of the nine nuclear-armed states are likely to join the TPNW in the immediate future, the underlying assumption is that they will ultimately be affected by the strong stigmatization of nuclear weapons in the Treaty.

In comparison, in NPT Article II non-nuclear weapon states commit themselves not to acquire nuclear weapons, whereas the five nuclear-armed states parties agree to pursue disarmament in Article VI. More specifically, the latter article requires ‘Each of the Parties to the Treaty…  to pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament, and on a treaty on general and complete disarmament under strict and effective international control.’

Further stressing the long-term goal of nuclear disarmament, the NPT preamble points to the need ‘to facilitate the cessation of the manufacture of nuclear weapons, the liquidation of all their existing stockpiles, and the elimination from national arsenals of nuclear weapons and the means of their delivery pursuant to a Treaty on general and complete disarmament under strict and effective international control.’

In other words, while the TPNW seeks to make nuclear weapons illegal for all countries, the NPT provided a monopoly on such weapons to the five countries that had proliferated before 1968. This exception and its subsequent acceptance by the nearly universal NPT membership reflected concerns about an uncontrolled spread of nuclear weapons, which were particularly high in the 1960s. At the same time—although it does not mention any specific time limits—the NPT clearly points to the need for the eventual disarmament by the five countries.

While not identical, the core obligations of the two treaties thus seem to be perfectly consistent with one another. For this reason, the recent flurry of legal analyses on the TPNW rarely problematizes the Treaty’s relationship with the NPT, but instead tends to focus on potential inconsistencies with existing security arrangements.

Indeed, the TPNW can be seen as putting the NPT Article VI into practice. (Whether the TPNW actually amounts to the kind ‘effective measure’ envisioned in Article VI or whether it will eventually become the normative framework regulating the complete abolition of nuclear weapons are speculative questions that are best answered with the benefit of hindsight at a later point in time.)


Impact on non-proliferation

While there is no apparent legal incompatibility between the two treaties, critics have argued that the TPNW might jeopardize the NPT’s non-proliferation objectives. One such argument was raised during the TPNW negotiations, when the drafters of the emerging treaty were warned about ‘forum-shopping’—that is, the possibility that non-nuclear weapon states joining the TPNW might choose to opt out from the NPT and thus free themselves from the verification requirements in the NPT.

Although this concern is addressed by TPNW Article 3—which requires states parties to maintain their existing IAEA safeguards ‘without prejudice to any additional relevant instruments’—concerns about forum-shopping continue to be made by critics. As noted by a recent report by the Norwegian Academy of International Law, however, TPNW ratification ‘by no means alters the requirements for withdrawal from the NPT’, nor does it ‘offer states a legal pretext to exit from the NPT’.

While it is possible that some countries do decide to withdraw from the NPT, the TPNW is unlikely to be the sole reason. Rather, the issue should be seen in the context of the broader legitimacy crisis within the NPT, which is caused mainly by the lack of implementation of Article VI, and which also contributed to the negotiation to the TPNW. States might also leave the NPT based on ‘extraordinary events’ (referring to Article X of the NPT) that they perceive as having jeopardized their ‘supreme interests’ and thus calling for the development of a nuclear deterrence capability of their own.

A related criticism is that the TPNW missed the opportunity to incorporate the highest existing standard for nonproliferation verification by not obligating non-nuclear weapon states to accept the Model Additional Protocol to the IAEA Comprehensive Safeguards (INFCIRC/540). Instead, the Treaty sets the IAEA Comprehensive Safeguards Agreement (INFCIRC/153 (Corrected)) as the minimum non-proliferation verification requirement. According to critics, this ‘outdated system... has been known for a quarter century to be inadequate to the challenge of rooting out clandestine nuclear activity’.

The specific mention of INFCIRC/153 (Corrected) in the TPNW can nevertheless be seen as an improvement from the NPT Article III, which does not specify any particular safeguards standard. Moreover, as noted above, the TPNW does not allow states parties to downgrade their existing verification arrangements, and hence it does not undermine the existing Model Additional Protocol agreements which are already in force in 134 countries, should they decide to join the Treaty.

Quite a different concern is that—to the extent that it succeeds in delegitimizing nuclear deterrence—the TPNW could undermine umbrella states’ trust in extended deterrence and thus drive them to acquire nuclear weapons of their own. This argument assumes that the USA—currently the sole provider of extended nuclear deterrence and one the staunchest opponents of the TPNW—would be disproportionately influenced by the TPNW’s normative standards, whereas its allies would continue to subscribe to the logic of deterrence. While there are long-standing credibility issues related to nuclear security guarantees, it is somewhat difficult to imagine that the TPNW would be the decisive factor pushing umbrella states to acquire nuclear weapons.

The concern about deterrence nevertheless captures one of the most fundamental points of divergence underlying the debate over the TPNW—that is, whether the perceived benefits of nuclear deterrence on national security and strategic stability justify risking the catastrophic consequences of nuclear weapons use. While the TPNW is very clear in rejecting this logic, pointing to the ‘effects on human survival, the environment, socioeconomic development, the global economy, food security and the health of current and future generations’, the NPT neither prohibits nor embraces deterrence. (However, critics have long argued that NATO’s nuclear sharing arrangements are inconsistent with Article I of the NPT, in which states parties commit themselves ‘not to transfer to any recipient whatsoever nuclear weapons or other nuclear explosive devices or control over such weapons or explosive devices directly, or indirectly.’)



It would be difficult to make the case of legal incompatibility between the TPNW and the NPT, as the former so clearly builds on NPT Article VI on disarmament. Instead, the perceived incompatibility between the two treaties mainly has to do with the indirect negative consequences that the TPNW could potentially have on the NPT’s non-proliferation objectives. While it is indeed possible that some non-nuclear weapon states could withdraw from the NPT and umbrella states might lose faith in extended deterrence, the TPNW is unlikely to be the sole or even primary trigger for such developments.

Essentially, the dispute over the TPNW is based on political disagreement regarding how to advance nuclear disarmament. While the NPT reflected the need to prioritise non-proliferation over the long-term goal of disarmament, the TPNW represents the view that—half a century after the adoption of the NPT—progress on disarmament is long overdue.

At the same time, the TPNW seeks to promote disarmament by delegitimising the continued possession of nuclear weapons by all countries, including the five nuclear-armed members of the NPT. This puts the Treaty at odds with the existing nuclear order. However, it does not make the TPNW incompatible with the NPT; in addition to codifying the existing nuclear monopoly of a few countries in 1970, the NPT also foresaw the need for change, and therefore cannot be used indefinitely to defend the status quo.


Dr Tytti Erästö is a Researcher in the SIPRI Nuclear Disarmament, Arms Control and Non-proliferation Programme.