In a Japanese public opinion poll conducted in the summer of 2021, 71 percent of respondents favored Japan joining the Treaty on the Prohibition of Nuclear Weapons (TPNW) while only 27 percent opposed it. But when the members of the Japanese Diet (parliament) were asked the same question, the numbers were starkly different: only 28 per cent supported joining the TPNW. This revealed a great gap between the public sentiment of the treaty and the view of political leaders.

Although Prime Minister Fumio Kishida was elected from a constituency that includes the City of Hiroshima and has pledged to work towards a world without nuclear weapons, he considers the TPNW to be an end goal. His ruling party, the Liberal Democratic Party, argues that Japan cannot join the TPNW while relying on the extended nuclear deterrence of the United States. Therefore, Japan will not sign the TPNW, nor send an observer to the first Meeting of the States Parties in Vienna starting on 21 June, despite support from the public and the ruling coalition partner Komeito. This view has hardened in light of the bloody, unprovoked invasion of Ukraine by Russia.

If and when a Japanese government decides to join the TPNW, it will need to make sure that Japan can do so while maintaining the US-Japan Security Treaty. In particular, Japan must clarify that Article 1, paragraph E of the TPNW– “Each State Party undertakes never under any circumstances to: “Assist, encourage or induce, in any way, anyone to engage in any activity prohibited to a State Party under this Treaty” – does not prohibit Japan from accepting the presence of US forces or its reconnaissance and communication facilities in Japan.

Japan, under its Three Non-Nuclear Principles, does not allow stationing of nuclear warheads on its soil. But if any part of the US forces stationed in Japan, its radar and other reconnaissance systems, or its communication facilities are somehow used to support the operation of the US nuclear forces, then it may be interpreted to be “assisting” the activity prohibited under the Treaty.

If it opts to join the TPNW, Japan will also have to tackle the issue of relying on US extended nuclear deterrence. Article 1, paragraph D says, “Each State Party undertakes never under any circumstances to: “Use or threaten to use nuclear weapons or other nuclear explosive devices.”

Nuclear deterrence is based on the assumption to use or threaten to use nuclear weapons. While Japan, which itself does not possess any nuclear weapons, cannot use or threaten to use nuclear weapons, does Japan violate the TPNW if it relies on a non-party’s use or threat of the use of nuclear weapons? A conservative interpretation of the treaty provisions may support this conclusion.

If Japan renounced US extended nuclear deterrence, it would easily clear the requirement of Article 1, paragraph D. However, such a renouncement would complicate the US-Japan alliance relationship. The United States would be required to defend Japan without nuclear deterrence and may have to adjust its defense assurances accordingly.

The Philippines has a mutual defense treaty with the United States, and has signed the TPNW, but it does not have explicit assurances from the US about extended nuclear deterrence. New Zealand, an ANZUS Treaty ally, has ratified the TPNW but its alliance relationship with the United States has been on a shaky ground since it denied the port of call of US naval vessels unless their non-nuclear nature was confirmed. That alliance is now virtually suspended.

Yet, as some TPNW adherents are eager to seek the support of countries allied with nuclear weapon states such as the United States, they may be amenable to more liberal interpretation of the provisions to allow Japan to join. The issue may be circumvented if Japan stops actively seeking US extended nuclear deterrence commitments to address it security concerns.  By ceasing, Japan may no longer be taken to be “encouraging or inducing” the United States to use or threaten to use its nuclear weapons.

The United States for its part may continue to cover Japan with its extended nuclear deterrence without being asked by Japan. Such passive benefit of extended nuclear deterrence may be taken outside the definition of “encouragement or inducement.”

In the current political climate where former Prime Minister Shinzo Abe is calling for the consideration of something akin to the NATO nuclear sharing arrangement after the Russian invasion of Ukraine, it may not be easy for Japan to stop seeking extended nuclear deterrence assurances. So, while Japan may not be able to join the TPNW, there are nonetheless several steps it can take to help the Treaty’s cause.

First, Japan can help raise awareness about the horrific consequences of any use of nuclear weapons by highlighting the consequences of the atomic bombing of Hiroshima and Nagasaki, inviting political, military or civic leaders to Hiroshima and Nagasaki, and letting the voices of hibakusha (bomb survivors) be heard. Several hibakusha will attend the Vienna meeting for this purpose.

Second, Japan can join the effort to implement Article 6 of the TPNW on victim assistance and environmental remediation. Japan has experience of treating Hiroshima and Nagasaki victims and of environmental remediation works after the Fukushima nuclear accident. Japan has been engaged, in the assistance of Kazakh victims of Semipalatinsk nuclear tests. A group of NGO leaders led by Akira Kawasaki of ICAN have presented recommendations to the Japanese government in this regard.

Third, for these purposes, it would also be useful for Japan to send observers to the meeting of States Parties and engage in an exchange of views with States Parties on these topics.

Fourth, the Japanese observers may also exchange views with the meeting participants on away to bridge the gap between the TPNW supporters and the Treaty’s skeptics. This is a subject that Prime Minister Fumio Kishida has been pursuing since his time as Foreign Minister.

Even if signing the TPNW and renouncing US nuclear deterrence assurances seems unlikely in the foreseeable future, Japan can still support key elements of the TPNW and close the gap between the Japanese public support of the treaty and political action.

About the Author

Abe Nobuyasu was the Commissioner of the Japan Atomic Energy Commission. He is a former United Nations Under-Secretary-General for Disarmament Affairs (2003-06) and former Director-General for Arms Control and Science Affairs (1997-99) of the Japanese Ministry of Foreign Affairs. He most recently served as Director of the Center for the Promotion of Disarmament and Non-Proliferation at the Japan Institute of International Affairs.

Disclaimer: The views expressed in this commentary are those of the author and do not necessarily reflect the official position of the Asia-Pacific Leadership Network or any of its members.

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