Comprehensive Nuclear-Test-Ban Treaty

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is a multilateral treaty to ban nuclear weapons test explosions and any other nuclear explosions, for both civilian and military purposes, in all environments. It was adopted by the United Nations General Assembly on 10 September 1996, but has not entered into force, as it has not been ratified by all the required states. The treaty will establish the Comprehensive Nuclear-Test-Ban Treaty Organization to oversee monitoring, which is currently done by a Preparatory Commission.

Despite not being in force, the CTBT has established a global norm against nuclear testing, reinforced by nuclear testing moratoria declared by the five nuclear-weapon states recognized under the Treaty on the Non-Proliferation of Nuclear Weapons (NPT): China, France, Russia, the United Kingdom, and the United States. Since the treaty's opening for signature in 1996, only sixteen nuclear tests have been conducted, all by non-signatory states: Pokhran-II by India and Chagai-I by Pakistan in May 1998, and six tests by North Korea from 2006 to 2017. Over 2,000 nuclear tests were conducted between 1945 and 1996, primarily by the United States and the Soviet Union.

The CTBT's International Monitoring System is a global nuclear detonation detection system. It is intended to comprise 321 monitoring stations and 16 laboratories across 89 countries, of which ~90% are already operational. The stations collect one of seismic, infrasonic, hydroacoustic, and radionuclide signatures of nuclear explosions. The IMS successfully characterized all six North Korean nuclear tests, and also collects large datasets valuable to scientists for astrophysics, biology, and geology and more.

As of 2024, 187 states have signed and 178 states have ratified the treaty. The treaty designates a "Annex 2" list of states, which must all ratify the CTBT for it to enter into force. These states possessed any nuclear reactors at the time. Nine Annex 2 states have yet to ratify: the six signatories China, Egypt, Iran, Israel, Russia, and the United States, and the three non-signatories India, Pakistan, and North Korea. Israel is also widely believed to possess nuclear weapons, and the nuclear program of Iran is heavily scrutinized internationally.

The CTBT was negotiated in 1995-96 in the Conference on Disarmament with a final phase of negotiations in the UN General Assembly. It built on two major previous treaties, the 1963 Partial Nuclear Test Ban Treaty and the 1968 NPT, as well as the 1974 Threshold Test Ban Treaty between the US and Soviet Union limiting the yields of their underground tests to less than 150 kilotons of TNT.

While the United State was the first nation to sign the CTBT, the United States Senate rejected ratification in 1999. In 2023, in the context of the Russo-Ukrainian war, Russia withdrew its ratification of the CTBT. Non-ratifying states typically explain their reasoning via the non-ratification of a rival, or other regional stability issues.