Contact: Daryl Kimball, Executive Director, (202) 463-8270 x107
The Comprehensive Test Ban Treaty (CTBT) prohibits “any nuclear weapon test explosion or any other nuclear explosion” anywhere in the world. The treaty was opened for signature in September 1996, and has been signed by 187 nations and ratified by 177. The treaty cannot formally enter into force until it is ratified by 44 specific nations, nine of which must still do so: China, India, Pakistan, North Korea, Israel, Iran, Egypt, Russia and the United States. Although Russia ratified the CTBT in 2000, it withdrew its ratification of the CTBT in 2023 to "mirror" the posture of the United States; as a treaty signatory, Russia remains obligated not to take any action contrary to the object or purpose of the treaty
In order to verify compliance with its provisions, the treaty establishes a global network of monitoring facilities and allows for on-site inspections of suspicious events. The CTBT contains a preamble, 17 treaty articles, two treaty annexes, and a protocol with two annexes detailing verification procedures.
Since the conclusion and opening for signature of the CTBT in 1996, nuclear testing has become taboo. Today, even those nuclear-armed states that have not signed or not ratified the CTBT, including India, Israel, and Pakistan, observe nuclear testing moratoriums. Only one country has conducted nuclear test explosions in this century, and even that country—North Korea—has halted nuclear testing in 2017. Although the CTBT has not formally entered into force, the treaty has, for now, achieved its primary goal: ending nuclear weapon test explosions.
The preamble, which lists disarmament principles and objectives, sets the overall political context of the treaty. In particular, it stresses the need for the continued reduction of nuclear weapons worldwide with the ultimate goal of their elimination. Also of significance, the preamble recognizes that a CTBT will constitute an effective measure of nuclear disarmament and non-proliferation by “constraining the development and qualitative improvement of nuclear weapons and ending the development of advanced new types of nuclear weapons.” It further recognizes that a test ban will constitute “a meaningful step in the realization of a systematic process to achieve nuclear disarmament.”
Article I establishes that all state parties are prohibited from conducting “any nuclear weapon test explosion or any other nuclear explosion.” On the basis of the negotiating record, this includes all nuclear explosions, in accordance with President Bill Clinton’s August 1995 “zero yield” proposal.
Article II establishes the Comprehensive Nuclear-Test Ban Treaty Organization (CTBTO), which ensures treaty implementation and provides states-parties with a forum for consultation and cooperation. The organization consists of a Conference of the States Parties, an Executive Council and a Technical Secretariat. The organization, which is located in Vienna, is structurally independent from, but operating in collaboration with, the International Atomic Energy Agency (IAEA).
The Conference of the States Parties is the overall governing body of the organization. It handles treaty-related policy issues and oversees the treaty’s implementation, including the activities of the Executive Council and the Technical Secretariat. The conference meets once a year, unless otherwise decided.
The Executive Council, which meets regularly and acts as the treaty’s principal decision-making body, consists of 51 members. In order to distribute membership evenly throughout the world, the Executive Council comprises 10 states-parties from Africa; seven from Eastern Europe; nine from Latin America and the Caribbean; seven from the Middle East and South Asia; ten from North America and Western Europe; and eight from Southeast Asia, the Pacific and the Far East. The states in each of these geographical regions are listed in Annex 1 to the treaty.
The members of the council are elected by the conference. In order to ensure that those countries with a vested interest in a comprehensive test ban are adequately represented in the council, at least one-third of the seats allotted to each region will be filled by states-parties on the basis of their nuclear capabilities applicable to the treaty, such as the number of monitoring facilities they contribute to the International Monitoring System (IMS). One seat allocated to each region will be designated on an alphabetical basis and the remaining seats will be determined by rotation or elections. Thus, each state-party will eventually have the opportunity to serve on the council.
The Technical Secretariat is the primary body responsible for implementing the treaty’s verification provisions. In this capacity, it supervises the operation of the IMS and receives, processes, analyzes and reports on the system’s data. It also manages the International Data Center (IDC) and performs procedural tasks related to conducting on-site inspections. Until the treaty enters into force, these functions are being handled by the Provisional Technical Secretariat.
Article III requires each state-party, in accordance with its constitutional process, to take any necessary measures to implement its treaty obligations.
Verification and Compliance
Article IV and the verification protocol establish the treaty’s verification regime, which consists of four basic elements: the IMS, consultation and clarification, on-site inspections, and confidence-building measures. The verification regime will not be completely operational until the treaty enters into force. For instance, on-site inspections cannot be authorized until the treaty formally comes into effect.
The purpose of the IMS is to detect nuclear explosions, which are prohibited under Article I. The monitoring system comprises a network of 50 primary and 120 auxiliary seismological monitoring stations designed to detect seismic activity and distinguish between natural events, such as earthquakes, and nuclear explosions. In addition, the system incorporates 80 radionuclide stations and 16 radionuclide laboratories that seek to identify radioactivity released during a nuclear explosion. The IMS also includes 60 infrasound (acoustic) and 11 hydroacoustic stations designed to pick up the sound of a nuclear explosion conducted in the atmosphere or underwater, respectively. The host state and the location of each facility is listed in Annex 1 to the protocol. There will be a total of 337 IMS certified facilities.
Information collected by the IMS is transmitted to the IDC—an essential part of the Technical Secretariat responsible for data storage and processing. Because the IMS generates an enormous amount of raw data, the IDC will regularly provide states-parties with a number of services designed to help them monitor compliance with the treaty’s provisions. In this regard, the data center produces integrated lists of all signals picked up by the IMS, as well as standard event lists and bulletins. In accordance with the parameters outlined in Annex 2 to the protocol, the center also generates standard event bulletins that screen out those events that appear to be of a non-nuclear nature. However, notwithstanding this analysis role, the IDC must make both the raw and processed information available to all states-parties.
The consultation and clarification component of the verification regime encourages states-parties to attempt to resolve, either among themselves or through the organization, possible instances of non-compliance before requesting an on-site inspection. A state-party must provide clarification of an ambiguous event within 48 hours of receiving such a request from another state-party or the Executive Council.
Each state-party has the right to request an on-site inspection in the territory of the party in question. The inspection request must be based on information collected by the IMS; data obtained through national technical means (NTM) of verification, such as satellites, in a manner consistent with international law; or a combination of IMS and NTM information. The request must contain the approximate geographical coordinates and the estimated depth of the ambiguous event, the proposed boundaries of the area to be inspected (not to exceed 1,000 square kilometers), the state-party or parties to be inspected, the probable environment and estimated time of event, all evidence upon which the request is based, the identity of the proposed observer (if available) and the results of the consultation and clarification process (if any).
The Executive Council would make a decision on the on-site inspection request within 96 hours of its receipt from the requesting state-party. The inspection would be authorized to proceed if it has been approved by at least 30 of the council’s 51-members, the so-called “green light” procedure. An inspection team would arrive at the point of entry within six days of the council’s receipt of the inspection request. During the course of the inspection, the inspection team may submit a proposal to extend the inspection to begin drilling, which must be approved by 26 council members. The duration of the inspection must not exceed 60 days, but may be extended by a maximum of 70 additional days (subject to council approval) if the inspection team determines that more time is needed to fulfill its mandate.
If the Executive Council rejects an on-site inspection request (or terminates an inspection already underway) because it is of a frivolous or abusive nature, the council may impose punitive measures on the requesting state-party. In this regard, it may require the requesting state-party to provide financial compensation for preparations made by the Technical Secretariat and may suspend the party’s right to request an inspection and serve on the council for an unspecified period of time.
The verification regime also incorporates confidence-building measures intended to promote treaty compliance. In order to reduce the likelihood that verification data may be misconstrued, each state-party voluntarily provides the Technical Secretariat with notification of any chemical explosion involving a magnitude of 300 tons or more of TNT-equivalent on its territory. Each state-party may also assist the Technical Secretariat in the calibration of IMS stations.
In order to ensure compliance with the treaty’s provisions, Article V empowers the conference to revoke a state-party’s rights under the treaty, recommend to the states-parties punitive measures such as sanctions or bring the case to the attention of the United Nations. Article VI describes the mechanism by which disputes pertaining to the application or interpretation of the treaty may be settled.
Under Article VII, each state-party has the right to propose amendments to the treaty after its entry into force. Any proposed amendment requires the approval of a simple majority of states-parties at an amendment conference with no party casting a negative vote.
Peaceful Nuclear Explosions
Under Article VIII, a conference will be held 10 years after the treaty’s entry into force to review the implementation of its provisions, including the preamble. At this review conference, any state-party may request that the issue of so-called “peaceful nuclear explosions” (PNEs) be put on the agenda. However, the presumption is that PNEs remain prohibited unless certain virtually insurmountable obstacles are overcome. First, the review conference must decide without objection that PNEs may be permitted, then an amendment to the treaty must also be approved without objection at a separate amendment conference, as is explained above. The amendment must also demonstrate that no military benefits would result from such explosions. This double hurdle makes it extremely unlikely that peaceful nuclear explosions would ever be permitted under the treaty.
Duration and Withdrawal
Under Article IX, the treaty has an unlimited duration. In addition, each state-party has the right to withdraw from the treaty if it decides, “extraordinary events related to the subject matter of this Treaty have jeopardized its supreme interests.” Notice of intent to withdraw must be given at least six months in advance.
Article X specifies that the treaty’s annexes, protocol, and annexes to the protocol are a formal part of the treaty. Article XI declares that the treaty is open to all states for signature prior to its entry into force. Article XII maintains that each signatory state will ratify the treaty according to its own constitutional procedures. Under Article XIII, any state that has not signed the treaty prior to its entry into force may accede to it at any time thereafter.
Entry into Force
Under Article XIV, the treaty will not enter into force until it has been signed and ratified by 44 states listed by name in Annex 2. These states include the five original nuclear weapon states—United States, Russia, Britain, France and China—as well as India, Israel, North Korea, and Pakistan. (Actual entry into force would occur 180 days after all 44 states deposit their instruments of ratification with the UN Secretary General.) The 44 states, all of which are participating members of the recently expanded Conference on Disarmament, possess nuclear power and research reactors as determined by the IAEA.
Progress toward CTBT entry into force has stalled for years due to inaction by the remaining Annex 2 hold out states, of which the United States is probably the most pivotal. After a brief and highly partisan debate, the U.S. Senate voted against ratifying the CTBT, including the six safeguards, in October 1999. Although President Barack Obama announced in 2009 his intention to seek Senate reconsideration of the treaty, he did not pursue the initative. But in 2016, the United States did see through UN Security Council Resolution 2310, which was the first UN Security Council resolution to support the CTBT.
The 2018 Trump administration Nuclear Posture Review walked back the United States support for the CTBT. It said: "Although the United States will not seek ratification of the Comprehensive Nuclear Test Ban Treaty, it will continue to support the Comprehensive Nuclear Test Ban Treaty Organization Preparatory Committee as well as the International Monitoring System [IMS] and the International Data Center [IDC]. The United States will not resume nuclear explosive testing unless necessary to ensure the safety and effectiveness of the U.S. nuclear arsenal, and calls on all states possessing nuclear weapons to declare or maintain a moratorium on nuclear testing."
In 2021 the Joe Biden administration reaffirmed U.S. support for the CTBT stating that "... the United States supports the Comprehensive Nuclear-Test-Ban Treaty (CTBT) and is committed to work to achieve its entry into force, recognizing the significant challenges that lie ahead in reaching this goal. In line with the goals of the CTBT, the United States continues to observe its zero-yield nuclear explosive testing moratorium and calls on all states possessing nuclear weapons to declare or maintain such a moratorium."
Until entry into force, conferences may be held for those states that have already deposited their instruments of ratification to “decide by consensus what measures consistent with international law may be undertaken to accelerate the ratification process.” Since 1999, the Conference Facilitating Entry Into Force of the CTBT has been convened every other year.
Article XV stipulates that the treaty’s provisions will not be subject to reservations. Article XVI establishes the UN Secretary General as the depositary of the treaty. Under Article XVII, the treaty will be authentic in six languages.