Frequently Asked Questions (FAQs)
Overview of the CTBT and CTBTO
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is an international agreement that prohibits all nuclear test explosions by everyone, everywhere: above ground, under water and underground. Adopted by the United Nations General Assembly in 1996, it enjoys near-universal support.
The working language of the CTBTO is English, meaning that daily operations are conducted in English. The official languages are Arabic, Chinese, English, French, Russian, and Spanish, as in the United Nations. This means that formal proceedings are conducted in all these languages, and the Treaty and other key documents are or will be available in all official UN languages.
The CTBTO Preparatory Commission, based in Vienna, Austria, is an interim Organization focused on creating a global system to monitor compliance with the CTBT. Once the Treaty enters into force (officially becomes legally binding on an international level), the Commission will be succeeded by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO).
The CTBTO is an independent international organization with its own membership and budget. Since 2000, it has had a Relationship Agreement with the United Nations. This agreement formalises their cooperation, establishing a framework for the two organizations to work closely together and consult on issues of mutual interest and concern.
Funding and Membership
The CTBTO is primarily funded through contributions from states that have signed the CTBT, known as Member States or States Signatories. These contributions are based on the United Nations scale of assessment, which considers each country's economic capabilities. This approach ensures that more economically developed states contribute a larger share. The CTBTO can also receive voluntary contributions from states or international organizations, which may include cash, equipment, or other resources, such as bequests and grants.
In signing and ratifying the CTBT, a state joins a group of like-minded countries that are dedicated to strengthening the international nuclear non-proliferation and disarmament regime, thereby contributing to international peace and security. Member States benefit in several key ways:
Access to Data and Technology: Member States can access both raw and processed data collected by the CTBT's global verification system. This data, including detailed analyses, helps them assess whether any suspicious activities might violate the CTBT.
Civil and Scientific Applications: Beyond monitoring compliance, CTBT data has valuable applications, which can help mitigate the effects of natural or man-made disasters, increase the wealth of knowledge about our planet and contribute to human welfare in a wide variety of ways.
National Data Centres (NDCs): The CTBTO helps states set up and maintain National Data Centres (NDCs), which are essential for managing and using CTBT data. Support includes providing the required hardware and software through an initiative called NDCs4All.
Training and Capacity Building: The CTBTO offers training programmes to help countries implement the Treaty effectively at the national level. These activities equip participants with the skills needed to operate within the CTBT framework.
A non-Signatory State can become an accredited observer state if it is listed in the CTBT as a host for an International Monitoring System (IMS) facility. As an observer state, it can participate in meetings, workshops, and the activities of the two Working Groups: Working Group A, which focuses on budgetary, legal, and administrative matters, and Working Group B, which addresses verification issues related to the Provisional Technical Secretariat (PTS).
Impact of the Treaty
Nuclear testing is crucial in developing and advancing nuclear weapons. By banning these tests, the CTBT helps prevent the spread of nuclear weapons, whether by states seeking to develop them, upgrading existing arsenals, or creating more advanced weapons. Additionally, the CTBT protects against the severe health and environmental risks posed by nuclear tests.
States may conduct nuclear tests for several reasons. Testing provides crucial data on the performance and reliability of nuclear weapons, including their explosive yield, electromagnetic pulse effects, and environmental impact. Additionally, successful tests can showcase a state's nuclear capabilities to the international community. This can enhance a state's strategic position and influence global perceptions of its military power.
The international community made efforts to limit nuclear testing before the CTBT. One significant attempt was the 1963 Partial Test Ban Treaty (PTBT), which banned nuclear explosions in the atmosphere, outer space, and under water. However, it did not cover underground nuclear tests. The CTBT expanded on the PTBT’s efforts by fully banning all nuclear test explosions, regardless of where they occur.
Approximately 75 percent of these tests (1,517 in total) were conducted underground. The remaining 25 percent (530 tests) were carried out in the atmosphere, with a few conducted under water, sometimes near inhabited areas.
The CTBT relies on the support of all states, whether they have nuclear weapons or not. The Treaty does not mandate any country to reduce its nuclear arsenal; instead, it asks that all states commit to halting nuclear test explosions. When every state, regardless of its nuclear status, agrees to refrain from such tests, it builds trust and encourages others to do the same. This collective commitment reinforces the Treaty and enhances global peace and security.
The CTBTO’s efforts make a significant contribution to several Sustainable Development Goals (SDGs). While the Organization’s primary focus is on banning nuclear testing, which supports SDG 16 (Peace, Justice, and Strong Institutions), its work also advances other SDGs through its one-of-a-kind monitoring network.
For example, the International Monitoring System (IMS) uses hydroacoustic, infrasound, and seismic technologies to track environmental changes, supporting SDG 13 (Climate Action). This data has even led to the discovery of a new species of Pygmy Blue Whale, enhancing our understanding of marine life and aligning with SDG 14 (Life Below Water).
Additionally, the IMS plays a crucial role in reducing the impact of natural disasters, as outlined in SDG 11. It can detect volcanic eruptions, earthquakes and other seismic events that may trigger tsunamis. This information is transmitted in near real-time to National Tsunami Warning Centres (NTWCs), enabling timely and accurate public alerts, which helps save lives and reduce risks.
In the four decades following the first atomic test in 1945, over 2,000 nuclear tests were conducted at 60 sites around the world. In response to the global impact of these tests, the CTBT was opened for signature on 24 September 1996. The Treaty represents a significant step towards creating a safer and more secure world by working to ban all nuclear test explosions. Since then, there have been fewer than a dozen nuclear test explosions. This reduction is largely due to a continued adherence to a voluntary moratorium on nuclear testing by the international community in the absence of a binding Treaty, as well as the CTBT’s role within the broader framework of non-proliferation and disarmament efforts.
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) and the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) are closely linked in their objectives to enhance global security and advance nuclear non-proliferation and disarmament.
The CTBT, which bans all nuclear test explosions, is explicitly supported by the NPT, whose preamble envisions a ban on ‘test explosions of nuclear weapons for all time.’ Since the CTBT opened for signature, it has been a fundamental part of every consensus outcome at the NPT Review Conferences, reflecting the global agreement that halting nuclear tests is crucial for preventing the spread of nuclear weapons and ultimately achieving complete disarmament.
While the NPT aims to prevent the spread of nuclear weapons and promote cooperation for peaceful uses of nuclear energy, the CTBT complements these goals by prohibiting all nuclear explosions. Together, these treaties strengthen the global framework for non-proliferation and disarmament, contributing to a safer and more secure world.
Technical Aspects and Monitoring
A nuclear explosion is an uncontrolled detonation of a nuclear device, whether used for military or civilian purposes. In contrast, nuclear test explosions are controlled detonations carried out to assess a weapon's performance or to advance nuclear weapons technology. These tests can take place in various environments, including above ground, underground, or under water.
Since the CTBT opened for signature in 1996, the CTBTO Preparatory Commission has been developing a verification system to ensure compliance with the Treaty. Central to this is the International Monitoring System (IMS), which uses seismic, radionuclide, hydroacoustic, and infrasound technologies to continuously monitor the planet for signs of nuclear test explosions.
The International Monitoring System (IMS) will consist of 337 facilities, including stations and laboratories, when complete. This unique global network uses seismic, infrasound, hydroacoustic, and radionuclide technologies to monitor the planet daily for any sign of nuclear test explosions. The IMS detects seismic activity, low-frequency sound waves, underwater acoustic signals, and radioactive particles that could indicate a nuclear test. The collected data is then transmitted to the CTBTO’s International Data Centre (IDC) in Vienna, Austria, where it is screened, processed, and analysed. First, specialised computer programmes review the data, and then experts determine whether the detected events are natural or man-made and, crucially, if they are of nuclear origin.
The data collected by the CTBT’s International Monitoring System (IMS) has valuable uses beyond detecting nuclear test explosions. This vast amount of data can be applied to a variety of civil and scientific purposes, from helping to save lives in a tsunami or tracking potentially harmful fallout from a nuclear accident or contributing to climate change research. The IMS data also enhances our understanding of the Earth and its natural processes.
The locations of International Monitoring System (IMS) facilities were determined through collaboration between the CTBTO, the international community, and scientific experts, and were outlined in Annex 1 to the protocol of the Treaty. The decision process considered a range of scientific, technical, diplomatic, and political factors. The primary goal was to place IMS facilities in strategic locations to ensure that a nuclear explosion anywhere on Earth would be detected. Negotiations also addressed logistical factors, data transmission, environmental concerns, and the need to protect sensitive information.
An On-Site Inspection (OSI) is the ultimate verification measure under the CTBT and can only be conducted once the Treaty is in force and if requested by a State Party. At that point, a team of 40 inspectors, including experts in visual observation, seismology, geophysics, and radionuclide detection, will be deployed to the field. Their role is to gather information for presentation to the Executive Council, which will then determine what took place. Currently, preparations are underway, including establishing and testing procedures and conducting exercises, to ensure readiness for when the Treaty enters into force.
Treaty Status and Compliance
Signing the CTBT shows a state’s intention to support the Treaty’s goals but does not create legal obligations. It indicates a commitment to avoid actions that would undermine the CTBT. Ratification, on the other hand, involves formally incorporating the Treaty into the state’s domestic law through its constitutional procedures. This step makes the Treaty legally binding, requiring the state to enforce its provisions and prevent any activities that would violate its terms. In summary, signing demonstrates intent, while ratification ensures legal commitment and enforcement within the state’s jurisdiction.
Not signing the CTBT does not indicate a state’s intention to conduct nuclear weapons testing. There are several reasons why a state might choose not to sign/ratify the Treaty, including political considerations or strategic interests. Many that have not signed/ratified the CTBT have nonetheless declared voluntary moratoriums on nuclear testing and are committed to nuclear non-proliferation and disarmament through other treaties and agreements.
Two of the five nuclear-weapon States have ratified the CTBT. France and the United Kingdom were the first to do so, ratifying the Treaty on 6 April 1998. The Russian Federation ratified it on 30 June 2000, but later revoked its ratification on 8 November 2023. China and the United States signed the CTBT on 24 September 1996 but have not yet ratified it.
For the CTBT to "enter into force" means it becomes legally binding under international law. This will occur only after 44 specific countries, known as Annex 2 states - those with nuclear technology (both energy and research) at the time the Treaty opened for signature - have signed and ratified it. Currently, ratification by nine of these Annex 2 states is still needed: China, Egypt, India, Iran, Israel, North Korea, Pakistan, the Russian Federation, and the United States. Among these, India, North Korea, and Pakistan have not yet signed the Treaty, which is why it has not yet become international law.
Once the CTBT enters into force, the CTBTO will rely on its robust verification regime to ensure compliance with the Treaty. This system includes four key components:
International Monitoring System (IMS): This global network of facilities will detect any nuclear test explosion anywhere on the planet at any time. It uses advanced technologies to provide real-time data to States Parties.
Consultation and Clarification: This mechanism facilitates communication among States Parties to address any concerns or potential violations swiftly and transparently.
On-Site Inspection (OSI): States Parties have the right to request inspections at locations suspected of nuclear test activities. These inspections help verify compliance and address any potential breaches.
Confidence-Building Measures: These mechanisms encourage States Parties to proactively declare activities that could be misinterpreted as violations, such as large-scale chemical explosions, to avoid misunderstandings.
The CTBTO currently provides near-real-time data to its Member States, including detailed information on the location, magnitude, time, and depth of the suspected test. This data is crucial for Member States to assess the situation and respond accordingly. However, since the Treaty has not yet entered into force, the CTBTO does not have the formal authority to directly confirm whether a nuclear test has occurred.
Once the Treaty enters into force, the CTBTO will gain formal powers as outlined in the Treaty. Under Article V, this includes the authority to investigate suspicious events and, through its Executive Council, refer matters to the UN Security Council if a nuclear test is suspected. Additionally, the Organization can provide States Parties with recommendations on collective measures.
Engagement and Opportunities
To explore job opportunities at the CTBTO, visit the careers portal where you can view current vacancies and find detailed application instructions. While many roles at the CTBTO require technical or scientific expertise, we also have numerous positions in non-technical areas. These include administration, conference management, external relations, finance, human resources, information technology, legal affairs, public information, and procurement. Therefore, a technical background is not always necessary to contribute to our work.
There are several ways to engage with the CTBTO and contribute to our mission. Our virtual Data Exploitation Centre (vDEC) offers scientists and researchers worldwide access to our data for research and publication. Scientists have the opportunity to meet and exchange knowledge and information at a range of fora, including the CTBT: Science and Technology Conferences, workshops, and technical meetings to exchange knowledge and collaborate with peers.
For those interested in youth and early-career opportunities, we offer initiatives such as the CTBTO Youth Group (CYG), the CTBTO Research Fellowship Programme, and the CTBTO Mentoring Programme, which supports early-career women from underrepresented countries in STEM fields.
You can also stay updated on our events and activities by visiting our events page.