What is the CTBT?

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The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is the Treaty banning all nuclear explosions on Earth. The Treaty was negotiated at the Conference on Disarmament in Geneva and adopted by the United Nations General Assembly. It opened for signature on 24 September 1996. Since then, the Treaty has reached near-universality. 184 countries have signed the Treaty – the last country to do so was Trinidad and Tobago on 8 Otober 2009. 164 countries have ratified the Treaty – most recently, Marshall Islands on 28 October 2009.

Why is the CTBT so important?

The CTBT is the last barrier on the way to develop nuclear weapons.  It prevents the development of new nuclear weapons and the improvement of existing nuclear weapon designs. When the Treaty enters into force it provides a legally binding norm against nuclear testing. The Treaty also helps prevent human suffering and environmental damages caused by nuclear testing.

How many nuclear tests were conducted and by whom?

Between 1945 and 1996 when the CTBT was adopted, over 2000 nuclear tests were conducted by the United States (1000+), the Soviet Union (700+), France (200+), the United Kingdom and China (45 each). Three countries have carried out nuclear explosions after the 1996: India and Pakistan in 1998, and the Democratic People’s Republic of Korea (DPRK) in 2006 and 2009.

Why has the Treaty not entered into force yet?

The Treaty’s entry into force depends on 44 specific States  that must have signed and ratified the Treaty.  These States had nuclear facilities at the time the Treaty was negotiated and adopted. As of August 2009, 35 of these States have ratified the Treaty. Nine States still need to do so: China, the Democratic People’s Republic of Korea, Egypt, India, Indonesia, Iran, Israel, Pakistan and the United States.  India, North Korea and Pakistan have not yet signed the Treaty. All 44 States are listed in the Treaty’s Annex 2.

What is the difference between signature and ratification?

The signature to a treaty indicates that the country accepts the treaty.  It commits not to take any actions that would undermine the treaty’s purposes. A treaty is signed by a senior representative of a country such as the president or the foreign minister.

The ratification symbolizes the official sanction of a treaty to make it legally binding for the government of a country.  This process involves the treaty’s adoption by the legislature of a country such as the parliament.  It also includes the submission of the so-called instrument of ratification to the treaty’s depository, which for the CTBT is the UN Secretary-General.  Only then is the process of ratification officially concluded. The ratification of a treaty may require the adjustment of a country’s legislation, reflecting its commitments under the treaty.


What is the CTBTO and what does it do?

The abbreviation stands for the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization.  The organization promotes the Treaty so that it can enter into force.  It also establishes a verification regime to monitor adherence to the Treaty. The organization was founded in 1996 and employs a staff of roughly 260 from the CTBT’s Members States.

What is the CTBT verification regime?

The CTBT verification regime is a unique, comprehensive system, consisting of the International Monitoring System (IMS),  International Data Centre (IDC) and on-site inspections (OSI). It constantly monitors the planet for nuclear explosions and shares its findings with Member States (= the 182 States that have signed the Treaty).

How does the CTBT verification regime work?

Monitoring stations

The 337 IMS facilities are located all over the globe and use four distinct technologies to look for signs of nuclear explosions:
Seismic: to detect shockwaves in the Earth.  The seismic network is comprised of 170 stations.  50 primary stations provide data continuously and 120 auxiliary stations provide data on demand. They register thousands of earthquakes and mine explosions every year.
Hydroacoustic: to detect acoustic signals in the oceans. Eleven stations are sufficient to monitor the big oceans as sound travels very efficiently in water. 
Infrasound: to detect low-frequency sound waves in the air with a network of 60 stations. 
Radionuclide: to detect radionuclide particles and noble gas. 80 stations provide the “smoking gun” evidence that an explosion was nuclear. Half of these stations are equipped with radionuclide noble gas detection technology.  The radionuclide network is complemented by 16 laboratories for detailed analysis.  

Data analysis

Two thirds of these facilities are already established and send data to the IDC for analysis. All raw data and the analysis reports are made available to Member States.

On-site inspections

After the Treaty’s entry into force, an OSI can be requested if monitoring data suggest that a nuclear explosion was carried out in violation of the test ban. This involves a team of 40 inspectors who search the area where data suggest that a nuclear explosion may have taken place. In September 2008, the CTBTO tested a complete OSI in a simulation exercise in Kazakhstan.

Did the CTBTO detect the nuclear explosions conducted by the DPRK?

Yes, it did. The Democratic People’s Republic of Korea detonated nuclear devices on two occasions, in October 2006 and in May 2009.  On both occasions, the CTBT verification regime was capable of detecting the explosions in a fast and reliable manner. 

Can monitoring data be used for other purposes?

CTBT monitoring data and technologies are also used for civilian purposes and scientific research. The CTBTO is providing monitoring data directly from some of its stations to Tsunami warning institutions in Asia and the Pacific since November 2006.