Comprehensive NuclearTestBan Treaty

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is a multilateral agreement designed to prohibit all nuclear test explosions for both military and civilian purposes. Adopted by the United Nations General Assembly on 10 September 1996, the Treaty aims to halt the qualitative development of nuclear weapons and reinforce global efforts toward disarmament. Although widely supported, the CTBT has not entered into force because several key states have yet to ratify it. Six required signatories—China, Egypt, Iran, Israel, Russia and the United States—have signed but not ratified, while India, Pakistan and North Korea have neither signed nor ratified the Treaty.
The CTBT emerged from decades of scientific concern, geopolitical rivalry and international diplomacy. Its development reflects broader attempts to control nuclear testing, reduce radioactive contamination and limit the spread of nuclear weapons.

Background to Nuclear Test Control Efforts

International interest in controlling nuclear weapons began almost immediately after the first nuclear explosions. In 1945, Canada and the United Kingdom called for global discussions on nuclear regulation. The United States advanced the Baruch Plan in 1946, proposing international oversight of atomic energy production. The Soviet Union rejected the plan, regarding it as an attempt to cement US nuclear dominance, and negotiations stalled during the early Cold War.
Between the first test at Trinity in July 1945 and the signing of the Partial Test Ban Treaty (PTBT) in August 1963, nearly 500 nuclear tests were conducted. Growing public anxiety over radioactive fallout from atmospheric and underwater tests—especially the hydrogen bomb era—drastically increased pressure for reform. The 1954 Castle Bravo test, whose fallout drifted over inhabited areas and irradiated Japanese fishermen, highlighted the severe environmental and health risks associated with nuclear testing. Atmospheric tests by the United States, Soviet Union, the United Kingdom and France together produced dangerous levels of radionuclide contamination worldwide.
Early diplomatic momentum gained support from political and civil actors. Jawaharlal Nehru’s 1954 appeal for a standstill agreement added moral weight, as did pressure from British political parties and civil society organisations. By 1955, the United States, the United Kingdom and the Soviet Union had begun formal negotiations on a comprehensive test ban. Verification issues, however, quickly became the central obstacle. Western states worried that the Soviet Union could use superior geological cover to conceal underground tests, while the Soviets opposed intrusive on-site inspections requested by Western negotiators. Detection difficulties were underscored by Operation Plumbbob (1957), the first contained US underground test.
Because of these disagreements, negotiations narrowed to a partial ban. In July 1963, the PTBT was agreed, banning nuclear detonations in the atmosphere, underwater and in outer space. The Treaty significantly reduced airborne radioactive particles but did not halt nuclear proliferation or underground testing. Underground explosions still risked venting radioactive gases, and between 1964 and 1996, more than 1,300 underground tests were carried out. China conducted the final atmospheric test in 1980.
The PTBT paved the way for the 1968 Nuclear Non-Proliferation Treaty (NPT), which committed states to disarmament goals. India, Pakistan and Israel, however, refused to sign the NPT, regarding it as discriminatory because it recognised the nuclear arsenals of five states while restricting others.

Moves Toward Comprehensive Prohibition

During the 1970s, diplomatic efforts resumed. In 1974, the United States and the Soviet Union agreed to the Threshold Test Ban Treaty (TTBT), restricting underground tests to yields below 150 kilotons. The 1976 Peaceful Nuclear Explosions Treaty (PNET) applied similar limits to non-military detonations. Both Treaties relied on national technical means of verification, information sharing and limited on-site access to ensure compliance. They entered into force in 1990.
Renewed negotiations involving the United States, the United Kingdom and the Soviet Union began in 1977 and advanced toward a full ban on all nuclear tests, including prohibitions on peaceful nuclear explosions. Persistent disputes over verification mechanisms, however, led to breakdowns in 1980 and early 1981. Progress revived when Soviet leader Mikhail Gorbachev declared a unilateral testing moratorium in 1985 and US leaders reaffirmed their long-term commitment to a comprehensive ban. Joint research programmes on underground test detection began in 1987.
By 1991, public protests—including those that closed the Semipalatinsk Test Site—forced additional unilateral moratoria. President George H. W. Bush signed a reciprocal US moratorium shortly before it expired, and President Bill Clinton extended it until the opening of the CTBT for signature in 1996.

Adoption and Ratification Challenges

Following the Cold War, states reopened negotiations on a comprehensive test ban. An amendment conference of the PTBT in 1991 recommended a fuller prohibition, and formal CTBT negotiations began in 1993. After extensive diplomatic work, the Treaty was adopted in 1996 and opened for signature on 24 September. The United States became the first signatory.
US ratification soon became a central obstacle. On 13 October 1999, the US Senate rejected the Treaty by a 51–48 vote. The vote followed minimal committee review and remains the first security-related treaty rejected since 1919. During the 2000 presidential election cycle, key political figures voiced opposition to ratification while maintaining support for the existing testing moratorium. The CTBT’s clause permitting withdrawal under “supreme national interest” fuelled speculation that nuclear testing could resume under future administrations.
In 2023, Russia announced its intention to revoke ratification, citing the lack of US ratification. The Russian parliament subsequently passed a law withdrawing ratification, formalised on 2 November.
Because the CTBT requires ratification by 44 specific nuclear-capable states to enter into force, its implementation remains stalled. China, Egypt, Iran, Israel, Russia and the United States have signed but not ratified; India, Pakistan and North Korea remain outside the Treaty entirely.

Continuing Negotiations and the Prospects for Entry into Force

Negotiations for nuclear test prohibition after 1996 have been shaped by shifting geopolitical tensions, emerging nuclear states and debates over verification capabilities. Although the CTBT has not entered into force, its International Monitoring System—comprising seismic, hydroacoustic, infrasound and radionuclide stations—operates globally and has demonstrated the ability to detect nuclear tests, including North Korea’s underground explosions.
The Treaty remains a central element of the international nuclear disarmament architecture. Its progress continues to depend on diplomatic engagement, confidence-building among nuclear states and the political will of those whose ratification is required to render its provisions legally binding.