Comprehensive Test Ban Treaty (CTBT)

Comprehensive Test Ban Treaty (CTBT)


The Comprehensive Test Ban Treaty (CTBT) is an international agreement designed to end the testing of nuclear explosives. As of March, 2003, the United States is one of the 166 states that have signed the treaty, but the CTBT will only "enter into force" (i.e., take on the force of law for all ratifying states) when 44 "nuclear-capable" countries specifically listed in the treaty have all ratified the treaty. Of these 44 states, India, Pakistan, and North Korea have refused to sign, and 13 (including the U.S.) have signed but not ratified.

Nuclear Testing. Nuclear testing is the detonation of nuclear weapons for test purposes. Testing is needed to verify new bomb designs and to observe the effects of nuclear weapons (e.g., types and amounts of radiation produced). The first nuclear test, codenamed Trinity, was conducted by the United States on July 16, 1945, near Alamagordo, New Mexico. Since that time, six other nations—China, France, India, Pakistan, the Soviet Union, and the United Kingdom—have conducted nuclear tests. (Some experts assert, based on U.S. intelligence satellite data, that Israel and South Africa may have conducted a joint nuclear test at sea in 1979.) The most recent nuclear test was conducted by India, on May 30, 1998.

Nuclear tests can be conducted underground, under water, in space, or in the atmosphere. No nuclear weapon has ever been tested in space, but approximately 2050 have been detonated in various environments on Earth. Before 1962, most tests were conducted in the atmosphere; the U.S. conducted 193 atmospheric tests between 1946 and 1962, and the Soviet Union conducted 142 such tests between 1948 and 1962. During the late 1950s and early 1960s, these atmospheric tests became a global political concern because of the radioactive substances they released into the air (fallout). The most problematic of these byproducts was iodine 131, a radioactive isotope of iodine. Iodine 131, which is chemically identical to ordinary iodine, can settle on grass, be consumed by cows, concentrate in milk, and further concentrate in the thyroid glands of human beings who drink the milk, especially children. Atmospheric testing in the 1950s and early 1960s released large quantities of iodine 131 into the atmosphere; in 1997, the U.S. National Cancer Institute estimated that 160 million people in the United States had been exposed to some level of iodine 131 from U.S. nuclear tests conducted in Nevada, and that these exposures would, over time, cause 30,000–75,000 cases of thyroid cancer. Although the extent of fallout exposure was not known at the time to be this large, public sentiment against testing became strong. As a result, the U.S., United Kingdom, and Soviet Union signed the Limited Test Ban Treaty on July 25, 1963. The Limited Test Ban Treaty forbade the detonation of nuclear weapons in the air, the sea, or space. The treaty went into effect on October 11, 1963; both superpowers conducted a flurry of atmospheric tests before the deadline, after which testing moved underground. The U.S. and Soviet Union had attempted to negotiation a "comprehensive" test ban treaty in 1963—that is, an agreement to ban all nuclear tests—but could not come to agreement on technical details. Also, military officials of both countries opposed a comprehensive test ban, wishing to continue developing new varieties of nuclear weapon. The Limited Test Ban Treaty committed its signatories to continuing to seek, in the words of the treaty's first article, "the discontinuance of all test explosions of nuclear weapons for all time"—in other words, a comprehensive test ban treaty.

The next legal step toward this goal occurred in 1974, when the Treaty on Underground Nuclear Weapons Tests (also known as the Threshold Test Ban Treaty) was signed by the U.S. and Soviet Union. This treaty forbade either nation to conduct an underground test of any nuclear weapon with an explosive force greater than 150 kilotons (i.e., equivalent to that of 150,000 tons of TNT [trinitrotoluene]). The treaty has been observed by both parties since 1974, but did not enter into full legal force until December 11, 1990, when U.S. concerns about verification had been met. (Verification of a nuclear test ban treaty requires the collection of seismic and other data to assure that no test has been secretly performed that exceeds the limits of the agreement.)

In 1991, Soviet President Mikhail Gorbachev announced that the Soviet Union would unilaterally cease nuclear testing for one year. In 1992, a bill was passed by both houses of the U.S. Congress mandating a unilateral U.S. testing moratorium to respond to the Soviet testing halt. This bill was signed into law by President George H. Bush on October 2, 1992. Neither Russia (the nuclear inheritor-state of the Soviet Union) nor the U.S. have, as of early 2003, conducted any nuclear tests since the beginnings of these moratoria.

Multinational negotiations toward a CTBT began in Geneva, Switzerland on January 25, 1994. In June 1995, while CTBT negotiations were still under way, France announced that it would resume nuclear testing. This decision aroused official protest from many governments, including that of the United States, and a worldwide boycott of French-made goods. China, too, was continuing to perform sporadic nuclear tests during this period, and on June 20, 1996 India announced that it would not sign the CTBT. Nevertheless, on September 10, 1996, the CTBT was approved by a 158-to-3 vote of a special session of the United Nations General Assembly. President Clinton signed the CTBT for the U.S. on September 24, 1996, and was soon followed by representatives of many other states, including China, the United Kingdom, France, and Russia.

Since signing of the CTBT began in 1996, the only nuclear explosions to have taken place have been the nuclear tests by Pakistan and India in 1998, a total of 11 explosions.

Ratification. President Clinton's 1996 signature did not make the CTBT binding law for the U.S. U.S. commitment to such a treaty, like that of most other states, occurs in two steps: first "signature" (by a president or qualified ambassador), then "ratification" (formal agreement to the treaty by the legislative body of the state, e.g., Parliament or Congress). Many states obey the terms of treaties that they have signed but not yet ratified, while reserving to themselves the right to begin disregarding the provisions of the treaty at any time.

The U.S. signed the CTBT in 1996, but the Senate refused in 1999 to ratify (51 to 48). As of March 2003, United States president George W. Bush's administration has stated that it intends to continue observing the CTBT's ban on testing, but will not support ratification of the CTBT. Also, administration officials have indicated that the U.S. may, at some time, withdraw from the treaty altogether. The Bush administration's Nuclear Posture Review of 2002, a document designed to guide nuclear-weapons strategy for years to come, has recommended that the U.S. develop a class of relatively low-yield nuclear weapons that would dive deep into the ground (probably at thousands of miles per hour) before exploding; the goal of such weapons, termed Robust Nuclear Earth Penetrators or "bunker busters," would be to destroy deeply buried targets. In order to develop such devices, the U.S. would have to resume testing of nuclear weapons.

Verification. Verification of the CTBT is accomplished by a global system of sensors termed the International Monitoring System (IMS). The IMS consists of sensors that detect bomb-type vibrations in the Earth, oceans, and air (termed seismic, hydroacoustic, and infrasonic vibrations, respectively) and that test the air for radioactive substances (radionuclides) which would reveal the occurrence of nuclear tests. The IMS is designed to accomodate 170 seismic monitoring stations, 11 hydroacoustic stations, 60 infrasound stations, and 80 radionuclide-detecting stations. These automatic sensors, deployed to provide global coverage, will report their data in real time via satellite to a monitoring center in Vienna, Austria, the International Data Centre (IDC). The IMS and IDC are run by an independent group, the Comprehensive Nuclear-Test-Ban Treaty Organization. (Since the CTBT is not officially "in force," the Comprehensive Nuclear-Test-Ban Treaty Organization has been funded by nonbinding international agreement.) Construction of the IMS began in 1997. Regardless of the legal future of the CTBT itself, the IMS will probably continue to provide high-quality, publicly-available information about nuclear testing worldwide.



Galindo, Marta and John Newton. "Installation of New Stations in the Hydroacoustic Monitoring Network for the Comprehensive Test Ban Treaty," in proceedings from the Oceans 2000 MTS/IEEE Conference and Exhibition, IEEE, 797–801, 2000.


"The Comprehensive Nuclear Test-Ban Treaty." United States Department of State. January 10, 2001. < > (March 10, 2003).

"The Limited Nuclear Test-Ban Treaty." United States Department of State. [No date on Web page.] < > (March 10, 2003).


Antiballistic Missile Treaty
Nuclear Weapons
Start I Treaty

User Contributions:

Comment about this article, ask questions, or add new information about this topic:

Comprehensive Test Ban Treaty (CTBT) forum