Nuclear Weapons

The CTBT: At the Intersection of Science and Politics

11.07.14 | 14 min read | Text by Private: Jenifer Mackby

Recent high-level meetings in Washington, D.C., the United Nations, California and Utah about the Comprehensive Test Ban Treaty (CTBT) might lead one to believe that finally action might be taken towards ratification of the treaty. At the meeting in New York, foreign ministers and senior officials from 90 countries met on September 29 to acclaim the treaty and its value—both scientific and political. “This treaty isn’t just a feel-good exercise. It’s in all of our national security interests, and it’s verifiable,” said U.S. Secretary of State John Kerry. “In fact, its verification regime is one of the great accomplishments of the modern world.” 1

In Washington, key U.S. officials—Secretary of Energy Ernest Moniz, NNSA Director Frank Klotz, Under Secretary of State for Arms Control and International Security Rose Gottemoeller, Assistant Secretary of Defense for Nuclear, Chemical and Biological Programs Andrew Weber–as well as Executive Secretary of the CTBT Organization Preparatory Commission Lassina Zerbo, held a public meeting on nuclear testing on September 15. “Today we can say with even greater certainty that we can meet the challenges of maintaining our stockpile with continued scientific leadership, not nuclear testing,” said Secretary Moniz. “So again, I repeat that the United States remains committed to ratification and entry into force of the Comprehensive Nuclear-Test-Ban Treaty, along with the monitoring and verification regime. And this administration will continue making the case for U.S. CTBT ratification to build bipartisan support.”2

Referring to the United States supercomputing and other capabilities, Mr. Klotz noted, “Thanks to this effort, today we have a greater understanding of how nuclear weapons actually work than we did when we were carrying out nuclear explosive testing.  This is a remarkable achievement in innovation for our national security, and it is foundational to an effective no-test regime.”3

In addition, the largest scale, on-site inspection (OSI) simulation to date will be launched for a month in November in Jordan, and includes a day of visiting dignitaries, possibly to include the king. An OSI is the final step in the verification regime; it is a complex endeavor that involves enormous amounts of equipment and scientific as well as operational expertise. The simulation will be a significant test of the system.

Politics meets Science

Although the treaty deals with the highly technical and sensitive subject of nuclear test explosions, it has been considered in a political context since the negotiations. Countries possessing nuclear weapons do not want others to know about their facilities or capabilities, so verification provisions of the treaty were exceptionally difficult to negotiate. World-renown scientists worked in their labs and academic institutions, as well as in Geneva, on the intricacies of devising an international monitoring regime. They advised some of the top diplomats negotiating the treaty in Geneva. Even now, those working on the treaty still grapple with scientific questions in a political setting, the CTBTO Preparatory Commission in Vienna, as well as in their labs or government offices. The scientists possess the expertise and deep knowledge of the various verification techniques, and they provided information and counsel to their ambassadors, but the diplomats make the decisions.

Originally the key issues in the treaty revolved around questions such as: who should be included in the negotiations? What was to be the scope of the ban—a few pounds equivalent TNT of explosive yield, hundreds, or zero? (Negotiators decided on zero.) Would the non-nuclear weapon states agree with the nuclear weapon states that this would be a treaty to “ban the bang, not the bomb?” What kinds of monitoring technologies should be included in the treaty verification regime? Where would monitoring stations be placed? How many stations would be installed in the nuclear weapon states? Who would decide to conduct an OSI, and how would it be conducted? How could access to sensitive facilities be managed? And a crucial question: which countries were essential for entry into force? All of these questions, and more, involve complex scientific issues, but are highly political and contentious.

The CTBT prohibits “any nuclear weapon test explosion or any other nuclear explosion” anywhere in the world. The verification provisions of the CTBT are more extensive and intrusive than those of other treaties, as they are designed to detect nuclear explosions anywhere on the planet: underground, in the oceans, and in the atmosphere. In order to verify compliance with its provisions, the treaty specifies a global network of 327 monitoring facilities in strategic locations in 89 countries, and allows for on-site inspections of suspicious events. The International Monitoring System (IMS) comprises four complementary or synergistic technologies: seismic, radionuclide, hydroacoustic and infrasound. The 50 primary and 120 auxiliary seismic stations monitor the ground for shockwaves that are caused by nuclear explosions. A radionuclide network encompassing 80 stations uses air samplers to detect radioactive particles released from atmospheric, underground or underwater explosions. Half of these stations will be capable of detecting noble gases upon entry into force of the treaty. In addition, 16 radionuclide laboratories will analyze samples of filters from the stations (evidence of radionuclides is called the “smoking gun” of a nuclear explosion). In addition, there are 11 hydroacoustic stations to detect explosions in the oceans, and 60 infrasound stations designed to detect nuclear explosions in the atmosphere.

The CTBT Organization (CTBTO) Preparatory Commission was established in March 1997 and has been building up the verification regime, which is about 90 percent complete. The IMS has been detecting global activities such as: some 100 earthquakes each day, the nuclear test explosions conducted by North Korea in 2006, 2009, and 2013, in addition to tsunamis, the dispersal of the radioactive plume from Fukushima, and other activities. Data from the IMS stations is transmitted for analysis to the International Data Center of the Preparatory Commission’s Provisional Technical Secretariat.

In November 2014, the Preparatory Commission will embark on its second full-scale on-site inspection (OSI) simulation in Jordan to test the operation and techniques of an OSI in an integrated manner. Although the treaty includes a timeline and specifics of the on-site inspection regime, details of the operational manual and other logistical arrangements were left for the Preparatory Commission to elaborate. The exercise in Jordan will be the most challenging endeavor to date, aimed to test the ability to conduct an on-site inspection under realistic and challenging conditions, and to demonstrate the progress made since the last Integrated Field Exercise in Kazakhstan in 2008 (IFE08). During Integrated Field Exercise 2014 (IFE14), the Preparatory Commission will simulate a CTBT on-site inspection in which 40 inspectors search a designated area of up to 1,000 square kilometers for evidence of a possible nuclear explosion. IFE14 aims to test 15 of the 17 inspection techniques listed in the treaty in an integrated manner, a significant increase in the technologies tested at the previous IFE in Kazakhstan.

There are numerous OSI techniques, from visual observations and over-flights to multi-spectral imaging, airborne gamma spectroscopy, gamma radiation monitoring, environmental sampling, measurement of argon-37 and radioxenon, seismological monitoring of aftershocks, magnetic field mapping, resonance seismometry, and drilling, among others. The IFE14 will not employ drilling (which is extremely expensive), or resonance seismometry. It plans to exercise each phase of an OSI, from the receipt of the request through the launch, pre-inspection and post-inspection activities, reporting preliminary findings, departure, and return of equipment and personnel. The exercise will involve transporting some 150 tons of equipment from Austria to Jordan. According to the PTS website, the IFE14 will also test newly developed operational elements of an OSI such as an enhanced operations support center, an improved in-field communications system and a rapid deployment system for transporting tons of inspection equipment anywhere in the world.4It should be noted that an OSI can only take place once the treaty has entered into force, thus the Preparatory Commission has had time to develop the procedures.

The provisions in the treaty for an OSI are quite demanding. Because some of the effects from a nuclear explosion can be short-lived, the Executive Council will need to decide on the on-site inspection request within 96 hours of its receipt from the requesting state party, and an OSI inspection team and its equipment must be deployed and initiate inspection activities within a six-day period. 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 inspection may continue for 60 days, but if the inspection team determines that more time is needed to fulfill its mandate, it may be extended by an additional maximum of 70 days, subject to Council approval.

Developments since 1996

Under the terms of the treaty, countries can use data outside of the IMS that is available from thousands of other seismological or radionuclide stations, satellite observations and other national technical means, as well as advanced data analysis in their efforts to monitor the treaty. Countries may submit this additional information as a basis for a request for an OSI. The IMS is performing far better than expected by the negotiators who designed it. Yet since the CTBT was negotiated in 1996, dramatic scientific and technical advances in monitoring and data analysis techniques have occurred. If countries use the data from the IMS, in combination with what is available outside of the IMS, they could enhance their monitoring capability significantly beyond that provided by the treaty, by an order of magnitude. Using this combination of information would also allow a country to focus its monitoring efforts on countries of concern, individually or in cooperation with others. Such “precision monitoring” would be useful to countries of a region that could pool their resources to support the effort.5 In contrast, the Technical Secretariat is not allowed to use information from stations or advanced technologies that are not included in the treaty. Further, the Secretariat must take a global approach; it is not allowed to focus on specific areas. Such precision monitoring capabilities would be of interest to states where verification might be an issue in the ratification process.

By focusing on specific areas of concern, precision monitoring would also increase the ability to accurately locate events. This is key to identifying areas for on-site inspections. A notable feature of the CTBT is that the decision regarding non-compliance or whether to conduct an on-site inspection rests with the States Parties, not the CTBTO Technical Secretariat. This is contrary to the role of the IAEA and the Nuclear Nonproliferation Treaty (NPT). It is therefore in the interest of the international community to expand the knowledge base on verification technologies in all countries in order to improve their ability to monitor the Treaty. Countries will need to send to Vienna representatives who are well versed in the provisions of the treaty and who have scientific expertise in the technologies it employs. This will increase the likelihood that a vote in the Executive Council (responsible for compliance with the treaty) on an on-site inspection or a decision about non-compliance will be based on scientific facts rather than concentrating on political concerns.  That is especially important, given that the decision to conduct an OSI must be made by 30 of the 51 members of the Executive Council. Critics of the treaty believe that it will likely be impossible to achieve such a number, although the criteria for membership in the Council are such that the nuclear weapon states will always have a seat on the Council. Although the United States and a few other countries have their own technical means to monitor compliance with the treaty, most countries have not yet established their national facilities to efficiently monitor it.

The treaty was opened for signature in September 1996, and has been signed by 183 nations and ratified by 163. The treaty cannot enter into force until it is ratified by 44 “nuclear capable” nations6 specified in the treaty, eight of which have yet to do so (China, Egypt, India, Iran, Israel, North Korea, Pakistan, and the United States). India, Pakistan, and North Korea have not signed it. Although many countries in the negotiations wanted to have a numerical provision (e.g., 65 ratifications), the five nuclear-weapon states in particular insisted that each of the five–and other states capable of developing a bomb–be on board for the treaty to enter into force.

After the United States triggered the negotiations on a CTBT in 1993 and committed considerable political will to conclude it in 1996 at the multilateral Conference on Disarmament, the Senate refused to ratify the treaty in 1999. Since then it has been sitting on the back burner of the U.S. Senate and its counterparts in the seven other countries required for entry into force. It is unlikely that the Obama administration will bring it up for a vote in the Senate unless it knows it has the votes.  Only 28 of the senators who voted on the ratification of the treaty in 1999 remain in the Senate (13 of whom voted against), and that figure may decrease in the November elections. A number of the other holdout countries claim to be waiting for the United States to ratify first, which makes entry into force a political exercise waiting to happen. As Dr. Zerbo said in Washington, “We have to be mindful of those who have signed and ratified this treaty long ago, and been waiting for its entry into force.”

China is the only other nuclear-weapon state among the five declared under the NPT that still needs to ratify. “The U.S. pushed for the negotiations and it has tested more than any other nation,” said Sha Zukang, former Ambassador to the negotiations. “I firmly believe that, were the U.S. to ratify the Treaty, China would definitely follow.” He added that the CTBT could be useful in promoting China-U.S. strategic mutual trust and building a “new model of major country relations.” Noting that the United States had conducted 1032 nuclear test explosions and China and the UK just 45 each, he claimed that China and the international community believed that the United States “wanted to ensure the overwhelming superiority of its nuclear arsenal, both in quantity and quality.” He added, “Serious efforts should be made to encourage U.S. law-makers to change the idea of seeking absolute security at the cost of leaving all other countries feeling insecure, and then to support Treaty ratification.”7

In an influential 2009 report on the Strategic Posture of the United States8, conducted by a bipartisan Congressional Commission and chaired by former Secretary of State James Schlesinger, and former Secretary of Defense William Perry, the CTBT was the only issue on which agreement could not be achieved. Opponents contended that the zero yield prohibition of the treaty cannot be verified and that other countries would cheat, thereby gaining a military advantage, while the United States observed the terms of the treaty. They faulted the fact that the treaty does not define a nuclear test, and this could result in different countries having different understandings of prohibitions and restrictions, to include the possibility of conducting tests with hundreds of tons of nuclear yield. In this context, they believe that Russia and possibly China are conducting low yield testing. They also believe that maintaining a safe, reliable stockpile of nuclear weapons will require testing over time.9 A number of senators and decision makers believe these and other aspects of the treaty will not confer benefits and would pose security risks to the United States.10 Proponents contend that the treaty is a strong nonproliferation tool which is verifiable, and that other states could develop and test new or improved weapons without constraints (posing a greater threat to U.S. security), and that the United States can maintain a safe, secure, and reliable nuclear weapons stockpile without additional testing.

A number of studies have been conducted on the scientific and verification capabilities of the treaty, including one by the U.S. National Academy of Sciences. The Academy released in March 2012 an update of its 2002 report on Technical Issues associated with the Comprehensive Test Ban Treaty. The newer study, conducted by eminent scientists in the field, found that the United States “has the technical capabilities to maintain a safe, secure, and reliable stockpile of nuclear weapons into the foreseeable future without nuclear-explosion testing” and “is now better able to maintain a safe and effective nuclear stockpile and to monitor clandestine nuclear-explosion testing than at any time in the past.” The study found that globally, the IMS seismic network provides complete coverage at magnitude 3.8 with about 80 percent of stations operational.11 This is a low magnitude, and the capability has likely improved since the study was conducted, with 90 percent of the stations now operational. As mentioned previously, the IMS detected all three low yield tests conducted by North Korea. “Other States intent on acquiring and deploying modern, two-stage thermonuclear weapons would not be able to have confidence in their performance without multi-kiloton testing,” the report states. “Such tests would likely be detectable (even with evasion measures) by appropriately resourced U.S. national technical means and a completed IMS network.”

Scientific arguments notwithstanding, politics usually get in the way. As former NNSA Administrator Linton Brooks is fond of saying, “The CTBT will not be ratified until there is a Republican president who supports it.” Ambassador Brooks, who was a member of the more recent NAS committee, said that although the report presented positive conclusions about the capabilities of the treaty and was favorably received by both supporters and opponents for its technical accuracy, “I don’t know anyone whose mind it changed.”12

Following the negotiations, member states of the Preparatory Commission in Vienna established a Working Group on Verification to implement the verification regime. They began by considering issues such as what stations to build first, when data from the stations should be transmitted to the International Data Center in Vienna, how to configure the global communications infrastructure, how to authenticate the data, the elaboration of the OSI regime (techniques, equipment, training, operational manual), what the budget should be prior to entry into force, etc. The Working Group breaks down into sub-groups that are quite technical, if not wonkish. Scientific experts from many countries gather to consider topics such as sources of noble gas backgrounds, testing regional seismic travel time, data fusion, autonomous buoys, new optical seismometers, infrasound calibration, and the Bayesian inference approach. Again, the scientists who work in the technical sub-groups advise the diplomats who make decisions in the Working Group on these issues. The CTBTO Provisional Technical Secretariat then carries out these decisions. (In this context, it should be noted that three women participated in the scientific meetings in Geneva, two of whom are the only women participating in Vienna.)

Arguments over the treaty’s benefits and drawbacks have preceded the completion of the current treaty and go back to several earlier attempts decades ago at negotiating a ban. In fact, the negotiators of the Limited Test Ban of 1963 (LTBT) couldn’t agree on the verification provisions of a comprehensive ban, which is why it was limited (i.e. it covered all environments except underground). Article 1 of the CTBT is the same as Article 1 of the LTBT, but expanded to include underground. The LTBT has not been contested over the years, regardless of the fact that it has no verification provisions. Politics have trumped science in a number of instances, and the CTBT is no exception. Secretary Kerry said at the UN in September, “I know some members of the United States Senate still have concerns about this treaty. I believe they can be addressed by science, by facts, through computers and the technology we have today coupled with a legitimate stockpile stewardship program.” It remains to be seen if he can trump politics.

Jenifer Mackby is a Senior Fellow for International Security at FAS. Ms. Mackby has worked on international security, nonproliferation, and arms control issues at the Center for Strategic and International Studies (CSIS), the Comprehensive Nuclear-Test-Ban Treaty (CTBT) Organization, the Conference on Disarmament (CD) and the United Nations. As a Fellow and Adjunct Fellow at CSIS, she has led projects on U.S.-U.K. Nuclear Cooperation, Asian Trilateral Nuclear Dialogues, 21st Century Nuclear Issues, and the CTBT, and has worked on Strengthening the Global Partnership, European Trilateral Nuclear Dialogues, Reduction of U.S. forces in Europe, among others. Previously, she was responsible for the negotiations on the CTBT in the CD, as well as the Group of Scientific Experts that designed the core monitoring system of the treaty. She then served as Secretary of the Working Group on Verification at the CTBTO in Vienna. Ms. Mackby served as Secretary of the Biological Weapons Convention Review Conference, the UN Special Commission on Iraq, the Convention on Environmental Modification Techniques Review Conference, Nuclear Nonproliferation Treaty Review Conference committee, and others. She is a Senior Adviser for the Partnership for a Secure America, and has written extensively about non-proliferation and arms control issues.

U.S. Secretary of State John Kerry, “Remarks At The Friends of the Comprehensive Nuclear-Test-Ban Treaty Ministerial,” United Nations, Sept. 26, 2014,
Conference on “Nuclear Weapons Testing, History, Prospects, Challenges,” United States Institute of Peace, Embassy of Kazakhstan, Embassy of Canada, Arms Control Association, the Atom Project, Green Cross, Sept 15, 2014, prepared remarks.
See Ola Dahlman, Jenifer Mackby, Svein Mykkeltveit, Hein Haak, Detect and Deter: Can Countries Verify the Nuclear Test Ban? Springer, 2011.
States participating in the negotiations and which were on the IAEA lists of countries possessing nuclear power and research reactors.
Sha Zukang, “The Entry Into Force Of The CTBT: The Chinese Perspective,” European Leadership Network, 27 August 2014,
See America’s Strategic Posture: The Final Report of the Congressional Commission on the Strategic Posture of the United States, United States Institute of Peace, 2009,
For a detailed analysis of the case for and against the treaty, see Jonathan E. Medalia, Comprehensive Nuclear-Test-Ban Treaty: Issues and Arguments, CRS Report RL34394, 2008.
National Academy of Sciences, National Research Council, Committee on Reviewing and Updating Technical Issues Related to the Comprehensive Nuclear Test Ban Treaty, The Comprehensive Nuclear Test Ban Treaty: Technical Issues for the United States, National Academies Press, 2012.
Conversation with the author.