Testing in the 21st Century
Understanding Nuclear Testing and its Potential Implications for Today’s World
Authors
Executive Summary
Nuclear testing has been restricted for many decades by powerful norms and international treaties, due to its severe environmental and health hazards, as well as the huge risks associated with nuclear weapons. The possibility of resumption in the 21st century could break an age-old moratorium and escalate global tensions, despite the fact that limits technical benefits will be derived from additional nuclear testing for most nuclear weapons states. # 1. Introduction On the 30th of October, President Donald Trump announced that the US would resume nuclear testing– something the US has not done since 1992.1 During conversations about the resumption of nuclear weapons testing, President Trump has also claimed that China, Russia and Pakistan are all conducting nuclear tests, and that it is in the United States’ interest to do the same.2 This issue brief provides an overview of nuclear testing, the treaties proscribing it, and the potential consequences of renewed nuclear testing.
2. Understanding Nuclear Testing
A nuclear weapons test refers to a controlled experiment designed to measure the functioning of a nuclear weapon through various parameters, including the effectiveness, the explosive capability, and the yield– the amount of energy released during the detonation.3 Countries have conducted nuclear tests for various reasons: to test the designs of new warheads and ensure that they work as intended, to assess what the destructive power of the weapon is (the heat, radiation and environmental impact), or to test their reliability and ascertain the condition of older weapons in a country’s stockpile. Beyond the physical functions, nuclear tests are also a form of political signalling, and can be used to demonstrate a state’s ability and willingness to employ nuclear weapons.
Since the first nuclear test was conducted in 1945, over 2000 tests of various kinds have been carried out across the globe. These tests are categorised based on the environment in which they are conducted, with broadly four kinds of tests:
Atmospheric tests refer to tests where the weapon is detonated in or above the Earth’s atmosphere. This can mean devices are dropped from balloons, planes, or are placed on towers. These tests have huge health and environmental hazards due to the large release of radioactive particles or ‘nuclear fallout’.
Underground tests are a form of nuclear testing that was designed to mitigate some of the issues caused by atmospheric testing. By detonating the weapon underground (often in a designated tunnel or shaft designed for this purpose), the radioactive material can be contained below the earth’s surface. While they are designed to contain radioactive contamination, underground testing can result in surrounding soil and water contamination, which can have long term health implications.
Underwater tests are explosions that are conducted under the surface of waterbodies. They were designed to evaluate the impact of nuclear explosions on submarines and ships, and understand how nuclear explosions occur in water. These tests have been seen to have detrimental implications for marine ecosystems and local populations.
Upper Atmospheric tests refer to tests that are conducted over 30 kilometres above the ground. They were designed to understand the impact of nuclear explosions on communications networks and satellites. Upper Atmospheric tests conducted by the Soviet Union revealed the huge electromagnetic pulse that was released by these explosions, could damaged power capabilities and telephone lines.4
3. The Test-Ban Treaties
Between 1951 and 1958, the US and the Soviet Union conducted 166 and 88 atmospheric tests respectively, some of which had serious environmental and health consequences.5 For instance, the United States’ ‘Castle Bravo’ test spread radioactive particles across 11,000 square kilometres.6 Additionally, by 1954, both countries had developed significantly sized nuclear arsenals, and the radioactive fallout from tests conducted in the preceding decade, along with the memory of the destruction from Hiroshima and Nagasaki steered conversations towards agreeing on some restrictions over nuclear testing and nuclear proliferation. Weeks after Castle Bravo, Indian Prime Minister Jawaharlal Nehru called for an immediate standstill on nuclear testing, and Clement Attlee demanded a ban on thermonuclear weapons.7 8 Communities in the path of the fallout also experienced a spike in health issues, such as infertility and cancer rates. The following year, discussions about a test-ban began. In 1961, the Soviet Union conducted the ‘Tsar Bomba’ which became the biggest nuclear explosion ever conducted.9 Although the fallout was contained, the destructive potential was more than evident.
The 1962 Cuban Missile Crisis compelled Premier Nikita Kruschev and President John F. Kennedy to find grounds for an agreement.10 The issue of the verification of underground testing had been a major roadblock to the progress of discussions up until 1962, since the United States wanted to conduct on-site inspections to ensure compliance with a ban on underground testing, which the USSR was not agreeable to. A practical compromise was reached in 1963, and a partial ban was agreed upon, wherein forms of testing that were easily detectable (atmospheric, upper atmospheric and underwater) were banned. The Partial Test Ban Treaty (PTBT) was signed by the United Kingdom, the United States and the Soviet Union in Moscow the same year.11
In the years that followed the PTBT, two other treaties were inked between the US and the USSR, which placed limitations on underground nuclear testing. In 1974, both countries signed the Threshold Test Ban Treaty (the TTBT), which prohibited underground explosions where the yield was over 150 kilotons.12 The significance of the TTBT went beyond the limits that were placed; the TTBT was also the first instance of an exchange of geological data between the US and the USSR on their test sites. This was a confidence-building measure that helped both sides trust the other not to try and evade remote verification. Two years later, both countries signed the Peaceful Nuclear Explosions Treaty (the PNET), which clarified a perceived loophole in the TTBT.13 The PNET added a limit of 1500 kilotons for group explosions, in addition to the 150 kiloton limit on individual explosions. This was a measure to try and ensure that civilian projects, such as dams, could not be used to conceal explosions that were designed for military weapons development. Despite the fact that both the PNET and the TTBT were signed over a decade earlier, they were only ratified in 1990 at the end of the Cold War, due to years of distrust and disagreements.
Coinciding with the collapse of the Soviet Union, the USSR and the United States both declared moratoriums on testing in 1991 and 1992. The following years saw discussions on a complete ban on testing in the Conference on Disarmament in Geneva. This time, they were rooted in powerful verification regimes that had provisions for both on-site inspections as well as an International Monitoring System with a network of stations that detected both sound and radiation. Finally, in 1996, the Comprehensive Test Ban Treaty (CTBT) finally opened for signature.14
Despite being rooted in these robust verification protocols, the CTBT never entered into force. This is because it required 44 specific states to sign and ratify it.15 These were countries that had some form of nuclear power or reactors at the time the negotiations for the CTBT were conducted. Out of these 44 states, 8 states did not ratify the treaty. The United States, China, Egypt, Israel and Iran signed the treaty but did not ratify it, and India, Pakistan and North Korea have not signed the CTBT. The US signed it in 1996, but after the Senate voted against the ratification of the treaty in 1999 (due to concerns about the reliability of its stockpile if a ban was imposed), it backed out and did not ratify the treaty.16 Other non-ratifying states have used the United States’ position as justification to continue to hold out themselves.
3.1 The CTBT Today
Although the CTBT never came into force, it has served as a powerful norm against nuclear testing. As seen in the table below, after the Cold War, most major powers began to wind down their testing programmes, and the US, the UK and the USSR had all conducted their last test by 1992.17 France and Germany both conducted their last nuclear explosive tests in 1996.18 Subsequent to 1996, the norm against testing was only broken for a brief period when India and Pakistan conducted a series of tests in 1998.19 Since then, both countries have upheld a self-imposed moratorium on testing. In the 21st century, only North Korea has conducted tests (in 2006, 2009, 2013, 2016 and 2017).20 Other countries have relied only on non-explosive forms of testing in the 21st century, such as computer simulations coupled with non-nuclear and sub-critical tests.
| Country | Approx Number of Tests | Testing Period | Test Sites Used |
| United States | 1030 | 1945–1992 | Nevada test site, Marshall Islands (Bikini & Enewetak Atolls), Pacific Ocean |
| Soviet Union | 715 | 1949–1990 | Semipalatinsk (Kazakhstan), Novaya Zemlya, Totskoye |
| France | 210 | 1960–1996 | Reggane & In Ekker (Algeria), Mururoa & Fangataufa Atolls (French Polynesia) |
| United Kingdom | 45 | 1952–1991 | Monte Bello Islands (Australia), Maralinga (Australia), Christmas Island, Nevada Test Site (USA) |
| China | 45 | 1964–1996 | Lop Nur Test Site (Xinjiang Province) |
| North Korea | 6 | 2006–2017 | Punggye-ri Nuclear Test Site |
| India | 6 | 1974 & 1998 | Pokhran Test Range (Rajasthan) |
| Pakistan | 6 | 1998 | Chagai Hills & Kharan Desert (Balochistan) |
Table 1. Nuclear Tests Conducted Globally
Although the CTBT makes no specific references to being focused on ‘zero yield’, it prohibits “any nuclear weapon test explosion or any other nuclear explosion”, which can be understood as a prohibition of any explosions of all yields, including those that are extremely low yield. As a result, it set a normative standard for all nuclear tests to be zero yield. This implies that even ‘supercritical’ tests that have a self-sustaining fission reaction that grows exponentially and results in a small nuclear yield are unacceptable.
Apart from North Korea’s tests, there has been no concrete evidence of other countries conducting explosive tests in the 21st century. However, US reports in the past have alleged that Russia may be conducting some supercritical tests and is not behaving in line with the moratorium.21 Russia has firmly denied these allegations. In recent months, the United States has also claimed that China has been conducting tests, but the Chinese government has denied this and urged the United States to uphold the moratorium. Since 1998, India and Pakistan have both upheld the moratorium, despite Pakistan’s nuclear signalling growing increasingly frequent in recent years. Although Pakistani civil society groups have claimed that there has been seismic activity in Sind, so far, there has been no evidence to suggest that Pakistan is conducting any nuclear tests.22 In West Asia, the United States and Israel have repeatedly insisted that Iran’s nuclear programme is focusing on clandestine weapons development, but Iran has conducted no nuclear tests, and has denied allegations about its nuclear programme.23 Israel is also believed to possess nuclear weapons, but has not declared them and is not a signatory to the CTBT. There has been speculation about an alleged joint nuclear test between Israel and South Africa in 1979, but evidence for this remains murky.24
If the United States were to resume explosive nuclear testing, it is likely to break the global moratorium and encourage others to conduct explosive tests in compliance with the PTBT and TTBT. If China were to conduct tests, India would likely feel compelled to test more advanced nuclear weapons, prompting a similar response from Pakistan.
4. Conclusion
Despite what President Trump may believe, there is relatively little technical benefit from conducting more nuclear tests. Although carrying out more tests may provide some additional data, for countries like the United States and Russia which already have copious amounts of data as a product of hundreds of tests, conducting more nuclear tests today will have diminishing technical returns. Additional explosions will risk major environmental and health repercussions without the promise of any ground-breaking data. Given this reality, the likelihood of the US conducting more explosive tests is low, the relatively low-effort alternative of using existing data for computer simulations is much more feasible.
If the US does end up resuming testing, it will likely be due to political reasons– perhaps a demonstration of the Trump Administration’s willingness to upgrade its nuclear arsenal as an indicator of how far it is willing to go to combat security threats.
Footnotes
Footnotes
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60 Minutes. “President Donald Trump’s Extended 60 Minutes Interview.” YouTube, November 2, 2025.↩︎
United Nations. “End Nuclear Tests Day - History.” United Nations, 2025.↩︎
Prăvălie, R. “Nuclear Weapons Tests and Environmental Consequences: A Global Perspective.” AMBIO 43, 729–744 (2014).↩︎
Archive of Nuclear Data. “NRDC: Nuclear Data - Table of Known Nuclear Tests Worldwide, 1945-1996.” Archive.org, 2025.↩︎
Rowberry, Ariana. “Castle Bravo: The Largest U.S. Nuclear Explosion.” Brookings, February 27, 2014.↩︎
Nehru, Jawaharlal. “Stand-Still Agreement.” Statement in the Lok Sabha. April 2, 1954.↩︎
TIME. “Great Britain: Labor & the Bomb.” TIME. nextgen, June 29, 1959.↩︎
Atomic Heritage Foundation. “Tsar Bomba - Nuclear Museum.” Atomic Heritage Foundation, August 8, 2014.↩︎
The Editors of Encyclopaedia Britannica. “Cuban Missile Crisis.” In Encyclopædia Britannica, May 6, 2024.↩︎
NTI. “Partial Test Ban Treaty (PTBT).” The Nuclear Threat Initiative, February 2008.↩︎
Arms Control Association. “Threshold Test Ban Treaty (TTBT) | Arms Control Association.” Armscontrol.org, 2025.↩︎
Schmalberger, Thomas. “In Pursuit of a Nuclear Test Ban Treaty,” 1991.↩︎
Kimball, Daryl. “Nuclear Testing and Comprehensive Test Ban Treaty (CTBT) Timeline | Arms Control Association.” Armscontrol.org, 2024.↩︎
United Nations General Assembly. “Comprehensive Nuclear-Test-Ban Treaty (CTBT): effective measures to facilitate establishing the norm against nuclear testing”, Un.org § (2016).↩︎
Arms Control Today. “Senate Rejects Comprehensive Test Ban Treaty; Clinton Vows to Continue Moratorium | Arms Control Association.↩︎
Schumann, Anna. “Fact Sheet: Nuclear Testing 101.” Center for Arms Control and Non-Proliferation, October 18, 2022.↩︎
Schumann, Anna. “Fact Sheet: Nuclear Testing 101.” Center for Arms Control and Non-Proliferation, October 18, 2022.↩︎
Schumann, Anna. “Fact Sheet: Nuclear Testing 101.” Center for Arms Control and Non-Proliferation, October 18, 2022.↩︎
Schumann, Anna. “Fact Sheet: Nuclear Testing 101.” Center for Arms Control and Non-Proliferation, October 18, 2022.↩︎
Heinrichs, Rebeccah L., and Lt. Gen. Robert Ashley Jr. “Transcript: The Arms Control Landscape Ft. DIA Lt. Gen. Robert P. Ashley, Jr.” Hudson Institute. October 21, 2025.↩︎
Reals, Tucker. “China Denies Trump’s Claim to 60 Minutes about Nuclear Weapons Tests, Calls on U.S. To Ensure Global Stability.” Cbsnews.com, November 3, 2025.↩︎
Wintour, Patrick. “Is Iran as close to Building a Nuclear Weapon as Netanyahu Claims?” the Guardian. The Guardian, June 13, 2025.↩︎
Uddin, Rayhan. “What Do We Know about Israel’s Own Nuclear Weapons?” Middle East Eye, 2025.↩︎