The United States and Russia have both recently threatened to resume nuclear testing, alarming the international community and undermining a global norm against such tests.
Experts warn that these threats from the world’s two largest nuclear powers put pressure on non-proliferation efforts and endanger global peace and security.
“Because of other countries’ testing programmes, I have instructed the Department of War to start testing our nuclear weapons on an equal basis,” U.S. President Donald Trump said in a post on his Truth Social site at the end of October.
“That process will begin immediately.” Moscow responded swiftly. Russian President Vladimir Putin told his Security Council that should the U.S. or any signatory to the Comprehensive Nuclear-Test-Ban Treaty conduct nuclear weapons tests, “Russia would be under obligation to take reciprocal measures.”
Here is a look at what a resumption of nuclear testing could mean. Concerns about the negative effects of nuclear weapons tests grew in the 1950s, when the U.S. and the Soviet Union carried out multiple powerful atmospheric tests.
As a result, a Limited Nuclear Test Ban Treaty was negotiated, prohibiting such tests, although underground tests remained permitted. Renewed international efforts to ban all nuclear tests led to negotiations for a Comprehensive Nuclear Test-Ban Treaty in 1994, culminating in its adoption by the U.N. General Assembly in 1996.
With 187 states having signed the treaty and 178 having ratified it, most experts believe the treaty has established a norm against atomic testing even without formally entering into force.
For the treaty to take effect officially, 44 specific states listed in an annex to the treaty must ratify it. Nine have not yet done so. China, Egypt, Iran, Israel, and the U.S. signed but did not ratify. India, North Korea, and Pakistan neither signed nor ratified the treaty.
Russia signed and ratified the treaty but revoked its ratification in 2023, citing the imbalance between its ratification and the U.S.’s failure to do so as “unacceptable in the current international situation.” Alongside the treaty, the Comprehensive Nuclear-Test-Ban Treaty Organization was established in Vienna.
It operates a global monitoring network to detect nuclear tests worldwide, with 307 monitoring stations using seismic, hydroacoustic, infrasound, and radionuclide technologies.
The organisation is mainly funded through assessed contributions from member states, with a 2025 budget exceeding $139 million.
Daryl Kimball, Executive Director of the Arms Control Association in Washington, warned that a resumption of U.S. nuclear tests would “open the door for states with less nuclear testing experience to conduct full-scale tests that could help them perfect smaller, lighter warhead designs,” which would “decrease U.S. and international security.”
Joseph Rodgers, a fellow at the Washington-based Center for Strategic and International Studies, said states such as China or India could benefit from a resumption of nuclear tests. “It makes more sense for them to test than it does for the U.S. or Russia,” he said, referring to the two states that have conducted most atomic tests to date. The U.S. conducted its last nuclear test in 1992.
Since 1996, only ten nuclear tests have been conducted by three countries: India, Pakistan, and North Korea. None of these states have signed or ratified the treaty. The vast majority of nuclear tests approximately 2,000 occurred before 1996, mostly by the U.S. and the Soviet Union.
Given the uncertainty around Trump’s announcement and the potential escalation of tensions, the Comprehensive Nuclear-Test-Ban Treaty Organization could play a role in resolving the situation.
Rodgers said the organisation is primarily scientific and should focus on providing data to the international community.
Kimball suggested that the organisation’s Executive Secretary, Robert Floyd, could “take the initiative and bring together” officials from the U.S. and other countries to clarify uncertainties, such as what type of nuclear tests the U.S. president was referring to.
Floyd told The Associated Press that he believes his organisation’s main role is providing “confidence to states” that they would know if a nuclear weapon explosion occurred “anywhere, anytime.” The monitoring network successfully detected all six nuclear tests conducted by North Korea between 2006 and 2017.
The White House has not clarified what kind of tests Trump meant or which countries he referred to. U.S. Energy Secretary Chris Wright said the new tests would not include nuclear explosions.
The treaty bans so-called supercritical nuclear tests, in which fissile material is compressed to start a self-sustaining nuclear chain reaction, producing an explosion.
The treaty follows a zero-yield standard, prohibiting any nuclear explosion. In contrast, subcritical experiments the type Wright mentioned produce no self-sustaining chain reaction and no explosion.
Nuclear-weapon states, including the U.S., conduct these routinely without violating the treaty. Kimball noted that underground hydronuclear tests with extremely small yields in metal chambers are “undetectable” by the monitoring system, creating a verification gap for such low-yield explosions.
The system, designed in the 1990s to detect explosions of one kiloton (1,000 tons of TNT), now performs even better, detecting explosions as small as 500 tons of TNT.
By comparison, the nuclear bomb dropped on Hiroshima was approximately 15 kilotons.
