Russia, US threatened to resume nuclear testing after several decades. Here's why it matters

The United States and Russia have both recently threatened to resume nuclear testing, alarming the international community and jeopardising a global norm against such tests.

Experts say these threats from the world’s two largest nuclear powers put pressure on nonproliferation efforts and endanger global peace and security.

“Because of other countries’ testing programs, I have instructed the Department of War to start testing our Nuclear Weapons on an equal basis,” US President Donald Trump said in a post on his Truth Social site at the end of October. “That process will begin immediately.” Moscow quickly responded.

Russian President Vladimir Putin told his Security Council that should the US or any signatory to the Comprehensive Nuclear-Test-Ban Treaty conduct nuclear weapons tests, “Russia would be under obligation to take reciprocal measures.” Here’s a look at what a resumption of nuclear testing could mean.

The treaty established a norm against nuclear testing.

Concerns about the negative effects of nuclear weapon tests grew in the 1950s when the US and the Soviet Union carried out multiple powerful atomic tests in the atmosphere. As a result, a limited nuclear test ban treaty was negotiated that prohibited such tests, but underground tests were still permitted.

Renewed international efforts to ban all nuclear tests resulted in the start of negotiations for a comprehensive treaty in 1994, culminating in its adoption by the UN 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 officially take effect, 44 specific states — listed in an annexe to the treaty — must ratify it. Nine of them have not yet done so.

China, Egypt, Iran, Israel and the US signed but didn’t ratify it. India, North Korea and Pakistan neither signed nor ratified the treaty. Russia signed and ratified the treaty but revoked its ratification in 2023, saying the imbalance between its ratification and the US failure to do so was “unacceptable in the current international situation.” Alongside the treaty, the Comprehensive Nuclear-Test-Ban Treaty Organisation was established in Vienna. It runs a global monitoring network to detect nuclear tests worldwide, operating 307 monitoring stations, using seismic, hydroacoustic, infrasound and radionuclide technologies.

The organisation is financed mainly through assessed contributions by its member states. Its budget for 2025 is more than $139 million.

China and India would profit from resuming tests Daryl Kimball, executive director of the Arms Control Association in Washington, said that a resumption of US atomic 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.” This would “decrease US and international security,” he said.

Joseph Rodgers, fellow at the Washington-based Centre for Strategic and International Studies, said that states such as China or India stand to profit from a resumption of nuclear tests.

“It makes more sense for them to test” than it does for the US or Russia, the two states that have conducted most atomic tests to date, Rodgers said.

The US conducted its last nuclear test in 1992. Since 1996, only 10 nuclear tests have been conducted by three countries: India, Pakistan and North Korea. None of them has signed or ratified the treaty.

The vast majority of nuclear tests — approximately 2,000 — occurred before 1996, mostly by the US and the Soviet Union.

The organisation creates confidence’

Given the uncertainty around Trump’s announcement and the potential for escalation of tensions around the issue, the test ban treaty organisation could play a role in resolving the situation.

Rodgers said that the treaty organisation is primarily a scientific one and should focus on providing scientific data to the international community.

But Kimball disagrees, suggesting the organisation’s Executive Secretary Robert Floyd could “take the initiative and bring together” officials from the US and other countries to help resolve some uncertainties, such as what type of nuclear tests the US president was referring to in his statement.

Floyd told The Associated Press that in the current situation, 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 organisation’s monitoring network successfully detected all six atomic tests conducted by North Korea between 2006 and 2017, he said.

Not all atomic tests create explosions

The White House has so far not clarified what kind of tests Trump meant and what other countries he was referring to in his statement. US Energy Secretary Chris Wright said the new tests would not include nuclear explosions.

Nuclear test explosions banned under the treaty are so-called supercritical tests, where fissile material is compressed to start a self-sustaining nuclear chain reaction that creates an explosion.

These tests produce a nuclear yield — the amount of energy released, which defines a weapon’s destructive power. The treaty bans any nuclear explosion with a yield, following a zero-yield standard.

In contrast, subcritical nuclear experiments, the ones Wright was referring to, produce no self-sustaining chain reaction and no explosion. Nuclear weapon states, including the US, conduct these experiments routinely without violating the treaty.

Some tests may remain undetected

Kimball says hydronuclear tests with extremely small yields conducted underground in metal chambers are “undetectable” by the organisation’s monitoring system.

“So that creates what I would say is a verification gap regarding this particular type of extremely low yield explosion,” he said.

When the organisation’s monitoring system was established in the 1990s, it was designed to detect nuclear explosions of 1 kiloton (1,000 tons of TNT). Floyd said the system actually performs better, detecting explosions below 1 kiloton, at 500 tons of TNT.

The nuclear bomb dropped on Hiroshima by the US was approximately 15 kilotons.