The renewed nuclear brinkmanship between the United States and Russia has reopened one of the most dangerous chapters of the post–Cold War era. Their public threats to resume nuclear testing strike at the heart of a decades-old global norm that discouraged explosive tests even without a fully enacted treaty. Washington’s sudden declaration that it would restart nuclear testing “on an equal basis” with rival nations, followed by Moscow’s announcement of reciprocal measures, signals a destabilising return to great-power muscle-flexing. These moves shake the fragile architecture of arms control built since the 1990s and raise fresh concerns at a time when geopolitical tensions are already high. The Comprehensive Nuclear-Test-Ban Treaty (CTBT), adopted by the United Nations in 1996, never formally entered into force but created a powerful behavioural standard. With 187 signatories and 178 ratifications, it effectively halted full-scale nuclear explosions across the world. Only North Korea, India and Pakistan have conducted such tests since 1996. The treaty’s impact was amplified by the establishment of a global monitoring system that detects seismic, atmospheric and underwater disturbances, allowing countries to verify compliance with unprecedented confidence. Yet the CTBT’s durability has always been vulnerable because key states, including the US, China, Israel and Iran, never ratified it. Russia revoked its own ratification last year, citing strategic imbalance. The result is a treaty that functions in practice but remains legally incomplete, susceptible to political shocks such as the ones unleashed today.
If nuclear testing resumes, the strategic landscape could shift in unpredictable and deeply troubling ways. Analysts argue that emerging nuclear powers or those with limited testing experience stand to gain the most from renewed field tests. Nations such as China and India, which are still modernising or expanding their arsenals, would have an incentive to refine warhead miniaturisation and reliability—developments that would alter the deterrence environment in Asia. The United States and Russia, with more than 2,000 tests between them, perfected their designs long ago. For them, the strategic gains of ticking clocks and underground detonations would be marginal, but the political costs enormous. The last US nuclear test was in 1992; since then, testing has been replaced by advanced simulations and subcritical experiments that avoid explosive yields. The uncertainty introduced by today’s rhetoric therefore poses more political than technical risks, eroding confidence among non-nuclear states and undermining already fragile nonproliferation compacts. Even the suggestion of renewed explosive testing creates incentives for regional powers to accelerate their own programmes, widening an arms race that global diplomacy has tried for decades to contain.
In this volatile environment, the CTBT’s monitoring organisation in Vienna remains one of the few stabilising forces. Its network of more than 300 stations provides near-real-time data on seismic and atmospheric disturbances and has reliably detected every North Korean nuclear test. But its capabilities are not limitless. Extremely low-yield hydronuclear experiments—small underground blasts designed to test weapon components—can evade detection. This technological gap adds new ambiguity at a moment when clarity is essential. Meanwhile, the absence of clear communication from Washington about what kinds of tests it intends to pursue further fuels speculation. US officials have hinted that any new activity would involve subcritical experiments, which do not create an explosion or violate treaty norms. But without transparency, mistrust grows, especially when geopolitical relations are already deeply strained. The world is therefore left confronting a dangerous paradox: a nuclear test-ban regime that has proved remarkably effective in practice, yet remains legally incomplete and politically fragile. If the two largest nuclear powers abandon restraint, the consequences would reverberate far beyond their own arsenals, weakening global security and eroding decades of painstaking progress in arms control. The current moment demands not escalation but renewed diplomatic commitment, scientific transparency and leadership that recognises that even the rhetoric of nuclear testing can have explosive consequences for international stability.