Speaking at the United Nations, the CTBTO chief said a renewed test by any state could start an unstoppable spiral, after Washington and Moscow raised the prospect late last year.
He urged coordinated ratification of the 1996 test-ban treaty by the US, China and Russia; it still lacks approval from nine of 44 required states, while Russia revoked ratification in 2023.
Floyd spoke as the UN reviews the non-proliferation treaty amid the Iran war, saying the CTBT monitoring system can detect even relatively small nuclear explosions worldwide.
With the last major arms treaty now expired, what prevents a new nuclear testing arms race?
If one superpower restarts nuclear testing, will the rest of the world inevitably follow suit?
Can advanced monitoring technology truly expose a secret nuclear test before it is too late?