Nuclear testing could start a new arms race

SEISMOLOGICAL detectors around the world could soon twitch not to the tremors of earthquakes, but of an underground nuclear explosion, at Novaya Zemlya in Russia’s Arctic region, or Lop Nur, in the Xinjiang region of China. Then, soon enough, a blast at the Nevada National Security Site in America.

None of the big three powers has detonated a nuclear device since 1996, the year the Comprehensive Test Ban Treaty (CTBT) was negotiated. Yet satellite imagery suggests intense activity at their test sites. A detonation at any of them could start an arms race more dangerous than that of the cold war.

Nuclear arms-control has been eroding since America withdrew from the Anti-Ballistic Missile Treaty (which limited anti-missile defences) in 2002. But nuclear dangers have become more acute with Russia’s invasion of Ukraine and its threats to use nuclear weapons. America and Russia have stopped exchanging information under the New start Treaty, which limits each side’s long-range “strategic” nuclear weapons. Russia is deploying tactical nuclear weapons to Belarus, and in late 2023 it set out to reverse its ratification of the CTBT. According to the Pentagon, China’s stockpile of nuclear weapons will grow from 500 warheads to more than 1,000 by 2030.

America and Russia are still abiding by the limits of New start (for instance, a maximum of 1,550 deployed strategic warheads, out of total stockpiles of 5,000 each). But after decades of two-sided nuclear stability, the new three-sided rivalry—“an existential challenge for which the United States is ill-prepared”, says a bipartisan commission of experts—will put pressure on President Joe Biden to build up America’s stockpile. For now, his administration is just modernising existing forces. A Republican successor might conduct a test, and expand the arsenal after New START expires in February 2026, if not sooner.

How likely is a test? Computer simulations can do a lot using data from previous tests. But they do not provide certainty. China has the greatest appetite for fresh data, having conducted just 45 tests, compared with 1,030 by America and 715 by Russia.

Russia probably has the greatest political incentive to test a weapon. It says the rationale for revoking the ctbt is to mirror America. If so, Russia would not test if America refrains from doing so. But President Vladimir Putin also says the warheads for new weapons may need testing. The deciding factor may be the war in Ukraine. The worse Russian forces perform on the battlefield, the likelier Mr Putin is to reach for nuclear weapons. An underground test would be a less risky form of escalation.

A new arms race would be hard to stop. Nuclear agreements are usually based on parity. Russia and China will each insist on parity with America. But America may want more than either, to fend off the two combined.

Counting warheads is hard enough. But if limits on their numbers are gone, it will be harder to control other technologies such as hypersonic missiles, anti-satellite weapons and artificial intelligence. The arms race could become a stampede. ■

Anton La Guardia, Diplomatic editor, The Economist, Washington, DC