Source: Bulletin of the Atomic Scientists

Nuclear disarmament is proceeding very slowly. Some have suggested that the pace might pick up if disarmament's goal were, instead of eliminating nuclear stockpiles completely, reducing them so that they constituted only a minimum deterrent. But realistically speaking, how would this approach affect the existing disarmament and nonproliferation regimes?

First, it would undermine the five nuclear weapon states' solemn political commitments to disarm. Second (and as a result), it would undermine the nonproliferation commitments made by the non-nuclear parties to the Nuclear Non-Proliferation Treaty. To these nations, complete disarmament is the core of the treaty. If abolition were no longer the goal, it would be very difficult for the nuclear weapon states to explain why they should be allowed to possess nuclear weapons while other countries should not. And non-nuclear states could be expected to withhold their support from important nonproliferation efforts.

Still, under certain circumstances, a minimum-deterrence approach could have some value. If focusing on minimum deterrence could achieve deep nuclear cuts faster than an abolition focus could achieve its goal, deep cuts would have to be considered a positive development. Even so, these cuts would represent only an interim step in the process toward achieving "zero"—not a replacement for disarmament's original goal.

Disruptive innovation. Over the years, one of the main principles guiding the nuclear reductions carried out by the United States and Russia (or the Soviet Union) has been strategic stability. According to the theory of strategic stability, nuclear rivals have very little incentive to launch a nuclear attack against the other, or for that matter to enlarge their nuclear arsenals, if the other side's arsenal contains a certain number of survivable weapons. Minimum nuclear deterrence, then, is the strategy of maintaining the smallest force necessary to deter nuclear attack.

In a given country, the size of a minimum nuclear deterrent depends on the offensive and defensive capabilities of its rivals. Today, US and Russian strategic nuclear forces seem too large for the purposes of minimum nuclear deterrence, while those of France, the United Kingdom, and China may come closer to the mark. If the United States and Russia reduced their nuclear forces to a level appropriate for minimum deterrence, and the other three nuclear weapon states joined in the process, this would represent real progress toward global disarmament.

But this doesn't tell the whole story. True, a multilateral arrangement for minimum nuclear deterrence would at first glance seem to promote stability—under such a regime, no one would have to worry about the size of other countries' nuclear forces. But this holds true only if nuclear factors are taken into account and non-nuclear factors are ignored. That is, new technological developments in the non-nuclear realm could change weapon states' nuclear calculations and complicate the situation radically.

One arena for such developments might be in intelligence capabilities. Improved intelligence in one nuclear weapon state always has the potential to reduce the survivability of nuclear weapons in another nation. The state with decreased survivability then must compensate somehow—one obvious solution being to increase the size of its nuclear arsenal. A second arena for disruptive technological developments is missile defense. If any state develops an effective missile defense system, its rivals may feel the need for a larger nuclear arsenal to penetrate the defenses. A third arena is that of precision conventional strikes. Some long-range conventional weapons may become capable of destroying an enemy’s nuclear weapons or disrupting nuclear launches. Again, increasing the size of nuclear arsenals would be a possible response. So even if a multilateral regime for minimum nuclear deterrence could be developed, the arrangement would be neither stable nor permanent. Nations might support the regime under certain circumstances but—when conditions changed in intelligence, missile defense, or conventional strike capability—become uneasy.

None of this would pertain if nuclear weapons were abolished. Under an abolition scenario, strong intelligence capabilities would be a positive force because they could detect violations against the disarmament regime. Missile defense could deter violations because it would make a small number of hidden nuclear weapons less effective. Overall, technological innovations would likely support rather than undermine a "global zero" world.

Define your terms. Perhaps a more fundamental problem with striving for minimum nuclear deterrence is that minimum deterrence is a difficult thing to quantify. First, no consensus exists regarding how many retaliatory warheads are sufficient to deter a nuclear attack. Estimates might vary from a few dozen to a few hundred. Second, no consensus exists regarding how many extra nuclear warheads might be needed to ensure survivability against an enemy's nuclear and conventional attacks and to ensure penetration of the enemy's missile interception capabilities (estimates will depend significantly on assumptions about a rival's counter-nuclear capabilities). In the absence of a universally accepted way to calculate the proper size of a minimum nuclear deterrent, limits would have to be arrived at through negotiations. Such limits, unavoidably, would have an arbitrary aspect. But as for defining "complete abolition of nuclear weapons?" It would be enough to say that no country can possess any nuclear explosive device.

Similarly, verification would be simpler in a nuclear-free world than in a regime built on minimum deterrence. In a nuclear-free world, nations would not need laboratories or production facilities for nuclear weapons. They wouldn't need stockpiles of fissile material. They wouldn't need military nuclear personnel. Any evidence that these facilities, stockpiles, or personnel existed would be evidence of a violation. So verification would be very straightforward. Moreover, the intrusiveness of verification procedures would be no great concern—if nations had no nuclear weapons facilities or capabilities, they would not have to worry that their nuclear weapon designs would be detected by intrusive inspections. Compare this to a minimum deterrence regime, where nuclear laboratories and all the rest would still exist, making verification much more complicated and doing nothing to reduce concerns about intrusiveness.

These difficulties with definitions and verification provide further evidence that minimum deterrence cannot be a workable long-term solution to the problem of nuclear weapons. A minimum deterrence regime might prove a useful interim step toward disarmament. But the ultimate goal must remain complete abolition of nuclear weapons.

This article was originally published in the Bulletin of the Atomic Scientists.