By Robert More

The Holy See is among 132 countries currently participating in negotiations at the United Nations on a treaty to ban nuclear weapons. It supports a treaty that would lead to the total elimination of such weapons. It is also a party to the 1970 Nuclear Non-Proliferation Treaty (NPT). Like other non-nuclear-weapon states that are parties to the NPT, it is prohibited by that treaty from acquiring nuclear weapons. It is also the smallest country in the world, and has no capacity to build a nuclear weapon. Moreover, ever since 1945, a succession of its leaders has condemned the use, spread, and—more recently—even the possession of nuclear weapons. In light of these facts, the question posed in the title of this essay sounds absurd.

But consider this hypothetical situation. A treaty banning nuclear weapons is agreed to and ratified by the great majority of the world’s non-nuclear-weapons states. Over time, moral and political pressure builds on nuclear-weapons states to give up their arsenals. Finally, they agree to do so on one condition, that a small stockpile of nuclear warheads is maintained in some neutral location. The world’s nations collectively ask the Holy See to serve as the repository, creating a special exception to the NPT. Also absurd? Probably.

But now consider these real-world facts. There are at least three existential threats to life on this planet. One is nuclear war. A large-scale nuclear war would produce direct and indirect effects that could eliminate a large part of the human population.1 Even a limited exchange of nuclear weapons could wreak havoc on global temperatures, the ozone layer, and agriculture.2

A second existential threat is runaway global warming. Unless the world’s nations achieve significantly greater reductions in greenhouse gas emissions than they have pledged so far, global temperatures could reach 3-4°C (5.4-7.2°F) above pre-industrial levels by 2100.3 At those levels, the climate may reach dangerous “tipping points”leading to even greater warming, eventually rendering large areas of the planet uninhabitable.4

A third existential threat is the impact from a large asteroid or comet. Such an event 66 million years ago is believed to have caused the extinction of the dinosaurs. Nearly 16,000 near-Earth asteroids and comets have been identified so far, and there is a high probability that a major impact will occur eventually unless defensive actions are taken.5 One of the leading defensive measures under active study is the use of a nuclear warhead to deflect or destroy an asteroid headed for Earth before it gets too close.6

Presumably no sane person would advocate the use of nuclear weapons to create global cooling and thereby offset the effects of global warming.7 But the precision use of a nuclear weapon in space may be one of our best strategies for avoiding a catastrophic asteroid impact. If so, nuclear weapons, when viewed as instruments of national defense, may be the ultimate weapons of mass destruction, but when viewed as instruments of a cooperative planetary defense, may be weapons of mass salvation.

The question arises, therefore, whether the treaty presently being negotiated to ban nuclear weapons should include an exception for a limited number of warheads to be retained for planetary defense. The draft treaty released on May 22 contains an absolute prohibition with no exceptions,8 and the subject does not appear to have been raised by either proponents or opponents of a ban treaty. A planetary defense exception to the prohibition on possessing nuclear weapons is of no concern to the nuclear-weapons states, since (despite the NPT) they have no present intention of surrendering their arsenals anyway. But the issue should be of at least theoretical concern to the non-nuclear-weapons states supporting the treaty.

One approach these states could take to the issue would be to conclude that there is no safe number of nuclear warheads that could be retained by anyone anywhere. Such a conclusion might be supported by either of two rationales.

  • One rationale is that the risk of a catastrophic asteroid impact is outweighed by the risk that even a small nuclear stockpile intended for planetary defense could be seized and misused by a state or non-state actor for nefarious ends, causing greater harm. But is that a realistic assessment of the risks? According to one assessment, a “collision between Earth and an asteroid a few [kilometers] in diameter would release as much energy as the simultaneous detonation of several million nuclear weapons.”9
  • A second rationale is that other strategies for deflecting an approaching asteroid are sufficient, without the need to rely on a nuclear weapon.10 None of the various planetary defense strategies has been tested with an actual asteroid, however, so giving up one strategy in advance would entail risks of its own.

Another approach would be to conclude that there is, in fact, some safe number of nuclear warheads that could and should be retained for use if necessary in planetary defense. If so, who should retain them and where?

  • Perhaps the nine current nuclear-weapons states could each retain a handful of warheads in a deactivated state, subject to oversight by the International Atomic Energy Agency (IAEA). If an asteroid threat were detected, the IAEA could allow one of the warheads to be placed on an asteroid intercept rocket and reactivated just before launch. Of course, if any of the nine countries decided to reactivate its nuclear warheads in the absence of an asteroid threat and without IAEA approval, it’s likely the others would promptly follow suit to deter unilateral use, potentially reigniting a nuclear arms race.
  • Or perhaps the warheads could be disassembled, with a few different countries holding separate components, again subject to IAEA oversight. If an asteroid threat were detected, the IAEA could allow one of the warheads to be reassembled, placed on an asteroid intercept rocket, and activated just before launch. This option would be safer, in that no one country could reactivate a nuclear warhead on its own.11 But given the enormous stakes involved once the asteroid threat was detected, each of the countries could be tempted to hold the rest of the world hostage by refusing to provide its components until its demands were met on some issue of national concern.
  • A third alternative would be to store the retained warheads in a deactivated state in one or more neutral locations agreed upon by the UN Security Council. This, of course, is where the hypothetical situation posed above comes in. At least in theory, the Holy See might be seen by the other nations of the world as possessing sufficient neutrality and moral authority to be trusted with this responsibility. As a practical matter, there is probably no place in the Vatican or other properties controlled by the Holy See where the retained warheads could be safely stored, given that the repository could be an attractive target for unscrupulous governments or terrorists. But perhaps some other suitable location would be found.
  • A combination of the second and third alternatives might be the safest: a limited number of retained warheads could be disassembled, and the components spread among a larger number of neutral locations. If a small inventory of each component were stored in a few countries, no one country could prevent the reassembly of a nuclear weapon for planetary defense. Potentially the Holy See could serve as one of the repositories for one of the components.

Yet another approach would be to acknowledge the risk of an asteroid impact, but decide to deal with it in the future. There is currently no “danger” that the world will run out of nuclear weapons to use for planetary defense. Hence, treaty negotiators may decide to focus for now on the abolition of nuclear weapons for national defense, assuming there will be plenty of time to deal with a planetary defense exception if and when substantial progress has been made in eliminating nuclear arsenals worldwide. To the extent the negotiators have thought at all about planetary defense, I suspect this is the approach they’re taking.

At least for people of faith, a final approach could be to work for the complete abolition of nuclear weapons, without exception, trusting in God to deal with the threat of an asteroid impact. Nuclear annihilation is a threat that humans have created, and complete abolition of nuclear weapons (with a rigorous inspection and enforcement regime) may be the only safe way to deal with that threat. Annihilation by asteroid impact is not a threat that humans have created, and there is no guarantee that human intervention with a nuclear warhead would succeed in averting the threat. So the aim of this approach would be to work to neutralize the threat we have created and leave it to God to prevent—or not, as God wills—the threat from space.12

For purposes of the current negotiations on a nuclear weapons ban, there is no practical difference between the first, third, and fourth approaches. But proponents of a ban treaty should at least consider the issue of planetary defense and what approach they would take to the issue.

1 Owen B. Toon, Alan Robock, and Richard P. Turco, “Environmental Consequences of Nuclear War,” Physics Today (Dec, 2008),

2 E.g., Alok Jha, “Climate Threat from Nuclear Bombs,” The Guardian (Dec. 12, 2006),

3 Climate Action Tracker, Atmospheric CO 2 concentrations are currently at about 400 ppm; a 3-4°C increase would correlate with concentrations of about 540-670 ppm. National Academy of Sciences, “Warming World: Impacts by Degree” (2011), warming_world_final.pdf, p. 16.

4 Doc Snow, “Mark Lynas’s ‘Six Degrees’: A Summary Review,” LetterPile (May 11, 2016), https://

5 “Near-Earth Object,” Wikipedia,; “Asteroid Impact Avoidance,” Wikipedia,

6 E.g., “Asteroid Impact Avoidance,” Wikipedia (link in n. 4); Mark Strauss, “Helpful Tips For Nuking An Asteroid,” National Geographic (Aug. 3, 2015), space-nasa-asteroids-comets-nuclear-weapons-defense/; Douglas Messier, “Nuking Dangerous Asteroids Might Be the Best Protection, Expert Says,” (May 29, 2013), asteroid-nuke-spacecraft-mission.html.

7 Even detonating a limited number of nuclear weapons over an uninhabited portion of the earth would have global negative consequences, and the reduction in global temperatures would be only a relatively short-term reversal of the long-term upward trend. See Charles Q. Choi, “Small Nuclear War Could Reverse Global Warming for Years,” National Geographic (Feb. 23, 2011), http:// science-climate-change/; Clyde Haberman, “Global Warming Gives Science Behind Nuclear Winter a New Purpose,” The New York Times (Apr. 3, 2016), gives-science-behind-nuclear-winter-a-new-purpose.html.

8 “Draft Convention on the Prohibition of Nuclear Weapons” (May 22, 2017),

9 “Asteroid Impact Avoidance,” Wikipedia (link in n. 4). See also “Effects of an Asteroid Impact on Earth” (Apr. 25, 2013), Note that, if risk equals the potential damage from an event multiplied by its probability of occurrence (“Risk Assessment,” Wikipedia,, and the potential damage from a large asteroid impact is hundreds of thousands or millions of times greater than the potential damage from the misuse of a small nuclear weapons stockpile, then one would have to assess the probability of the latter as hundreds of thousands or millions of times greater than the probability of the former, in order for the risk of the latter to be the same as the risk of the former.

10 See the list of other possible strategies in “Asteroid Impact Avoidance,” Wikipedia (link in n. 4).

11 Of course, a rigorous inspection program would be needed to deter cheating by any of the former nuclear-weapons states.

12 Other people of faith might conclude that planetary defense is the reason God has provided humanity with the natural resources and knowledge for creating nuclear weapons, and that we should not give up the option of a peaceful use of such weapons. Still others might pair their trust in God with the willingness to rely on other strategies for deflecting an asteroid, without retaining nuclear weapons as an option.