The Ever-Shrinking Odds of Nuclear Terrorism

For over a decade now, one of the most oft-repeated threats raised by policymakers—the one that in many ways justified the invasion of Iraq—has been that of nuclear terrorism. Officials in both the Bush and Obama administrations, including the presidents themselves, have raised the specter of the atomic terrorist. But beyond mere rhetoric, how likely is a nuclear terrorist attack really?

While pessimistic estimates about America's ability to avoid a nuclear terrorist attack became something of a cottage industry following the September 11th attacks, a number of scholars in recent years have pushed back against this trend. Frank Gavin has put post-9/11 fears of nuclear terrorism into historical context (pdf) and argued against the prevailing alarmism. Anne Stenersen of the Norwegian Defence Research Establishment has challenged the idea that al Qaeda was ever bound and determined to acquire a nuclear weapon. John Mueller ridiculed the notion of nuclear terrorism in his book Atomic Obsessions and highlighted the numerous steps a terrorist group would need to take—all of which would have to be successful—in order to procure, deliver, and detonate an atomic weapon.  And in his excellent, and exceedingly even-handed, treatment of the subject, On Nuclear Terrorism, Michael Levi outlined the difficulties terrorists would face building their own nuclear weapon and discussed how a “system of systems” could be developed to interdict potential materials smuggled into the United States—citing a “Murphy’s law of nuclear terrorism” that could possibly dissuade terrorists from even trying in the first place.

But what about the possibility that a rogue state could transfer a nuclear weapon to a terrorist group? That was ostensibly why the United States deposed Saddam Hussein’s regime: fear he would turnover one of his hypothetical nuclear weapons for al Qaeda to use.

Enter into this discussion Keir Lieber and Daryl Press and their article in the most recent edition of International Security, “Why States Won’t Give Nuclear Weapons to Terrorists.” Lieber and Press have been writing on nuclear issues for just shy of a decade—doing innovative, if controversial work on American nuclear strategy. However, I believe this is their first venture into the debate over nuclear terrorism. And while others, such as Mueller, have argued that states are unlikely to transfer nuclear weapons to terrorists, this article is the first to tackle the subject with an empirical analysis.

The title of their article nicely sums up their argument: states will not turn over nuclear weapons terrorists. To back up this claim, Lieber and Press attack the idea that states will transfer nuclear weapons to terrorists because terrorists operate of absent a “return address.” Based on an examination of attribution following conventional terrorist attacks, the authors conclude:

[N]either a terror group nor a state sponsor would remain anonymous after a nuclear attack. We draw this conclusion on the basis of four main findings. First, data on a decade of terrorist incidents reveal a strong positive relationship between the number of fatalities caused in a terror attack and the likelihood of attribution. Roughly three-quarters of the attacks that kill 100 people or more are traced back to the perpetrators. Second, attribution rates are far higher for attacks on the U.S. homeland or the territory of a major U.S. ally—97 percent (thirty-six of thirty-seven) for incidents that killed ten or more people. Third, tracing culpability from a guilty terrorist group back to its state sponsor is not likely to be difficult: few countries sponsor terrorism; few terrorist groups have state sponsors; each sponsor terrorist group has few sponsors (typically one); and only one country that sponsors terrorism, has nuclear weapons or enough fissile material to manufacture a weapon. In sum, attribution of nuclear terror incidents would be easier than is typically suggested, and passing weapons to terrorists would not offer countries escape from the constraints of deterrence.

From this analysis, Lieber and Press draw two major implications for U.S. foreign policy: claims that it is impossible to attribute nuclear terrorism to particular groups or potential states sponsors undermines deterrence; and fear of states transferring nuclear weapons to terrorist groups, by itself, does not justify extreme measures to prevent nuclear proliferation.

This is a key point. While there are other reasons nuclear proliferation is undesirable, fears of nuclear terrorism have been used to justify a wide-range of policies—up to, and including, military action. Put in its proper perspective however—given the difficulty in constructing and transporting a nuclear device and the improbability of state transfer—nuclear terrorism hardly warrants the type of exertions many alarmist assessments indicate it should.

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