9/11, Al Qaeda and the nuclear terror threat

Revisiting the nuclear terrorism threat following events in Afghanistan

With Afghanistan now under Taliban rule and the terror threat the worst it has been in years, it is time to reassess the nuclear terror threat. The 20th anniversary of 9/11 approaches, and as we remember the most world-shifting terror attack to date, we must consider – and work to prevent – the harrowing possibility of nuclear terrorism, writes Philipp C. Bleek.


The September 11, 2001 terrorist attacks on New York and Washington, DC galvanized fears of even worse attacks with nuclear weapons. The 9/11 attacks made clear that some terrorists were motivated to kill large numbers, contrary to the conventional wisdom that terrorists want more people watching than dead. Sophisticated planning and patient execution over many years supported the attacks, including from Al Qaeda’s safe haven in Afghanistan. And Bin Laden explicitly said his organization sought nuclear weapons, and undertook at least some efforts to obtain them. Twenty years later, and as Afghanistan returns to the control of Al Qaeda’s Afghan patrons the Taliban, how should we think about nuclear terrorism risks?

I’ve spent more than twenty years thinking about and trying to reduce the risk of nuclear terrorism, working in academia, think tanks, and inside the US government. I’ve long been struck by the fact that smart, well-informed people differ so dramatically about the severity of the threat.  

Many of those who work on the topic take the threat very seriously, which is unsurprising: their fears are what motivate them to work on it. Others concede how challenging threat assessment is, but argue that the potential consequences are so severe that even a small likelihood warrants concerted action, an argument made by, among others, former Vice President Dick Cheney. It’s hard to argue with that, but it’s also not a very satisfying basis for allocating finite resources between, say, efforts to combat nuclear terrorism and pandemic preparedness. At the other end of the spectrum, those who regard the threat as overblown sometimes suggest motivated biases help explain why others—who are professionally and personally invested in addressing nuclear dangers—take it so seriously.

Acknowledging the fact that reasonable people can—and do—disagree about the severity of the threat, what can one say about it? 

All other terrorist nuclear weapons efforts fall well short of what Al Qaeda did.

First, at least based on information in the public domain, there have been no close calls to date. Al Qaeda is the closest of them; Bin Laden expressed interest, and met with Pakistani nuclear weapons scientists, and was scammed trying to buy nuclear material, and engaged in at least rudimentary planning. But Al Qaeda’s efforts fell well short of a serious bomb effort, though of course it’s hard to be sure about what might have happened had the group not lost its Afghan safe haven after 9/11. And all other terrorist nuclear weapons efforts fall well short of what Al Qaeda did.

Of course, no one flew aircraft into buildings until someone did. Those who work on national security need to think about things that haven’t happened yet but might some day, even as the relative dearth of past nuclear terrorism activity provides some comfort.

Second, terrorist motivation and capabilities are often inversely correlated—those who are highly motivated usually have little capability, those who are more capable are usually less motivated. Part of what’s going on here is that actors with grandiose or even delusional ambitions are attracted to nuclear weapons, and tend to undermine their own efforts. And conversely, capable, well-resourced, patient actors—Hezbollah, say—often have good reasons to steer clear of nuclear plots.

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But this raises an important question, which is under what conditions we might expect exceptions to this rule, terrorists who combined motivations with more significant capabilities. One way to think about this is to focus on terrorists who already check one box—whether motivations or capabilities—and identify the conditions under which they might also check the other. For example, if Hezbollah’s stake in Lebanon’s politics and accountability to broader constituencies make it unlikely to consider nuclear weapons, we might worry more if those factors changed.

Third, terrorists stealing, being given, or buying a state nuclear weapon can’t be ruled out, but is widely regarded as extremely unlikely. States have huge incentives to secure their nuclear weapons. That’s true even for states that use terrorists as proxies, because sharing nuclear weapons—or even weapons-related materials and technology—risks their being used in ways that blow back on the state. And in addition to fences and guards, all nuclear weapons include mechanisms to prevent their use should they fall into the wrong hands, though the specifics vary considerably.

But just because the risks of willing or unintended state complicity in a nuclear terrorism plot are low doesn’t mean they’re zero. There are things we can do to both help and pressure states to reduce them yet further.

Fourth, a crude device assembled with highly-enriched uranium is the most plausible terrorist pathway to the bomb, and the biggest hurdle to that is obtaining the needed uranium. Uranium—in particular forms—is the only material that can form the core of the crudest nuclear weapons design, a design so conservative that the United States dropped it on Hiroshima in 1945 without ever having tested it (the Manhattan Project scientists did test the more sophisticated, plutonium-based design that was dropped on Nagasaki). And unfortunately, there’s a lot of uranium, some of it used for civilian applications and relatively less secure than what’s in military stockpiles.

In recent years, much of that civilian uranium has either been eliminated or subjected to more stringent security, especially under President Obama, who prioritized this particular threat. But some concerning material remains, and merits further efforts.

Fifth, designing and building a crude nuclear weapon doesn’t require highly specialized expertise, but it does require a long time, a lot of people, and a lot of resources. A nuclear terrorism effort would be more demanding than Al Qaeda’s preparation for the 9/11 attacks, but not orders of magnitude more demanding.

Those who are more sanguine about the threat will assess current efforts as sufficient, or in some cases perhaps even a bit excessive. Those who are more fearful will urge redoubling our efforts.

Thankfully, this also means a lot of opportunities for governments to become aware of such a plot and squelch it, if they’re looking for it. Importantly, a nuclear terrorism plot is likely to take shape across multiple countries and to have international ramifications wherever it occurs, so international cooperation is critical.

Nuclear terrorism is sometimes described as an existential threat, and that’s both wrong and right. It’s wrong in the most direct sense; while state arsenals could wipe out much of humanity, nuclear terrorism itself couldn’t. This does merit a caveat, highlighting the risk of what might be termed catalytic nuclear terrorism, where non-state actors spoof or galvanize governments into attacking.

But nuclear terrorism could also be conceived of as an existential threat in the sense that you wouldn’t recognize your country, or the world, in its aftermath. Think about how much the 9/11 attacks reshaped both particular countries—obviously to include the United States, Afghanistan, Iraq, and many others—and the international environment more generally. Now imagine a nuclear terrorism plot—perhaps even a failed one—and what sort of changes it might catalyze.

Given the challenges of assessing this threat, the fact that it’s hard to rule out, and the fact that the consequences of a successful, but perhaps also a failed attack, would be extremely serious, perhaps there’s enough agreement to support a baseline of meaningful efforts, and that’s arguably a pretty good description of where we’re at today. Former US Senator Sam Nunn, who’s invested huge efforts into ameliorating nuclear threats broadly and nuclear terrorism specifically, likes to ask, the day after a nuclear terrorism attack, what will we wish we had done?

Those who are more sanguine about the threat will assess current efforts as sufficient, or in some cases perhaps even a bit excessive. Those who are more fearful will urge redoubling our efforts, building on the very significant progress that’s been made in the past two decades to make it even less likely the nightmare scenario of a nuclear terrorism attack is ever realized.

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