Imagine that on September 11, 2006, the fifth anniversary of the September 11 attacks, terrorists successfully executed a nuclear terrorist attack in New York City. On a normal working day, more than 500,000 people crowd the area within a half-mile radius of Times Square. The explosion of a Hiroshima-sized nuclear device in midtown Manhattan would have killed all of them instantly. Hundreds of thousands of others would have died in the hours thereafter. The blast would have generated temperatures reaching 540,000 degrees Fahrenheit, instantly vaporizing the Theater District, the New York Times Building, and Grand Central Terminal. The ensuing firestorm would have stretched from Rockefeller Center to the Empire State Building, and buildings from the Metropolitan Museum near 80th street and the Flatiron Building near 20th street would have looked like the Murrah Federal Office Building following the Oklahoma City bombing.

With the recent North Korean nuclear test bringing nuclear danger into sharp relief, many citizens are now asking: how real is the threat of terrorists exploding a nuclear bomb and devastating a great metropolis? Former US Senator Sam Nunn believes the likelihood of a single nuclear bomb exploding in a single city is greater today than at the height of the Cold War. I believe the chances of a nuclear terrorist attack in the next decade are greater than 50 percent, given current trends. Former Secretary of Defense William Perry believes I underestimate the risk of an attack. Warren Buffet, the world’s most successful investor, believes a nuclear terrorist attack “will happen. It’s inevitable. I don’t see any way that it won’t happen.” Companies that sell catastrophic terrorism insurance exclude nuclear attacks from their policies. Otherwise these insurance companies would be “vulnerable to extinction,” in Buffett’s words.

In April, Bill Emmott stepped down from the helm of The Economist after 13 years as its leader. As is the tradition at The Economist, his final act was a substantial review of developments in the world during his tenure. In his essay, Emmott noted the unbelievable pace and extent of globalization that has occurred over the last 13 years. As he looked to the future, his forecast was faster and deeper globalization. But in conclusion, he asked: what could upset that forecast and even reverse the trend? His answer: a single nuclear bomb exploding in any capital in the world.

Nuclear Dangers Today

The face of nuclear danger today is a nuclear September 11. As Nobel Prize winner and head of the IAEA Mohamed ElBaradei has warned, “The threat of nuclear terrorism is real and current.” UN Secretary-General Kofi Annan noted, “Nuclear terrorism is still often treated as science fiction. I wish it were. But unfortunately we live in a world of excess hazardous materials and abundant technological know-how, in which some terrorists clearly state their intention to inflict catastrophic casualties...Were a nuclear terrorist attack to occur, it would cause not only widespread death and destruction, but would stagger the world economy and thrust tens of millions of people into dire poverty.”

To assess the threat of nuclear terrorism, it is necessary to answer five questions. One, who could be planning a nuclear terrorist attack? Two, what nuclear weapons could be used? Three, where could terrorists acquire a nuclear bomb? Four, could terrorists launch the first nuclear attack? Five, could terrorists deliver a nuclear weapon to its target?

Who could be planning a nuclear terrorist attack?

Al Qaeda remains a formidable enemy with clear nuclear ambitions. According to Michael Scheuer, the former head of the US Central Intelligence Agency’s Bin Laden task force, Bin Laden acquired a fatwa from a Saudi cleric in May 2003 which provided religious justification for the use of nuclear weapons against the United States. Entitled “A Treatise on the Legal Status of Using Weapons of Mass Destruction Against Infidels,” it asserts that “if a bomb that killed 10 million of them and burned as much of their land as they have burned Muslims’ land were dropped on them, it would be permissible.” Scheuer is particularly troubled by “the careful, professional manner in which Al Qaeda was seeking to acquire nuclear weapons.”

But the threats are not limited to Al Qaeda. In 2004 Chechen guerilla forces demonstrated their organizational capacity to seize facilities inside Russia as well as their readiness to murder ruthlessly—this time killing 186 children after seizing a school in Beslan. On the first day of the hostage crisis, President Vladimir Putin dispatched additional troops to guard Russia’s under-secured nuclear facilities. Whatever the security at these facilities was the day before the school seizure, Putin understood the day after that it was not sufficient.

What nuclear weapons could terrorists use?

Terrorists could acquire a bomb one of two ways: by obtaining a ready-made weapon from the arsenal of one of the nuclear weapons states or by constructing an elementary nuclear bomb from highly enriched uranium made by a state. Theft of a warhead by insiders, or a combination of insiders and intruders, would not be easy. But attempted thefts of bomb-making materials in Russia and elsewhere are not uncommon.

Once a terrorist group acquires 100 pounds of highly enriched uranium (HEU), building an elementary nuclear bomb no longer takes the mind of an Oppenheimer. Standing on these shoulders, with fissile material acquired from a weapons state, using publicly available documents and items commercially obtainable in any technologically advanced country, terrorists could construct a gun-type bomb like the one dropped on Hiroshima.

Where could terrorists acquire a nuclear bomb?

If a nuclear terrorist attack occurred, Russia would be the most likely source of the weapon or material—not because the Russian government would intentionally sell or lose it, but because Russia’s 11-time-zone expanse contains more nuclear weapons and materials than any other country in the world, and much of it remains vulnerable to theft. Another possible source is through the network of A.Q. Khan, the father of Pakistan’s nuclear bomb, who was also—simultaneously—the world’s first nuclear blackmarketeer. As evidence from Libya has revealed, A.Q. Khan directed a global supply network selling centrifuges for enriching nuclear material, uranium hexafluoride in quantities necessary for a nuclear bomb, most likely from North Korea, nuclear warhead designs from China, and consulting services to help assemble the pieces. As the IAEA director observed, A.Q. Khan was running a “Wal-Mart of private-sector proliferation.”