We have just had the second Nuclear Security Summit, in Seoul. It got surprisingly little attention from the international media although 53 countries attended. For the media, nuclear weapons are yesterday's issue, because nobody expects a nuclear war. But a nuclear weapon in terrorist hands is the defining nightmare of the post-9/11 decade, and that's what the summit was actually about.
"It would not take much, just a handful or so of these (nuclear) materials, to kill hundreds of thousands of innocent people, and that's not an exaggeration," said President Barack Obama on his way home from Seoul.
Keeping bomb-grade nuclear material out of the wrong hands requires a high level of international co-operation. Some progress was made on this issue in Seoul, in terms of co-ordinating police and intelligence operations, but the real problem is that there are far too many nuclear weapons in the world.
Nobody has ever come up with a plausible scenario in which a terrorist group creates a nuclear bomb from scratch. Mining uranium, refining it to weapons-grade material, and constructing a bomb that will actually produce even a 20-kiloton explosion (like the Hiroshima bomb) are tasks that require the scientific, technical and financial resources of a state.
What terrorists need is a ready-made bomb, or at least enough highly enriched uranium or plutonium that the only job left is to assemble the bomb. The only plausible source of a terrorist bomb, therefore, is the nuclear weapons programmes of the various states that own them. And the bigger those programmes are, the greater the chance that either a nuclear weapon or a large amount of fissile material will fall into the wrong hands.