Nuclear crises require a lot of unlikely events to occur at once, like all the holes in slices of Gruy?re cheese lining up. But as the nuclear ambitions of the Iranian president remind us, that is not a reason to ignore the perils of atomic weapons.

There are two theories on nuclear weapons. For some they are just another weapon, albeit bigger. There is nothing a nuclear weapon can do, they say, that you can't do with a hammer. It's just a matter of scale. Indeed the "conventional" incendiary bombs dropped on Tokyo one night in 1945 killed 100,000 people - more than either of the bombs dropped soon afterwards on Hiroshima and Nagasaki. And, far from such technological sophistication, consider  that during about 100 days in 1994, a lot of simple, cheap machetes made in China caused the death of more than 800,000 Tutsis and moderate Hutus in  Rwanda.

Thus the defenders of nuclear weapons maintain that the small number of deaths they have caused, in comparison with conventional weapons, is the best argument against their prohibition. In other words, the deterrent effect of nuclear weapons is so great that we owe decades of peace to them. Better to prohibit the Kalashnikov.

On the other hand, it is well to remember the reflections of Robert McNamara, Kennedy's defence secretary during the Cuban missile crisis, in the documentary The Fog of War. Everyone knows, he says, that in a war many mistakes are made - tragic mistakes that cost people's lives. Errors of  judgment are inherent in war, because the information you have is always imperfect. But with nuclear weapons in the picture, things are different. This was seen in the Cuban missile crisis, where a single error of calculation about the adversary's intentions could have caused whole nations to be annihilated and disappear from the face of the Earth.

Aviation experts tell us that air crashes are never due to one single cause. Since safety systems overlap and intentionally duplicate each other, a major accident requires a concatenation of several human and/or technical failures. An interesting metaphor puts it this way: for an accident to happen, all the holes in several slices of Gruyère cheese would have to line up perfectly, which is highly unlikely. In 1962, however, all the holes came near to lining up, in a series of errors of calculation on the part of Russians, Cubans and Americans.

Now the Iranian president, Mahmoud Ahmadinejad, is working hard to find a new holey alignment, while the international community is trying to prevent nuclear proliferation. It has been said that in the financial crisis, economics has displaced politics, even on the international chessboard. But it is hard to imagine an economy-driven change as drastic as that which might occur in international relations, were Iran to have a nuclear arsenal.

From the preventive bombings apparently meditated by Israel to reconciliation with an openly nuclear Iran, all the options are bad. As James M. Lindsay and Ray Takeyh point out in the recent Foreign Affairs article After Iran Gets the Bomb, if we rule out war as an answer on the grounds that the evils of the cure would be worse than the disease, then the diplomatic and military effort of containment that the European Union and the United States would have to make to prevent a nuclear arms race in the Middle East would be of unprecedented intensity. Iran might achieve just the opposite of what it wants, by uniting the whole region - Egypt, Turkey, Saudi Arabia and Iraq - against it. One axiom of international relations holds that the total security of one actor means total insecurity for all the others. Whether Iran stops short of the bomb or not, there is no doubt that, whatever Obama may say about eradicating nuclear weapons, their proliferation is still the gravest threat that hangs over us. Hence the importance of the conference that began yesterday in New York and that will go on until May 29. In it, 189 countries are trying to keep the holes in the cheese from lining up. An event to keep an eye on.  

This article was published in El País English edition on 4 May 2010.

(English translation)

The Spanish version is already uploaded to José Ignacio Torreblanca's blog A golpe de azul (Blue strokes):

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The European Council on Foreign Relations does not take collective positions. This commentary, like all publications of the European Council on Foreign Relations, represents only the views of its authors.