The Second Nuclear Age may be more difficult to survive than the Cold War

There is a greater risk of a nuclear weapon being used now than at any time since the Cuban missile crisis

If you mention nuclear weapons in a political context, you immediately make people think of a world gone by: Michael Foot shaking a stick before a Hyde Park crowd, Reagan and Gorbachev at an icy summit, nightmares about mushroom clouds over Sheffield. Nukes seem in a British context as real a political issue as coal mines, incomes policies or Harold Wilson's paranoia - even though we are supposed to have just fought a war to prevent nuclear proliferation. All this corduroy-clad distance obscures a central - and terrifying - fact: there is a greater risk of a nuclear weapon being used now than at any point in the Cold War other than during the Cuban missile crisis.

Margaret Thatcher - in her recent book Statecraft - explains that "battlefield nuclear weapons will probably be used in the next 20 years". She is right and I, for one, am terrified. The US Senate authorised the Bush administration on Tuesday to begin research on "mini-nukes", which would have around a third of the power of the weapon that in a few seconds ended more than 100,000 human lives in Hiroshima. (The same number died the following week in Nagasaki, one of the great war crimes of the 20th century).

Senator Edward Kennedy has a unique insight into nuclear war, since his brother Jack was the president who reined in hardline military figures during the Cuban missile crisis. Curtis LeMay, the then US air force chief of staff, wanted to launch a "tactical nuclear strike" against the Soviet Union's provocative decision to locate missiles in Cuba; if Kennedy had not stopped him, you would not be reading this newspaper today. So what did Jack's sibling and political heir say on Tuesday? "The hardliners [in the Bush administration] say things are different today. A nuclear war won't be so bad if you just make the nukes a little smaller," he explained. "That's nonsense. Is half of Hiroshima okay? Is a quarter of Hiroshima okay?"

Donald Rumsfeld, the US Secretary of State, claims that the Bush administration just wants to study these weapons, "not to develop, not to deploy, not to use" them. This is howlingly disingenuous: tens of millions of dollars aren't being spent simply to see the pretty pictures these plans might make on a page. If there is no intention to use these weapons, then why not spend this money on some of the 40 million people who have no healthcare insurance in his country? Or on Iraq, where - despite the euphoria following Saddam's downfall - there is a danger of a cholera outbreak? Yet the neo-cons privately ask liberals who backed the recent war: if it was okay to use massive firepower to overthrow Saddam, why not the possibility of a teeny-weeny nuke if the war had dragged on for years, or the Iraqis had used weapons of mass destruction? Come on, they nudge; don't be a wuss now.

The answer to this is clear. Even the horrible weaponry that was used in the Gulf could be wielded with a degree of precision; it is a testament to this fact that, in a country of 22 million people, 13,000 people (10,000 of whom were soldiers) died in the recent war. A nuke - even a "small" one - is an entirely different question. These weapons are immense, blunt instruments of mass murder, entirely incapable of minimising civilian deaths - and that's an insurmountable problem before you even consider their environmental impact.

Regular readers will know that I am not reflexively critical of the US, which can sometimes be a force for great good in the world as well as bad. But liberals who backed the war now have a responsibility (perhaps especially so) to point out that the Bush administration's current nuclear policy is - without hyperbole - extremely dangerous not just for the US but for all life on this planet. It is not just the "mini-nukes" (a preposterous term which makes them sound like something you might find under your Christmas tree); it is the decision to pursue National Missile Defence, to trash the Anti-ballistic Missile Treaty, and to refuse to ratify the Comprehensive Test Ban Treaty.

These choices need to be seen in the context of a revolution in the role of nuclear weapons in international relations. The Yale political scientist Paul Bracken, in his 1999 book Fire in the East, writes that we have entered "the Second Nuclear Age." The First Nuclear Age began with the attack on Hiroshima and built into the Cold War stand-off between the US and Russia. It was a very dangerous period, and our world was nearly destroyed at least once. It was, however, regulated by the doctrine - understood by everyone - of Mutually Assured Destruction. Although its acronym MAD was apt, it made a strange, awful sort of sense.

The Second Nuclear Age is very different, and less easily comprehended. One of the reasons why anxiety about nukes has evaporated is that we have no replacement for the old narrative of how nuclear war will affect us individually. In the old world, a three-minute warning would come over the radio, and we would scramble into our cellars and wait to be incinerated. But nobody quite knows how a nuclear war between, say, India and Pakistan would affect us. Would sheep in the Lake District die, as they did after Chernobyl? Would the global economy collapse? Would there be a nuclear winter, and the slow extinction of man? The truth is that it depends on who launches the weapons, who retaliates, and other unknowable factors; but all of these are real risks.

The new, second era is one of massive nuclear proliferation, as the technologies needed to produce these weapons become ever easier to acquire. Instead of a bipolar world where two big power blocs confront - and restrain - each other, we have a multipolar world where a whole range of countries wave their nukes as protective devices, status symbols, and potential weapons. This is far more dangerous. Does anybody honestly doubt that at least one of the dozen countries that now have nukes will one day have a leader who makes a terrible misjudgement and launches a nuclear attack?

This nearly happened last year, after all, over Kashmir, and Clinton administration officials still turn pale when they talk about the similar Indo-Pakistani crisis that happened in 1996. A nuclear attack is nearer now than ever, and the risk of terrorist networks getting hold of these weapons is only one among many.

It is hard to know what to recommend. More wars of counterproliferation by the US might be necessary, even though the Iraq war has not yet produced any WMD. Yet it is hard to see how any American president will be able to justify restraining others countries' behaviour towards nukes when his own is so palpably irresponsible. George Bush is blithely waving his lighter around in a gunpowder factory. There is certainly more need for a credible campaign for global nuclear restraint and disarmament now than there has ever been.

But CND as an organisation seems to have become obsessed with preventing conventional wars, and opposed the just action in Iraq. They should now focus their energies on their defining mission: pressuring politicians to reduce the number of nuclear weapons on Earth. Otherwise, the oldest of clichés might yet come true: we might leave it too late, and I will get no pleasure from saying "I told you so" as we are all starving and freezing to death during a nuclear winter.