'Peaceniks" is not the word that immediately comes to mind as you contemplate this ­array of smartly dressed present and former presidents, prime ministers, foreign ministers, generals and ambassadors, their neat if thinning coiffures reflected in the gilded mirrors of an ornate hall in one of Paris's grand hotels. Yet they have come together to advance a goal as ambitious as any ponytailed peaceniks ever had: the total, worldwide elimination of all nuclear weapons by 2030. Global zero.

I have signed up to support this goal, as you can at www.globalzero.org, but we have to acknowledge that the ­obstacles along the road to zero are enormous. They include France itself. The current approach to this issue recalls the name of one of its nuclear submarines: L'Inflexible. The head of the French foreign service coolly told this audience that nuclear deterrence had served his country very well for half a century, as it had the US, and then wished them "a beautiful stay in Paris".

Russia has joined with the US in supporting the initiative, in principle, and envisaging further big cuts in their still outsize nuclear arsenals. But if the US Senate were to demand the introduction of a modernised nuclear weapon as its price for ratifying a new Start agreement with Russia, already there would be angry voices in Russian politics ­asking what was going on.

The smaller the nuclear arsenals became, the heavier the United States' superiority in so-called conventional weaponry would appear to weigh. Although this is a cosmopolitan gathering, the driving voices here are American. Suspicious Russians and Chinese will say there is a reason for that.

Effective nuclear disarmament will require intrusive verification, which most of the sovereignty-conscious great powers of this world are extremely reluctant to concede. Indeed, when it comes to sovereignty, they are more French than the French. It is not just Iran which is working strenuously to move in the opposite direction to acquire, not renounce, a nuclear weapon capacity. Dictatorships around the world may survey the last decade and say: well, Iraq didn't have nuclear weapons and got invaded; North Korea did, and did not.

As a justification of the invasion of Iraq, Tony Blair's invocation of the diabolic mixture of terrorists, rogue or failed states and weapons of mass destruction has lost any credibility it ever had. This does not mean that those three fateful ingredients won't come together somewhere else. A very impressive report from an international commission on nuclear non-proliferation and disarmament, chaired by the former Australian foreign minister Gareth Evans and the former Japanese foreign minister Yoriko Kawaguchi, has a little diagram showing the likely impact of a Hiroshima-size bomb ­detonated inside the back of a van in Trafalgar Square. Estimated fatalities, 115,000; casualties, 149,000.

There's a story about a French ­nobleman who, having been executed, lifted up his own head, placed it under his arm and walked 50 paces. Asked how he did it, he replied, "Ce n'est que le premier pas qui coûte", which translates roughly as "the first step is the hardest". But in this case, that does not apply. The first step is hard; then it gets even harder. The most difficult of all would be the last stage, from very low nuclear ­stockpiles to zero.

As the sceptical strategic thinker Thomas Schelling points out, if you get it wrong, this could actually make the world a more dangerous place. Most of today's nuclear powers, writes ­Schelling, would have "hair-trigger mobilisation plans to rebuild nuclear weapons and mobilise or comandeer delivery systems, and would have ­prepared ­targets to preempt other nations' nuclear ­facilities, all in a high-alert status … It would be a nervous world". And that's not to mention the danger of terrorists getting hold of a stray weapon, then holding the world to ransom.

To avert this danger would require intrusive, coercive forms of global government which even today's ­sovereignty-sharing European states would find it hard to accept, let alone the sovereignty-loving great ­powers, from the US to China, and from ­Russia to India. Since uranium used for ­peaceful nuclear energy can relatively easily be enriched to weapons grade, it would also require effective international control of all nuclear fuel used anywhere: a very tall order.

Faced with the daunting requirements of the last mile, the Evans-Kawaguchi report, unlike the Global Zero initiative, declines to give a target date for global zero. They content themselves with identifying a "minimisation point", with no more than 2,000 nuclear warheads in the world, by 2025. This has the advantage of not provoking a premature hypothetical debate about complex, unprecedented arrangements whose creation is anyway more than a decade away. It has the disadvantage of not giving the ­citizens and netizens of the world any clear target to mobilise towards.

Ultimately, governments have to do the business, but they won't do it without pressure from below. The actor Michael Douglas, who lent some gravelly glamour to these proceedings, looked around the hall of mirrors and said: "I see the chiefs, but where are the indians?" The metaphor was perhaps a little old-fashioned, but we know what he means. The mass mobilisation around this goal has yet to begin in earnest.

On balance, I come down in favour of the target date: 0 in 2030. But what happens after 2025 is not the most important subject to be debating now. The big issue is what happens in 2010. This May sees a major conference to review the Nuclear Non-Proliferation Treaty (NPT). Article 6 of that treaty commits signatories to work towards the reduction and eventual elimination of their nuclear weapons. That was always supposed to be the other side of the non-proliferation coin. Will they finally get serious about it? Will they then find a way to bring along non-signatory nuclear-armed states, such as India, Pakistan and Israel? Will they convince the rest of the world that they mean what they say?

What matters is the direction of travel. To decide which way you're heading, it does usually help to identify a final destination. At the moment – let us be very clear – the world is going in the opposite direction. We are close to a nuclear proliferation tipping point. As the strategic expert François Heisbourg warns in an interview in Le Monde, "if the non-proliferation regime is not reinforced, we risk returning to the dynamics of the 1950s when every country wanting the bomb could have it – except that now it's much easier to get". If the established nuclear weapons states do not this year take a decisive lead in reducing the number and diffusion of nuclear weapons, it may soon be too late. And, by the way, in the excruciating choices about public spending that now confront us all, they can save some much-needed money this way, too.

So we need less of L'Inflexible and more of l'inspiration. We have, with thanks to the head of the French diplomatic service, had a "beautiful stay" here in Paris. For beautiful stays, this city is hard to beat. But in nuclear matters, Paris may be a good place for the world to start being a little less French.