Barack Obama will on Thursday become the first US president to chair a session of the United Nations Security Council. That, in itself, is a moment to celebrate, an event that testifies to his administration’s respect for the UN and its determination to act multilaterally. But Mr Obama’s presence at the Security Council will be more than symbolic. For the subject he has chosen for debate – the need to secure global agreement to stop the proliferation of nuclear weapons – is more than ever an issue of significance.

Mr Obama is experiencing tough times over foreign policy, not least because of his agony over what to do next in Afghanistan. But nine months into office, one of his most important achievements has been to raise the nuclear question to the top of the international agenda. The issue is critical now for two reasons. First, there is a real prospect that, in the next decade, nuclear weapons will proliferate well beyond the club of eight or nine powers that currently possess them. This must be stopped if global security is to be maintained. But second, those states that genuinely want civil nuclear energy for electricity supply must be encouraged to acquire it. For the spread of peaceful nuclear power is essential if the world is to prevent climate change and guarantee energy security.