Barack Obama normally likes to talk about hope. Last week at the United Nations he had the audacity to fear. The US president conjured up a vision of a dystopian world: “Extremists sowing terror . . . Protracted conflicts that grind on and on. Genocide and mass atrocities. More and more nations with nuclear weapons. Melting ice caps and ravaged populations.” That is our collective future, according to Mr Obama, unless the world's leaders co-operate to find “global solutions to global problems”.

As if to illustrate his point about this dangerous new world, two days later it was revealed that Iran has a second, secret, nuclear site. The mental image of bearded mullahs watching spinning centrifuges in a secret nuclear-facility hidden in a mountain sounds like something out of a James Bond film. It is, however, exactly the kind of international challenge Mr Obama was referring to. The question is whether the world's leaders can rise to the occasion.

If the major powers can establish a united front and force a change in Iranian behaviour, it would be a triumph for the co-operative internationalism that underpins Mr Obama's foreign policy. Unfortunately, the odds are on failure.