A Martian visiting this week's United Nations conference on global warming might conclude that there is no other issue with so much international consensus and momentum. There must be hope for humanity yet. But the inconvenient truth is that the odds of a binding treaty when leaders reconvene in 10 weeks in Copenhagen are slim.

The bogeyman of Kyoto, George W. Bush, may have been replaced by a passionate, internationalist Barack Obama and a Democratic Congress, but the US delegation is unlikely to have a specific pledge when it arrives in Denmark. Healthcare and financial system reform are centre-stage, while a climate bill passed by the House languishes. Even that plan, for a 17 per cent reduction in emissions from 2005 levels by 2020, falls short of European and Japanese pledges.

The Senate ratifies treaties and its main objection to Kyoto was the exemption granted to developing nations, which is why President Hu Jintao's bold language at this week's summit inspired hope. China has since claimed the top spot in carbon emissions and its participation, with perhaps a slight nod to its lower per capita output, is critical. The same is true for smaller developing nations who, as a group, have requested an unrealistic $400bn compensation from rich countries for binding limits.