Barack Obama is right to visit the Copenhagen climate talks. The meeting will achieve less than was once hoped for, and Mr Obama's hands, to be sure, are tied by domestic politics. But his personal commitment is still valuable.

Governments have already said that the meeting will produce no new treaty to curb greenhouse gases. And Mr Obama's proposal to cut US emissions by 17 per cent from 2005 levels by 2020 amounts to little, as yet. Bills aiming to achieve such cuts – smaller, in any case, than those proposed by the European Union – are bogged down in Congress. But it is not nothing that Mr Obama signals his determination to make progress.

US commitment to this task is indispensable and there would be little hope of such commitment if Mr Obama were unwilling to spend some of his diminishing stock of political capital on the endeavour.