It is not often that record high petrol prices prove helpful to American politicians. But with prices now riding at more than $3 a gallon in many parts of the country, voters are listening more attentively to how the 2008 presidential contenders will tackle global warming.

Those plans grow more ambitious by the week – and they are not confined to the Democratic field of White House aspirants. Unlike President George W. Bush, who first conceded the possibility of “man-made” climate change only last January, all the leading Republican candidates have publicly ac­cepted the scientific consensus that it is occurring.