Forget Iraq, forget global warming. The soaring price of oil, and the cost of filling a car with petrol, have concentrated the minds of cash-strapped US voters. It has pushed energy to the front of an increasingly fractious debate between John McCain and Barack Obama, Republican and Democratic presidential contenders. Both men have tried to win support with populist gestures, be they petrol tax relief or a windfall levy on oil companies. A more rounded approach is needed.

Several inconsistencies lie at the heart of the Obama-McCain debate. They both acknowledge the need for the US to become less reliant on foreign oil imports and improve energy efficiency. They back a cap-and-trade system for limiting carbon dioxide emissions, an essential step for putting a cost on pollution. But it is hard to know whether the next president will curb energy use or subsidise it and whether America wants to punish oil companies with heavier taxes or liberate them by relaxing long-standing curbs on oil exploration.