Last month, a major climate change bill began winding through Congress. Meanwhile, carmakers, environmental regulators and the Obama administration announced with great fanfare a plan to raise the fuel efficiency of new vehicles – and energy secretary Steven Chu announced that a petrol tax was “not on the table” politically.

Yet almost everyone who has studied the subject – including Mr Chu before his latest job – agrees that a petrol tax would be much superior to directives such as those announced last month. It is hard for the government to choose the right fuel efficiency targets; and when consumers see fuel is cheap it encourages them to drive big, fuel-hungry cars and to drive them further. A petrol tax would help consumers to make choices that face the environmental facts, instead of having the government nag them to do the right thing.