The Climate Change Committee, in its 6th Carbon Budget, tells us that the answer is not very much, if anything, once fuel savings are taken into account. Is this really true? Could the conversion of our entire economy – energy, transport, heating and agriculture – be switched from a carbon-intensive one to zero within just 30 years at little or no cost? If it is true then we can look forward to the phase-out of subsidies to renewables, a withering of the need for state intervention except for infrastructure and R&D, a falling tax burden and lower consumer bills. Miracles might happen, but it sounds too good to be true and it is. More likely is the opposite: more and more public expenditure and the need for tax rises, and higher energy, transport, food and heating bills. It is a price worth paying if we are to switch from our carbon-intensive lifestyles and stop living beyond our environmental and climate means. Pretending otherwise – convincing voters and consumers that they can have their cake and eat it – is a dangerous game.