Domestic cars, typically weighing well over a tonne, will always use large amountsof energy to move around the country. This is a simple outcome of the laws ofphysics, and we should distrust those who claim that any new type of car will somehow avoid being bound by the usual rules. Hydrogen or electric cars don’t escape this generalization. In fact, though fuel efficiency continues to rise, the increase in the typical size of cars means that total petrol consumption is not declining in the UK. Even taking into account innovations in alternative fuels, the impact of car transport on global warming is not going to decrease. Nevertheless, the typical car user can reduce his or her carbon dioxide emissions by 50 per cent by making some simple choices.