Fifteen years to go

Chris Luebkeman ("Yes, we can save the world . . . if we want to", 29 January) quotes an anonymous source as having "calculated that if every Chinese citizen drove a car, the world's known oil supply would be consumed in six months". This is not the case. If the citizens of China were each to consume the same amount of oil as the citizens of the United States - a fair proxy for driving - world consumption would still only less than double. A commonly accepted and probably conservative estimate is that known oil reserves will last 30 years, half of which is not six months, but 15 years.

William Claxton-Smith
London N5