HUMANITY is doomed. Or it was in 1798, when English scholar Robert Malthus published his influential An Essay on the Principle of Population. Malthus predicted that unchecked growth in human numbers would condemn our species to a "perpetual struggle for room and food" and an unbreakable cycle of squalor, famine and disease. Nearly two centuries later, biologist Paul Ehrlich was no less pessimistic. We had exceeded the planet's "carrying capacity", he declared in his 1968 bestseller The Population Bomb. "The battle to feed humanity is over. Sometime between 1970 and 1985, the world will undergo vast famines. Hundreds of millions of people are going to starve to death." In 2012, our mood has hardly improved. The focus has shifted from how to feed ourselves to our rapacious appetite for energy and raw materials, and the greenhouse gases we pump into the atmosphere to satisfy it. Sooner or later, the argument goes, we must send our planet's climate and ourselves past the point of no return - if we haven't done so already.