Washington Post: It is an odd-sounding idea, because the problem is usually assumed to be a modern one, the product of a world created by the Industrial Revolution and powered by high-polluting fossil fuels. But a professor emeritus at the University of Virginia has suggested that people began altering the climate thousands of years ago, as primitive farmers burned forests and built methane-bubbling rice paddies. The practices produced enough greenhouse gases, he says, to warm the world by a degree or …