To Save the Planet, Should We Be Moving Slower?

John Maynard Keynes once observed that dating from "say, to two thousand years before Christ-down to the beginning of the 18th century, there was no very great change in the standard of life of the average man living in the civilised centres of the earth. Ups and downs certainly. Visitations of plague, famine, and war. Golden intervals. But no progressive, violent change." At best, he calculated, the average standard of living had no more than doubled in the previous four millennia, essentially because, when that epoch began, we already knew about fire, banking, the sail, the plow,...