"Prior to the widespread use of coal, oil, and natural gas, agrarian societies saw cyclical periods of rise and fall. But the scale of expansion since the dawn of the fossil-fueled industrial revolution, beginning roughly at the start of the 19th century, has been unprecedented. Energy usage per capita has grown 800 percent, as has population. Meanwhile, the contours of society have been transformed: for the first time in human history, most people now live in cities."