"Global human population has doubled three times in the past 200 years, surging from 1 billion in 1820 to 2 billion in 1927, to 4 billion in 1974, to 8 billion today. Its highest rate of growth was in the 1960s, at over 2 percent per year; that rate is now down to 1.1 percent. If growth continues at the current rate, we’ll have about 18 billion people on Earth by the end of this century. All of this would be fine if we lived on a planet that was itself expanding, doubling its available quantities of minerals, forests, fisheries, and soil every quarter-century, and doubling its ability to absorb industrial wastes. But we don’t. It is essentially the same beautiful but finite planet that was spinning through space long before the origin of humans."