"How we live and consume matters just as much as the growing density of our numbers combined with the proliferation of our machines that devour energy on our behalf. (Roads and cell phones all consume energy and materials too.) All three demographic issues are increasing at unsustainable rates and feed each other to propel more economic growth, more emissions and more fragility. The world’s current population is 7.9 billion and grows by 80 million a year. It has slowed down in recent years because the affluent don’t need the energy of children as much as the poor. Even so civilization will add another billion to the planet every dozen years. Redistributing energy wealth (and emissions) from the rich to the poor will not avert disaster if human populations don’t overall decline. Our numbers also reflect a demographic anomaly that began with fossil fuels, a cheap energy source that served as Viagra for the species. Prior to our discovery of fossil fuels, the population of the planet never exceeded one billion. Our excessive numbers are purely a temporary artifact of cheap energy spending and all that it entails — everything from fertilizer to modern medicine."