"History shows a repeated pattern of overshoot and collapse. A population would grow until the carrying capacity of the local area was reached. Food surpluses would become lower and lower, so less food could be saved up for fluctuations in rainfall and temperature. Eventually, civilizations would succumb to one or another problem: disease, attack by a neighboring group, climate fluctuations, or governments overthrown by unhappy citizens. We tell ourselves that overshoot and collapse cannot happen now, but human population is high relative to fossil fuel resources, and intermittent wind and solar are not working out well as substitutes."