Too many humans! It is the underlying cause of all things anthropogenic. Ehrlich and Holdren's equation sums it up: I=PAT. Ecological impact (I) is proportional to the human population (P) times the consumption per capita (A), times the ecological impact per unit of consumption (T). Everyone talks about the problem, but no one talks about the best approach to deal with it. Even when they do, the talk is superficial (just decrease the birth rate!), or even fantastical (just find another planet!). The only way to solve a problem is to discuss it. Let's discuss.