This is how many people that can live sustainably per square kilometre, depending on latitude. There are also other local variables like the terrain, altitude, climate and ocean currents that need to be considered.

Converting the 50-60 million square kilometres of land that is currently in use into sustainable communities would sustain 5-6 billion people. Making marginal land arable with water catchments, 7 billion people is sustainable. Reforesting the grasslands and the deserts (made by people since we got fire), starting at the forests, 10 billion people is possible.

​Once we secure the future our population will find its balance. Overpopulation is caused by fear. Fear of the future and fear of the other. Any attempt at population control will inevitably backfire.