Our current world houses over seven billion people and we show no signs of stoping even though the earths carrying capacity may have already been reached. However, the problem with the population is that we won't know our carrying capacity until after it has been reached. One way to reach zpg ( zero population growth) is to make sure every country is under there recommended tfr (total fertility rate). Even though there will be some population momentum it will decrease over time. I also heavily believe in family planning. Why wold you want to bring a child into this world unless you could support it anyway. Many countries criticize China for their one child law yet their population has been rapidly declining from what it once was. Their free contraceptives to couples and free family planning services have drastically helped to country. If we don't correct the population problem the world will naturally correct it. This could come in the form of disease or famine.