Well, we haven't begun to populate any other planet yet and time does appear to be running out in terms of us seeing the effects of such a huge mass of humans.

Well, we haven't begun to populate any other planet yet and time does appear to be running out in terms of us seeing the effects of such a huge mass of humans. Getting a population started on another planet is going to require a LOT of investment of both money and natural resources and also it'll involve a mind-boggling amount of energy to get enough equipment out of our gravity well.