The article is about exoplanets, so Mars etc isn't what he is talking about. That said, if we are talking about Mars, I would guess that by the time it becomes

The article is about exoplanets, so Mars etc isn't what he is talking about. That said, if we are talking about Mars, I would guess that by the time it becomes an economically viable solution to overpopulation, early 21st century technology will be insignificant. (sorry, Elon) We have an immense amount of space on Earth that is cheaper to populate, and will remain so for a long time. While it's sad to think of all the regions of Earth becoming densely populated with humans, its unrealistic to think we'll populate Mars prior to having all our oceans and deserts covered with people.