I don't see how Aussies expect to live on the least densely populated continent right next to the most densely populated continent much longer. The only question is on whose terms we reclaim arable land and begin the process of populating currently unpopulated regions. I reckon the average population density of Japan is a pretty good target, and that's what I'm basing the 500m figure on.

My point is that people assume we can turn Mars, an entire arid planet with no water, into a habitable place but that we can't turn deserts on earth into habitable, arable land.