Not only that, but people in cities, especially, don't appear to realize that land mass doesn't usually represent arable land; much of it is rocky and relatively infertile. Fertilizers have to come from somewhere, and even those have a finite applicability. We need forested areas for oxygen. Recent findings are that overfishing has reached a far more critical point than ever previously thought, and the oceans were believed to represent the earth's true breadbasket.
We have to start being more aware and taking better care of this planet. Contrary to what's been thought in the past, it won't take several generations to reach crisis point; this could even happen during our own lifetime, and realistically we don't have anywhere else to go.