> Land use is actually staying constant or going down.
That's consistent with my claim that all the good farmland is already taken. The shrinkage in use of farmland could be that marginal farmland is falling away due to soil exhaustion and economic effects.
> humans are becoming more urban.
That sounds like the path towards arcologies.
You can see it now: former single-family dwellings in the large cities are being rented out to groups of yuppies, each of whom, despite being high earners, would struggle to pay the rent alone. The low earners are being forced out, but to where? Where does this road lead, if not to arcologies?
> It has nothing to do with McMansions, humans are becoming more urban.
Only if you define "urban" as identical to "metropolitan area."
Take any large US city, then include its complete metropolitan area, which I'll define here as the area of continuous land surrounded by either farmland or wasteland. I'll stretch the definition of farmland to include single-family-owned parcels of land which are large enough to support small alfalfa crops, horse pasturage, etc.
How many "cities" are in that metropolitan area? Why are they called "cities," even though there is no farmland between them? I'm fundamentally a rural sort, all my life, but I've been in such areas many times, and the only way I can tell that I've traveled from one city to another is that there's a sign situated between a laundromat and a strip mall, with the city boundary going down the alley between them. Once upon a time, they were in fact separate cities.
Take Los Angeles, California as an example. In what meaningful way is Anaheim not "L.A."? I get that its streets don't look much like those of Beverly Hills or Monrovia or Pasadena, but the whole area is one urbanized mess. You used to pass through farmland to get from each of these cities to the next. As an occasional visitor to the area, "L.A" to me extends from Ventura to the north down to San Clemente in the south, and inland almost to the Salton Sea. All that former farmland is paved over now.
> There is also tons of lower quality land that could be farmed if you really needed to as well.
Less productively, by definition.
> Around 45% of corn production is used to make transport fuel rather then food.
Sure, but that's just part of the same problem: as population and wealth rises, the wish to have personal rapid transit also rises, which leads to either:
1. Greater consumption pressure on our oil reserves.
2. A switch to biofuels of some sort, which in turn puts pressure on the rest of the bioeconomy.
3. A switch to electric vehicles, which requires massive solar cell arrays and massive distributed mines for rare earths, which stresses the environment still further.
...or some combination of the three, of course.
It's all an interdependent system. You can't move one part without affecting many other parts.
> food is not becoming more expensive other then being more expensive because of oil and transport cost.
The increasing transport costs are in part because of my original premise: cities used to have nearby farms to draw from. Now that we've pushed the boundaries of so many of our conurbanizations out to the wastelands, we've got to truck in food from much farther away than before.
In the US, some of the areas of most rapid population growth are out in the desert, places like Las Vegas and Phoenix. Why do you suppose that is?
> Most move to urban centers voluntary.
Yeah, voluntary in the same way that having children work in the coal mines was "voluntary" to our forebears. They had a choice: starve or go farming. Back then, we still had much of the West available for expansion. That's largely gone now.
At the grandparent level, my family were farmers. The land they did all of that on is now sold off for houses. My forebears made the desert bloom. The thing is, though, they did it around rivers which now run dry because the remaining farms are sucking up all of the water that isn't going into the houses or being dumped back on the desert to keep all those middle-America lawns green.
You speak of increasing productivity for our existing farmland, but all increasing curves flatten out eventually. There are no exponential curves in ecologies, only S-curves that haven't started to flatten out yet. (Or, collapsing curves!)