all the land is in use?
I beg to differ, well, at least in the UK
massive chunks of land was removed from farming duties thanks to the good old EU, or more specifically because of the French ;)
said land was "set aside" and farmers even get paid to NOT use it, in the coming years much of this land was sold and turned in to massive housing estates. So we have a situation where a country that was super farming nation, who could have sold goods to folk who need it, cant because we were not aloud to make too much because other EU countries would have been at a disadvantage. It doesn't matter that the world is going to run out of food to support the population long before we run out of oil, what matters is that we don't defy those EU directives.
anyhow, its academic now, huge chunks of the land we used to use for food has been built on. I don't know if the that's the same in the rest of the world, presumably other places have more common sense, like Canada and the USA with its immense food producing lands... I dunno but lets hope so!