Personally, if we can't enforce some kind of population control in the world, by the time we get to a food shortage, I think farmers will go out of work. There'll be no need for them, because who knows if we'll have to resort to some kind of cloning, for genetically modified food to keep up with the demand? Scary thought... But plausible. Because seasons only come at certain times of the year in which we're able to grown and plan for the replenishment for the stock of the food we see in grocery stores.
The only thing with that I believe, is that i've heard food value goes down from tests they've done with GM food, and cloning. So how do we keep that?
Before this ever happens though, i'd say water shortages will happen first. Possibly in our lifetime.