Those are, in a way, encouraging statistics. It shows that at least there is some land where some stuff can be grown... but it's just under the suburban backyard.
Now my thing is that if peak oil hits TOO quickly and agriculture does not have time to relocalize around New Urbanism and local city markets, then we could be in serious trouble... even here down in Australia. We have also followed your suburban pattern.
But if we simply rezone suburban homes into New Urbanism, and don't replace a suburban home when it "dies of old age" but instead sell it and move the family into a New Urban home somewhere else, bulldoze the house, and return it to local land... America and Australia could undo a lot of the Suburban mistake in about 50 years.
Check this out.
"A normal city is changing all the time - buildings grow old and are replaced. Just look at a picture of your city fifty or a hundred years ago. If the average building life is 60 years, then the city changes at the rate of 1.6% per year.
I took as the basis for this scenario the average size of an average Swedish municipality - 36,000 inhabitants. I assumed that instead of building the houses on that same plot as the one demolished you build eco units on the periphery of the city, along the roads preferably. Then you start to ruralise at the same pace as the normal replacement rate. After 50 years, only ten percent of the city is left."
Folke Günther
Also not that after 10 years, that's 16% of domestic suburban oil dependency permanently removed from the marketplace. A walk, pushbike or local tram should do the job in a well designed New Urban district. Beautiful places to live, quiet, friendly, the smell of your favourite coffee shop as you walk to work instead of getting stressed driving in peak hour.
And, getting back to the subject, then it's not just a tiny little pocket of backyard land, but a more efficient farmers block nearer a New Urban outpost. More on New Urbanism here.
http://eclipsenow.blogspot.com/2007/06/relocalize.html