It's like almost any finite resource.  Oil, trees, minerals...we've overconsumed, and now need the rest of the world not to catch up to our levels while we do a very poor job/no job at all of cutting back.

One thing about which I've never been sure, though, is the practicality/viability of organic/non-intensive agriculture without animals as part of the mix?  In crop rotation, haven't the nitrogen-fixers traditionally been used as animal food?