I second your response to an extent. I feel unfomfortable when people talk about population reduction though.
My two cents on this issue is that speed up the migration to cities and increase our conservation of the open expanses. I think the only way to survive is in ubercities with a definite attempt to take care of the environment beyond those cities and the freedom and encouragement for people to go out and roam but leave no trace. In other words to start acting like true stewards. There are numerous advancements in greenhouse technology, ways for cities to grow the types of vegetables they need in limited spaces and shunning grains and other dangers.
The most complex problem to solve will be the animal source of food. I don't claim to have answers, but I know for certain, and I'm not the only one who thinks this, but compact ubercities are the way for us to reduce our carbon footprint. megacities like New York and Tokyo have a smaller carbon footprint than smaller cities like my Houston and San Antonio. The problem is sprawl not population.
But there has to be a way to feed everyone the meat they need without stripping the land bare. The technology exists for the vegetable issue if we can just take it out of the hands of big aggri.
Sorry I went on a meaningless tangent.