My opinion is that feeding 9 billion people is possible, but only with industrial agriculture. I could try to argument this, but I am very bad at writing (long) articles and there are already some that have done much better than I could possibly manage. A start could be this very good article by Stuart Staniford at The Oil Drum.
   Regarding the local vs globalised agriculture I think there is no argument here. The food supply needs to be global, otherwise a period of bad weather in a local area could mean famine. Now this does not mean that we need automatically more free market, since that would imply more volatility than there is already, which is by definition bad for the security of supply.