David has written about the food-price and conflict linkage before, and we've discussed the association between climate and conflict a few times here. In general, I don't think a linkage has been demonstrated conclusively with data, but that doesn't seem to get in the way of people referencing it.
The debate is interesting and entertaining, highlighting a few of the differences in how some policy-folk, economists and ecologists view theses various ideas.
Kyle was asked to participate because he was an author of our 2011 Nature paper on ENSO and conflict. He also happens to be on the job market right now.