You can't argue with the facts. Observe the UN FAO Food Price Index:
Now, it turns out that wheat held steady and rice declines slightly, so the increase is due mainly to maize (corn). The biggest exporter of maize is the US, and this past year, 40% of the US maize crop went to ethanol rather than into food. That's 40%. So, yes, food crops have decreased due to global warming; viz., the hysteria over it has diverted food away from the mouths of the poor into the gas tanks of the well-to-do in order that they may feel really good about their moral superiority.
Sorry for the intemperate remarks, but I'm one of those "feed the hungry" nuts.