Global warming is one of the root causes of the rise in food costs. Global climate change has brought an increase in natural disasters, which can affect crops and in turn, food prices. The turmoil of long winters in some places, and drought in others, has changed the food landscape, and we are slow to adapt.
Global warming is every ones scapegoat for any problem that they cannot explain. The amount of people increasing on the planet every year paired with lack of jobs and resources are the reason. We need new ways and technology to grow food safely for the mass populations or eradicate some people.
Global warming may or may not have some influence on the cost of food, but it would not be a huge cause. Food cost rising is because of two things; inflation and people wanting more money. Large corporations simply want more money. There is no food shortage in the world, it's whether or not someone wants to transport the food or not.
I think that temperature and weather conditions have made some food more expensive, but I don't think we can fully attribute this to global warming. There was all those citrus bugs down south that destroyed thousands of plants and then raised the price of fruit and other food price increases that had nothing to do with the weather.