Do farmers’ markets help to reduce greenhouse gas emissions?

Many articles claim that farmer’s markets help the environment because of the fewer food miles travelled from farm to fork. Is this true? A recent Newscientist article, which discusses how your dietary choices affect your carbon footprint, says that buying local food maybe less important than other factors:

"Household greenhouse gas emissions from food account for almost twice those produced by driving. Most of this comes from the food production process itself, rather than food-miles, as is often believed." Trivedi 2008

Trivedi goes on to state that 83% of emissions come from food production, whereas only 11% comes from transporting the food from farm to fork. A food's emission total is calculated by including the following:

"the tilling of the land, sowing the crops, making fertilisers and pesticides, harvesting the food and shipping it to processing plants, as well as electricity for cleaning, processing and packing your food, and finally transporting it to your store. Finally, the loss of carbon sinks when forests are cleared for grazing or crops has to be accounted for."