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Steve Sexton's article on "The Inefficiencies of Local Food" offers a good opportunity to clarify precisely what we in the food movement mean by "local" food. I think we mean much more than food produced around the corner. I think we mean human food grown in sustainable or organic systems, rather than commodities grown in chemically dependent systems. Sexton's overall framing is that global human population is growing, and agriculture must increase production to avoid mass starvation. His secondary framing is that global climate change is a very real threat, and that agricultural emissions are a significant part of that problem. I think most Greenhorns would agree with those characterizations. However, Greenhorns in particular, and the food movement in general, would frame solutions to those problems very differently.
Lets start with greenhouse gas emissions. Mr. Sexton is exactly correct that greenhouse gas emissions from transport are a relatively minor part of our food system's total greenhouse gas emissions. The major emission from today's agriculture is nitrous oxide which is produced when nitrogen fertilizer volatilizes into the atmosphere. Preliminary evidence suggests that replacing synthetic fertilizer with nitrogen derived from organic sources like cover crops, compost or manure reduces those emissions. (http://www.sciencedirect.com/science/article/pii/S0167880905003749). I think those are the sorts of farming practices Greenhorns and the food movement generally are interested in. The second major source of agricultural greenhouse gases is methane from manure lagoons. As a pastoralist movement, Greenhorns and the food movement should generally reduce those emissions as well. Finally, by increasing the period of the year during which plants are removing carbon dioxide from the atmosphere by planting cover crops, and by building soil's ability to hold carbon with organic amendments and elimination of toxic chemicals, Greenhorns and sustainable farmers are increasing the amount of carbon dioxide removed from the atmosphere by agriculture. So when it comes to greenhouse gas balance, sustainable farming is what really matters, not food miles-- and in that regard, many Greenhorns and Food Movement activists have the right idea. I would add that in thinking about adaptation to climate change, farming systems rich in soil organic matter and diversity, like organic farming systems, would be better able to handle fluctuating water cycles and temperatures. Here is just one example: http://motherjones.com/tom-philpott/2011/08/mexico-monsanto-climate-change
Mr. Sexton's analysis is perhaps more compelling when he turns to assessing how much additional resources would be required to produce food "locally". He states that fuel and chemical use would increase by about 20-30%. From what I can tell of this method, this is based on the idea that corn and soybeans have lower yields in some regions and thus would require more inputs to produce in those regions. The basis of his analysis is "assume that a local food system must maintain existing levels of per capita production for each crop." Considering that existing levels of per capita production for each crop are causing a massive obesity epidemic that is the second largest healthcare cost to the United States (after smoking), ( http://www.usatoday.com/news/health/weightloss/2009-11-17-future-obesity-costs_N.htm) and 15% of households to be food insecure (http://www.ers.usda.gov/Briefing/FoodSecurity/) this very assumption is a death sentence.. Rather than grow commodity corn and soybeans destined for high fructose corn syrup in soda pop and feedlot cattle, Greenhorns and Food Movement farmers grow foods like fruits and vegetables. They do so using sustainable and organic farming methods that can yield just as much as conventional methods, without chemical inputs (http://www.grist.org/article/2011-03-25-rodale-data-show-organic-just-as-productive-better-at-building). If Sexton's primary assumption is challenged, the remainder of his analysis does not hold.
Returning to Mr. Sexton's original challenge of feeding a growing population in a changing climate, I could not agree more with the urgency of the task. Local food is not inherently sustainable or organic just because it is produced around the corner. But the Greenhorns and the Food Movement stand for much more than food produced in physical proximity to consumers. They stand for a personal relationship of consumer with farmer. And they believe deeply in the power of that relationship to incentivize sustainable farming practices that use few or no chemicals, build the health of soil and reduce greenhouse gases. They also believe that a "local" farmer will grow healthy, edible food, rather than commodities that require processing before they can be included in coca-cola. They finally believe that the social and ethical implications of building these relationships has a moral and lasting value. I understand that it is difficult to challenge our basic assumptions and envision a healthy food system. It will require moving to the future rather than the past, and imagining some very new relationships between farmers, food and eating. But if we are to feed a growing planet, it is increasingly necessary.