Local foods good for the environment?

A couple months ago the journal Frontiers in Ecology and the Environment published a paper by Andrew Zumkehr and Elliott Campbell.  The paper was widely reported in the press.  For example the Washington Post the headline: As much as 90 percent of Americans could eat food grown within 100 miles of their home.  Another outlet: Most Americans could eat locally.  

I promptly wrote a blog post asking: even if Americans could eat locally, should they?  Shortly thereafter, I exchanged several emails with Pierre Desrochers, the author of the excellent book The Locavore's Dilemma: In Praise of the 10,000-mile Diet.  We decided a more formal reply was warranted.  

I'm pleased to report that a couple days ago Frontiers in Ecology and the Environment published a letter by Pierre and me.

We write:

In a recent paper, Andrew Zumkehr and Elliott Campbell (2015; Front Ecol Environ 13[5]: 244–248) present a simulation study that assesses the technological feasibility of providing enough local calories to feed every American. In so doing, they suggest turning back the clock on one of Homo sapiens sapiens’ greatest evolutionary achievements: the ability to trade physical goods over increasingly longer distances, producing an attending ever-widening division of labor (Horan et al. 2005). The main benefit of this process is that one hundred people who specialize and engage in trade end up producing and consuming far more than one hundred times what any one individual would achieve on his or her own. By spontaneously relocating food production to regions with higher biotic potential for specific types of crops and livestock in order to optimize the overall use of resources, trade and the division of labor have delivered more output at lower costs.

Zumkehr and Campbell largely sidestep these benefits. They cite a few studies suggesting that (re)localized food systems would deliver environmental, economic, food security, and social benefits, but neglect to mention critiques of those claims

We offer these specific critiques of their model:

We also take issue with the authors’ use of yield data from each county to infer the agricultural potential of each location. This approach suffers from selectivity bias; the effect of increasing local food production onto more marginal local lands will likely deliver less-productive results than current average yields. In a competitive market economy, observed crop yields near urban locations are likely to represent an upper bound for the overall level of productivity in the area because only lands productive enough to outcompete other uses are currently devoted to agricultural production. The authors are also silent on the environmental consequences of removing wildlife from current idle lands to make room for domesticated plants and animals.

Moreover, the authors exclude cost considerations and conclude that the “current foodshed potential of most US cities is not limited by current agronomic capacity or demographics to any great extent”, but rather by “social and economic” considerations. However, an economic barrier is just as real and restrictive as an agronomic one. Resource and budget constraints simply will not allow all wants and desires to be realized. It is all very well telling people with limited means to eat local cake, but they should also be told of its price tag.