A recent trend lauds the supposedly obvious benefits of locally produced diets and of urban agriculture in particular. These benefits, they say, offer antidotes to pollution, poverty, and illness, and many
To evaluate these proposals, it is helpful to compare the claims with facts. A central idea of urban agriculturists is that the transportation of non-local food creates pollution. In fact, transportation constitutes a minute percentage of the agricultural sector's greenhouse gas emissions, and the production inefficiencies inherent in farming on small plots could easily erase gains made in transportation. Large rural farms transport production workers and equipment much more efficiently. Moreover, mode of transportation affects the carbon footprint of a meal. The shipment of food over long distances by train or tractor-trailer often consumes less fuel than does transportation more locally using smaller vehicles.
For urban planners, land use is potentially the most contentious aspect of urban agriculture. Sunlit spaces, especially in the largest and most densely populated cities, often come at a premium. Given the limits on yields and profit margins for food agriculture, costs and benefits must be weighed against those of other businesses in terms of job creation, aesthetic value (since agriculture is a messy business), and scalability (local food's high price limits the market and raises the possibility of saturation).
It is obvious that there is not enough data on urban agriculture to justify implementation of agriculture-promoting policies within the limits of the largest cities. Many faddish environmental projects in the last two centuries have failed to live up to their promises and subsequently waned, and so might the urban agriculture movement. Meanwhile, the many urban farms currently in operation will have the chance to defy such cynicism, and city governments would do well to allocate resources to those that do.