The Locavore's Dilemma

    Urban farms do more harm than good to the
    environment

By Edward L. Glaeser
Boston Globe
June 16, 2011

http://articles.boston.com/2011-06-16/bostonglobe/29666344_1_greenhouse-gas-carbon-emissions-local-food

All that is grassy is not green. There are many good
reasons to like local food, but any large-scale
metropolitan farming will do more harm than good to the
environment. Devoting scarce metropolitan land to
agriculture means lower density levels, longer drives,
and carbon emission increases which easily offset the
modest greenhouse gas reductions associated with
shipping less food.

Last year, I chaired the Citizen's Committee for the
Future of Boston, and our report endorsed urban
vegetable gardens. Super-chef and committee member
Barbara Lynch emphasized the educational value of
letting children see food grow and I agreed with her. I
share the locavore view that local food tastes better
(especially oysters), and that there is something
wonderful about eating something you've grown yourself.

But while neighborhoods benefit from the occasional
communal garden, it is a mistake to think that
metropolitan areas could or should try to significantly
satisfy their own food needs. Good environmentalism is
smart environmentalism that thinks through the total
systemic impacts of any change. Farm land within a
metropolitan area decreases density levels and pushes
us apart, and carbon emissions rise dramatically as
density falls.

In 2008, two Carnegie Mellon researchers analyzed the
reduction in carbon emissions that might come from
moving to local food. They found that American food
consumption produces greenhouse gas equivalent to 8.9
tons of carbon dioxide per household per year. Food
delivery represents .4 tons of that total; all
agricultural transportation up and down the food chain
creates one ton of carbon dioxide per household
annually.

We must weigh the environmental benefits from shipping
less food against the environmental costs of producing
and storing local food in a state that doesn't exactly
have ideal conditions for every kind of produce. One
recent UK report found that the greenhouse gas
emissions involved in eating English tomatoes were
about three times as high as eating Spanish tomatoes.
The extra energy and fertilizer involved in producing
tomatoes in chilly England overwhelmed the benefits of
less shipping. Even New Zealand lamb produced less
greenhouse gases than English lamb. Berkeley graduate
student Steven Sexton estimates that an American switch
to more local corn production would require 35 percent
more fertilizer and 22.8 percent more energy.

But the most important environmental cost of
metropolitan agriculture is that lower density levels
mean more driving. Today, about 250 million Americans
live on the 60 million acres of this country that are
urban - which is about four people per acre. By
contrast, America uses 442 million acres for cropland
and 587 million acres for pastureland, which is about
1.4 and 1.9 acres per person respectively. If we
allocated just 7.2 percent of this agricultural land
into metropolitan area, we would halve metropolitan
area densities.

The National Highway Travel Survey teaches us that when
densities drops in half, holding fixed location within
the metropolitan area, households buy about 107 gallons
more gas per year. If halving densities also doubled
distance to the metropolitan area center, this would
add an extra 44 gallons of gas annually. Together, the
increased gas consumption from moving less than a tenth
of agricultural farmland into metropolitan areas would
generate an extra 1.77 tons of carbon dioxide per year,
which is 1.77 times the greenhouse gases produced by
all food transportation and almost four and a half
times the carbon emissions associated with food
delivery.

It is implausible to imagine anything like an extra .24
acres of farm land per person in metropolitan America,
but smaller land changes will also have commensurately
smaller reductions in the greenhouse gas emissions from
shipping food. If just a twentieth of an acre of
metropolitan farm land per person could (implausibly)
eliminate half of food delivery emissions, this would
typically be associated with 41 more gallons of gas per
household. Those driving-related greenhouse gas
increases would be 2.4 times higher than the emissions
savings from reduced food transport.

The connection between higher density living and less
energy use is strong. Urban farms mean less people per
acre which in turn means longer drives and more
gasoline consumption. Shipping food is just far less
energy intensive than moving people. If the First Lady
wants to help the environment, she should campaign for
high rise apartments, rather than plant vegetables.
__________________

Edward L. Glaeser, a professor of economics at Harvard
University, is director of the Rappaport Institute for
Greater Boston.

___________________________________________

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