A 2005 study by the United Kingdom Department for Environment, Food and Rural Affairs
(DEFRA) remains to this day the most comprehensive discussion of the food-miles controversy.
Among other findings, its authors showed that 82% of the transportation-induced greenhouse
gas emissions are generated within the country, with car transport from shop to home
accounting for 48% and heavy goods vehicles (trucks) for 31% while air and sea transport
each amounted to less than 1%.
This latter result can be explained by the fact that a container boat floats and
uses highly efficient diesel engines. Shipping food items halfway around the world
this way often requires less energy per unit transported than using a truck for a
few hundred kilometers.
Even more interesting, long-distance transportation is, overall, an insignificant
cause of greenhouse gas emissions when compared to the most energy-intensive segments
of the agricultural production chain (fertilizers, pesticides, irrigation, energy
required to power machinery, etc.).
In the United States, a study even suggests that 4% of food-related greenhouse gas
emissions were attributable to the long-distance transportation segment as a whole,
while 83% came from the production stage.
The importance of seasonality in terms of energy input and CO2 emissions is also
too often forgotten by activists. And yet, because the southern hemisphere’s growing
season coincides with the northern hemisphere’s winter, shipping freshly picked from
New Zealand or Argentina to U.K. consumers during their winter season entails less
greenhouse gas emissions than the purchase by U.K. consumers of local apples that
have been put in cold storage for several months (and, of course, the southern hemisphere
apples will taste much better).
As a rule, physical environments that require significant heating and/or cold protection
facilities and technologies entail much greater energy consumption than more favorable
climates, typically on a scale that dwarfs the energy requirements associated with
the transportation of agricultural products from more remote locations.