Perhaps spawned by the immense popularity of Michael Pollan's book The Omnivore's Dilemma or just the recent explosion of interest in both food safety and climate change, people are demanding locally grown. Such "locavores" are participating in the 100 Mile Diet and are making the local farmers' market the place to be. In March 2005 the BBC published an article entitled "Local food 'greener than organic'" in which they quoted a report in the journal Food Policy that states "Food miles are more significant than we previously thought, and much now needs to be done to encourage local production and consumption of food." Foodmiles is a term coined by Tim Lang, professor of food policy at London's City University, that refers to the distance that a given amount of food travels from farm to plate.

In a recent (April 27th) Financial Times article Sarah Murray wrote "the 'question of transportation' has become caught up in worries about the quantities of carbon dioxide being generated by an increasingly mobile food supply. The further our food travels, so the theory goes, the more damage it does to the climate through transport-related carbon dioxide emissions. In short, globetrotting food stands accused of helping destroy the planet." But is all of this worry about foodmiles justified? Some think not, so I will explore the topic a bit further. Ms. Murray goes on to write "In a study published last year, New Zealand's Lincoln University measured everything from electric fences to farm sheds, tractors and animal feed, and found that dairy and lamb production in New Zealand was more energy efficient than the British equivalent, even when the 12,000-mile trip to the UK was included."

The macroeconomic concepts that drive globalization state that production of goods should occur in the country or region best suited to maximize the economic efficiency. This is why most bananas come from Central America and not a greenhouse in Central Park and why Silicon Valley is the home of high-tech rather than the Gobi Desert. But do these economic concepts take into account the impact of transportation? Probably not. The impact of transportation, primarily the climate change effects of the resulting greenhouses and security issues surrounding petroleum fuel, is typically externalized to society. That is, society pays for the poor environmental decision-making of the market.

According to a 2005 report by DERFA "The rise in food miles has led to increases in the environmental, social and economic burdens associated with transport. These include carbon dioxide emissions, air pollution, congestion, accidents and noise." Additionally they presented several findings:

1. A single indicator based on total food kilometers is an inadequate
   indicator of sustainability.
   
2. Data is available to provide and update a meaningful set of indicators on
   an annual basis.
   
3. Food transport has significant and growing impacts.
   
   • Food transport accounts for 25% of all HGV vehicle kilometres in the UK.
     
   • Transport of food by air has the highest CO2 emissions per tonne, and
     is the fastest growing mode.
   
   

But my readers demand numbers, so let's look at an example. I am very confident about some calculations that I made on the production of Cherries. I used a cost study from UC Davis to determine the energy input versus the yield. I arrived at roughly 4.85 kg of CO2e (carbon dioxide equivalent units) for each kg of cherries. If we assume 500 km of transportation by semi we add 0.06 kg CO2e, or about 1.2%. If the same cherries are grown in Argentina and flown to the US (21,000 km) the emissions jump to 16.82 kg CO2e per kg of cherries, or 71.1%. Quite a difference! It is possible that the cherries would be shipped by container ship in a refrigerated compartment but then we would have to account for the refrigeration as well.

What if the cherries are dehydrated first and the transported by ship? Removing moisture from agricultural products is one way to cut back on transportation costs and emissions. Dried cherries have about 15% moisture content (vs. 75% in fresh cherries) so the CO2e from cultivation per kg of dried cherries will be higher, around 12.14 kg CO2e per kg of dried cherries. Trucking over 500 km would again add 0.06 kg CO2e, or 0.5%, but shipping by container ship over 25,000 km (more than air cargo because you can't ship point-to-point) contributes only 0.42 kg, or 3.3%.

So, the impact of foodmiles depends on several factors:

• The distance transported.
  
• The transport mode.
  
• The concentration of the agricultural product (dehydrated or concentrated is better).
  
• The relative agricultural productivity and the amount of fertilizer required in each location.

To get an idea of the relative impact of different transit modes here are several emissions factors that I use:

• Air Cargo - 570 g CO2e / tkm
  
• Truck - 102 g CO2e / tkm
  
• Train - 56 g CO2e / tkm
  
• Container Ship - 17 g CO2e / tkm

Emissions factors vary widely from source to source. My emissions factors include the emissions between the resource extraction and the fuel tank (including transportation and refining), they also include all greenhouse gases, not just CO2. But until there is an internationally recognized standard for greenhouse gas accounting all you can do is just state the assumptions as clearly as possible.

For more information on how to calculate food miles, see the Leopold Center for Sustainable Agriculture (Iowa State University) paper entitled Calculating Food Miles for a Multiple Ingredient Food Product.

Special thanks to Andre for giving me the idea for this week's column topic and for sending me some of the articles quoted.

Pablo Päster, MBA
Sustainability Engineer

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