The Environmental Impact of Food

Goal: Understand where different foods are grown and the energy and environmental costs of getting them from farm to table.
Objectives: Students will…

  • Hypothesize where foods in school menu were grown
  • Analyze USDA crop maps to determine where different foods are grown
  • Calculate energy used to transport food
  • Calculate CO2 emissions from transportation of food
  • Interpret pie chart to look at other uses of energy in commercial food system

Materials: access to internet to show students USDA maps
Advance Preparation: if you cannot project images from the internet on your classroom computer, make arrangements that will allow students to see food production maps, pull food miles table and pie chart into format you can share with students
Time Estimate: 1 class
15 min Food origin guess and comparison with USDA maps
15 min Calculate miles traveled, fuel consumed and GHG released from transportation
15 min Share and discuss big picture of food energy use

The Environmental Impact of Food

Instructional Plan
Guess Where that Food was Grown
Most likely the food being served in your cafeteria comes from far away and has already been processed before it arrives in the kitchen.
Ask students to guess where the fruits and vegetables in the cafeteria menu you analyzed came from. Make a list on the board with the ingredient and its potential source.  Compare their guesses against the crop data shown on the maps at: http://www.agcensus.usda.gov/Publications/2007/Online_Highlights/Ag_Atlas_Maps/Crops_and_Plants/index.asp
If you have the capacity to interact with this map during class, that would be ideal, otherwise, you may want to prepare in advance by capturing the relevant images so you can show them to students during class.
Calculate Food Miles
Using the ingredients from the menu breakdown, ask students to estimate the number of miles the fruits and vegetables in their lunch traveled. They can either use the conventional source estimation column in the table below, or calculate miles between map locations (above) and the school campus.
table_image
Source: Checking the food odometer: Comparing food miles for local versus conventional produce sales to Iowa institutions: http://www.leopold.iastate.edu/pubs/staff/files/food_travel072103.pdf
Calculate Energy Use and Emissions from Food Miles
How much energy is used by the transportation of the produce on your menu coming from a conventional source? From a local source?Use the formula below, based on 6 mpg fuel efficiency for a diesel tractor trailer (train transport is more efficient).

Calculate the greenhouse gas emissions released during the miles traveled for conventional and locally sourced foods.

In addition to carbon dioxide, which contributes to the greenhouse effect, diesel trucks also emit large quantities of nitrogen oxides, particulate matter and hydrocarbons, which have negative impacts on human and environmental health.

Although transporting food is the most obvious use of energy in the conventional food system, it only represents 14% of energy used to produce and deliver food to American tables. The pie chart below shows the number of calories expended (by purpose) to get one calorie of food onto a plate in the US. Remember a calorie is the energy needed to increase the temperature of 1 gram of water by 1 °C, which is equivalent to

The energy represented in these figures could take a variety of forms, so it is difficult to calculate gallons of fuel or tons of pollution resulting from it, but it can be eye opening to show to your students so they think through all of the other energy inputs into their food. Ask them to try to define how energy is being used in each of these sectors and what type of energy it might be. Here are some suggestions:

  • Farming: food energy for farmers, gas and diesel for farm equipment, petroleum products used to make synthetic pesticides and fertilizers
  • Processing: powering buildings and operating machinery to cut, cook and/or freeze food
  • Packaging: powering buildings and operating machinery to package foods, petroleum products used to make plastics
  • Food retail: electricity to power store lights and refrigerators
  • Commercial food service/Household storage and preparation: electricity to power fridge, microwave, stove, gas for stove or oven

Buying food locally, especially directly from the farmer who produces it, significantly reduces the energy used to get that item from farm to table. Buying from farmers who are using natural strategies to enrich soil and deter pests further decreases the amount of energy that goes into the production of food.
Do any students in the class know farmers or grow any of their own food at home?