Middle School Students (6 -8th Grade)
After completing this unit, students will be able to:
- Understand the basic principles of greenhouse gases and activities that increase GHG emissions
- Make a real world connection between global climate change and the students’ own lives, more specifically, to understand how their food decisions impact their carbon footprint
- Process information and find an answer to a question that isn’t given directly in the text
- Understand the benefits of buying (more) food from local producers
Nowadays, it is not only tropical foodstuffs such as sugar, coffee, chocolate, tea, and bananas that are shipped long distances to come to our tables, but also fruits and vegetables that once grew locally, in household gardens and on small farms. An apple imported to California from New Zealand is often less expensive than an apple from the historic apple-growing county of Sebastopol, just an hour away from San Francisco. It is estimated that the average American meal travels between 1,500 and 2,500 miles to get from farm to plate.[i] Why is this cause for concern? There are many reasons. This long-distance, large-scale transportation of food consumes large quantities of fossil fuels and generates great quantities of carbon dioxide emissions. In order to transport food long distances, much of it is picked while still unripe and then gassed (fruit is sprayed with ethylene gas which ripens the fruit without it being attached to the plant) to "ripen" it after transport, or it is highly processed in factories using preservatives, irradiation, and other means to keep it stable for transport and sale. The inefficiencies of food travel are continually adding carbon dioxide to our atmosphere, increasing greenhouse gas concentrations and thereby exacerbating global climate change.
Key Concepts and Vocabulary
Food Mile: Term that defines the distance that food has to travel to get from the production location to the consumer location. Food miles are used to assess environmental impacts of various foods.
Carbon dioxide emissions: Carbon dioxide (CO2) is emitted into the atmosphere two different ways, naturally through the carbon cycle or by the combustion of fossil fuels.
Carbon footprint: A carbon footprint is a measure of the impact our activities have on the environment, and more specifically on climate change. A carbon footprint summarizes the amount of greenhouse gases produced in our daily lives through our consumption of various forms of energy.
Emission factor: The average emission rate of a given pollutant from a given source or activity, for example grams of carbon dioxide released per megajoule of energy produced. Emission factors for many different types of pollutants are reported by federal agencies and the Intergovernmental Panel on Climate Change (IPCC). Some examples of the activities for which emission factors are available include fuel combustion, animal husbandry, industrial production, and travel.
Fuel economy is a measure of the efficiency of automobile travel in terms of miles driven per gallon (MPG) of gasoline consumed. The U.S. tracks the total average fuel economy of vehicles operated and sold in the U.S. The current average fuel mileage of the American vehicle is 21.4 mpg.[ii] Standards are set to define the corporate average fuel economy (CAFE), which is an average of all of the vehicles sold by an individual manufacturer. The 2011 CAFÉ standards for passenger cars is 27.5 MPG.
- Food is grown all over the world as well as in our own backyards, yet Americans import many of the same goods that we export. Keeping more foods local and consuming the food produced here on American soil will reduce food miles, thereby benefiting our environment and economy.
- Understanding and calculating a carbon footprint requires an understanding of human activities and how given activities are better or worse than others in terms of their impact on climate change.
- A GHG inventory for the journey of goods between the field and your table requires knowledge of the miles traveled between the field, any processing plants, and your home. Other key information includes the method of transportation (train, plane, cargo ship or your local farmer’s tractor), its respective fuel economy, and emission factors for greenhouse gases.
- There are fewer GHG emissions associated with the consumption of local food and local products than with imported goods. If the opportunity to use local or domestic products is available, the long run benefits will out weight those of using imported goods.
On average, food travels between 1,500 to 2,500 miles every time it travels to a consumer. However, in 2007 products travelled an average of 25% further than they did in 1980,i resulting in a substantial increase in the amount of energy consumed by the transportation of food that we could alternatively find in our backyards. It is estimated that the food industry accounts for 10% of all fossil fuel used in the United States.i Of all of the energy used by the food system, only 20% is used in the production of food products, with the remaining 80% used for transportation, processing, home refrigeration and preparation.i It was shown that the average American uses between 170 and 680 million BTUs annually of energy for personal transportation and 400 million BTUs annually in food consumptionii. This is a significant use of energy.ii According to one study, food transportation amounts for 14% of energy use within the food system. The energy consumption of various aspects of food production is illustrated in Figure 1.
While food miles are a relatively small fraction of the total U.S. energy consumption, as a whole they are a large source of carbon dioxide emissions. The Leopold center for Sustainable Agriculture is the leading research center studying food miles in the United States. In 1998 they conducted a study where they examined the distance that fresh produce traveled to get to the Chicago terminal market. The results of the 1998 study are shown in Figure 2.
There are several different methods to calculate food miles. The method most appropriate for foods that contain many different raw ingredients the weighted total source distance (WTSD) and was developed by the Leopold Center for Sustainable Agriculture[iii] it includes the weight and distance for each ingredient. The weighted average emissions ratio (WEAR), developed by the non-profit organization LifeCycles in 2004,i takes into account the distance traveled as well as the emissions related to the distance and method of transportation. The mode of transportation is an important factor in determining emissions associated with food miles; some food items may travel shorter distances, but depending on their mode of transportation they may produce more net emissions that a food item that traveled longer distances using a more efficient transportation method. Table 1 provides emission factors for various forms of freight transport.
Table 1: Emission factors for given forms of freight transporti
Primary Energy Consumed (kJ/ton/mile)
Carbon dioxide emissions (g/ton/mile)
(“ton” = metric ton = 1000 kg
PBS Podcast on food miles http://www.pbs.org/e2/podcasts.html
PBS excerpt out of their video on food miles http://www.pbs.org/e2/teachers/teacher_309.html
Before the activity can begin the students must have an introduction to greenhouse gas inventories, including emission factors (g CO2 emissions/ton/mile), and the other factors related to climate change. They should also understand the connections between these factors and the driving forces of climate change. In the case of this activity, students should be introduced to the impact that transportation of food products, or food miles, has on global climate change.
Students will need computer access. Students may work alone or in groups, depending on the availability of computers. They should have access to MS PowerPoint, MS Excel, Google Earth and the Internet. Through the Internet and MS PowerPoint students will have access to information resources about each cookie ingredient as well as other ingredients not included in the PowerPoint. Google Earth will allow students to find the miles between the students and the locations where their food is grown or produced.
Following the instructions in the student worksheet, students will choose a cookie recipe, calculate the number of food miles associated with their cookie, and compare their results to a cookie made with ingredients that are grown or produced locally.
Anticipatory Set Have students read, or read aloud to the class, the children’s book All in Just One Cookie by Susan E. Goodman, a story about what goes into each ingredient in a chocolate chip cookie. Then project or guide students to the YouTube video titled “Watch your (Fo)Odometer,” that describes how far food travels and the amount of energy consumed by the process of getting food to our plates. Use the video as an introduction to food miles and the concept that the transportation of food is adding to greenhouse gas emissions and the problem of global climate change.
Procedure Students will choose a favorite cookie recipe. Using the given resources in the MS PowerPoint presentation on where ingredients come from, as well as the student worksheet, students will be able to calculate the amount of food miles and carbon dioxide emissions associated with the cookie they choose. There is a short example for students to follow.
Closure The activity should finish with a comparison of the different types of cookies and their calculated food miles. After the activity and discussion, the following conclusions should be apparent:
- Local foods have significantly less food miles than imported goods.
- You can make choices to reduce your food miles and reduce the amount of emissions caused by your food choices.
- Students will be able to relate how their food choices will impact the global greenhouse gas inventory.
This activity is designed to be an environmental sciences unit. However there are several optional additional lessons that can be worked into the unit. Teachers may incorporate a social studies unit into the activity by having the students study the countries where their cookie ingredients come from. In addition there is the option for a health and nutrition unit, where students can learn how to read nutritional labels and how to apply that knowledge to making healthy (and local) food choices.
The following New York State, Mathematics, Science and Technology (MST) Standards are supported by this unit: (http://www.p12.nysed.gov/ciai/standards.html)
STANDARD 1: Students will use mathematical analysis, scientific inquiry, and engineering design, as appropriate, to pose questions, seek answers, and develop solutions.
- The observations made while testing proposed explanations, when analyzed using conventional and invented methods, provide new insights into phenomena,
STANDARD 2: Students will access, generate, process, and transfer information, using appropriate technologies.
- Information technology is used to retrieve, process and communicate information and as a tool to enhance learning.
STANDARD 4: Students will understand and apply scientific concepts, principles, and theories pertaining to the physical setting and living environment and recognize the historical development of ideas in science.
- Human decisions and activities have had a profound impact on the physical and living environments.
STANDARD 7: Students will apply the knowledge and thinking skills of mathematics, science, and technology to address real-life problems and make informed decisions.
- The knowledge and skills of mathematics, science, and technology are used together to make informed decisions and solve problems, especially those relating to issues of science/technology/society, consumer decision making, design, and phenomena.
A completed student worksheet will be handed in for grading. Additional discussion questions may be handed in by students individually or presented as a group discussion with the class.
Cookie Ingredients interactive information resource Cookie Ingredients.ppt
Index cards with the listed ingredients required to make six different types of cookies Cookie Recipe Cards.doc
Using Google Earth Tutorial Google Earth_Tutorial.pdf
Student Worksheet Student Worksheet.docx
Carbon dioxide emission calculation worksheet Calculating CO2 worksheet.xls
[ii] "Project America." Transportation: Cars: Average Miles per Gallon.” 2008. Accessed 2 Aug 2011, http://www.project.org/info.php?recordID=384
[iii] Leopold Center for Sustainable Agriculture, Information on Food Miles http://www.leopold.iastate.edu/searchresults.html?cof=FORID%3A9&ie=UTF-8&q=food+miles&sa=Search&cx=015090543261715722465%3Abajpth5ze5u&siteurl=www.leopold.iastate.edu%2Fsearch_main.htm