The world is abuzz with talk of climate change, greenhouse gas emissions, agricultural sustainability, and carbon footprints. At the same time, there is concern about long-term petroleum reserves. Our food system is an important user of fossil fuels and producer of greenhouse gases. Buyers are asking their food suppliers for their carbon footprint along with information about how sustainable their farming practices are. New legislation has been proposed, and in California a new law (AB32) requires a 20% reduction in greenhouse gas emissions across all sectors by 2020 and 80% by 2050.
Recent studies indicate that our food system consumes close to 16% of the total energy use in the U.S., yet only 2% of the total energy is used to grow the food we eat. Since fossil fuels are the predominant energy source, this results in significant greenhouse gas emissions and a large carbon footprint for the food industry. However, the carbon footprint is not the same for all types of food. It varies depending on how they are produced, processed, packaged, and transported.
For example, organic production uses less energy in the form of nitrogen fertilizer than conventional production, but hauling organic chicken manure more than 20 miles can eliminate the advantage. Tomato sauce requires energy to process but it weighs less and requires less energy to ship than the equivalent amount of tomatoes required to make the same amount of spaghetti sauce.
A detailed and systematic analysis of the differences in energy use and greenhouse gas emissions of individual foods is required to allow producers, buyers, and consumers to make informed choices. A life cycle analysis approach is needed to develop a complete understanding of the greenhouse gas emissions of various foods.
Is it more or less sustainable to ship freshly harvested produce items across the globe rather than producing them locally and storing for off-season supply? This depends on the produce item and how it is handled after harvest, and the answer is not always obvious. Products shipped by sea may have a much smaller carbon footprint on a per pound-mile basis than products transported by truck or passenger car in much shorter distances. To enjoy apples produced locally for nearly 12 months of the year, the apples must be kept in refrigerated storage in an atmosphere of low oxygen and elevated carbon dioxide. Marketing these fruit throughout the U.S. involves truck transit to markets that may be thousands of miles away.
Is it more sustainable to buy only produce items produced within 100 miles of home? The distance you must travel by car to purchase these products is critical in the analysis because of the small amount of product transported by automobiles. Compare a refrigerated truck hauling 40,000 pounds of apples with a 6 mile-per-gallon (mpg) efficiency with a car hauling 2 pounds of apples with 20 mpg efficiency. Food miles and carbon footprint must be calculated on a per unit of food basis.
Less Waste, Post Haste
Postharvest technology can make a significant contribution to reducing the carbon footprint of food systems. Energy for cooling can be reduced by using efficient cooling operations and managing them well. In addition, harvesting products during the cooler parts of the day and avoiding exposure to the sun after harvest through the use of shade materials will reduce the heat load that must be removed from the product. Maintaining the cold chain once the product has been thoroughly cooled will prevent the need for re-cooling and reduce energy use.
Reducing wasted food is something everybody can do to reduce the greenhouse gas emissions in our food system. Depending on the commodity, postharvest losses range from 5% to 25% in developed countries and 20% to 50% in developing countries. A recent survey carried out in the UK claims that an estimated 4.4 million apples are tossed every day along with 5.5 million potatoes, 2.8 million tomatoes, 1.6 million bananas, and 1.2 million oranges due to deterioration problems. Based on these estimates, these five items alone add up to 525,000 tons of food waste a year (according to www.lovefoodhatewaste.com).
The USDA Economic Research Service estimates that in 2005, 57% of fresh fruits and 51% of fresh vegetables, by weight, were not consumed. According to a recent article in the Hindustan Times, up to 30% of food produced in India is wasted because of poor postharvest handling.
Given the electricity, fuel, fertilizer, and water invested in producing a crop, to have 57% of it never consumed is a tremendous waste of resources that greatly increases the carbon footprint of the food industry. The industry has invested in harvest aids, packing equipment, packaging, cooling facilities, storage technologies, and air-ride suspended truck trailers that help maintain the quality of fresh fruits and vegetables, allowing them to make it to market in good condition for purchase and consumption. However, there is still room for considerable improvement, and we should invest at least as much energy and resources into improving postharvest handling as in improving our production practices.