Circle of Responsibility

The modern food system (growing, fishing, processing, transporting, preparing, packaging, and disposing) contributes abundant amounts of four of the six principal greenhouse gases that create the “greenhouse effect.” These gases are carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O) and chlorofluorocarbons (CFCs). Understanding the sources and effects of these greenhouse gases is essential to begin making food choices that will help reduce climate change.

 

The most abundant and commonly-known greenhouse gas, carbon dioxide, comes from burning fossil fuels to transport our food by plane, truck, rail, car or boat. Many people encourage reducing your “food miles” – the distance your food travels from the farm to your plate – which is a good starting point to think about the environmental impact of your food. Buying local foods has been a standard at Bon Appétit and with our Low Carbon Diet, we’re taking it to the next level by looking at choices in terms of “fossil fuel miles” – the total amount of energy and emissions expended in food production. Why? Some transportation modes are more efficient than others covering equal distances and manufacturing processes – that is, energy used to process, package, heat or chill food—are also significant sources of CO₂ emissions.

 

Although carbon dioxide is the ‘baseline’ greenhouse gas, methane gas is critically important because it is 23 times more potent at trapping heat on the earth’s surface than CO₂. The food system is responsible for a tremendous portion of all methane produced worldwide. Cows and other ruminants (e.g., sheep and goats) are the largest single source of methane emissions in the United States if we add their biological processes (scientifically, “enteric fermentation” but colloquially known as belching) and management of their manure. According to a comprehensive study, backed by several others, livestock production accounts for 18% of the world’s greenhouse gas emissions (2). Another study also demonstrated how the typical American diet consisting of a high percentage of red meat contributes more to global warming than driving a typical sedan (3).

 

A second source of methane in our food system comes from food waste in landfills. People frequently dispose of leftovers on their plates thinking it’s natural and biodegradable without realizing that organic matter (primarily food scraps) in a landfill contributes to methane gas production (4). A study by a British environmental organization concluded that we “could make carbon savings equivalent to taking an estimated 1 in 5 cars off the road if we avoided throwing away all the food that we could have eaten.” Household refuse rates in the U.S. appear to be comparable to those in Great Britain (5).

 

N₂O, which is 300 times for potent than CO₂, is emitted by bacteria in soils and oceans, but agricultural practices (cultivating soil, over-using nitrogen fertilizers, and handling animal waste) are sources of human-produced nitrous oxide that stimulate naturally occurring bacteria to produce more nitrous oxide. The livestock sector (primarily cows, chickens, and pigs) produces 65% of nitrous oxide, and crop agricultural processes contribute another 15% of all human-related sources (6)

 

Chlorofluorocarbons (CFCs) have been used in refrigeration, air conditioning, and as solvents but are now known to be one of the main contributors to ozone depletion. Although this is different than global warming (referring to an increase in the Earth’s surface temperature), ozone depletion is also problematic because the stratospheric ozone layer is responsible for absorbing harmful UVB rays, which can lead to skin cancer in humans. Therefore, CFC gas production is currently being eliminated under existing international agreements. Other fluorocarbons that are also greenhouse gases are being used as substitutes for CFCs in some applications; although currently very small, their contributions to climate change are expected to rise.