How Food Contributes to Greenhouse Gas Emissions

By Vidyawini Ganapathy Introduction The past few years have seen an increase in consumer awareness about how food affects the environment. They now realize that food production and processing is responsible for the emission of greenhouse gases. These gases, when released into the atmosphere, trap heat and raise global temperatures. Greenhouse gases are quantified in terms of carbon dioxide equivalents (CO2e), which measure the amount of CO2 that would have a commensurate heating impact as the specified gas. Of the approximate 50 gigatonnes (Gt) of CO2e, between a quarter and a third came from food production. Agricultural adaptation, manufacture and transport of fertilisers and pesticides, resource consumption by animals reared for food, and food processing all come with a carbon footprint. To quantify the ecological impact of products, a system called ‘life-cycle assessment’ (LCA) is employed. Also called ‘cradle-to-grave’ analysis, LCA determines the resources and energy expended to acquire raw materials and inputs to produce an item (cradle), process and manufacture the product, and dispose of it or its packaging (grave).

Global greenhouse gas emissions from food production A 2020 study showed that reducing greenhouse gas emission from food production is critical to meeting the goal of keeping global warming under 2 degrees Celsius, as outlined in the Paris Agreement. Current trends in food production alone would be able to push the heating to over 2 degrees—even if fossil fuel consumption was stopped immediately. Animal-based foods account for approximately57% of food emissions, or about 14.5% of total global greenhouse gas emissions. Meat and dairy are the two highest emitters of greenhouse gasses; their production and processing emits carbon dioxide, methane, and nitrous oxide. Almost half of all emissions from livestock are methane, followed by nitrous oxide at 29% and carbon dioxide at 27%. Beef and cattle milk are responsible for the most emissions, contributing 41% and 20% of the livestock sector’s overall emissions respectively. They are followed by pig meat at 9%, buffalo meat and milk and chicken meat and eggs at 8% each, and 6% from small ruminant meat and milk. The remaining output is contributed by other poultry species and non-edible products. Cattle Meat Cattle, reared for beef, milk, and other non-food items like manure, contribute nearly two-thirds of animal-based emissions. Producing and processing fodder for cattle accounts for 45% of this. Enteric fermentation, a digestive process in which methane is released as a by-product, contributes 39%. Manure processing and storage emits 10% of emissions from cattle, and the rest comes from processing animal products. One cow will contribute around 220 pounds of methane due to enteric fermentation in a year. The heating effect of this methane is 28 times more than that of carbon when compared over 100 years. In many places, although the count of cattle has decreased, the amount of beef produced has increased. This increased efficiency means that more people are being fed which emission intensity is being reduced. Also, mixed crop livestock systems have been shown to yield higher productivity while decreasing land use change emissions by preventing deforestation. There is also evidence that introducing 1% of Asparagopsis armata seaweed into the diets of cattle can reduce methane production by almost 70%. Dairy Products The main contributor to emissions from the dairy and related sector is milk production. One pound of cow’s milk produces around 1.2 pounds of CO2e. For dairy products that are processed further, processing the milk also contributes to greenhouse gas release. Hard cheeses, like cheddar, emmental, and gruyère, produce 0.4–0.6 pounds of CO2e from processing one pound of cheese. This amount varies for different cheeses based on: Type: Hard cheeses emit more greenhouse gases per pound. This is because they require more milk to produce than softer cheeses like brie, feta, and ricotta. 10 pounds of milk will make around one pound of a hard cheese or two pounds of a soft cheese. Aging: Drier cheeses also need to be stored at low temperatures for anywhere from two months to a year. This requires constant refrigeration which requires more energy and therefore, contributes to more emissions. Overall, from milk production to disposal of packaging, one pound of a hard cheese like American cheddar releases around 8.8 pounds of CO2e. Cheese ranks third in terms of emissions per pound of different foods, after beef and lamb. Yogurt and other fermented milk products contribute around 2.2 pounds of CO2e per pound of product. They require multiple servings of milk to produce one serving of product. This number increases for products like Greek yogurt, which is strained to remove the whey. One pound of Greek yogurt requires four times that amount of milk to produce. Furthermore, the whey left behind is acidic and is therefore difficult to dispose of safely. Lamb Similar to cattle, lamb are ruminants, which means they also produce methane through enteric fermentation. Lamb production is the second biggest emitter of greenhouse gasses by volume. Pound for pound, lamb meat produces more greenhouse gasses than beef. This is because the proportion of edible meat to the animal’s live weight is lower for lamb than beef. Lamb also uses more land than beef for the production of one pound of each. Other foods Among meat, white meat like pork and poultry contribute less in terms of greenhouse gas emission. Chicken produces the least amount, with turkey a close second. However, poultry still produces 11 times more emissions than beans per serving, i.e. the lowest-impact meat protein still contributes more than the highest-impact plant-based protein. 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