The One Billion Ton Opportunity Cont'd - Part IV: Diet and Food Waste


UPDATE 3/18: Table edited.

Today, Matt Eisenson continues his series of blogs on the Behavioral Wedge Project with the fourth of five posts, focusing on the climate impacts of changes to our daily diets. (For more on this work, check out Matt’s previous posts here and here). 

Diet is the perennial hot topic, and “green” is the current theme.  We know that what we eat matters for the environment, but how do we reduce our impact without disrupting our familiar eating habits or breaking the bank?  A recent NRDC fact sheet addressed this issue in the broader context.  For the purposes of this project—an examination of the potential for Americans to reduce greenhouse gas (GHG) emission by 1 billion metric tons of carbon dioxide equivalent (MtCO2e) in 2020 through small behavioral changes—we have singled out two dietary behaviors, swapping red meat for chicken and cutting back on dairy, and also targeted reducing food waste as a whole.

Figure 1: Proposed measures for reducing emissions from diet and food waste.


Eat Less Red Meat and Dairy

Livestock are a leading cause of global warming, responsible for at least 18% of global GHG emissions, according to a United Nations study, when deforestation and land use change for grazing are taken into account.  Cattle (both meat and dairy), sheep, and goats contribute more than their fair share.  Due to their ruminant (multi-stomach) digestive systems, these animals emit vast quantities of methane (CH4), a GHG 23 times more potent than CO2.  Perhaps surprisingly, grass-fed livestock produce more methane emissions than their grain-fed counterparts that comprise the majority of animals raised for milk or meat in the United States.  But digestion is only part of the story.  After accounting for the extensive upstream emissions of grain production and transportation, grain-fed livestock usually have a higher carbon footprint.  In terms of production, the nitrogenous fertilizer applied to grain crops is energy-intensive to produce, and degrades into nitrous oxide (N2O), a GHG 300 times more potent than CO2.  Feed crops are often grown thousands of miles from livestock operations, creating long supply chains with fuel-intensive transportation requirements. (That said, you might be surprised to learn that transportation as a whole accounts for only 11% of life-cycle emissions and final delivery from the producer to the retailer accounts for only 4% for the average calorie we consume across our diet).

Red meat’s environmental impact is strikingly disproportionate to that of other foods on a calorie by calorie basis.  According to the chart reprinted below from the New York Times, beef produces roughly 4 times the emissions of pork, 10 times the emissions of chicken, and 100 times the emissions of carrots, pound for pound.  Pigs are voracious consumers of energy, but, as non-ruminants, they expel less methane.  And cheese?  Six times the emissions of chicken, 2 times the emissions of salmon, and 20 times that of wheat flour.



The environmental impact of red meat and dairy is so large that substituting 15% of your red-meat-and-dairy budget for chicken yields the same GHG reduction as shifting to a 100% localized diet—a staggering figure, given the fact that the average calorie we eat travels 6,760 km (4,200 miles) across the supply chain and 1,640 km (1,000 miles) for final delivery, from farm to fork. 

Including pork, the average American eats about 340 calories of red meat a day.  For context, a quarter pound (4 oz.) of ground beef contains about 200 calories; 340 calories corresponds to almost 7 ounces of ground beef.  According to the 2005 University of Chicago model developed by Gidon Eshel and Pamela Martin, a substitution of 2/7 of red meat-derived calories for poultry would save 210 kg CO2e per person, and a total of 70 MMtCO2e across the U.S. population in 2020. (The model employs detailed FAO data for average consumption, and lifecycle analyses that measure the relative “efficiencies” of each food group—kcal output/kcal input—and the related non-CO2 emissions.  The calculations do not account for the application of fertilizer, and suggest a relatively conservative individual carbon footprint).

The average American consumes 430 calories of dairy products every day.  In terms of reducing the carbon impact of dairy consumption, however, the specific product makes a big difference: cheese is 10 times more carbon-intensive than milk.  A small reduction in cheese goes a long way; one would have to sacrifice a lot of milk to keep cheese consumption constant.  If every American replaced 2/7 of their dairy-derived calories in favor of plant-based calories, this would yield a personal GHG emissions reduction of over 100 kg CO2e and a total countrywide reduction of 35 MMtCO2e in 2020.

To put this in perspective, if every American made these small changes to their diets, the impact would be equivalent to taking 17 million cars off the road.

Cut Food Waste by 25%

According to the USDA’s latest comprehensive survey, 27% of the nation’s food supply is wasted as it passes through retail, food service, and consumer stages of its lifecycle.  Other studies place these post-farm losses closer to 40% or 50%.  One study suggests that the average family of four in the U.S. throws away 112 pounds of food per month, or about half of the food we buy.

The average U.S. household has an annual carbon footprint for food of 8.1 MtCO2e.  If there are 2.6 people per household, this works out to approximately 3.1 tons per person.  Ignoring the impacts of dietary change for a moment, if we multiple this per capita “foodprint” by the expected population in 2020 (341 million), we find that the emissions of our food system will exceed 1 billion tons.  Subtracting the abatement from the two dietary changes described above (to avoid double counting), we find the total emissions for household consumption to be 955 MMtCO2e.  Multiplied by 27% (the USDA estimate of how much of our food in the U.S. is wasted), we find that the emissions related to the production and transportation of wasted food will exceed 250 MMtCO2e in 2020—not including the downstream emissions related to decay (which produces methane) or the transport of waste to landfill.  If every American were to reduce their personal food waste by a modest one quarter, the result will be a sizable 65 MMtCO2e of abatement in 2020.

We were especially careful to be conservative with these calculations (the true number could well be double this figure, assuming a higher rate of wastage and considering downstream emissions) because we recognize that cutting food waste is not fully in the hands of the individual.  There are many steps along the distribution process that are inevitably out of our control.  But what our results show is that we can come a long way from throwing out half of our groceries and take advantage of this important opportunity to reduce emissions.

Figure 2: the share of total projected emissions reductions achieved through each of our recommended diet and food-waste measures.



The next post will tackle other measures for waste reduction.  Stay tuned.  In the meantime, we invite you to join the Simple Steps community at “My Simple Steps” to track your progress in reducing emissions through behavioral change.

This project is collaboration between NRDC and the Garrison Institute’s Climate, Mind and Behavior (CMB) Project,  working to integrate emerging research findings about what drives human behavior into new thinking on climate solutions.  It envisions a "behavioral wedge" empowering people to eliminate a gigaton of GHG emissions by simply changing our behavior, starting now, even as we continue to work on other fronts to achieve institutional, regulatory and market changes.  CMB is convening leading thinkers and practitioners in the fields climate change and environmental advocacy, neuro-, behavioral and evolutionary economics, psychology, policy-making, investing and social media, working together on ways to shift behavior on a large enough scale to realize this potential 1 gigaton emissions reduction.