“A carbon footprint is the total greenhouse gas (GHG) emissions caused directly and indirectly by an individual, organization, event or product.”1 It is calculated by summing the emissions resulting from every stage of a product or service’s lifetime (material production, manufacturing, use phase, and end-of-life disposal). Throughout a product’s lifetime, or lifecycle, different greenhouse gases (GHGs) may be emitted, such as methane and nitrous oxide, each with a greater or lesser ability to trap heat in the atmosphere. These differences are accounted for by calculating the global warming potential (GWP) of each gas in units of carbon dioxide equivalents (CO2e), giving carbon footprints a single unit for easy comparison. See the Center for Sustainable Systems' "Greenhouse Gases Factsheet" for more information on GWP. A typical U.S. household has a carbon footprint of 48 t CO2e/yr.2
Sources of Emissions
- Food accounts for 10 - 30% of a household’s carbon footprint, typically a higher portion in lower-income households.2 The production of food accounts for 68% of emissions, while its transportation accounts for 5%.4
- Food production emissions consist mainly of carbon dioxide (CO2), nitrous oxide (NO2), and methane (CH4), which result primarily from agricultural practices.5
- Meat products have larger carbon footprints per calorie than grain or vegetable products because of the inefficient transformation of plant energy to animal energy, along with the methane released from manure management and enteric fermentation in ruminants.5
- Ruminants such as cattle, sheep, and goats produced 175 million metric tons (mmt) in CO2 equivalents of enteric methane in the U.S. in 2017.6
- Eliminating the transport of food for one year could save the GHG equivalent of driving 1,000 miles, while shifting to a vegetarian meal one day a week could save the equivalent of driving 1,160 miles.5
- A vegetarian diet greatly reduces an individual’s carbon footprint, but switching to less carbon intensive meats can have a major impact as well. For example, replacing all beef consumption with chicken for one year leads to an annual carbon footprint reduction of 882 pounds CO2e.7
Greenhouse Gases Contribution by food type in average diet3
Pounds of CO2e per Serving13
(4 oz. meat, 1/2 c. asparagus & carrots, 8 oz. liquids)
- For each kilowatt hour generated in the U.S., an average of 0.998 pounds of CO2 is released at the power plant.8 Coal releases 2.2 pounds, petroleum releases 2.0 pounds, and natural gas releases 0.86 pounds. Nuclear, solar, wind, and hydroelectric release no CO2 when they produce electricity, but emissions are released during upstream production activities (e.g., solar cells, nuclear fuels, cement production).6,9
- Residential electricity use in 2017 emitted 633.6 mmt CO2e, 10% of U.S. total.6
- Residential space heating and cooling are estimated to account for 41% of energy in US homes in 2019.10
- Refrigerators are one of the largest users of household appliance energy; in 2015, an average of 726.9 pounds of CO2e per household was due to refrigeration.11
- 26 mmt CO2e are released in the US each year from washing clothes. Switching to a cold water wash once per week, a household can reduce their GHG emissions by over 70 lbs anually.12
- U.S. fuel economy (mpg) declined by 12% from 1987-2004, then improved by 29% from 2004-2017, reaching an average of 24.9 mpg in 2017.14 Annual per capita miles driven increased 9% since 1995 to 9862 miles in 2017.15
- Cars and light trucks emitted 1.1 billion metric tons CO2e or 17% of the 2017 total U.S. greenhouse gas emissions.6
- Of the roughly 66,000 lbs CO2e emitted over the lifetime of an internal combustion engine car (assuming 93,000 miles driven), 84% come from the use phase.16
- Gasoline releases 19.6 pounds of CO2 per gallon when burned, compared to 22.4 pounds per gallon for diesel.17 However, diesel has 11% more BTU per gallon, which improves its fuel economy.18
- The average passenger car emits 0.79 pounds of CO2 per mile driven.14
- Automobile fuel economy can improve 7-14% by simply observing the speed limit. Every 5 mph increase in vehicle speed over 50 mph is equivalent to paying an extra $0.19-$0.37 per gallon.19
- Commercial aircraft GHG emissions vary according to aircraft type, the length of trip, occupancy rates, and passenger and cargo weight, and totaled 129.2 mmt CO2e in 2017.6 In 2017, the average domestic commercial flight emitted 0.41 pounds of CO2e per passenger mile. Emissions per domestic passenger-mile decreased 42% from 1990-2017, due to increased occupancy and fuel efficiency.6,20
- Domestic air travel fuel efficiency (passenger miles/gallon) rose by 118% from 1990 to 2018, largely due to increased occupancy.20
- In 2017, rail transportation emitted 45 million tons CO2e, accounting for 2% of transportation emissions in the U.S.6
Transportation Greenhouse Gases, 20176
Solutions and Sustainable Actions
Ways to Reduce Carbon Footprint
- Reduce meat in your diet and avoid wasting food.
- Walk, bike, carpool, use mass transit, or drive a best-in-class vehicle.
- Make sure your car’s tires are properly inflated, fuel efficiency decreases by 0.3% for each 1 PSI decrease.21
- Smaller homes use less energy. Average household energy use is highest in houses (82.3 million BTU), followed by mobile homes (59.8 million BTU), apartments with 2-4 units (53.5 million BTU), and apartments with 5+ units in the building (34.2 million BTU).11
- If you have a dishwasher, use it! Hand washing uses more energy and water than a machine dishwasher.22
- Energy consumed by devices in standby mode accounts for 5-10% of residential energy use, adding up to $100 per year for the average American household. Unplug electronic devices when not in use, or plug them into a power strip and turn the power strip off.23
- Choose energy-efficient lighting and transition away from using incandescent light bulbs.24
- Reduce what you send to a landfill by recycling, composting, and buying products with minimal packaging.
- Shop smart and purchase items with a comparatively low carbon footprint when possible. Some manufacturers have begun assessing and publishing their products’ carbon footprints.
- Replacing 80% of conditioned roof area on commercial buildings in the U.S. with solar reflective material would offset 125 mmt CO2 over the structures’ lifetime, equivalent to turning off 31 coal power plants for one year.25,26
- Replacing the global fleet of shipping containers’ roof and wall panels with aluminum would save $28 billion in fuel.27
U.S. Greenhouse Gas Emissions, 201228
Carbon Footprint Calculator
Use one of these tools to estimate your personal or household greenhouse gas emissions and explore the impact of different techniques to lower those emissions:
- The Carbon Trust (2012) Carbon Footprinting.
- Jones C., Kammen D. (2011) “Quantifying Carbon Footprint Reduction Opportunities for U.S. Households and Communities.”
- Heller, M.C., et al. (2018). Greenhouse gas emissions and energy use associated with production of individual self-selected US diets. Environmental Research Letters, 13(4), 044004.
- Boehm R., et al. (2018) “A Comprehensive Life Cycle Assessment of Greenhouse Gas Emissions from U.S. Household Food Choices.”
- Weber, C. and H. Matthews (2008) “Food miles and the Relative Climate Impacts of Food Choices in the United States.” Environmental Science & Technology, 42(10): 3508-3513.
- U.S. Environmental Protection Agency (EPA) (2019) Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 - 2017.
- Fiala, N. (2009) How Meat Contributes to Global Warming. Scientific American.
- U.S. EPA (2018) “Emissions & Generation Resource Integrated Database (eGRID).”
- U.S. Energy Information Administration (EIA) (2019) Electric Power Monthly with Data from July 2019.
- U.S. EIA Annual Energy Outlook 2019.
- U.S. EIA (2018) Residential Energy Consumption Survey 2015.
- Mars C., (2016) Benefits of Using Cold Water for Everyday Laundry in the U.S.
- Heller, M. and G. Keoleian. (2014) Greenhouse gas emissions estimates of U.S. dietary choices and food loss. Journal of Industrial Ecology, 19 (3): 391-401.
- U.S. EPA (2019) The 2018 EPA Automotive Trends Report: GHG, Fuel Econ & Technology since 1975.
- U.S. DOE, Oak Ridge National Lab (2019) Transportation Energy Data Book: Edition 37.1.
- Pero, F. et al. (2018) Life Cycle Assessment in the automotive sector: a comparative case study of Internal Combustion Engine and electric car.
- U.S. EIA (2016) “How Much Carbon Dioxide is Produced by Burning Gasoline and Diesel Fuel.”
- U.S. DOE, Alternative Fuels Data Center (2015) “Fuel Properties Comparison Chart.”
- U.S. DOE, EERE (2019) “Driving More Efficiently.”
- U.S. Department of Transportation Bureau of Transportation Statistics (2019) National Transportation Statistics 2019.
- U.S. DOE, EERE (2009) “Gas Mileage Tips: Keeping Your Car In Shape.”
- Porras, G. (2019) Life Cycle Comparison of Manual and Machine Dishwashing in Households.
- U.S. DOE (2012) “3 Easy Tips to Reduce Your Standby Power Loads.”
- Liu, L., Keoleian, G. A., & Saitou, K. (2017). Replacement policy of residential lighting optimized for cost, energy, and greenhouse gas emissions. Environmental Research Letters, 12(11), 114034.
- Levinson, R. (2012) The Case for Cool Roofs. Lawrence Berkeley National Laboratory, Heat Island Group.
- U.S. EPA (2017) “Greenhouse Gas Equivalencies Calculator.”
- Buchanan, C., et al (2018) “Lightweighting shipping containers: Life cycle impacts on multimodal freight transportation.” Transportation Research Part D 62:418-432.
- U.S. EPA (2013) Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2012. CRF Tables.