Carbon Footprint Factsheet

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“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, and end-of-life). Throughout a product’s lifetime, or lifecycle, different GHGs may be emitted, such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), each with a greater or lesser ability to trap heat in the atmosphere. These differences are accounted for by the global warming potential (GWP) of each gas, resulting in a carbon footprint in units of mass of carbon dioxide equivalents (CO2e). 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 metric tons CO2e/yr.2

Sources of Emissions

Food

  • Food accounts for 10-30% of a household’s carbon footprint, typically a higher portion in lower-income households.2 Production accounts for 68% of food emissions, while transportation accounts for 5%.4
  • Food production emissions consist mainly of CO2, N2O, and 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 conversion of plant to animal energy and due to CH4 released from manure management and enteric fermentation in ruminants.5
  • Ruminants such as cattle, sheep, and goats produced 179 million metric tons (mmt) CO2e of enteric methane in the U.S. in 2019.6
  • In an average U.S. household, 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, beef's GHG emissions per kilogram are 7.2 times greater than those of chicken.7

Greenhouse Gases Contribution by food type in average diet3

Greenhouse Gases Contribution by Food Type in Average Diet

Pounds of CO2e per Serving13

(4 oz. meat, 1/2 c. asparagus & carrots, 8 oz. liquids)

Pounds of CO2e per Serving

Household Emissions

  • For each kWh generated in the U.S., an average of 0.889 pounds of CO2e is released at the power plant.8 Coal releases 2.2 pounds, petroleum releases 1.9 pounds, and natural gas releases 0.9 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 2019 emitted 598.8 mmt CO2e, 9.1% of the U.S. total.6
  • Space heating and cooling are estimated to account for 42% of energy in U.S. homes in 2021.10
  • Refrigerators are one of the largest users of household appliance energy; in 2019, an average of 672 lbs CO2e per household was due to refrigeration.8,11
  • 26 mmt CO2e are released in the U.S. each year from washing clothes. Switching to a cold water wash once per week can reduce household GHG emissions by over 70 lbs annually.12

Personal Transportation

  • U.S. fuel economy (mpg) declined by 12% from 1988-2004, then improved by 29% from 2004-2019, reaching an average of 24.9 mpg in 2019.14 Annual per capita miles driven increased 9% since 1995 to 9,919 miles in 2018.15
  • Cars and light trucks emitted 1.1 billion metric tons CO2e or 17% of the total U.S. GHG emissions in 2019.6
  • 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 0.78 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 $0.20-$0.40 per gallon.19
  • Commercial aircraft GHG emissions vary according to aircraft type, trip length, occupancy rates, and passenger and cargo weight, and totaled 135.4 mmt CO2e in 2019.6 In 2019, the average domestic commercial flight emitted 0.39 pounds of CO2e per passenger mile.6,20
  • Domestic air travel fuel efficiency (passenger miles/gallon) rose by 115% from 1990 to 2019, largely due to increased occupancy.20 Emissions per domestic passenger-mile decreased 45% from 1990-2019, due to increased occupancy and fuel efficiency.6,20
  • In 2019, rail transportation emitted 40.8 mmt CO2e, accounting for 2% of transportation emissions in the U.S.6

Transportation Greenhouse Gases, 20196

Transportation Greenhouse Gases, 2019

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.
  • Ensure car tires are properly inflated. Fuel efficiency decreases by 0.2% 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
  • Whether you hand wash dishes or use a dishwasher, follow recommended practices to decrease water and energy use and reduce emissions.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 incandescent light bulbs.24
  • Reduce what you send to a landfill by recycling, composting, and buying products with minimal packaging.
  • Purchase items with a comparatively low carbon footprint. Some manufacturers have begun assessing and publishing their products’ carbon footprints.
  • Covering 80% of roof area on commercial buildings in the U.S. with solar reflective material would conserve energy and offset 125 mmt CO2 over the structures’ lifetime, equivalent to turning off 32 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, 201828

U.S. Greenhouse Gas Emissions, 2018

Carbon Footprint Calculator

Estimate your personal or household greenhouse gas emissions and explore the impact of different techniques to lower those emissions:

References: 
  1. The Carbon Trust (2018) Carbon Footprinting.
  2. Jones C., Kammen D. (2011) "Quantifying Carbon Footprint Reduction Opportunities for U.S. Households and Communities."
  3. 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.
  4. Boehm R., et al. (2018) "A Comprehensive Life Cycle Assessment of Greenhouse Gas Emissions from U.S. Household Food Choices."
  5. 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.
  6. U.S. Environmental Protection Agency (EPA) (2021) Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990 - 2019.
  7. Heller, M., et al. (2020). Implications of Future US Diet Scenarios on Greenhouse Gas Emissions.
  8. U.S. EPA (2021) “Emissions & Generation Resource Integrated Database (eGRID).”
  9. U.S. Energy Information Administration (EIA) (2021) Electric Power Monthly with Data from February 2021.
  10. U.S. EIA (2021) Annual Energy Outlook 2021.
  11. U.S. EIA (2018) Residential Energy Consumption Survey 2015.
  12. Mars C. (2016) Benefits of Using Cold Water for Everyday Laundry in the U.S.
  13. 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.
  14. U.S. EPA (2021) The 2020 EPA Automotive Trends Report: Greenhouse Gas Emissions, Fuel Economy, and Technology since 1975.
  15. U.S. Department of Energy (DOE), Oak Ridge National Lab (2021) Transportation Energy Data Book: Edition 39.
  16. Pero, F. et al. (2018) Life Cycle Assessment in the automotive sector: a comparative case study of Internal Combustion Engine and electric car.
  17. U.S. EIA (2016) “Carbon Dioxide Emissions Coefficients."
  18. U.S. DOE, Alternative Fuels Data Center (2015) “Fuel Properties Comparison Chart.”
  19. U.S. DOE, Office of Energy Efficiency and Renewable Energy (EERE) (2021) “Driving More Efficiently.”
  20. U.S. Department of Transportation Bureau of Transportation Statistics (2020) National Transportation Statistics 2020.
  21. U.S. DOE, EERE (2016) "Gas Mileage Tips: Keeping Your Car In Shape."
  22. Porras, G. (2019) Life Cycle Comparison of Manual and Machine Dishwashing in Households
  23. U.S. DOE (2012) “3 Easy Tips to Reduce Your Standby Power Loads.”
  24. 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.
  25. Levinson, R. (2012) The Case for Cool Roofs. Lawrence Berkeley National Laboratory, Heat Island Group.
  26. U.S. EPA (2021) “Greenhouse Gas Equivalencies Calculator.”
  27. Buchanan, C., et al (2018) “Lightweighting shipping containers: Life cycle impacts on multimodal freight transportation.” Transportation Research Part D 62:418-432.
  28. U.S. EPA (2020) 2020 Common Reporting Format (CRF) Table.
Cite as: 
Center for Sustainable Systems, University of Michigan. 2021. "Carbon Footprint Factsheet." Pub. No. CSS09-05.