How was your carbon footprint calculated?
This carbon calculator determines carbon dioxide and other greenhouse gas emissions for personal and household behaviors. The following information explains how emissions are calculated.
Greenhouse gas emissions are typically reported worldwide in metric tons. Carbon dioxide emissions are calculated from the weight of carbon. Other emissions, such as methane and nitrous oixde, are reported in carbon dioxide equivalents so that the emissions can be compared. Short tons (equivalent to 2,000 lb.) are the units used to report emissions in this calculator. One metric ton can be converted to short tons by multiplying the total by 1.1023.
References to "CO2 emissions" or "carbon emissions" typically include emissions from all greenhouse gasses.
For this calculator, emissions attributed directly from individual behaviors, such as miles flown, as well as indirect emissions, such as the CO2 emitted in building airports, are included in the overall emissions calculation.
Total Emissions Per Person
In 2004, the United States emitted 7074 million metric tons of carbon dioxide equivalent green house gasses1. This equates to 27 tons per person2. In this calculator, direct emissions (calculated from home energy use, personal transportation, diet and waste) make up 45% of the total U.S. emissions, with the remaining 55% representing indirect emissions.
To determine the indirect emissions for each user, we apply an indirect emissions factor to all personal behaviors. This is simply the ratio of total U.S. CO2 emissions to the total emissions for the personal behaviors we are considering. For example, direct emissions from one long flight is approximately 1 ton and indirect emissions add 1.2 tons, for total emissions of 2.2 tons. The emissions for specific behaviors included in the calculator are documented below.
For the specific behaviors evaluated in the calculator, we rely on data regarding typical consumption to determine an average contribution. In most cases, we also calculate high and low endpoints for each behavior. These three points are used to frame the specific responses for each behavior. For example, we used data from residential energy surveys to determine the average maximum emissions for a household that has not implemented energy saving behaviors and the average minimum for a household that has implemented many energy savings behaviors.
Home energy emissions are based directly on how much electricity and other fuels are used in your home. This is determined from the cost or kilowatt hours entered for each heating or cooling season, multiplied over the months in each season, plus yearly energy consumption entered for other fuels. State is used to determine carbon dioxide equivalent emissions per kilowatt hour of electricity3. 2010 cost data per state for electricity is used to determine kilowatt hours from cost.4
Average: Emissions factors are determined based on the type of car selected and then multiplied by the number of miles driven per car, assuming gasoline-based vehicles.5
Average: Air travel per-mile emissions are significantly affected by the length of the flight because a high percentage of fuel use and emissions are expended on take-off. We estimate an average length of 300 miles for a short flight.6
Food & Diet
Average: Agricultural activity (crop, land, and animal including management, and including farm vehicles) accounts for 7% of all greenhouse gas emissions in the United States, with 91% of that being from methane and nitrous oxide emissions.7
Behaviors: Vegan and vegetarian diets emit 72% and 42% less than the typical American diet, respectively. A heavy meat diet emits 24% more than the average.8 For the organic food responses, "Most of the time" reduces your emissions by 29%, "Sometimes" reduces emissions by 15%, and "Never or rarely" is the average emissions figure. 9
Recycling and Waste
Average: 246 million short tons of waste were landfilled in 2004.10 This produces 2.1 tons of carbon dioxide equivalent greenhouse gases per year per person.11
Behaviors: Recycling household trash can reduce your overall waste stream, and thus emissions by 42%.12 Composting can reduce emissions by 24%.13
Averages are based on US EPA Inventory of Greenhouse Gas Emissions and Sinks14 and behavior emissions (savings or additions) are determined from the answers submitted.
World average for greenhouse gas emissions are 3.2 billion metric tons carbon dioxide equivalent. This equates to 5.5 short tons per person.15
1. U.S. Environmental Protection Agency. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2004. Executive Summary. 2006.
2. U.S. Census Bureau. National and State Population Estimates. 2006.
3. U.S. Energy Information Administration. Updated State-Level Greenhouse Gas Emission Coefficients for Electricity Generation 1998-2000. Table 1. 1998-2000 Average State-level Carbon Dioxide Emissions Coefficients for Electric Power. April 2002.
4. U.S. Energy Information Administration. Table 5.6.A. Average Retail Price of Electricity to Ultimate Customers by End-Use Sector, by State, July 2010 and 2009.
5. UK DEFRA (Table 7, Annexes to Guidelines for Company Reporting on Greenhouse Gas Emissions, updated July 2005), UK DEFRA (Table 2, Annexes to Guidelines for Company Reporting on Greenhouse Gas Emissions, updated July 2005) and Average Fuel Economy of (Civic, Escape, Prius, Insight – Adjusted 55/45) U.S. Environmental Protection Agency. Light-Duty Automotive Technology and Fuel Economy Trends: 1975 Through 2006, Appendix B: Model Year 2006 Nameplate Fuel Economy Listings
6. Emission Factors for short haul and long haul flights from UK DEFRA (Table 9, Annexes to Guidelines for Company Reporting on Greenhouse Gas Emissions, updated July 2005).
7. U.S. Environmental Protection Agency. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2004. Table 6-1, Table A-104. 2006.
8. Martin, Pamela A. and Gidon Eshel, "Diet, Energy, and Global Warming". Earth Interactions. 2006. Paper 10-1009.
9. Pimentel, D., et. al. "Environmental, Energetic, and Economic Comparisons of Organic and Conventional Farming Systems" Bioscience (Vol. 55:7)
10. U.S. Environmental Protection Agency. Municipal Solid Waste in the United States: 2005 Facts and Figures. Table ES-1. 2005.
11. U.S. Environmental Protection Agency. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2004. Table 8-1. 2006.
12. U.S. Environmental Protection Agency. Personal GHG Calculator.
13. U.S. Environmental Protection Agency. Municipal Solid Waste in the United States. Figure ES-3. Composting can reduce emissions by 25%.
14. U.S. Environmental Protection Agency. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2004. Tables: 3-6, A-104, A-106, 6-1, and 8-1. 2006.
15. U.S. Energy Information Administration. Greenhouse Gases, Climate Change, and Energy. 2004