National Average

The average carbon dioxide (CO2) emissions from one kWh of electricity generated by utilities in the U.S. is 1.36 lbs.¹

The average U.S. household uses 11,040 kWh of electricity per year³. About 9% of the energy generated by the utilities is lost in the transmission system before it reaches the home², so the average use of 11,040 kWh actually requires about 12,034 kWh to be generated.

National Average based on type of Household:

Entering kWh or Dollars:

House: Electricity
kWh is the most accurate way, while dollars per month uses a national average. And don’t worry if you’re not sure, you can always use the national household average of 1,003 kWh a month or $106 a month. If you know your exact kWh or dollars, these are the formulas used to determine the annual amount of CO2 produced by your electricity consumption:

If you know your kWh per month:

If you know your dollars per month:

As we mentioned above, because prices for electricity vary by utility, by state and by region, the most accurate way to obtain the carbon footprint of your home electricity use is to enter the kWh that you use every month. However, because it might be easier to remember how much money you spend per month on your electricity bill, we’re happy to provide you with a way to calculate an estimate of your carbon footprint by entering the dollars you pay for electricity every month.

If you’re curious, we’ll explain how we came up with the 8.81 kWh/$ factor above. The US Department of Energy’s Energy Information Administration regularly publishes information on the average retail price of electricity in the US. (See this link for more info: http://www.eia.doe.gov/cneaf/electricity/epm/table5_3.html). We pulled the most recent average, annual price available, $0.1135/kWh, from that site and used a bit of algebra to convert it into the 8.81 kWh/$ figure included in the formula above.

This section asks you to pick the type of fuel you use to heat your home or office. If you heat with electricity, then your heating energy use is already included in the electricity calculation you did previously. If you heat with another fuel, you are asked to select natural gas, oil, or propane.

Once you've selected the fuel, you can choose to enter your own information based on what you actually consumed over a year, or, you can choose to use the national average.

Entering your own information

Based on the fuel source you choose, the calculator computes the emissions by multiplying the appropriate emissions factor and the number of units you used (gallons, CCF, or Therms) for each fuel.

Emissions factors for each fuel type are :

• Natural gas = 12.0593 lbs. CO2/CCF or 11.708 lbs. CO2/Therm
• Oil = 22.384 lbs. CO2/gallon
• Propane = 12.669 lbs. CO2/gallon

For demonstration, if you use 800 CCF of natural gas annually, then:

Choosing the national average

The average U.S. home uses one of the following:

• 756 CCF- national average of natural gas use per household
• 491 gallons- national average of fuel oil use per household
• 468 gallon- national average of LPG (propane) use per household

NOTE: Each average includes only the set of households using that particular fuel

House: Lawn

The calculation for auto travel works differently depending on whether you choose to enter you own annual miles driven, and your own miles per gallon, or you choose to use national averages.

Entering your own information

The first step is to enter the miles per gallon for your vehicle (let's say 25).

Then enter your own annual miles driven (let's say 10,000).

The calculator then divides your annual miles driven by your miles per gallon- in this example:

The calculator then multiplies your fuel consumption by 19.564, which is the amount of CO2 released by burning one gallon of gasoline-4.

Choosing the national average

The calculation is performed the same as above, but uses the following information:

The average annual distance driven per vehicle in the U.S. is 12,578 miles.

The average car gets about 25.9 miles per gallon, the average SUV gets 19.7 miles per gallon.

Why are aircraft emissions treated differently than other emissions?

Before we start explaining, let’s define some terms:

Now, on with the explanation:

We know that burning fossil fuels results in emissions of carbon dioxide. Burning of fossil fuels also results in emissions of SOx, NOx, CO, and particulates called soots or aerosols. When released at the surface of the earth, these substances are widely dissipated and thus have a lower net impact on chemical reactions within the atmosphere when compared to carbon dioxide, which rises into the upper atmosphere.

Aircraft get special attention because they commonly operate in parts of the atmosphere known as the Upper Troposphere (UT) and the Lower Stratosphere (LS). This is significant because many of the chemical reactions that dictate the insulating properties of our atmosphere occur in these two regions. When SOx, NOx, CO, water vapor, and aerosols are released directly into the UT and LS as a result of aircraft fuel combustion, they have immediate effects on the regional atmospheric chemistry. It is important to note that the effects of these compounds in the upper atmosphere are greater than they would have been if emitted at the surface.

NOx emissions in the UT and LS result in an increase in ozone production. Ozone, like CO2 and methane (CH4) is a natural component of our upper atmosphere, and while it helps shield us from harmful UV rays, it is also a greenhouse gas. In other words, increases in ozone in the upper atmosphere lead to net warming of the earth.

SOx emissions are also a result of jet fuel combustion. Chemically speaking, they actually lead to a decrease in UT and LS ozone, BUT they also lead to production of sulfates and aerosols. Both of these substances serve as potential sites for atmospheric reactions that negate the impact of the ozone decrease and result in net warming.

You’ve probably seen a jet flying overhead and noticed a white line trailing it across the sky. That line is called a condensation trail, or contrail for short. Contrails are comprised of water vapor and various particles (aerosols). Persistent contrails can linger in the sky for extended periods of time and actually have a direct warming effect. Even if they dissipate quickly, the water vapor and particles can contribute to the formation of cirrus clouds.

While thick cumulus clouds block solar energy from reaching the earth’s surface, high, thin, cirrus clouds act like a one-way door, allowing solar energy to reach the surface, and then reflecting it, or trapping it there. Clearly, cirrus clouds can, and do, occur naturally, and should hardly be considered a problem as part of natural atmospheric cycles. However, emissions from aircraft can ultimately lead to an increase in cirrus cloud coverage. When compared to the cloud coverage that would exist in the absence of aircraft emissions, the net effect is warming of the earth.

Rolling all of these factors together, we use the RFI to quantify how large the total impact of aviation emissions is on climate change. Generally, the RFI of non-aviation emissions is approximately one. The IPCC (Intergovernmental Panel on Climate Change) estimates that the overall radiative forcing by aircraft emissions (excluding that from changes in cirrus clouds) is a factor of 2 to 4 times larger than the radiative forcing by aircraft carbon dioxide alone. What that means is that the total climate change impact of aviation can be more accurately quantified by multiplying the carbon dioxide emissions value by a factor of 2 to 4. BEF and the Climate Neutral Network have mutually agreed to use a conservative factor of 2. Many carbon calculators on the Internet ignore RFI and hence, understate users’ contribution to climate change.

[This a synopsis of research reports from the IPCC’s "Aviation and the Global Atmosphere". Full text can be found at: http://www.grida.no/Climate/ipcc/aviation/index.htm]

One-Way Flights:

FORMULA: # one way flights x 713 lbs CO2 per one way flight = lbs CO2 per year

To give you a better idea of how we reached the conclusion on 713 lbs CO2 per one-way flight, we’ll walk you through our process. So, the average flier takes 4 round trips per year (source: Arbitron Airport Television Study, 2007), which is equal to 8 one-way trips. The average flier, with their 4 round trip flights, emits 2.8519 tons of CO2 every year. (To get to the 2.8519 tons/year we multiplied the average flier’s annual fuel consumed per gallon (135.2) by the pounds of CO2 emitted per gallon of fuel (21.095 lbs/gallon; source: IPCC fuel emissions data base) by the Radiative Forcing Index (2) divided by 2000.) We converted the 2.8519 tons of CO2 emitted by the average passenger into pounds and then divided that number by 8 one-way flights to give us the average number of pounds of CO2 emitted per one-way flight.

Short, Medium, or Long-Haul Flights:

The data used in used in our event calculator to determine the number of BEF Carbon Offsets needed to green the electricity consumption at your event is from the U.S. Department of Energy, Energy Information Administration- Commercial Buildings Energy Consumption Survey (2003). For example, if you wanted to offset the CO2 from an event at a large Convention Center:

First, from the drop-down menu choose: Large Convention Center.

Then, select or enter the total square footage (or choose the national average): 89,999 sq.ft.

Finally, choose the amount of time you plan to occupy this space (in hours or days): 4 days

The calculate button will tell you the number of pounds of CO2 your event will produce.

Simply press the Order Now button and offset the CO2 from your entire event.

• Electricity

  The average carbon dioxide (CO2) emissions from one kWh of electricity generated by utilities in the U.S. is 1.36 lbs.-¹

  The average U.S. home uses 11,040 kWh of electricity per year³. About 9% of the energy generated by the utilities is lost in the transmission system before it reaches the home², so the average use of 11,040 kWh actually requires about 12,034 kWh to be generated.

• Home Heating

  To simplify this calculation we assume the home is heated with natural gas.

  Burning one CCF of natural gas releases 12.0593 lbs. of CO2.

  The average U.S. home uses 756 CCF per year.

• Auto Travel

  The average miles driven per vehicle per year in the U.S. is 12,578.

  The average automobile gets about 23.7 miles per gallon (Most SUVs get less.)

  The calculator then multiplies your fuel consumption by 19.564, which is the amount of CO2 released by burning one gallon of gasoline-⁴.

• The Total

  Electricity = 16,366 lbs. of CO2 per year.

  Home Heating = 9,792 lbs. of CO2 per year.

  Auto Travel = 10,383 lbs. of CO2 per year.

  Total = 36,541 lbs. of CO2 per year.

We use the most trusted data available to determine the environmental impact of burning fossil fuels, relying on analysis done and values provided by the most commonly accepted and reliable sources, such as the EPA, the Department of Energy, the Bureau of Transportation Statistics and other U.S. government agencies. Still, when the results of these analyses are applied to any single individual or household, the resulting number will be an approximation.

The average passenger miles per gallon for a coach class, domestic or international trip originating in the U.S. equals 33.4, according to "Transportation, Energy, and the Environment", Section A - U.S. Energy Consumption and Transportation Sector Energy Consumption, Table 4-21. (Note that this is not much better than the average automobile, if driven with only one occupant.)

Burning a gallon of jet fuel releases 21.095 lbs.4 of CO2. Combining these two factors:

Air travel also releases significant amounts of non-CO2 greenhouse gas emissions, and their impact is magnified by the fact that they are released directly into the upper atmosphere. The effect of these gases is accounted for by a factor called the radiative forcing index (RFI).

In its 1999 Special Report on Aviation in the Global Atmosphere, the Intergovernmental Panel on Climate Change (IPCC) estimated the RFI from air travel in 1990 to be between 2 and 4, averaging 2.7 times the carbon impact alone. More recently, the TRADEOFF project of The Fifth Framework Programme of the European Commission of the EU, suggested an RFI of 1.9. The Climate Neutral Network (CNN) conducted significant research on this topic, and after considerable discussion, BEF and CNN agreed that the appropriate RFI factor is 2. Hence, our calculator doubles the 0.63 lbs. of CO2, with a result of 1.26 lbs. of total CO2 equivalents (or CO2e) per passenger mile.

Based on the Climate Neutral Network’s analysis, an additional 8% has added to the total, to account for the emissions associated with the upstream refining of jet fuel. The result is that 1.36 lbs. of CO2e are created for each passenger mile traveled (0.63 x 2 plus 8%). It is important to note that many carbon calculators on the Internet do not accurately account for these additional emissions and hence, significantly underestimate total Greenhouse Gas emissions.