Electricity: In the United States, producing the average kWh at an electrical generating plant results in 1.397 pounds of carbon dioxide entering the atmosphere (West and Marland, 2000; CDIAC,) mostly from the burning of fossil fuels such as coal, oil, and natural gas. However, some electrical generating sources, including solar, wind, hydro, and nuclear, produce no climate-affecting emissions. If all or a portion of your electricity is generated by one of these means, remove that percentage of kWh to reflect the reduced impact. (One site, www.greenmountain.com, offers information on each state's electrical generating portfolio under "Where Does Your Electricity Come From" on its home page.)

Wood Stoves and Fireplaces: Some people consider wood stoves and fireplaces as a zero net emissions category despite the fact that burning one ton of wood (approximately one cord of dried hardwood) releases nearly 4000 pounds of carbon dioxide when fully combusted. They correctly assert that the carbon dioxide produced from wood combustion was already a part of the planet's natural carbon cycle, and therefore burning wood cannot be considered an anthropogenic addition to the atmospheric carbon dioxide load. On the other hand, one could make the same argument about deforestation in general, which some experts contend causes 20% of the measured anthropogenic effect. An additional point to consider is that if wood is burned for heating purposes, its carbon is no longer in storage, as it might be if one chose solar power to generate electricity for heat, plus most wood combusts incompletely and the smoke causes other environmental problems. Choose for yourself whether to include wood burning in your energy calculations.

Waste Disposal: Our overall impact on the environment can be measured, to some degree, by our waste products. For the purposes of this Calculator, we measure garbage as having a climate change impact coefficient of 3 and recycling as a 2. Recycling still carries a cost in this instance because it represents use of natural resources during production, transport, and disposal. A thousand TV dinners are not erased from our climate impact simply because the trays are made of recyclable aluminum.

Refrigerators: The primary climate impact of today's household refrigerators and freezers is the electricity they need to operate; all modern refrigerators are closed coolant systems that do not leak under normal use. So unless you thoughtlessly dispose of your refrigerator without having its refrigerant recovered, or you continue to run a system that needs regular recharging, the refrigerant itself is not a factor in your climate impact.

By Type of Vehicle: Your choice of vehicle is the greatest determinant in factoring your climate change impact. Generally speaking, a sport utility vehicle that gets 15 mpg has a greater climate change effect than a traditional automobile with the same mpg, in part because the vehicles are classified differently under U.S. law. The figures in our Calculator were derived from class-based averages of the EPA’s Estimated Combined Mileage figures for 2000 model vehicles. (As they say, your mileage may vary.) The average fuel efficiency was then divided by the average miles per year for U.S. passenger cars (11,300) or trucks and vans (11,800) to arrive at an average number of gallons used. This number was then multiplied by the carbon dioxide emission coefficient (19.594) of unleaded gasoline to arrive at the number of pounds of carbon dioxide emitted.

Vehicle Air Conditioning: As with household refrigerant systems that increase your power bill, the greatest effect that vehicular air conditioning has on the climate is to lower your fuel efficiency. The average automobile air conditioning system operates four years before it loses 30% (avg. of .6 lbs.) of its refrigerant and requires a recharge. Dividing this amount over four years results in an average annual leakage of .15 pounds of R-134-A (GWP=1300). Multiplying the annual leakage by the GWP shows that an average automobile air conditioner can be said to cause annual climate change effects equal to the emission of 195 pounds of carbon dioxide.

Diesel Automotive Fuel: The carbon dioxide coefficient for unleaded gasoline is 19.594 per gallon, for diesel motor fuel it is 22.384.

Airline Travel: The measurement of a single passenger’s portion of a jet aircraft’s contribution to climate change is subject to a great many variables based on the number of seats, the number of passengers, and the type and efficiency of the aircraft’s engines. The Calculator offers an average based on the number of flights you have taken. To determine your portion of each flight’s carbon dioxide emissions, we have chosen to use the Federal Aviation Administration’s estimates for the average length of a domestic flight (830.5 miles) and their published average "miles-per-gallon-per-seat" (48). This figure takes into account non-revenue passenger miles such as those incurred while taxiing and in holding patterns. Remember to enter the total number of one-way seat tickets you used last year: yours and your family’s as well.

A Selection of Sources Consulted:
U.S. Department of Energy and its Energy Information Administration
Federal Aviation Administration
U.S. Environmental Protection Agency
The Intergovernmental Panel on Climate Change
duPont Corporation
The National Audubon Society
The Uranium Institute (U.K.)