How do our calculators estimate carbon dioxide emissions?
The DriveNeutral calculator estimates the annual carbon dioxide emissions from your vehicle based on your vehicle type and total annual miles driven. Here is how the calculator works.
First, DriveNeutral uses the latest average miles per gallon (mpg) figures for each vehicle type, available from the US Environmental Protection Agency (EPA), to estimate your vehicle’s fuel consumption.
Second, the calculator uses your annual miles driven to determine the total fuel burned in your vehicle. If you are uncertain about how many miles you drive a year, the calculator defaults to the US EPA’s estimated annual miles of 12,000 miles per year.
These two numbers, MPG and annual miles driven, tell us how much fuel your vehicle consumes in a given year. Finally, the total fuel burned is then converted to CO2 (not CO2e) using the most credible emission factors currently available from the WBCSD/WRI protocol.
It is important to note that the calculations determine only the CO2 from vehicle emissions and do not account for other greenhouse gases (CO2e) associated with fossil fuel combustion. This is because currently there are no commonly accepted factors for measuring the additional GHG emissions from the burning of vehicle fuel.
The FlyNeutral calculator estimates the carbon dioxide (CO2e) emissions from passenger aircraft based on the distance you travel. Because new information is frequently coming to light about greenhouse gas emissions, our calculator is only as accurate as the current flight emissions factors available from the WBCSD/WRI protocol and the IPCC. Here is how the calculator currently operates.
First, the non-stop distance between your departure and final destination city is calculated using the great circle distance trigonometric equation. The calculator assumes you are taking a direct flight, but you can easily determine the emissions from stopovers by entering them as separate trips. Should you choose to calculate each stopover, keep in mind that your emissions will be greater than if you calculated a direct flight. This is because jets burn tremendous amounts of fuel during takeoff and landing.
Second, the calculator determines if your flight is a short, medium, or long-haul flight and applies a category-specific emissions factor that estimates carbon dioxide emissions per passenger mile. Again, because takeoffs and landings burn more fuel than high altitude cruising, short flights consume more fuel per passenger mile than long or medium flights.
Lastly, the FlyNeutral calculator employs a Radiative Forcing Index to arrive at a more accurate estimate of the overall climate change contribution from aircraft emissions. It is important to note that CO2 is not the only greenhouse gas associated with aircraft emissions. Nitrous oxides, water vapor, and a complex interplay between these compounds at high altitudes, effect climate change more intensely than terrestrial greenhouse gas emissions; therefore, the RFI metric is used to account for the particular role aircraft emissions play in global climate change.
Does all this information get you excited to learn more about the science of climate change? For more detailed information on climate change, global warming potential of various emissions, and air travel calculations, read this paper, prepared by Shep Burton PhD, an advisor to the IPCC who is also on LiveNeutral’s advisory board.
*Note: It is important to note that CO2 and CO2e are not the same. CO2 is an abbreviation for carbon dioxide, while CO2e is short for carbon dioxide equivalents. CO2e is an internationally recognized measure of the global warming potential of greenhouse gases other than carbon dioxide. Here is an example. Methane is a potent greenhouse gas that is 23 times more powerful at trapping atmospheric heat than carbon dioxide; therefore, one metric ton of methane is equivalent to 23 metric tons of CO2e.