Carbon Calculator

As we confront global climate change, we all seek to understand our own personal contribution to greenhouse gas emissions. This simple calculator is designed to estimate the carbon dioxide (CO₂) produced from travel activities. There are other sources of greenhouse gas emissions from our daily activities, with emissions associated with agriculture, energy consumption, resource use, appliances, and many other factors. Here, we focus only on travel, but encourage you to consider your contributions to greenhouse gas emissions in all parts of your life.

As part of the inaugural Green Commencement initiative, we have designed this carbon calculator to estimate the pounds of CO₂ emitted from your travel to Commencement Weekend (either via airplane or car). For automobiles, the calculator offers three choices of vehicles with different average miles per gallon, and estimates the resultant CO₂ emissions. While values will be supplied for driving from non-contiguous land areas (e.g., London), these are obviously not correct! For airplanes, the calculator estimates CO₂ using averages for short, medium, and long distance trips (see FAQs for details on the assumptions).

After you have fun with the calculator, please take part in our short survey (WIN AN MHC SWEATSHIRT!) to help us characterize the demand for initiatives aimed at reducing CO₂.

* In order to account for the non-linear nature of roads, a 15% mileage addition factor has been added to the CO₂ calculations for driving.

Frequently Asked Questions

Q. How is carbon created when I travel?
A. Carbon dioxide (CO₂) is emitted as exhaust from combustion of fossil fuel in cars and airplanes.

Cars
On average, cars travel 22.3 miles per gallon of gasoline. SUVs, minivans, and pickup trucks travel about 17.6 miles per gallon of gasoline.

So, if you figure that each gallon of gasoline that is burned (to propel your vehicle) emits 20 pounds of CO₂, then approximately 1 pound of CO₂ is emitted per mile travelled (assuming an overall average of 20 mpg). Of course, a small, fuel efficient car will emit less (up to 30% less), and a larger vehicle will emit more (up to 30% more).

Airplanes
Airplane travel is estimated using pounds of CO₂ per passenger mile. Interestingly, longer flights are more efficient, resulting in fewer pounds CO₂ per passenger mile. All of the airplane emission factors used in our calculator include a radiative forcing index of 2 to account for the global warming impact of all air travel, such as the warming effect of contrails. Here are the estimates for the various types of airplane trips:

• Short haul: 1.3 lb per passenger mile
• Medium haul: 0.9 lb per passenger mile
• Long haul: 0.8 lb per passenger mile
  

Q. What do the short, medium, and long haul classifications mean?
A. Short haul is less than 300 miles, medium haul is between 300 and 500 miles, and long haul is more than 500 miles.

Q. How does 1 gallon of gas, which only weighs 7 pounds, emit 20 pounds of CO₂?
A. Gasoline is a hydrocarbon; that is, it is made up of carbon and hydrogen atoms. Hydrogen is the lightest element, but when gasoline is combusted, the carbon combines with oxygen from the air. So, one product of combustion is CO₂, which is made up of 74% oxygen and 27% carbon by weight.

Q. How do greenhouse gases work?
A. Greenhouse gases provide a useful service, warming parts of the earth not receiving direct radiation from the sun by reflecting back radiation as it leaves the earth, sort of like a blanket. We call them greenhouse gases because they work the same way the warming in a greenhouse works: energy from the sun passes through the greenhouse glass in many wavelengths, some of which are absorbed by the plants and soil in the greenhouse. A portion of the energy is reflected from the greenhouse benches and from all the other surfaces. As that energy bounces back up, though, not all of it can exit through the glass. Much of it remains trapped in the greenhouse as heat.

Q. I’ve heard that CO₂ isn’t the only greenhouse gas. What are other greenhouse gases?
A. Other greenhouse gases (sometimes shortened to GHGs) include methane (CH₄), ozone (O₃), nitrous oxide (N₂O), chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), sulfur hexafluoride (SF₆), and even water vapor.

Q. Is CO₂ the most common greenhouse gas?
A. The most common greenhouse gas is water vapor, but it moves through the atmosphere very quickly, and the water cycle is an essential and uncontrollable part of life on earth that is reactive primarily to temperature. If we really want to control water vapor, we need to control temperature. CO₂ is the next most common greenhouse gas.

Q. Is CO₂ the worst greenhouse gas?
A. We can assess the global warming potential (GWP) of each greenhouse gas by examining its ability to trap heat in comparison to that of the most common, controllable greenhouse gas, CO₂, over a specified period of time (usually 100 years). Global warming potential is the ratio of heat trapped by one unit mass of a gas to the heat trapped by one unit mass of CO₂. Because GWP examines both heat trapping ability and a time frame, the amount of time a greenhouse gas spends in the atmosphere (atmospheric life) is important.

According to the IPCC, the most potent greenhouse gas seems to be sulfur hexafluoride (SF₆) with a GWP more than 22,000 higher than CO₂ over 100 years. While used in small amounts, SF₆ is used for insulation and current interruption in electrical power transmission and distribution equipment, as well as in other industrial applications.

The atmospheric lifetime of SF₆ is about 3200 years, which means that reducing our use of SF₆ by one pound is approximately the same as removing 11 tons of carbon from the atmosphere.