Carbon Offsets: Start with the Footprint

As part of our ongoing series on carbon offsets, it’s time to peel back another layer and look at how entities determine exactly what their carbon footprint is, so that they know how much they want to offset, whether it’s for a specific action (like an overseas flight) or an overall operation.

Simply put, carbon emissions generally occur as the result of energy consumption in one form or another. More specifically they emanate from the combustion of fossil fuels, though there are certain industries, like concrete production, that give off CO2 as a byproduct of different kinds of chemical reactions.

Figuring out the carbon emitted by various fuels is straightforward. The Energy Information Administration (EIA) created a chart that provides the number of pounds of CO2 emitted for a variety of common fuels.

So, for example, it tells us that a gallon of gasoline emits 19.6 pounds of carbon dioxide when burned. It doesn’t tell us that, based on each vehicle’s efficiency, the amount of carbon emitted per mile will vary. For example, a Prius will emit 0.39 pounds per mile, while something like a Jeep Grand Cherokee will emit 1.03 pounds per mile. Still, a company that owns a fleet of vehicles can simply add up the amount of fuel purchased, from which the carbon footprint can easily be computed. Diesel fuel emits 22.6 pounds of carbon per gallon. There are other considerations, such as where the gasoline came from, how the oil was extracted and refined and how far it was transported, but these are generally ignored since it would be extremely difficult to track.

Some companies may want to offset the carbon footprint of their supply chains. This could include shipping raw materials and value-add assemblies along the supply chain, or shipping finished products to retailers or directly to consumers. Other companies might offset the footprint of their employees as they commute to work or provide an opportunity for the employees to do so.

Electricity is also difficult to track for similar reasons: Most people today receive electricity from a variety of sources, which could include wind, solar, gas, coal, geothermal, hydro and nuclear. Most utilities will provide an estimate of the mix that they provide -- some in real time and others on a monthly-average basis.

Here are some of the carbon values for various fuels, which can help companies estimate their carbon impact and reduce their footprints. Values per million Btu are included (in parentheses) for comparison purposes.

• Coal: 4,631.5 pounds per short ton (210.2)


• Natural gas: 119.9 pounds per thousand cubic feet (117.0)


• Propane: 12.7 pounds per gallon (139.0)


• Heating oil: 26 pounds per gallon (173.7)

Renewable sources are generally considered zero at the point of use, though there are certain lifecycle emissions associated with their fabrication and construction -- much like those for the transportation and refining of fossil fuels that we mentioned earlier.

Getting more complicated: Diversified grids and server efficiency

The electricity mix is further complicated by the fact that we can’t really trace individual electrons on the grid. So, it’s not possible to know whether, for example, the power that’s lighting up my monitor as I type this is coming from wind, nuclear, coal or natural gas generation. But when a utility buys a certain amount of wind, for example, that wind power goes into the grid somewhere. The person using it may not be the person who paid for it, but it did offset an equal amount of power that would have been produced in a different way.

Similarly, a company could provide offsets for employee travel. Jet fuel emits 21.1 pounds of CO2 per gallon, about midway between gasoline and diesel. A Boeing 747 burns approximately 1.2 gallons of fuel per second, during which time it covers approximately 5 miles. Of course, what an individual’s actual travel footprint will be depends on the type of aircraft flown and how full it was. Based on the numbers I just gave you, if the 747 had 100 passengers on board, it would emit 0.05 pounds per passenger mile -- about as much as eight Priuses or 2o Jeep Grand Cherokees. A Boeing 737 is far more efficient, burning through a gallon of fuel in 4.5 seconds.

Finally, there are servers, which are an increasingly substantial source of energy consumption to any company doing any kind of e-business, whether they do it directly or contract it out.

Figuring out your footprint

The easiest way to figure all this out is to use an online calculator, such as this one from TerraPass that will walk you through calculating your footprint, based on industry standard assumptions.

I checked a couple of different carbon footprint calculators online to see the footprint of a one-way trip from New York City to London. The total distance is 3,443 miles. ClimateCare, a U.K.-based company that offers carbon offsets and calculators, gave a total of 0.77 metric tons, which is equivalent to 1,698 pounds.

TerraPass gave the same answer, provided I selected the 'refractive forcing' option. Refractive forcing is the effect of emitting certain gases and particles at high altitudes, which directly impacts the greenhouse effect, otherwise known as radiative forcing. Without that option, the footprint is only 737 pounds. Clearly, ClimateCare used that option as the default.

I asked Jeremy Richardson, senior energy analyst at the Union of Concerned Scientists (UCS), about the equivalency of buying offsets versus investing directly in the energy efficiency of your own business. While he has no problems whatsoever with buying offsets, as long they are verifiable, he sees a number of advantages in doing what you can in your own facilities first.

For one thing, most investments in energy efficiency will continue to pay back, year after year. You get to see it actually being done, and in some cases experience intangible benefits like a more comfortable workspace. It also provides the opportunity to communicate your values to your customers and employees and perhaps inspire to carry the ball forward in their own worlds.

Image credit: Flickr/pagedooley

RP Siegel, PE, is an author, inventor and consultant. He has written for numerous publications ranging from Huffington Post to Mechanical Engineering. He and Roger Saillant co-wrote the successful eco-thriller Vapor Trails. RP, who is a regular contributor to Triple Pundit and Justmeans, sees it as his mission to help articulate and clarify the problems and challenges confronting our planet at this time, as well as the steadily emerging list of proposed solutions. His uniquely combined engineering and humanities background help to bring both global perspective and analytical detail to bear on the questions at hand.

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