Calculating personal footprint

All together consumers control over 40% of greenhouse gas emissions through choices about efficiency in heat, electricity, transportation consumption and diet.

Here are some very rough calculators.

• EPA calculator (also available as a more transparent spreadsheet)
• British Petroleum’s calculator
• Inconvenient truth calculator
• Personal carbon worksheet from the Vermont Earth Institute.
• For many more calculators, Google “personal carbon calculator”.

 In thinking about total carbon consumption, bear in mind the following:  Most of the calculators compute transportation emissions and emissions in the home through heating and electricity.  They do not provide any standardized measure of emissions in the industrial and commercial sectors that are indirectly influenced by consumer choices.

Further, the online calculators are helpful, but each home and each household is different and the calculators tend to make it harder to see the underlying numbers.  Here are some of the key numbers. 

     Gasoline — 19.5 pounds of CO2 per gallon (1 pound per vehicle mile if your car happens to get 19.5 miles to the gallon).  Note:  This quantity refers only to the direct chemical carbon production in burning a gallon of gasoline. It does not include the full “well to wheels” cost of producing and delivering gasoline which does run a little higher; this is variable and harder to estimate.  It also does not include other greenhouse gases, which amount to another the equivalent of another pound or so of carbon. See the EPA calculator above and backup or see EIA Emission Coefficients.

     Commercial air travel — 0.5 pounds of CO2 per passenger mile.  Note: If four people are travelling, multiply by four.  This is an average number.  Any particular plane is going to travel whether or not one additional passenger is on it.  But the system is responsive to overall demand over time, so it is fair to use average costs.  These numbers are based on energy intensity of certificated air carriers and carbon emissions per BTU of jet fuel (see Table A-204 at this link) or see EIA Emission Coefficients.  Again, this is carbon dioxide only and also not a fully loaded “well to wheels” number.  For shorter flights, a little higher number like .6 lbs is appropriate to reflect take off and landing, for longer flights, a slightly lower number like .4 lbs may be right; see the Inconvenient Truth calculator backup.

     Mass transit travel — 0.5 pounds of CO2 per passenger mile.  Note:  This surprisingly expensive figure is an average figure that should be treated with caution — loading factors on transit systems and parts of transit systems vary widely.  See theTransportation Energy Data Book, Edition 25, Tables 2.11 and 2.12.  See Figure 2.2 for the energy intensity of the Boston transit system (not different).  Transit buses and rail transit look only slightly better than cars in these statistics, but the comparison may be unfair because transit buses typically are doing short haul runs in congested areas.  Unfortunately, the 25th edition is no longer online.  The 26th edition doesn’t include these tables.  However, an equally troubling couple of numbers can be gleaned from 2004 data in tables 9.12 and 2.13 in the 26th edition which place energy use of transit buses at 4,323 BTU per passenger mile as compared to 3,496 for automobiles and 2,750 for rail transit. 

     Electricity in Massachusetts — 1.3 pounds of CO2 per kilowatt hour.  This figure reflects the mix of energy sources for power generation in Massachusetts in 2003.   

     Natural gas — 11.7 pounds of CO2 per therm.  The gas unit of sale is by heat content.  A therm is 100000 BTU which happens to be about 97 cubic feet of  gas.  The computation per therm follows directly from carbon to BTU ratios in EPA Greenhouse Gas Emissions Inventory, Table A-204 (multiply by 3.67 to get CO2 from carbon content) or see EIA Emission Coefficients.

     Heating oil — 22 pounds of CO2 per gallon.  A little more carbon dense than gasoline.  Compare EPA Greenhouse Gas Emissions Inventory, Table A-204 under “distillate fuel” or “residual oil” or see EIA Emission Coefficients.