Roughly 40% of carbon emissions are under direct individual control — half from transportation and half from electricity and heating in the home (as a nationwide average). An additional few points can be controlled by diet changes.
The 20% half from heating and electricity in the residential sector is documented in another post. It varies from region to region — in cold climates there is more to save from heating.
The transportation sector is harder to allocate to personal consumption. From Table 3-7 in the new EPA inventory of all greenhouse gas emissions, we have for 2005, the following breakdown of CO2 emissions from fossil fuel consumption in the transportation sector:
|Ships and Boats||3.4%|
A similar breakdown is available in Bureau of Transportation Statistics, National Transportation Statistics, Table 4-6 (a table compiling multiple sources for fuel consumption by different types of vehicles which doesn’t quite foot to the MER for total energy consumed in the transportation sector — lower by about 5%). See also the Environmental Defense Fund’s study of the rolling stock, EPA’s computations of emissions per mile for different vehicles, and the Oak Ridge National Laboratory’s Transportation Energy Data Book.
Considering each of these categories, and even if all car and light-duty truck use were personal use, it appears reasonable to attribute no more than 2/3 of total transportation energy consumption to personal, as opposed to business use — i.e., under 2/3 of the approximately 30% of U.S. carbon emissions that derive from transportation are personal — 20% of the U.S. total.