How the Carbon Emissions Were Estimated
Carbon dioxide emissions are the main component of greenhouse gas emissions caused by human activity. Carbon dioxide is emitted mostly as a byproduct of the combustion of fossil fuels for energy, although certain industrial processes (e.g., cement manufacture) also emit carbon dioxide. The estimates of energy-related carbon emissions require both data on the energy use and carbon emissions coefficients relating energy use to the amount of carbon emitted.
The Energy Information Administration (EIA) is the main source of data on U.S. energy use. Emissions of Greenhouse Gases in the United States 1998 used annual data provided by energy suppliers. However, to obtain more detail on how different sectors use energy, the emissions estimates in Energy and GHG Analysis rely on data from surveys of energy users, such as manufacturing establishments and commercial buildings.
All carbon emissions estimates in "Energy-Related Carbon Emissions Estimates in Manufacturing" were based on tables published in Manufacturing Consumption of Energy 1994, the main data publication of the 1994 Manufacturing Energy Consumption Survey (MECS). The MECS is a national sample of 22,000 manufacturing establishments, subsampled from the Census of Manufactures and conducted for EIA by the Bureau of the Census. The carbon emissions estimates were based on the total first use of energy, which accounts for all energy sources delivered to manufacturers, regardless of subsequent use. Total first use of energy includes both energy used as a fuel and energy used for nonfuel (feedstock) purposes. (For detailed MECS energy definitions, see Calculation of MECS Energy Measures.)
The same emissions coefficients (relating carbon emissions to energy use), and the same estimation procedures, were used in both Emissions of Greenhouse Gases in the United States 1998 and "Energy-Related Carbon Emissions Estimates in Manufacturing". The coefficients originated with the Intergovernmental Panel on Climate Change (IPCC), with additional coefficients for additional energy sources covered by EIA surveys. More details on the estimation methodology can be found in Appendix A of the Greenhouse Gases report.
The basic emissions coefficients, giving the amount of carbon released at full combustion, are contained in Table B1 of that report. The emissions coefficients in Table B1 represent the maximum theoretical amount of carbon that could be released from the energy source. In practice, nearly all the carbon is released during combustion for fuel use, but significant proportions are sequestered when potential energy sources are used other than as fuel. Table A2 in the Greenhouse Gases report gives the proportions of the carbon assumed to be released by different uses of energy sources.
Table B1 of the Greenhouse Gases report does not contain a coefficient for electricity use. The coefficient used for electricity was calculated as the total amount of carbon emitted to generate electricity (calculated from Table 16 of the State Energy Data Report) divided by the total Btu value of net electricity delivered to end-users (calculated from Tables 12 through 15 of the State Energy Data Report).
Given energy data (for both fuel and nonfuel use) and emissions coefficients, carbon emissions were estimated as the product of the quantity of energy used (Btu value), the emissions coefficient (Table B1), and the proportion emitted (Table A2).
File Last Modified: May 31, 2000