This flow chart shows the sources and activities across the U.S. economy that produce greenhouse gas emissions. Energy use is by far responsible for the majority of greenhouse gases. Most activities produce greenhouse gases both directly, through on-site and transport use of fossil fuels, and indirectly from heat and electricity that comes "from the grid."
Emissions data comes from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003, U.S. EPA (using the CRF document). Allocations from "Electricity & Heat" and "Industry" to end uses are WRI estimates based on energy use data from the International Energy Agency (IEA, 2005). All data is for 2003. All calculations are based on CO2 equivalents, using 100-year global warming potentials from the IPCC (1996), based on total U.S. emissions of 6,978 MtCO2 equivalent. Emissions from fuels in international bunkers are included under Transportation. Emissions from solvents are included under Industrial Processes. Emissions and sinks from land use change and forestry (LUCF), which account for a sink of 821.6 MtCO2 equivalent, and flows less than 0.1 percent of total emissions are not shown.