Agriculture (including on-farm energy emissions) accounted for about 8 percent of U.S. greenhouse gas (GHG) emissions in 2010. Since farm production represents about 1 percent of total U.S. gross domestic product (in real gross value-added terms), the sector is relatively GHG-intensive. In all U.S. sectors except agriculture, the largest contributor to GHG emissions is fossil fuel combustion for energy. In agriculture, crop and livestock activities are unique sources of nitrous oxide and methane emissions, notably from soil nutrient management, enteric fermentation (a normal digestive process in animals that produces methane), and manure management. These emissions dominate the contribution of energy related emissions in the sector. The land-based activities of agriculture—as well as forestry—also have the unique capacity to withdraw (“sequester”) carbon dioxide (CO2) from the atmosphere and store it in soil and biomass sinks through activities such as no-till on cropland or land use change from croplands to grasslands. EPA estimates that U.S. carbon land-sinks offset close to 15.8 percent of total U.S. emissions in 2010. Agriculture provided 4 percent of U.S. sinks in 2010. This chart updates one found in the ERS report, Economics of Sequestering Carbon in the U.S. Agricultural Sector, TB-1909, March 2004.