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Abstract
The U.S. Agriculture and Forestry Greenhouse Gas Inventory: 1990–2018 was developed as part of a periodic series that presents greenhouse gas emissions and sinks from the agriculture and forest sectors. It serves as an update to previous USDA greenhouse gas inventories and revises estimates for previous years based on improved methodologies. This inventory provides a comprehensive assessment of the contribution of U.S. agriculture (i.e., livestock and crop production) and forestry to U.S. greenhouse gas (GHG) emissions. The document was prepared to support and complement information provided in the official Inventory of U.S. GHG Emissions and Sinks (U.S. GHG Inventory), which is prepared annually by the U.S. Environmental Protection Agency. Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) concentrations in the atmosphere have increased by approximately 46 percent, 165 percent, and 23 percent respectively since about 1750. In 2018, U.S. GHG emissions totaled approximately 6,677 million metric tons of carbon dioxide equivalents (MMT CO2 eq.), rising 3.7 percent from 1990 estimates. Carbon sequestration in the land use, land-use change, and forestry (LULUCF) sector—which includes managed forests, urban trees, and harvested wood products—reduced emissions to a net 5,903 MMT CO2 eq. in the United States in 2018. Agriculture, defined as CH4, N2O, and CO2 emissions from cropped and grazed soils as well as on-farm energy use, accounted for approximately 10 percent of total U.S. emissions (677 MMT CO2 eq.). The primary GHG sources from agriculture are N2O emissions from cropped and grazed soils (338 MMT CO2 eq.), CH4 emissions from livestock enteric fermentation (178 MMT CO2 eq.), CH4 and N2O emissions from managed livestock manure (81 MMT CO2 eq.), and rice cultivation (13 MMT CO2 eq.). CO2 emissions from on-farm energy use contributed 79 MMT CO2 eq. in 2018. Managed forests, which sequestered 774 MMT CO2 eq., are the largest managed carbon sink in the United States. In aggregate, the U.S. agriculture and forestry sector provided a net sink of 227 MMT CO2 eq. in 2018 (including GHG sources from crop and livestock production, grasslands, on-farm energy use, and GHG sinks for cropped and grazed soils, forests, harvested wood products, and urban trees). This report serves to estimate U.S. GHG emissions for the agricultural sector and to quantify uncertainty in emission estimates.