The Earth's temperature is rising as a result of increased atmospheric concentrations of greenhouse gases (see Basic Information on Climate Change from U.S. Environmental Protection Agency). According to National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA) data, the Earth's average surface temperature has increased by an estimated 1.3º F over the last century. If greenhouse gas (GHG) emissions continue increasing at a high rate (essentially business-as-usual), climate models predict that warming could increase 7.2º F above 1986–2005 levels by the end of this century (Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report Vol. I, Summary for Policy Makers). While alternative scenarios with lower rates of increase in atmospheric greenhouse gases and temperatures exist, they all call for more frequent and lengthy heat waves in the future. As the Earth warms, currently wet regions are expected to receive more rainfall, and currently dry regions receive less, although there will be exceptions.
Human activities across the globe—including fossil fuel use, land cover conversion (deforestation), and agricultural practices—are contributing to the buildup of atmospheric carbon dioxide and other greenhouse gases. Since 1750, land-use change has been responsible for roughly 32 percent of human emissions of carbon dioxide (IPCC Fifth Assessment Report, Vol. I).
Within the United States, agriculture and forestry together accounted for 9.4 percent of U.S. greenhouse gas emissions in 2012, or 10.4 percent when electricity sector emissions are allocated to the sectors using electricity.
The greenhouse gas profile of the agricultural and forestry sector differs substantially from the profile of other sectors. Agriculture is an emission-intensive sector; it accounted for less than 1 percent of U.S. production (in real gross value-added terms), but emitted 10.4 percent of U.S. GHGs in 2012. Energy-related CO2 emission sources—which dominate GHG emissions in most other production sectors—are dwarfed in agriculture by unique crop and livestock emissions of nitrous oxide and methane. Crop and pasture soil management are the activities that generate the most emissions, due largely to the use of nitrogen-based fertilizers and other nutrients. The next largest sources are enteric fermentation (digestion in ruminant livestock) and manure management. Agriculture and forestry are unique in providing opportunities for withdrawing carbon from the atmosphere through biological sequestration in soil and biomass carbon sinks. The carbon sinks, which are largely due to land use change from agricultural to forest land (afforestation) and forest management on continuing forest, offset 13.5 percent of total U.S. GHG emissions in 2012.
Land-based activities with highest potential for sequestering carbon are conversion of cropland and pasture land to forest uses (afforestation), and management of forest land. In addition, changes in agricultural practices and land uses can reduce GHG emissions. For land remaining in crop and pasture uses, activities with the highest potential include improved grazing management on rangeland and pasture, retirement of cropland (through the Conservation Reserve Program, for example), adoption of no till on cropland, and land use change from cropland to less intensive farmland uses. Improved fertilizer management (e.g., reducing application rates and using slow-release fertilizer or nitrification inhibitors) can reduce GHG emissions from soils. Changes in livestock management that focus on the reduction of methane emissions and the capture of biogas (e.g., improved diet and installation of anaerobic digesters) also offer mitigation potential; however, some manure management approaches (such as handling manure in solid form, via composting) could increase GHG emissions.