Applied Engineering in Agriculture Vol. 25(3): 431‐442 2009 American Society of Agricultural and Biological Engineers ISSN 0883-8542 431 WHOLE‐F ARM GREENHOUSE GAS EMISSIONS: A REVIEW WITH APPLICATION TO A PENNSYLVANIA DAIRY F ARM D. S. Chianese, C. A. Rotz, T. L. Richard ABSTRACT. Greenhouse gas (GHG) emissions to the atmosphere and their potential impact on global climate have become important concerns world‐wide. Livestock production systems, such as dairy farms, provide both sinks and sources for GHGs. Typical emissions have been quantified in Europe and synthesized to estimate farm‐level GHG emissions. However, fewer data are available in the United States, and little has been done to estimate emissions for our farms. Through an extensive literature review, average GHG flows were quantified for each major farm source and sink including the soil, growing crops, animals, and manure storage. These typical gas exchanges were then combined to estimate farm‐level net emissions for a representative, 100‐cow dairy farm in Pennsylvania. Emissions from animal facilities primarily consisted of animal respiration (532 Mg CO 2 yr ‐1 ) and enteric fermentation (16.9 Mg CH 4 yr ‐1 ) with a total annual emission of 971 Mg CO 2 equivalent (CO 2 e) where each unit of CH 4 is equivalent to 25 units of CO 2 in global warming potential. Manure storage emissions included CO 2 , CH 4 , and N 2 O for a total annual emission of 216 Mg CO 2 e with each unit of N 2 O equivalent to 298 units of CO 2 . Cropland provided a net flux or sink of ‐784 to ‐168 Mg CO 2 e yr ‐1 depending upon the amount of manure carbon sequestered in the soil. The estimated whole‐farm net annual GHG emission ranged from 2.5 to 5.8 Mg CO 2 e per 500 kg livestock unit or 0.50 to 1.2 kg CO 2 e kg ‐1 of milk produced. This review and farm analysis has helped direct modeling efforts by determining the important processes that drive emissions of CO 2 , CH 4 , and N 2 O in dairy production along with expected ranges for these emissions. Such data expand the knowledge base of researchers, farm planners, and policymakers as they work to develop and maintain sustainable farming systems in the United States. Keywords. Greenhouse gas, Dairy farm, Carbon dioxide, Methane, Nitrous oxide. he control of greenhouse gas (GHG) emissions has become an important international issue. Although farmland can serve as a sink or storage for carbon sequestered from atmospheric carbon dioxide (CO 2 ), agriculture is also an important source of emissions. Potential sources of GHGs on dairy farms include the soil, growing crops, animals, and manure. Globally, agriculture contributes approximately 10% of anthropogenic GHG emissions (IPCC, 2007c); similarly, agriculture contributes approximately 6% of U.S. GHG emissions (EPA, 2008). Extensive research in Europe has quantified emissions from individual sources, as well as total farm emissions. Studies have also been performed in the United States to quantify GHG emissions from individual farm sources; however, these data have not been compiled to provide estimates of total farm‐level emissions. This research gap needs to be addressed considering that, as a sector, agriculture is reported Submitted for review in October 2008 as manuscript number SE 7777; approved for publication by the Structures & Environment Division of ASABE in February 2009. Presented at the 2007 ASABE Annual Meeting as Paper No. 074096. The authors are Dawn Sedorovich Chianese, ASABE Member Engineer, Associate, ENVIRON International Corporation, Los Angeles, California; C. Alan Rotz, ASABE Fellow, Agricultural Engineer, Pasture Systems and Watershed Management Research Unit, USDA/ARS, University Park, Pennsylvania; and Tom L. Richard, ASABE Member Engineer, Associate Professor, Agricultural and Biological Engineering Department, The Pennsylvania State University, University Park, Pennsylvania. Corresponding author: C. Alan Rotz, Pasture Systems and Watershed Management Research Unit, USDA/ARS, Building 3702, Curtin Road, University Park, PA 16802; phone: 814‐865‐2049; fax: 814‐863‐0935; e‐mail: al.rotz@ars.usda.gov. to be the greatest contributor of nitrous oxide (N 2 O) and the second greatest contributor of methane (CH 4 ) emissions (EIA, 2007a). Legislative pressure may necessitate the quantification, and eventual reduction, of GHG emissions. Internationally, the results of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) has documented that the effects of climate change are already being felt and that these changes are causing negative impacts in many regions of the globe (IPCC, 2007b). On a national level, the U.S Supreme Court has determined that GHGs are pollutants and, as such, they must be regulated by the EPA (Commonwealth of Massachusetts vs. U.S.E.P.A., Docket No. 05‐1120). As of 2009, no legislation has been passed at the federal level. However, the Supreme Court decision is likely to precipitate movement on the national level for either regulation under existing statutes or new legislation to reduce emissions. In fact, there are several bills and initiatives at the regional and state level, which indicates that concern for addressing GHG emissions is increasing within the U.S. Two regional initiatives are the Western Climate Initiative (WCI) and the Regional Greenhouse Gas Initiative (RGGI); both are consortiums of states investigating the potential reduction of GHG emissions. In 2008, RGGI became the first initiative to auction GHG allowances within the United States. On a state level in 2009, only California had a bill signed into law regulating GHG emissions. Assembly Bill 32 (AB 32) commits California to reducing state‐wide GHG emissions to 1990 levels by 2020, approximately a 25% reduction compared to current emissions. Under AB 32, the California Air Resources Board (CARB) is required to T