21 Beef Cattle and Global Warming

Abstract

Abstract Beef cattle production is an important contributor to global warming both nationally and globally. Through a national life cycle assessment, we have determined that the production of beef cattle in the U.S. produces about 243 Tg of carbon dioxide equivalents (CO2e) in global warming with an intensity of 21 kg CO2e/kg of carcass weight. This is about 3.5% of the national inventory of greenhouse gas (GHG) emissions. Globally, the Food and Agriculture Organization (FAO) estimates the direct GHG emissions from all cattle other than dairy and their manure to be about 2,260 Tg or about 4.5% of the total global GHG emission. An important consideration in calculating the contribution of beef cattle is the assumed global warming potentials (GWP) used to relate the warming effect of methane and other compounds to that of CO2. Recommended values have varied over the past 20 years as we learn more about the warming potential of various gases. Values assumed affect published assessments, so it is important to consider the GWP values used when comparing studies. Methane is unique among the major compounds affecting global warming because it has a relatively short life in the atmosphere (half-life of about 8 years). Methane released by cattle and their manure oxidizes in the atmosphere returning the carbon originally fixed by growing plants back to CO2 completing a natural cycle. To better represent the warming effect of methane in the atmosphere, a model called GWP* has been introduced. To use this model, the change in emission rate over time must be quantified. Compared with 50 years ago in the U.S., we are now producing 20% more meat using about 15% fewer cattle. We estimate that the GHG intensity in cattle production has decreased 34%, and the total GHG emission related to beef cattle production has decreased 21% over this period. Considering the change that has occurred, using the GWP* model reduces the global warming impact of U.S. beef cattle by over 50% relative to the use of the commonly accepted current GWP factors. Global change is more difficult to quantify. The FAO estimates that over the past 50 years, the global number of non-dairy cattle has increased about 39% with a 78% increase in meat production and 36% increase in related methane emissions. Applying these data indicates that use of the GWP* model decreases the warming effect of global cattle by about 20%. When making policy decisions to mitigate GHG emissions, it is important to properly represent the relative warming effect of the important greenhouse gases.