Whenever the causes of climate change are discussed, fossil fuels top the list. Oil, natural gas, and especially coal are indeed major sources of human-caused emissions of carbon dioxide (CO2) and other greenhouse gases (GHGs). But we believe that the life cycle and supply chain of domesticated animals raised for food have been vastly underestimated as a source of GHGs, and in fact account for at least half of all human caused GHGs. If this argument is right, it implies that replacing livestock products with better alternatives would be the best strategy for reversing climate change. In fact, this approach would have far more rapid effects on GHG emissions and their atmospheric concentrations—and thus on the rate the climate is warming—than actions to replace fossil fuels with renewable energy.
Livestock are already well-known to contribute to GHG emissions. Livestock’s Long Shadow, the widely-cited 2006 report by the United Nations Food and Agriculture Organization (FAO), estimates that 7,516 million metric tons per year of CO2 equivalents (CO2e), or 18 percent of annual worldwide GHG emissions, are attributable to cattle, buffalo, sheep, goats, camels, horses, pigs, and poultry. That amount would easily qualify livestock for a hard look indeed in the search for ways to address climate change. But our analysis shows that livestock and their byproducts actually account for at least 32,564million tons of CO2e per year, or 51 percent of annual worldwide GHG emissions.
This is a strong claim that requires strong evidence, so we will thoroughly review the direct and indirect sources of GHG emissions from livestock. Some of these are obvious but underestimated, some are simply overlooked, and some are emissions sources that are already counted but have been assigned to the wrong sectors. Data on livestock vary from place to place and are affected by unavoidable imprecision; where it was impossible to avoid imprecision in estimating any sum of GHGs, we strove to minimize the sum so our overall estimate could be understood as conservative.
The Big Picture
The table to the right summarizes the categories of livestock-based emissions and our estimates of their size. We begin with the FAO’s 7,516 million tons of CO2e per year attributable to livestock, an amount established by adding up GHG emissions involved in clearing land to graze livestock and grow feed, keeping livestock alive, and processing and transporting the end products. We show that 25,048 million tons of CO2e attributable to livestock have been undercounted or overlooked; of that subtotal, 3,000 million tons are misallocated, and 22,048 million tons are entirely uncounted. When uncounted tons are added to the global inventory of atmospheric GHGs, that inventory rises from 41,755 million tons to 63,803 million tons. FAO’s 7,516 million tons of CO2e attributable to livestock then decline from 18 percent of worldwide GHGs to 11.8 percent. Let’s look at each category of uncounted or misallocated GHGs:
Breathing.
The FAO excludes livestock respiration from its estimate, per the following argument:
Respiration by livestock is not a net source of CO2…. Emissions from livestock respiration are part of a rapidly cycling biological system, where the plant matter consumed was itself created through the conversion of atmospheric CO2 into organic compounds. Since the emitted and absorbed quantities are considered to be equivalent, livestock respiration is not considered to be a net source under the Kyoto Protocol. Indeed, since part of the carbon consumed is stored in the live tissue of the growing animal, a growing global herd could even be considered a carbon sink. The standing stock livestock biomass increased significantly over the last decades…. This continuing growth…could be considered as a carbon sequestration process (roughly estimated at 1 or 2 million tons carbon per year).
