The Estimation and Mitigation of Agricultural Greenhouse Gas Emissions from Livestock

Abstract

Emissions of methane (CH4) and nitrous oxide (N2O) from agricultural activities currently comprise 10-12% of the world’s total anthropogenic greenhouse gas (GHG) emissions. They are also forecast to rise by 30% above current levels by 2050. At the Conference of the United Nations Framework Convention on Climate Change (UNFCCC) held in Paris in December 2015, more than 100 countries indicated that they would reduce agricultural GHG emissions as part of the global effort to keep warming to a maximum of 2°C. Emissions from ruminant livestock present a particular challenge as enteric CH4 emissions alone comprise ~40% of total agricultural emissions. Estimating emissions from animal agriculture can be done through simple estimates, generically available data on animal populations and regional-level fixed emission factors per animal. But these estimates are subject to very large uncertainties and their appropriateness for estimating emissions at the country level is questionable. More appropriate country-specific methods can be developed using local data and expert opinion in the first instance, even in the absence of country-specific emission factors. Reducing GHG emissions from ruminant livestock is challenging technically even if livestock production is constant, and is particularly challenging if the sector is increasing in size. Internationally the quantity of GHG produced per unit of product has been declining consistently and for both cattle meat and milk than 50 years ago. This decline is largely due to increased efficiency of production. Increasing efficiency is therefore a key component of agricultural GHG mitigation. Increasing efficiency,while essential, may not be enough on its own. New technologies are therefore needed and for ruminant livestock there are some promising products; compounds that inhibit enteric CH4, vaccines, low emitting sheep have been successfully bred and, a variety of low emitting feeds, and feed additives.