Global Livestock Environmental Assessment Model (GLEAM)
Results FAO, 2016.
The livestock sector contributes significantly to the total human emissions of greenhouse gases, it is estimated that livestock production chains emitted a total of 7.1 gigatonnes of CO2-eq globally in 2005, which represents 14.5% of the total anthropogenic emissions. Cattle are the largest emitter of GHG with about 4.6 gigatonnes of CO2-eq, which account for 65% of all emissions, poultry correspond to the lowest emissions, beef is the product with the higher emissions intensity, with a global average of 342 kg of CO2-eq per kg of protein. The emissions linked to animal feed and enteric fermentation represent 47% and 40% of the total of the sector. Latin America-the Caribbean and East Asia have the highest emission levels 1.7 and 1.0 gigatonnes of CO2-eq respectively.
Emissions from livestock supply chains
The livestock sector is a significant contributor to global human-induced GHG emissions. Livestock supply chains emitted an estimated total of 7.1 gigatonnes CO2-eq in 2005. This represents 14.5 percent of all human induced GHG emissions (IPCC, 2007). Methane (CH4) accounts for about 44 percent of the total. Nitrous oxide (N2O) and carbon dioxide (CO2) represent almost equal shares with 29 and 27 percent, respectively.
Emissions by species
Cattle are the main contributor to the sector’s emissions with about 4.6 gigatonnes CO2-eq, which represents about 65 percent of sector’s emissions. Beef and dairy cattle generate similar amounts of greenhouse gases. Pigs, poultry, buffaloes and small ruminants have much lower emissions, representing between 7 and 10 percent of sector’s emissions.
Emissions by commodity and emissions intensities
Beef meat and cattle milk are the two commodities with the highest total emissions, accounting for 2.9 and 1.4 gigatonnes CO2-eq, respectively. They are followed by pig meat, with 0.7 gigatonnes CO2-eq, buffalo meat and milk (0.6 gigatonnes CO2-eq), chicken meat and eggs (0.6 gigatonnes CO2-eq) and small ruminant’s meat and milk (0.4 gigatonnes CO2-eq). The rest of emissions are allocated to other poultry and non-edible products.
A way to compare the performance of different commodities is to express the emissions in terms on a per protein basis. By doing so, beef meat is the commodity with highest emission intensity, with an average of 342 kg CO2-eq per kg of protein. Meat and milk from small ruminants present the second and third highest emission intensities among commodities with averages of 165 and 112 kg CO2-eq per kg of protein. Cattle milk, chicken meat and eggs and pork have lower emission intensities, all below 100 kg CO2-eq per kg of protein. Emission intensities vary greatly among producers, especially in ruminant products. This reflects different agro-ecological conditions, farming practices and supply chains management. Is within this gap between high and low emission intensities where opportunities for mitigation can be found.
Emissions by source
Emissions from livestock supply chains originate from four main processes: enteric fermentation, manure management, feed production and energy consumption. GLEAM provides disaggregated information on emissions from those pathways. Enteric fermentation accounts for the methane generated during the digestive process of ruminants and monogastrics. Feed production accounts for almost 47 percent of total sector’s emissions, with over 3.3 gigatonnes CO2-eq. Enteric fermentation is the second largest source of emissions, with 2.7 gigatonnes CO2-eq or about 40 percent of total emissions. Manure management is responsible for about 10 percent of the total, or 0.7 gigatonnes CO2-eq. Energy consumption, both on-farm and postfarm, account for 0.3 gigatonnes CO2-eq, or nearly 5 percent of the total.
Livestock emissions by region
Regional emissions and production figures vary widely. Differences are explained by variations on the share of ruminant and monogastric species and emission intensities. GLEAM distinguishes different livestock production systems (LPS), namely grassland and mixed for ruminants; backyard, layers and broiler for chicken and backyard, intermediate and industrial for pigs. It allows a more accurate analysis of feed ration composition, MMS, energy consumption and the implications on GHG emissions.
Latin America and the Caribbean have the highest level of emissions, with 1.7 gigatonnes CO2-eq, caused by the specialized production of beef. Although it has dramatically reduced its pace in the last years, historical land-use changes contributed to high CO2 emissions arising from deforestation and pasture expansion. East and Southeast Asia, with over 1.0 gigatonnes CO2-eq, is the second highest emitting region. North America and Western Europe show similar levels of emissions (over 0.6 gigatonnes CO2-eq). South Asia presents a similar level of emissions as the latter region, but only about half of protein production level. Sub-Saharan Africa and Near East and North Africa present comparable emissions figures -slightly above 0.3 gigatonnes CO2-eq, while Eastern Europe, Oceania and Russian Federation share much lower emission levels (around 0.1 gigatonnes CO2-eq).
Emissions reduction from the livestock sector can be achieved by reducing production and consumption, by lowering emission intensity of production, or by a combination of the two. GLEAM does not evaluate the potential of reduced consumption of livestock products. Mitigation potential estimates in GLEAM are based on the wide gap in emission intensities that exists on a global and regional scale and within production systems and agro-ecological regions. The estimation for mitigation is around 30 percent, or about 1.8 gigatonnes CO2-eq, with respect to the baseline scenario. This figure arises from the assumption that producers in a given system, region and agro-ecological zone were to apply the practices of the 10th percentile of producers with the lowest emissions intensities, while maintaining constant output.