The model uses a classification of farming systems based on the feed use and agro-ecological conditions. GLEAM distinguishes three farming systems for cattle (grazing, mixed and feedlot), two for other ruminant species (grazing and mixed), three for pigs (backyard, intermediate and industrial) and three for chicken (backyard, layers and broilers). Three agro-ecological zones are considered: temperate -which includes temperate regions and tropical highlands, arid -including arid and semi-arid tropics and subtropics, and humid -comprising humid and sub-humid tropics. Overall, this amounts to over 9,000 discrete supply chains, defined as unique combinations of commodity, country, farming system and climatic conditions.

Life Cycle Assessment

The use of Life Cycle Assessment (LCA) in environmental impact analysis is becoming increasingly common. LCA provides a holistic picture of production processes and identifies key stages where impacts are highest. LCA has also the capacity to evaluate intervention options and to avoid possible trade-offs or shifts of impact from one phase to another, thus providing valuable information for stakeholders and decision making processes.

Sources of GHG and global warming potential

GLEAM identifies three main groups of emissions along production chains. Upstream emissions include those related with feed production, processing and transportation. Animal production emissions comprises emissions from enteric fermentation, manure management and on-farm energy use. Downstream emissions are caused by the processing and post-farm transport of livestock commodities.