Methodology: Tackling climate change through livestock

FAO's assessment is based on its newly-developed Global Livestock Environment Assessment Model (GLEAM), which enables the production of disaggregated estimates of GHG emissions and emission intensities for main commodities, farming systems and world regions.

GLEAM uses spatially explicit information from a wide range of sources and predominantly relies on the IPCC (2006) guidelines to compute emissions. Geography is highly important to the assessment of agro-ecological processes, which depend on factors such as soil quality, climate and land use that have contrasted spatial patterns. This methodological development is a major improvement on other global assessments, typically relying on national averages.

The analysis uses a life cycle assessment (LCA) method for the identification of all main emission sources along supply chains; starting from land use and the production of feed through to animal production to processing and transportation of products to the retail point.

The three major GHGs emitted from food and agriculture chains are covered - namely methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2).

Livestock species included in the assessment are large ruminants (cattle and buffalo), small ruminants (sheep and goats), and pigs and poultry (chicken, turkey, ducks and geese).

The year of reference is 2005, as this is the year with the most recent complete set of data required to carry out the analysis. To capture recent trends in land-use change, more recent references were also used.

The robustness of model assumptions were tested through sensitivity analysis and results were compared for plausibility with other studies.

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