Following a life-cycle analysis approach, the report evaluates "that livestock are responsible for 18% of greenhouse gas emissions."[3] Greenhouse gas (GHG) emissions arise from feed production (e.g. chemical fertilizer production, deforestation for pasture and feed crops, cultivation of feed crops, feed transport and soil erosion), animal production (e.g. enteric fermentation and methane and nitrous oxide emissions from manure) and as a result of the transportation of animal products. Following this approach the report estimates that livestock "is responsible for 18 percent" of total anthropogenic carbon dioxide emissions,[4] but 37% of methane and 65% of nitrous oxide emissions[citation needed]. The main sources of emissions were found to be: