Table 2. Changes in main elements in IPCC guidelines

Elements	1996 GL	2006 GL	2019 Refinement
Characteristic
Regional characteristic	·Regional only (i.e., North America, Asia, Latin America, Africa, and Middle East)	·Regional only (i.e., North America, Asia, Latin America, Africa, and Middle East)	·Regional only (i.e., North America, Asia, Latin America, Africa, and Middle East)·Productivity based (low productivity, high productivity)
Climate characteristic	·Only based on mean annual temperature (cool, temperate, warm)	·Based on mean annual temperature (cool, temperate, warm)·Able to choose specific annual temperature	·Based on mean annual temperature (cool, temperate, warm)·Based on the elevation, MAP, MAP:PET ratio (i.e., temperate moist, boreal moist, tropical wet)
Equation
CH4 enteric fermentation	Population × EF	Population × EF	Population × EF
CH4 manure management	Population × EF	Population × EF	Population×VS×AWMS×EF1000
N2O manure management	Population × Nex × AWMS × EF3 × 44/28	Population × Nex × AWMS × EF3 x 44/28	Population × Nex × AWMS × EF3 × 44/28
Unit of default value
Emission factors CH4 enteric	Kilogram CH4 per head per year	Kilogram CH4 per head per year	Kilogram CH4 per head per year
Emission factors CH4 manure	Kilogram CH4 per head per year	Kilogram CH4 per head per year	Gram CH4 per kg VS per animal per year
Nitrogen excretion	Kilogram nitrogen per head per year	Kilogram nitrogen per head per year	Kilogram nitrogen per head per year
EF3	Kilogram N2O-N per kilogram nitrogen	Kilogram N2O-N per kilogram nitrogen	Kilogram N2O-N per kilogram nitrogen

IPCC, Intergovernmental Panel on Climate Change; MAP, mean annual precipitation; PET, potential evapotranspiration; EF, emission factor; VS, volatile solid; AWMS, animal waste management systems; N_ex, nitrogen excretion.