NPR indicates that agriculture contributes about 10% of GH gasses worldwide. Geographic areas with high concentrations of agriculture, such as Iowa, contribute up to 30%. The Sierra Club indicates that there are three main components to agricultural GHG: 1) CO2 generated by petroleum products used in farm operations, equipment, and transport; 2) CH4 generated by the storage of animal digestive waste; and 3) N2O released from the ground in the tilling process.