Energy drives the primary source of greenhouse gases (GHGs), of which CO2 is the largest fraction of total CO2 equivalent annual emissions. However, En-ROADS models the emissions more generally of well-mixed GHGs, including CO2, CH4, N2O, PFCs, SF6, and HFCs, the source of each potentially from energy production, energy-consuming capital, agriculture, and waste. Initial emissions of each GHG that comes from each source are taken from 1990 data from PRIMAP 2021, assuming Agriculture includes PRIMAP MAG and LU categories, and Waste includes PRIMAP Waste and Other categories. Land use CO2 emissions are a function of the land use changes and uses as defined in Land Use, Land Use Change, and Forestry and Terrestrial Biosphere Carbon Cycle.
Emissions from Energy Production🔗
Energy production emissions include those from production capacity, production capacity construction, and from production use. Each of these sources applies to extracted fuel, delivered fuel, and electricity generation from each power source. Emissions from energy use depend on the energy intensity, the efficiency of, losses from, and energy produced by each source, i.e., primary energy. The emissions intensity is a measure of GHGs emitted per amount of energy produced. For bioenergy, this is a calculated variable that is a function of the terrestrial biosphere dynamics and the fraction of bioenergy from crops. Energy production capacity emissions default to CH4; energy production construction emissions default to CO2; and energy production use emissions default to CO2, CH4, and N2O. However, each phase of production is a potential source of each GHG, subject to the user’s assumptions.
Emissions from Energy Consuming Capital🔗
Emissions from energy consuming include those from the end use capital, the construction of that capital, and the use of that capital. Consumption capital capacity and use emissions default primarily to PFCs, SF6, and HFCs. However, industry end use capital also emits CH4 and N2O. The construction of energy consuming capital defaults to CO2 emissions only. Despite those defaults, each phase of end use capital is a potential source of each GHG, subject to the user’s assumptions. While policy levers can affect all end use emissions, there is also the option to phase out HFCs only, to capture the Kigali Amendment of the Montreal Protocol which calls for HFCs to be phased out to 80% reduction of 2012 levels by 2047.
Emissions from Agriculture🔗
Emissions from agriculture depends on the area of farmland and the use of that land. Food demand increases with population and GDP per capita. The livestock fraction of diet increases the crops needed because of the feed for the livestock. Moreover, the CH4 and N2O intensity of farmland is greater for livestock than for crops. Crop yield, i.e., the crops produced per hectare of land, also increases in time, thereby requiring less land for the same crop production. The use of crops for bioenergy also puts pressure on farming.
Actions in the food and agriculture system also affect emissions from agriculture. We model simple emission factors, the ratio between production and emission. There are separate factors for methane and nitrous oxide and for crops for food and animal products, in kilogram of gas per ton of production. All four emission factors have been declining historically and are expected to decline in the future, with baseline rates calibrated to FAO data and SSP projections. The rate of change can increase or decrease based on the methane and other gas sliders, representing actions like better feed and manure management, fertilizer runoff reduction and so on.
Both production emissions intensity of production affect methane and nitrous oxide emissions.
Emissions from Waste🔗
Emissions from waste depend on the production ratio, i.e., how much is produced, and the GHG intensity of that which is produced. While waste sources default to emit only CH4 and N2O, they are also a potential source of each GHG, subject to the user’s assumptions.