Emissions🔗
En-ROADS models the emissions of well-mixed greenhouse gases (GHGs), including CO2, CH4, N2O, PFCs, SF6, HFCs, CFCs and HCFCs. For each gas, each potential source is modeled: energy production, energy-consuming capital, agriculture, and waste. CO2 from energy is the largest source of total equivalent annual emissions, driven by total energy demand, energy choices, and energy supply infrastructure constructed to meet that demand. Other emission sources are ultimately driven by demand along with technology and practices which determine the emissions intensity of each activity for each gas.
Data for calibrating emissions are found under Initialization, Calibration, Model Testing. In particular, initial values for the non-CO2 GHGs are taken from 1990 data from PRIMAP 2021, assuming Agriculture includes PRIMAP MAG and LU categories, and Waste includes PRIMAP Waste and Other categories. Values for CO2 are calibrated to multiple sources.
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 (infrastructure), construction of that production capacity, and from energy use. Emissions from each stage are calculated for electricity generation and non-electric use from each power source.
Energy use of fossil fuels and bioenergy produce the largest share of emissions. These depend on the GHG intensity of each source and use, and the primary energy used. Primary energy in turn depends on demand for each fuel, efficiency, and losses. Fossil fuels produce mostly CO2 in every application; a small amount of CH4 and N2O are produced in some non-electric applications from incomplete combustion. Bioenergy produces CO2, CH4, and N2O when burned.
Construction of all energy infrastructure, including renewable energy, produces CO2 reflecting the energy used for construction and materials, modeled as a constant amount per unit of electricity or fuel capacity. Fossil fuel infrastructure produces CH4 from off-gassing and leaks, the rate of which can be affected by policy controls.
Emissions from Energy Consuming Capital🔗
End use capital represents all the constructed and manufactured materials that use energy or cause emissions. Capital is modeled in three economic sectors (residential & commercial, industry, transport) and three ages (vintage 1, 2, 3). CO2 is emitted when new capital is constructed, similar to energy infrastructure, a fixed amount per unit of capital. Besides the energy used by capital and the emissions calculated under energy use above, there are direct emissions specific to each sector.
Industrial capital emits F-gases (PFCs, SF6, and HFCs), N2O, and a tiny amount of CH4 as a byproduct of some processes. Byproduct emissions are modeled as directly proportional to total industrial capital. The ratios are subject to changes in practices and technology. Included in these calculations are the emissions of F-gases used as propellants in foams, aerosols, fire extinguishers, etc - they might be emitted in any sector but are produced by industrial capital. Industry also uses F-gases as solvents, insulating gases, etc. This application is modeled as a stock of each F-gas in use which can leak, and will be discarded, recycled, or destroyed at end of life. The fractions for each flow are subject to changes in practices and technology, and the demand for F-gases for these applications can change if alternatives are adopted.
The largest emissions source from capital is refrigerants in cooling systems: refrigerators, heat pumps, air conditioners, etc. Demand for cooling (in GW capacity) is estimated from electric demand in the residential and commercial sector, and total energy demand in the transportation and industry sectors. The ratio of HFCs as refrigerants per GW of cooling demand is estimated from initial emissions rates and trends, and can change if alternatives are adopted. There are stocks of HFCs in current equipment and in discarded equipment, which emit depending on leak, recycling, and destruction rates, subject to changes in practices and technology.
Finally, ozone-depleting substances (ODSs, also called “Montreal gases”, principally CFCs and HCFCs) are modeled as an aggregate group with averaged characteristics. There is an exogenous emission - calibrated to observed atmospheric concentrations - plus a user-adjustable assumed stock representing the uncertain remaining chemicals in stockpiles and obsolete equipment. ODS leak rates are fixed, but the stocks of ODS can be destroyed before they leak if action is taken.
Emissions from Agriculture🔗
Agriculture is the largest sector source of both methane and nitrous oxide, as well as the largest driver of deforestation. Emissions from livestock and crops are modeled individually. The demand as described in the Land Section determines the amount of animal product, and crop production, including the crops grown for energy and livestock feed. The emission factors for CH4 and N2O for both crops and livestock have base improvement rates as observed from production and emission data. Policies to lower emissions from agriculture are modeled as an adoption process of best practices, such as better feed and manure management, fertilizer runoff reduction and so on. This brings the emission factors towards their minimum practical values.
Actions in the food and agriculture system also affect emissions from agriculture. Reducing the trend towards greater consumption of food from animals lowers emissions in two ways: by shifting some demand to crops, which have lower emission factors; and by reducing the need for crops for animal feed. Reducing food waste lowers the production needed to meet food demand, lowering the activity that produces emissions in both crops and livestock.
Emissions from Waste🔗
The waste sector represents both landfill (garbage / trash / municipal solid waste) and wastewater (sewage). Both subsectors emit both CH4 and N2O. The production of waste is modeled as a ratio of waste per person, representing only the waste relevant for emissions. Waste per person follows a declining trend. The emission factors for waste are calculated from initial data. Both the production ratio and the emission factors are reduced by policy, as many actions (such as recycling and composting) overlap in their effects.
Model Structure🔗
