Last reviewed on August 29, 2013

Greenhouse Gas Inventory - Archived 2020 Forecast


This California 2020 GHG emissions forecast, used in the AB 32 Scoping Plan, is the projected emissions that would occur in 2020 if no mitigation actions were taken, i.e., "business-as-usual" (BAU). This forecast was necessary to assess the amount of GHG reductions necessary to return California to 1990 emission level and is based on the first GHG inventory published by ARB, covering years 1990 to 2004, available in the archive section of this site. The current edition of California's GHG Inventory covers years 2000 to 2008 and is available on the current data page. The current edition of California's 2020 GHG emissions forecast is available on the current forecast page.


Archived 2020 GHG Emissions Forecast

Bar plot of the GHG emissions in 1990, 2004 anf forecast for 2020
(Forecast last updated: October 2008)
Inventory Summary for Scoping Plan Emissions (MMTCO2E)
2002-2004 Average 2020 Forecast
Transportation 179.3 225.4
On Road 168.7 209.1
- Passenger Vehicles 133.9 160.8
- Heavy Duty Trucks 34.7 48.3
Ships & Commercial Boats 3.3 6.3
Aviation (Intrastate) 3.2 4.8
Rail 3.0 3.8
Unspecified 1.2 1.4
Electric Power 109.0 139.2
In-State Generation 52.5 87.2
- Natural Gas 44.2 78.8
- Other Fuels 8.4 8.4
Imported Electricity 56.5 52.0
- Unspecified Imports 24.3 26.1
- Specified Imports 32.2 25.9
Commercial and Residential 41.0 46.7
Residential Fuel Use 28.5 32.1
- Natural Gas 26.9 30.6
- Other Fuels 1.6 1.5
Commercial Fuel Use 11.9 14.0
- Natural Gas 10.5 12.3
- Other Fuels 1.4 1.6
Commercial Cogeneration Heat Output 0.6 0.7
Industrial 95.9 100.5
Refineries 35.0 36.7
General Fuel Use 21.3 19.8
- Natural Gas 14.0 11.7
- Other Fuels 7.3 8.1
Oil & Gas Extraction 14.2 14.2
- Fuel Use 13.4 13.4
- Fugitive Emissions 0.8 0.7
Cement Plants 9.7 12.6
- Clinker Production 5.7 7.6
- Fuel Use 4.1 5.0
Cogeneration Heat Output 9.2 9.3
Other Process Emissions 6.4 7.9
Recycling and Waste 5.6 7.7
Landfills1 5.6 7.7
High GWP 14.7 46.9
Ozone Depleting Substance Substitutes 12.9 45.0
Electricity Grid SF6 Losses 2 1.0 1.0
Semiconductor Manufacturing1 0.8 0.8
Agriculture 27.7 29.8
Livestock 13.9 16.2
- Enteric Fermentation (Digestive Process) 7.0 8.2
- Manure Management 6.9 8.0
Crop Growing & Harvesting 9.2 9.2
- Fertilizers 7.1 7.1
- Soil Preparation and Disturbances 2.0 2.0
- Crop Residue Burning 0.1 0.1
General Fuel Use 4.6 4.5
- Diesel 3.3 3.3
- Natural Gas 0.7 0.5
- Gasoline 0.4 0.4
- Other Fuels 0.2 0.2
Forestry 0.2 0.2
Wildfire (CH4 & N2O Emissions) 0.2 0.2
Forestry Net Emissions (-4.7) 0.0
1 These categories are under the Industrial Sector in ARB's GHG Emission Inventory
2 This category is under the Electric Power Sector in ARB's GHG Emission Inventory

Forecasting Approach

ARB is responsible for developing the California Greenhouse Gas Emission Inventory. The Inventory accounts for all greenhouse gas (GHG) emissions within the state of California and supports the AB 32 Climate Change Program. The Inventory also serves as the basis for developing future year GHG emission forecasts necessary to support measure development and Scoping Plan recommendations. ARB staff has developed a year 2020 BAU forecast of GHG emissions for use in developing the Scoping Plan.

Greenhouse Gas Emission Inventory

ARB’s GHG emission inventories are based on statewide fuel use, process, and activity data to estimate emissions. These estimates use the actual amount of all fuels combusted in the state, which accounts for over 85 percent of the greenhouse gas emissions within California.

This approach to inventory development is referred to as “top-down” because data are collected in the aggregate for the entire state, not at the level of the individual facility or emission-point. In contrast, a “bottom-up” inventory uses data from individual sources to determine emissions and sums those emissions to form a statewide total. Once ARB’s mandatory reporting regulation is implemented, facility-specific data will become available and will be used to further improve the inventory. Current GHG emissions data can be found on the inventory data page

Business-as-Usual 2020 Emissions

ARB staff estimated 2020 business-as-usual GHG emissions, which represent the emissions that would be expected to occur in the absence of GHG reductions. ARB staff estimates the statewide 2020 business-as-usual greenhouse gas emissions will be 596 MMTCO2E. Emission reductions from the recommended measures in the Scoping Plan total 169 MMTCO2E, enabling California to attain the 2020 emissions limit of 427 MMTCO2E.

The 2020 BAU emissions estimate was derived by projecting emissions from a past baseline year using growth factors specific to each of the different economic sectors. For the purposes of the Scoping Plan, ARB used three-year average emissions, by sector, for 2002-2004 to forecast emissions to 2020. At the time the Scoping Plan process was initiated, 2004 was the most recent year for which actual data were available.

This 3-year average of known emissions will dampen unusual variations in any given year that would make the baseline year unrepresentative for forecasting. For example, an unusually hot, dry year might cause much higher power consumption and less hydroelectric power generation, and therefore increased emissions associated with power generation than would have otherwise been expected.

Forecasting Method

Growth factors are sector-specific and are derived from several sources, including the energy demand models generated by California Energy Commission (CEC) for their biennial Integrated Energy Policy Report (IEPR), business economic growth data developed for ARB’s criteria pollutant forecast system (CEFS), population growth data from the California Department of Finance, and projections of vehicle miles traveled from ARB’s on-road mobile source emissions model, EMFAC2007. For the electricity and other energy sectors, ARB consulted with CEC to select the most appropriate growth factor.

ARB’s forecasting method is similar to other GHG forecasting approaches, including the method used in the Climate Action Team 2006 Report. Where appropriate, ARB used updated and improved growth factors for estimating 2020 emissions sector-by-sector. These future emissions are projected in the absence of any policies or actions that would reduce emissions. The resulting BAU estimates are compared to the 2020 target set by the Board in December 2007 to determine the total statewide GHG reductions needed.

Sector Forecasts

Descriptions of the 2020 BAU forecasts for the major sectors of the inventory are given below with key assumptions staff used to estimate these future emissions.


The 2020 business-as-usual emissions forecast for the electric power sector is 139.2 MMTCO2E. These emissions are the result of in-state power generation plus specified and unspecified imported power. BAU forecasted emissions assume that all growth in electricity demand by 2020 will be met by in-state natural gas-fired power plants. Expected growth in renewable power to meet the current and proposed Renewables Portfolio Standard (RPS) is not included in the BAU. This allows the Scoping Plan reductions from increasing renewable power generation to be additive with the BAU forecasted 2020 emissions.

The 2020 BAU forecast for emissions from specified sources of imported electricity (i.e., power received from specific out-of-state power plants) is assumed to decrease resulting from the closure of one coal-fired power plant (i.e., Mojave) previously supplying imported electricity. The demand previously served by the closed plant is now replaced by in-state natural-gas generation.

Based on outputs from the CEC’s electricity demand models, in-state electricity generation and specified imports will not meet the State’s full electricity demand in 2020. The remaining demand is assumed to be met by unspecified imported electricity (i.e., power received from a mix of power generating sources outside the State).


GHG emissions in 2020 from the transportation sector as a whole are expected to increase from current levels to 225.4 MMTCO2E. This forecasted increase is dominated by increases in emissions from on-road transportation, i.e., passenger cars and heavy-duty trucks. To forecast on-road transportation emissions, ARB staff used 2007 fuel sales data obtained from the California Board of Equalization and estimated 2020 emissions based on the growth in projected vehicle miles traveled (VMT) derived from EMFAC2007. This BAU forecast assumes no change in vehicle fleet mix over time.


The industrial sector consists of large stationary sources of GHG emissions and includes oil and gas production and refining, cement plants, and large manufacturing facilities. Emissions for this sector are forecasted to grow to 100.5 MMTCO2E by 2020, an increase of approximately five percent from the average emissions level of 2002-2004.

Business-as-usual forecasted emissions for this sector are variable, but overall are not expected to grow substantially. Most of the growth from this sector comes from the fuel use and process emissions of two industries: Cement Plants and Refineries.

Emissions from the combustion of natural gas are expected to grow for some industries (e.g., cement plants) and decline for others (e.g., food processors). These assumptions of growth and decline in natural gas demand are based on outputs from energy demand modeling conducted by CEC staff for the 2007 IEPR.


Forecasted BAU emissions in 2020 for landfills are 7.7 MMTCO2E. This forecast uses a recognized landfill gas emissions model developed by the Intergovernmental Panel on Climate Change (IPCC) and data from the California Integrated Waste Management Board (CIWMB).

The forecast reflects assumptions regarding the continued decay of existing waste in landfills and estimates on the amount and character of new waste deposited in landfills through 2020.

Commercial & Residential

The Commercial and Residential sector is expected to contribute 46.7 MMTCO2E or about eight percent of the total statewide GHG emissions in 2020. Forecasted BAU emissions from the Commercial sector include combustion emissions from natural gas and other fuels (i.e., diesel) used by office buildings and small businesses. Residential emissions result primarily from natural gas combustion used for space heating and for hot water heaters.

Growth in emissions from the Commercial and Residential sector is due primarily to the expected increase in population and assumed increase use of natural gas. Emissions from the use of other fuels, such as diesel fuel, are assumed to remain relatively constant over time.

High Global Warming Potential Gases

The forecasted BAU 2020 emissions of High Global Warming Potential (High-GWP) gases are 46.9 MMTCO2E. High-GWP gases, including sulfur hexafluoride (SF6) from electric utility applications, substitutes for ozone depleting substances (ODS) (primarily HFCs and PFCs), and other High-GWP gases used in semiconductor manufacturing and other industrial processes are combined under one sector for purposes of the Scoping Plan. Assumptions used to forecast business-as-usual emissions of High-GWP gases vary by GHG.

SF6 emissions occur primarily from leaks in electrical transmission system equipment in which SF6 is used as an electrical insulator. SF6 leaks are constant from a given piece of electrical equipment and are not related to the use of the equipment. The probable expansion of the electrical transmission system infrastructure is assumed to result in more SF6 emissions from leaks. However, at the same time, technical improvements to the transmission system equipment result in fewer leaks, reducing SF6 emissions. ARB assumes that the effect of an expansion of the electrical transmission system infrastructure, combined with the technical improvements to the equipment in the system, will result in no net change in emissions in 2020.

Emissions of HFCs and PFCs as ODS substitutes occur from their use in refrigeration and air conditioning systems, among other commercial and industrial applications. The high business-as-usual forecasted emissions in 2020 comes about as ODS's are rapidly replaced by ODS substitutes, as more ODS's are phased out.


BAU emissions from the agriculture sector are forecasted to increase about seven percent from current levels to 29.8 MMTCO2E in 2020, due exclusively to the assumed increase in livestock population. The agriculture sector includes emissions from livestock, i.e., digestive processes and manure management; combustion of liquid and gaseous fuels used for irrigation and crop production; emissions from fertilizer use and application of other soil additives; and emissions from agricultural residue burning.

Agricultural residue burning and livestock emissions were forecasted using ARB’s criteria pollutant forecasting approach. Forecasted emissions from the combustion of natural gas were estimated using outputs from the 2007 IEPR developed by CEC. Other agriculture-rated emissions were either held constant or extrapolated using historical trends to obtain a 2020 BAU estimate.


The forestry sector is unique in the inventory because it includes emissions from forest and rangeland disturbances, such as wildfires and wood decomposition, as well as removal (or sinks) of CO2 from the atmosphere due to carbon sequestration into woody tissues. The inventory combines positive emissions and negative removals into a single, net value.

Several factors are operating to potentially decrease net GHG emissions from the forest sector. These factors include loss of forest land due to conversion to other uses and increased threat of wildfires. Because of this, forest sinks have decreased from the 1990 estimate (-6.7 MMTCO2E) to a current level of approximately a -5 MMTCO2E. As a result of the continuing effects of these factors, the 2020 forecast for net emissions from the forest sector is zero. This assumes that forest emissions and sinks will balance in 2020.