Chapter 4

Greenhouse Gas Emissions Accounting

With contributions by Eli Krispi

Greenhouse gas (GHG) emissions accounting is a set of methods and approaches for quantifying GHG emissions in support of climate action planning, implementation, monitoring, evaluation, and reporting. It is mostly a technical exercise requiring data collection, analysis, and management and usually follows established protocols and uses specialized software and databases. GHG emissions accounting is now a specialized area of practice and even has a professional certification through the World Bank.1 GHG emissions accounting is generally divided into three distinct areas: inventory, forecast, and reduction strategy quantification.

Principles of GHG Emissions Inventories

The technical definition of a community GHG emissions inventory is an accounting of GHGs emitted into (and, in some cases, removed from) the atmosphere by a community over a period of time, usually a calendar year. The inventory provides the baseline or existing condition from which to measure progress toward a GHG reduction target. It is a form of gathering quantitative data to support planning, similar to transportation studies that quantify the amount of traffic on roadways or housing studies that quantify the housing stock and assess its affordability.

A GHG emissions inventory can be likened to an assessment you might do to begin a weight loss plan. First, you may weigh yourself and do an overall health assessment. You may consider your weight, cholesterol level, and percentage of body fat. Then you determine the sources of your calories and nutrients: cereal for breakfast; a burger, fries, and soft drink for lunch; and pasta, salad, and a glass of wine for dinner. You will use the information gathered in this inventory to understand where your calories come from and to change your intake of food and nutrients for a healthier future. In the same way, a community needs to understand its current emissions level, how community choices affect that level, and how it can change.

At the community scale, inventories focus on identifying sources and estimating quantities of GHG emissions from each source. The primary sources are motor vehicles that directly consume fossil fuel as well as buildings and operations that consume fossil fuels directly (e.g., gas for heating and cooking) and indirectly (e.g., fossil fuels needed to generate electricity).

There are a number of other sources of GHG emissions at the community level, but transportation and energy sources emit the majority of GHG emissions in most communities. GHGs are not measured directly; instead, they are calculated based on measurements of a certain activity, such as how much electricity and natural gas is used in the community, how much people drive, and how much waste is generated. Each of these can be measured or estimated for a community and then converted to GHG emissions using standardized tools and databases. Because GHGs are calculated in this indirect fashion, they should be considered estimates, not exact measures. Box 4.1 provides an example set of estimates relating GHG emissions to community actions. By following appropriate protocols, these estimates can be sufficiently accurate for climate action planning.

Box 4.1

Conversion of Greenhouse Gas Emissions to Familiar Equivalents

One thousand metric tons (MT) of CO₂ emissions is approximately equivalent to the following:

• • CO₂ emissions from 112,524 gallons of gasoline consumed
• • CO₂ emissions from 2,315 barrels of oil consumed
• • CO₂ emissions from the electricity use of 174 homes for one year
• • CO₂ emissions from burning 5.5 railcars’ worth of coal
• • annual CO₂ emissions of 0.0003 coal-fired power plants
• • CO₂ emissions from 40,880 propane cylinders used for home barbecues
• • greenhouse gas emissions avoided by recycling 350 tons of waste instead of sending it to the landfill
• • carbon sequestered by 16,535 tree seedlings grown for 10 years
• • carbon sequestered annually by 210 acres of pine or fir forests
• • carbon sequestered annually by 8 acres of forest preserved from conversion to cropland in one year

Source: “Greenhouse Gas Equivalencies Calculator,” U.S. Environmental Protection Agency, https://www.epa.gov/energy/greenhouse-gas-equivalencies-calculator.

A typical GHG emissions inventory will report the total annual emissions attributed to the community and a breakdown of their sources. Table 4.1 is an example from Placer County, California, which displays the conversion factors used to calculate GHG emissions.

Table 4.1. Example of conversion and emissions factors used by Placer County, California, to calculate community-wide GHG emissions

Quantity	Value	Notes
Standard unit conversions
1 pound (lb.)	0.0004536 metric tons (tonnes)	Engineering standard
1 short ton (ton)	0.9072 metric tons (tonnes)	Engineering standard
1 metric ton (tonne)	1.1023 short tons (tons) 2,204.62 pounds (lbs.)	Engineering standard
1 kilowatt hour (kWh)	3,412 Btu (Btu)	Engineering standard
1 therm	100,000 Btu (Btu)	Engineering standard
Placer County—sample CO2 (only) emissions factors
1 megawatt hour (MWh) of electricity	404.51 lbs. CO2	PG&E 2015 emissions factor certified by the California Climate Action Registry
1 MMBtu of natural gas	53.02 kilograms (kg) CO2	USCP, appendix C
1 vehicle mile traveled (passenger car)	0.323 kilograms (kg) CO2	CARB EMFAC 2014 County Emissions Inventory Model

Note: The emissions factors used by Placer County are average estimates of the greenhouse gases (CO₂ specifically in this example) produced by a unit of natural gas, electricity, and VMT within Placer County in the year 2015. The full set of emissions factors are documented in the inventory: https://placer.ca.gov/sustainplacer.

Abbreviations: MMBtu, million British thermal units; PG&E, Pacific Gas & Electric (utility); CARB, California Air Resources Board; EMFAC, motor vehicle emissions model; USCP, U.S. Community Protocol; VMT, vehicle miles traveled

Source: Placer County, Community-Wide and County-Operations 2015 Greenhouse Gas Emissions Inventories (2015).

These are a combination of standard unit conversions and conversion factors derived from data specific to Placer County. These factors are used to quantify the GHG emissions produced by a community. Table 4.2 is an example of a standard summary of total emissions attributable to a community. The table shows emissions in metric tons of carbon dioxide equivalents (CO_2e). As discussed in appendix A, not all GHGs are equivalent to CO₂ in their global warming potential, so they are usually converted to the same units. The table also shows the breakdown by the four most common sectors: residential energy, nonresidential energy, transportation, and waste. In some inventories these sectors are further subdivided (e.g., separating nonresidential into commercial, industrial, and agricultural), and some communities also break down total emissions by fuel type (e.g., gasoline, natural gas, coal).

Table 4.2. Example of community-wide greenhouse gas emissions inventory summary

Sector	Metric tons CO2e/year	Percent of total
Residential energy	49,178	18.4
Commercial/industrial energy	54,619	20.4
Transportation	150,663	56.4
Waste	12,777	4.8
Total community-wide emissions	267,237	100

Local governments most commonly use two types of inventories: a community-wide inventory and a local government operations inventory. It is considered best practice to conduct community-wide inventories that include assessing local government operations as a distinct subset of the total emissions.2 Local government operations typically comprise between 3% and 8% of community-wide emissions. Some communities do not break out local government operations. Conversely, some communities choose to inventory only local government operations emissions. Usually this is because they are adopting reduction targets and emissions reduction strategies for local government operations only.

Current best practice suggests that communities should prepare a baseline GHG emissions inventory prior to the development of a climate action plan or climate strategies. Communities that are members of ICLEI–Local Governments for Sustainability3 or signatories to the Global Covenant of Mayors for Climate & Energy4 commit to doing so. Though preparing an inventory is good practice, a community does not need to know its specific GHG emissions to know that taking actions to improve energy efficiency and conservation and reduce fuel consumption are prudent cost-saving measures that also provide community quality of life benefits. The GHG emissions inventory is a detailed, technical exercise that will take time and expertise beyond the capacity of some communities, but there are good reasons to undertake this task. Additionally, there are numerous resources available to help local governments prepare inventories, including those provided in the “Additional Resources” chapter at the end of this book.

The most effective GHG emissions reduction strategies are tied specifically to sources of GHG emissions identified and quantified in an inventory, with an emphasis on reducing emissions from a community’s largest sources of GHGs. The most effective strategies will also quantify the expected GHG reduction benefits and contribution of the strategies toward achieving the overall reduction target. According to the U.S. Environmental Protection Agency, communities use GHG inventories to do the following:

• • identify sources of emissions and their current magnitude within an area
• • identify and assess emissions trends
• • establish a foundation for projecting future emissions
• • provide a basis for future reduction targets
• • set a benchmark for tracking progress toward a reduction target
• • quantify the benefits of proposed emissions reduction strategies
• • provide a basis for developing a climate action plan5

Inventories form the basis for decision-making; they should be transparent and reproducible and should follow established protocols. This will also ensure consistency and comparability with future updates and other inventories. There are five accounting and reporting principles to ensure that “GHG data represent a faithful, true, and fair account” of a local government’s GHG emissions:

1. 1. Relevance: The GHG inventory should appropriately reflect the GHG emissions of the community and should be organized to serve the decision-making needs of users.
2. 2. Completeness: All GHG emission sources and emissions-causing activities within the chosen inventory boundary should be accounted for. The inventory should clearly explain why any sources of emissions were excluded or why any additional sources beyond those in the community were included.
3. 3. Consistency: Consistent methods should be used in the identification of boundaries, analysis of data, and quantification of emissions to enable meaningful trend analysis over time, demonstration of reductions, and comparisons of emissions. Any changes to the data, inventory boundary, methods, or any relevant factors in subsequent inventories should be disclosed.
4. 4. Transparency: All relevant issues should be addressed and documented in a factual and coherent manner to provide a trail for future review and replication. All relevant data sources and assumptions should be disclosed, along with specific descriptions of methodologies and data sources used.
5. 5. Accuracy: The reported GHG emissions in an inventory should be as accurate as possible. The calculation of GHG emissions should not be systematically over or under the actual emissions. Accuracy should be sufficient to enable users to make decisions with a reasonable assurance as to the integrity of the reported information. Uncertainties in the quantification process should be reduced to the greatest extent possible.6

It is important to keep in mind that while GHG emissions inventories based on current best practices are quite robust, they are still estimates with a degree of error. Preparers should not spend substantial energy trying to account for the last 1% of emissions or estimating to significant digits that are not warranted by the many assumptions and estimates that make up the inventory calculations.

The Basic Inventory Process

The process of preparing a GHG emissions inventory entails a number of decisions and procedural steps that have been codified through a variety of GHG emissions inventory protocols and related software developed by national and international organizations. The basic steps for conducting a GHG emissions inventory in most protocols are as follows:

1. 1. Data collection
2. 2. Emissions calculations and reporting
3. 3. Emissions forecasting
4. 4. Emissions reduction target setting

This book does not provide a step-by-step explanation of how to conduct a GHG emissions inventory. Communities should refer to the chosen protocol manual for guidance. Instead, this book answers the following questions:

1. 1. Who will prepare the inventory?
2. 2. What is the appropriate methodology or protocol?
3. 3. How should a baseline year be established?
4. 4. What is the scope of the inventory?
5. 5. What is a GHG emissions forecast?
6. 6. How are emissions reduction targets selected?

Preparing the Inventory

Communities have several choices as to who will prepare the GHG emissions inventory. Local government staff members, community volunteers, college faculty members and students, and consultants have been the most common choices. These vary by cost, experience and aptitude, and accountability. Preparing an inventory is detailed, time-consuming work that requires strong math and logic skills, solid organizational capabilities, and a willingness to deal with uncertainties and assumptions. If the GHG reduction strategies will have a legal status, the inventory will need to be as accurate as possible, thoroughly documented, and defensible. A community will have to consider all these factors and make the best choice for its own circumstances.

Inventory Methodology/Protocol and Software

Protocols establish what will be measured in an inventory and how it will be measured. There are a variety of GHG assessment protocols for businesses, governments, individuals, and other organizations, and some adventurous communities have created their own approaches by mixing and modifying a variety of existing protocols. Although this may work for some communities, most communities should use the widely adopted, standard protocols when they are able to, although some may need to rely on other methods if they have an emissions source that is not covered. The most common protocols for communities are the Local Government Operations Protocol, the U.S. Community Protocol for Accounting and Reporting of Greenhouse Gas Emissions, and the Global Protocol for Community-Scale Greenhouse Gas Emission Inventories.7 These pertain to the two types of emissions inventories mentioned previously—local government operations inventories and community-wide inventories, respectively.

Local Government Operations Protocol

The Local Government Operations Protocol (LGO Protocol)8 was developed in 2008 through the collaboration of the California Air Resources Board, ICLEI, the California Climate Action Registry,9 and The Climate Registry.10 The LGO Protocol is a tool for accounting and reporting GHG emissions across all of a local government’s operations and is intended for use by local governments throughout the United States, Canada, and Mexico. The LGO Protocol is based on the Greenhouse Gas Protocol: A Corporate Accounting and Reporting Standard developed by the World Resources Institute and the World Business Council for Sustainable Development (WRI/WBCSD). The protocol is a guidance document available for use by any local government engaging in a GHG inventory exercise. It brings together GHG inventory guidance from a number of existing programs—namely, the guidance provided by ICLEI to its Cities for Climate Protection campaign members, the guidance provided by the California Climate Action Registry and The Climate Registry through their general reporting protocols, and the guidance from the State of California’s mandatory GHG reporting regulation.

U.S. Community Protocol for Accounting and Reporting of Greenhouse Gas Emissions

The U.S. Community Protocol for Accounting and Reporting of Greenhouse Gas Emissions (U.S. Community Protocol) was released by ICLEI in 2012. It is a tool for accounting and reporting community-wide GHG emissions designed to complement the LGO Protocol. The U.S. Community Protocol is tailored for use in U.S. communities.

Global Protocol for Community-Scale Greenhouse Gas Emission Inventories

The Global Protocol for Community-Scale Greenhouse Gas Emission Inventories (Global Protocol; GPC) was released in 2015 through a partnership of the World Resources Institute, the C40 Cities Climate Leadership Group, and ICLEI–Local Governments for Sustainability.11 It provides a framework for communities to determine and report their GHG emissions. The Global Protocol is applicable to communities around the world and includes additional GHG sectors, such as land use changes and crop cultivation, that are not included in the U.S. Community Protocol.

Greenhouse Gas Inventory Software

There are two basic options for using the protocols to conduct the inventory and deal with the necessary calculations. The first is to use the detailed information in the protocols on data needs, assumptions, transformations, and calculations to manually construct an inventory spreadsheet in one of the commonly available spreadsheet programs, such as Microsoft Excel, Apple Numbers, or Google Sheets. Anyone who chooses this route should be very comfortable with spreadsheets and with math. The protocols provide sufficient detail and direction to do this successfully. This approach offers more flexibility to adjust the data and assumptions for the local context. There are also accessibility benefits to using commonly available spreadsheet software.

The second option is to use a GHG emissions inventory software package or online platform. ICLEI–Local Governments for Sustainability’s ClearPath tool has become one of the most widely used software platforms for this purpose. It allows users to calculate the GHG emissions of a community by entering activity data and using either customized emissions factors or default factors that are already included in the platform. The inventories prepared in ClearPath are compliant with the U.S. Community Protocol and the Global Protocol. ClearPath reports emissions from the three major GHGs (CO₂, CH₄, and N₂O) as well as combined carbon dioxide equivalent units (CO_2e). A professional version of the platform also allows users to forecast multiple emissions scenarios and track their GHG reduction progress over time. Access to the basic version of ClearPath is free to any U.S. community that is a signatory to the Global Covenant of Mayors, and access to ClearPath Pro is free to California communities through the Statewide Energy Efficiency Collaborative. Access by others requires an ICLEI membership or the purchase of an annual subscription.

Choosing Protocols and Software

The selection of a protocol, methodology, and software will depend on the purpose of the inventory and the resources available to the jurisdiction. The decision will depend on city staff support, budget allocations, time constraints, and the availability of other resources or services, such as consultants, volunteers, nonprofit organizations, or college faculty and students. Consultants or other organizations may develop tools and/or software tailored to the jurisdictions’ needs. In addition, local governments must consider any regulatory mandates or guidance from state or regional agencies when applicable. It is generally recommended that communities follow the U.S. Community Protocol and the Global Protocol. Also, any communities that have signed pledges, joined organizations such as C40 or the Global Covenant of Mayors, or committed to external reporting may be required to use certain protocols and tools.

Establishing a Baseline Year

The GHG emissions inventory requires the choice of an initial inventory year, usually referred to as the “baseline year.” Communities should select the most recent calendar year for which consistent, comprehensive, and reliable data can be collected. The LGO Protocol recommends that local agencies select a baseline year that is “typical” and not a year in which emissions were influenced by unusual conditions such as extremely high or low economic growth, abnormal weather, or other outliers. Another issue may be whether the community wants to be consistent with state or neighboring jurisdictions’ baseline years. If the community wants to be consistent with another adopted GHG reduction target, such as a statewide reduction target, it should consider using the same baseline as the adopted goal. In addition, if a community has implemented several emissions reduction strategies, it may want to choose a year far enough in the past that the impact of recent GHG emissions reduction strategies can be clearly seen. Finally, if a community has been implementing climate action strategies for a while, it may want to conduct two inventories: one for a baseline year and one for the current year so that it can see its progress. These should be at least five years apart to see meaningful differences.

Inventory Coverage

The typical sectors of a GHG inventory are residential energy and nonresidential energy, waste, and transportation. Other sectors, depending on the community, may include agriculture, water and wastewater, and off-road equipment. The seven greenhouse gases that should be quantified from these sectors and included in a GHG emissions inventory are carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF₆), and nitrogen trifluoride (NF₃). Other GHGs may be inventoried; however, methodologies for other GHGs may not be in the most commonly used protocols. According to the common protocols, emissions of CO₂, CH₄, and N₂O from fossil fuel combustion, electricity generation (the indirect emissions associated with electricity used in the community), waste disposal, and wastewater will be the most significant sources of GHG emissions in community-wide and local government operations inventories. Table 4.3 shows an example from Placer County, California, of a detailed breakout of community-wide emissions and the data sources.

Table 4.3. Placer County, California, 2005 and 2015 greenhouse gas emissions inventory

Activity/sector	2005 Equiv. CO2 (metric tons)	2015 Equiv. CO2 (metric tons)	Percentage change	Data sources
Residential
Electricity use	181,107	110,380	−39	PG&E; SMUD; NV Energy / Liberty Utilities; CEC
Electricity T&D losses	10,110	6,893	−32	USEPA eGRID
Natural gas use	98,045	91,812	−6	PG&E; Southwest Gas
Propane use	49,979	33,591	−33	USEPA; EIA; U.S. Census
Fuel oil / kerosene use	1,810	674	−63	USEPA; EIA; U.S. Census
Wood use	5,012	8,038	60	USEPA; EIA; U.S. Census
Subtotal residential	346,063	251,389	−27
Nonresidential
Electricity use	140,981	87,325	−38	PG&E; SMUD; NV Energy / Liberty Utilities; CEC
Electricity T&D losses	7,004	5,297	−24	USEPA eGRID
Natural gas use	59,691	39,356	−34	PG&E; Southwest Gas
Subtotal nonresidential	207,676	131,979	−36
Transportation
On-road passenger vehicles	145,693	151,441	4	VMT: Fehr and Peers Fuel Use: CARB EMFAC
On-road light-duty trucks and SUVs	218,484	208,116	−5	VMT: Fehr and Peers Fuel Use: CARB EMFAC
On-road heavy-duty trucks	161,260	144,049	−11	VMT: Fehr and Peers Fuel Use: CARB EMFAC
Off-road vehicles and equipment	9,786	9,413	−4	VMT: Fehr and Peers Fuel Use: CARB EMFAC
Subtotal transportation	535,222	513,019	−4
Water, wastewater, and solid waste
Subtotal water and wastewater	18,034	11,548	−36	Water and wastewater service companies, utilities (PG&E, NV Energy), USCP and CA Water Boards defaults, EPA / CA DOF / U.S. Census population data
Subtotal solid waste	65,577	87,526	33%	CalRecycle Disposal Reporting System, Landfill gas capture data from facilities
Agriculture
Rice cultivation	201,029	135,244	−33%	Crop reports
Equipment use	26,547	26,475	−0.3%	CARB
Other agriculture and livestock	38,304	22,273	−41%	DFA; DPR
Forest management open burning (nonbiogenic)	2,462	2,462	0%	DFW
Subtotal agriculture	268,341	186,454	−31%
Grand total	1,440,913	1,181,915	−18%

Abbreviations: CA DOF, California Department of Finance; CARB, California Air Resources Board; CEC, California Energy Commission; DFA, California Department of Forestry & Agriculture; DFW, California Department of Fish & Wildlife; DPR, California Department of Pesticide Regulation; eGRID, Emissions & Generation Resource Integrated Database (Environmental Protection Agency); EIA, U.S. Energy Information Agency; EMFAC, Emissions Factors; PG&E, Pacific Gas & Electric; SMUD, Sacramento Municipal Utility District; USEPA, U.S. Environmental Protection Agency; USCP, U.S. Community Protocol

Source: Placer County, Community-Wide and County-Operations 2015 Greenhouse Gas Emissions Inventories (2015).

Inventories must be clear about the sources of emissions included and excluded, as these sources will form the basis of reduction measures. The inventory is conducted by compiling activity data describing energy and fuel use and waste generation (see table 4.4 for typical activity data sources) and multiplying the activity data by emissions factors for each type of energy used and each waste disposal site and technology. Protocol methodologies direct the application and selection of emissions factors. Emissions are reported in terms of activity data, metric tons of each GHG, and metric tons of CO_2e. Converting emissions of non-CO₂ gases to units of CO_2e provides a comparison of GHGs on a common basis (i.e., on the ability of each GHG to trap heat in the atmosphere). Non-CO₂ gases are converted to CO_2e using internationally recognized global warming potential (see appendix A).

Table 4.4. Example of greenhouse gas emissions sectors, units of measurement, scope, and data source

Sector	Information	Unit of measurement	Emissions scope	Activity data source
Residential	Electricity consumption	kWh	Scope 2	Local utility provider
	Natural gas consumption	Therms	Scope 1	Local utility provider
Commercial and industrial	Electricity consumption	kWh	Scope 2	Local utility provider
	Natural gas consumption	Therms	Scope 1	Local utility provider
Transportation	Local road VMT	Annual average VMT	Scope 1	State database or local travel model
	Highway and interstate VMT	Annual average VMT	Scope 1	State database or local travel model
Solid waste	Solid waste tonnage sent to landfill from activities in jurisdiction	Short tons	Scope 3	Local landfill operator(s) or state reports
Off-road equipment	Emissions from off-road equipment and vehicles	Tons/year of N2O, CO2, and CH4	Scope 3	State model or local estimates
Agriculture	Emissions from cattle and sheep	Head of cattle	Scope 3	County crop report
	Emissions from fertilizer use	Pounds of nitrogen	Scope 3	County crop report
Aircraft	Emissions in the landing and take-off operations (LTOs) zone	Grams of N2O, CO2, and CH4	Scope 3	Local airport operator / aircraft operations study

Abbreviations: CH₄, methane; CO₂, carbon dioxide; kWh, kilowatt-hours; N₂O, nitrous oxide; VMT, vehicle miles traveled

Emissions are quantified and tracked separately, and the results are presented in inventory reports by sector and source. Some communities will also present emissions by scope, which is one way to help reduce the possibility of double counting and misrepresenting emissions when reporting while still allowing all policy-relevant information to be captured. In addition, tracking emissions sources separately allows decision-makers to tailor reduction strategies. Three classifications—scopes 1, 2, and 3—are used to categorize emissions sources when preparing an inventory using a scope framework. The scopes vary slightly when applied in the context of government operations and community-scale inventories (see table 4.3 for examples). Among the most commonly used protocols, the LGO and Global protocols both use a scope-oriented framework, while the U.S. Community Protocol does not. Scopes are defined by the LGO Protocol and Global Protocol as follows:

• • Scope 1 emissions are all direct GHG emissions (with the exception of direct CO₂ emissions from biogenic sources). These are primarily emissions from motor vehicles and stationary sources such as power plants or factories located within the community.
• • Scope 2 emissions are indirect GHG emissions associated with the consumption of purchased or acquired electricity, steam, heating, or cooling from power plants located outside of the community.
• • Scope 3 emissions are all other indirect emissions not covered in Scope 2, such as emissions resulting from the extraction and production of purchased materials and fuels, transport-related activities in vehicles not owned or controlled by the reporting entity (e.g., employee commuting and air travel), outsourced activities, waste disposal, and so forth.

Data for Scope 3 emissions can be difficult to obtain, and their accuracy is questionable. Also, Scope 3 emissions are more economically and culturally complicated and less amenable to emissions reduction strategies (because they include things like household purchasing decisions and global manufacturing chains). However, there is increasing attention to overcoming these limitations for Scope 3 emissions, and improved data analysis methods are making it easier for communities to accurately assess these emissions through what are commonly called consumption-based inventories (see box 4.2). For example, the Global Protocol requires communities to account for and report Scope 3 emissions associated with some energy, transportation, and waste-related activities.

Box 4.2

Consumption-Based GHG Emissions Inventories

A Consumption-Based Emissions Inventory (CBEI) assigns responsibility to the final consumer for lifecycle GHG emissions of consumed goods and services. Upstream embedded emissions within goods and services, use emissions, and downstream disposal emissions are all assigned to the final consumer within the subject jurisdiction. Consumption inventories usually focus on household and government consumption because most business consumption is for the purpose of production of goods and services.

Consumption inventories usually do not include production-related emissions within the jurisdiction except to the extent that within-jurisdiction production serves in-jurisdiction consumption. Consumption inventories have been prepared for relatively few municipalities to date, and California does not have a consumption inventory for the state as a whole.

Consumption inventories for embedded emissions in goods and services are usually based on regional economic consumption data, combined with national/international state lifecycle emissions factors, for a standard list of products or product bundles. While consumption inventories will sometimes use local or regional data on economic consumption, factors for upstream GHG emissions usually employ state and national average activity and emissions intensity data, compared to the more local data commonly used for production-based and activity-based inventories.

Source: Definition from Association of Environmental Professionals, California Chapter, Climate Change Committee, Production, Consumption and Lifecycle Greenhouse Gas Inventories: Implications for CEQA and Climate Action Plan (August 2017); see also C40 Cities, Consumption-Based GHG Emissions of C40 Cities (March 2018).

In some cases, not all sources of GHG emissions may be included in an inventory. There are several reasons emissions may be excluded. Often, data needed to determine emissions may not be available and there is no reasonable way to estimate the data. In other cases, the effort required to accurately assess emissions from a small source may be so considerable that it is not worth going through a lengthy and intensive effort if the overall impact on the inventory will be small (such sources are called “de minimis” and generally should be no more than 5% of the total estimated emissions). The inventory report or documentation should clearly note any emissions that are not included as well as the reason for leaving them out. The U.S. Community Protocol recommends a simple notation key for describing these excluded sources:

• • IE—included elsewhere: The emissions are accounted for in the inventory but are treated as part of another activity.
• • NE—not estimated: The emissions are not estimated.
• • NA—not applicable: The activity is occurring, but no emissions are attributed to the community.
• • NO—not occurring: The activity does not take place in the community.

Occasionally, an inventory will report GHG emissions even if the calculations are known to be inaccurate or if the emissions occur in but are not attributable to the community. These emissions are presented but are not counted toward the community’s total emissions or used to establish reduction targets. This is often done because decision-makers or community members are curious about these emissions even if they are not appropriate to include in the total inventory. Such emissions are called “informational items.”

The designation of an inventory’s coverage also has a relationship to the spatial boundaries of the inventory. Before collecting data, inventory preparers must identify spatial boundaries for the inventory and include all important sources of GHG emissions occurring within these boundaries. Community-wide inventories are typically based on the local government’s political boundary. A jurisdiction may elect to inventory emissions outside of its political boundary. The most common reason to inventory emissions outside of a political boundary is to be consistent with a comprehensive plan that may establish planning area boundaries for future land use beyond the community’s current political boundaries. If this is done, it should be explained in the inventory. The standard use of political boundaries for community-wide emissions can be confusing when one is preparing an inventory using a scope-based framework and is considering Scope 2 emissions. In some communities, electricity is produced within the political boundaries of the jurisdiction, which would be a Scope 1 emissions source, but in most, it is produced outside of the community and is thus a Scope 2 emission. Either way, the activities that create the demand for the electricity—powering homes and businesses—do occur within the political boundaries of the jurisdiction and should be inventoried. This distinction of Scope 1 and Scope 2 emissions and political boundaries is certainly a debatable area of GHG emissions inventory practice, so whatever choice a community makes about this should be documented and justified.

Local government operations emissions include emissions arising from the use and operations of all facilities, buildings, equipment, and activities that are owned, operated, or managed by the local government. These are usually within the political boundaries of the jurisdiction, but some may exist outside the jurisdiction. For example, a local government may own a landfill or a water supply and transmission pipes outside its political boundaries. Since all emissions that are a consequence of the local government’s operations must be included, these types of facilities and operations would be as well. The LGO Protocol provides clear guidance on criteria for operational or financial control:

A local government has operational control over an operation if the local government has the full authority to introduce and implement its operating policies at the operation. One or more of the following conditions establishes operational control:

• • Wholly owning an operation, facility, or source; or
• • Having the full authority to introduce and implement operational and health, safety and environmental policies (including both GHG- and non-GHG-related policies). . . .

A local government has financial control over an operation for GHG accounting purposes if the operation is fully consolidated in financial accounts. The LGO Protocol strongly recommends the use of the operational control approach to defining a jurisdiction’s boundary for the local government operations inventory.12

Greenhouse Gas Emissions Forecast13

It is common practice to prepare a GHG emissions forecast once the inventory has been completed. GHG forecasts are projections of possible future GHG emissions from all sectors of the inventory. Local forecasts for population, jobs, and housing are used to develop a forecast of future emissions; this is referred to as the business-as-usual (BAU) forecast (see figure 4.1). The BAU forecast can be thought of as what the emissions would be in the future if nothing new was done to try to reduce them. The development of the BAU forecast is often accompanied by the setting of a GHG emissions reduction target for the forecast year. The difference between the likely increase in emissions estimated in the BAU forecast and the emissions reduction target establishes the amount of emissions reduction that must be accomplished through climate action strategies or through other means, such as state regulations. This is sometimes called the “reduction wedge” due to its appearance when graphed (see figure 4.1).

Figure 4-1 Example of a community-wide greenhouse gas (GHG) emissions forecast and reduction target. The upper line, business-as-usual (BAU), indicates the projected emissions if no additional actions to reduce emissions are taken. The middle line, adjusted BAU, represents the local consequences of state and federal policy such as fuel-efficiency regulations, renewable energy portfolio requirements, and energy-efficient building standards. The bottom line represents a community’s adopted GHG emissions reduction target. The wedge that is the difference between BAU and the reduction target represents the amount of emissions that must be reduced in a given community through a combination of local, state, and federal actions. The difference between the adjusted BAU and reduction target identifies the reductions to be achieved through local climate action.

Selection of Forecast Year(s)

During the selection of a baseline year, it is common practice for a municipality to select one or more forecast years. Forecast years are usually at least five years from the baseline year, with 10 to 20 years being common. The first principle is that the forecast years should be consistent with the emissions reduction target years (described later in this chapter). Other considerations include the availability of a jurisdiction’s forecasts for population, jobs, and housing and the relationship of the inventory to other long-range planning documents or regulations. For example, most municipalities in California use 2020 and 2030 as forecast years to be consistent with the goals of California’s Global Warming Solutions Act and its subsequent implementation documents. The choice of a forecast year or years for the inventory also essentially establishes the planning horizon.

Adjusting the Forecast

Some GHG emissions forecasts show an adjusted BAU forecast. Since the forecasts for population, jobs, and housing used to develop the standard BAU forecast are typically simple extrapolation models based on historic data, they do not capture more complex factors that may affect these community measures. These factors are usually referred to as external (or exogenous) factors, since they are not accounted for within the simple extrapolation model.

There are several types of external changes that will affect future levels of GHG emissions in a community: technological, social/behavioral, legislative and regulatory, demographic, and economic. Issues for technological innovation and change include automotive technology and fuels, electricity generation and fuels, and building technology. Social/behavioral changes may include commuting habits, household energy use, and purchasing habits. Potential legislative and regulatory changes may include cap-and-trade legislation, renewable energy portfolio standards, and fuel-efficiency standards (e.g., the Corporate Average Fuel Economy [CAFE] federal standard). Demographic changes that may influence GHG emissions include population growth, poverty level, and housing tenure and occupancy. Long-term GHG emissions may also be influenced by economic changes in gross domestic product, industrial and manufacturing mix, and balance of trade. This sampling of issues shows that considerable uncertainty exists in forecasting future levels of GHG emissions, particularly at the community level.

Two common solutions when dealing with uncertainty in forecasting are either to ignore it and use the original BAU forecast or to develop multiple forecast ranges or scenarios. The problem with the former is that change seems almost certain at this point. For example, vehicle miles traveled (VMT) has become increasingly difficult to predict. After multiple decades of steady growth, in the mid-2000s, VMT went down, then leveled off. Just when it appeared that VMT, especially per capita, was on a long-term flat trend, it started going up again. And the rapid changes in mobility—Lyft/Uber, scooters, bicycling, and possible autonomous vehicles—have made predicting future VMT almost a guessing game. Emissions forecasts that assume long-term trends will persist and do not consider the potential for dramatic changes over the short term may have important policy consequences.

The policy implications of ongoing external change that decreases or increases GHG emissions could include the setting of unduly aggressive or conservative reduction targets, “sticker shock” reactions to how much effort would be required to meet aggressive reduction targets, or despondency created from a sense that the future growth of emissions is inevitable. Additionally, assuming no external changes puts communities in the position of misjudging the level of local GHG emissions reductions needed. Too little reduction and the community misses its reduction target. Too much emissions reduction and the community may incur high costs (an economically inefficient outcome) or bear an unfair share of state and national reduction targets. Yet this is the most common assumption made.

The problem with addressing uncertainty by developing multiple forecast ranges or scenarios is that making assumptions about future changes in the areas listed would likely exceed the capability of most local governments. Moreover, no standardized approach for addressing this has been developed for community-level emissions inventories.

The issue of external change is one of the most difficult technical issues in GHG emissions forecasting. Guidance is poor and often conflicting; moreover, the rapid rate of technical, legislative/regulatory, and social change makes it challenging to adjust BAU forecasts to account for change. Yet these changes will have a significant impact on the ability of communities to develop mitigation actions to adequately account for their share of needed GHG emissions reductions. In fact, some communities are counting on this external change to help them achieve their targets. The best current advice is for communities to identify future emissions reductions resulting from statewide policies such as requirements for vehicle fuel mileage or targets for electricity production from low-carbon fuel sources. If the state has a climate action plan or similar document, these types of policies may be specified and linked to forecasted GHG emissions reductions. Since federal policy appears uncertain at this time and the rate of technology change is very difficult to predict, it is not recommended to adjust the BAU forecast based on these factors. In the future, better assistance from federal and state agencies on this issue is needed.

Selection of Emissions Reduction Targets

The emissions reduction target is the quantity of GHG emissions the jurisdiction wants to reduce by the forecast year. The reduction target is typically expressed as the percentage by which emissions will be reduced relative to a baseline year (e.g., 15% reduction from the 2015 baseline level by 2030). A jurisdiction may select more than one reduction target. Reduction targets may be short term, midterm, or long term—or all three. The period will influence the range of actions and policy options used to achieve them. A local government may set a long-term goal but also have shorter-term targets that serve as incremental steps toward that goal. Communities may also have sector-specific targets or goals in addition to overall community-wide reduction targets. Target setting may include consideration of targets adopted by other levels of government, neighboring or peer communities, feasibility of achievement or implementation, scientific studies and reports, and the urgency of the issue. Separate baseline years, target years, and reduction percentages may be established for local government operations and community-wide emissions.

Adopted Reduction Targets

Many communities choose to adopt reduction targets that have been established by other organizations or government agencies. The benefit is that these targets have usually been vetted scientifically, they relieve the community of having to develop their own analysis and standard setting, and they create consistency among communities. The downside is that they may not adequately capture local conditions and contexts and may not reflect local values.

International Standards

At this time the most notable international attempt to establish GHG emissions reduction targets has been the Paris Agreement, a protocol of the United Nations Framework Convention on Climate Change (UNFCCC) that was established in December of 2015 in Paris, France. The Paris Agreement has been signed by 195 countries and ratified or agreed to by 183 countries as well as the European Union. The Paris Agreement set a goal of reducing GHG emissions sufficiently to keep the increase in global temperatures to “well below 2°C above pre-industrial levels, and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels.”14 It allows each country to establish its own GHG reduction target, called a “Nationally Determined Contribution” (NDC), and calls on countries to report on their progress and adopt new, increasingly stringent targets every five years.

The challenge with using the 1.5°–2°C standard is that it does not provide clear guidance or meaning at the local level. In 2009, a group of climate scientists asserted that atmospheric CO₂ should not exceed 350 parts per million (ppm; ~ 450 CO_2e) if the 2°C threshold was not to be crossed.15 As of July 2018, atmospheric CO₂ was 412 ppm.16 Although it is difficult to translate these standards to a reduction target, research suggests that this would necessitate a 50% to 95% reduction from 1990 levels by 2050.17 The Under2 Coalition of states and regions around the world have endorsed “reducing greenhouse gas emissions equivalent to 80 to 95 percent below 1990 levels or to less than 2 annual metric tons per capita by 2050” in order to stay below the 2°C threshold.18

National and State Standards

There are no official U.S. GHG emissions reduction targets, and states vary as to whether they have adopted standards (see box 4.3).19 In March 2016, the United States established its NDC under the Paris Agreement at 26% to 28% below 2005 levels by 2025; local governments could use this target, though there is no post-2025 target. Moreover, in 2017 the United States indicated its intent to withdraw from the Paris Agreement, although under the language of the agreement, formal notice of withdrawal cannot occur until at least November 2019 and would take one year to become effective.

Box 4.3

National, Regional, and State Greenhouse Gas Reduction Targets

National-Level Targets

• • U.S. Paris Agreement NDC (provisional): 26–28% below 2005 by 2025
• • Canada: 17% below 2005 by 20201

U.S. State-Level Targets2

• • Arizona: 2000 levels by 2020 and 50% below 2000 by 2040
• • California: 1990 levels by 2020, 40% below 1990 by 2030, and 80% below 1990 by 2050
• • Colorado: 26% below 2005 by 2025
• • Connecticut: 10% below 1990 by 2020 and 80% below 2001 by 2050
• • Florida: 2000 levels by 2017, 1990 levels by 2025, and 80% below 1990 by 2050
• • Hawaii: Carbon-neutral by 2045
• • Illinois: 1990 levels by 2020 and 60% below 1990 by 2050
• • Maine: 1990 levels by 2010, 10% below 1990 by 2020, and 75%–80% below 2003 in the long term
• • Maryland: 40% below 2006 by 2030
• • Massachusetts: 25% below 1990 by 2020 and 80% below 1990 by 2050
• • Michigan: 20% below 2005 by 2025 and 80% below 2005 by 2050
• • Minnesota: 15% below 2005 by 2015, 30% below 2005 by 2025, and 80% below 2005 by 2050
• • New Hampshire: 20% below 1990 by 2025 and 80% below 1990 by 2050
• • New Jersey: 1990 levels by 2020 and 80% below 2006 by 2050
• • New Mexico: 2000 levels by 2012, 10% below 2000 by 2020, and 75% below 2000 by 2050
• • New York: 40% below 1990 by 2030 and 80% below 1990 by 2050
• • Oregon: 10% below 1990 by 2020, and 75% below 1990 by 2050
• • Rhode Island: 10% below 1990 by 2020, 45% below 1990 by 2035, and 80% below 1990 by 2050
• • Vermont: 40% below 1990 by 2020, and 80–90% below 1990 by 2050
• • Washington: 1990 levels by 2020, 25% below 1990 by 2035, and 50% below 1990 by 2050

Note: Check with your nation, state, or region for updates.

1. See http://www.climatechange.gc.ca/default.asp?lang=en&n=72f16a84-1.

2. See https://www.c2es.org/document/greenhouse-gas-emissions-targets/.

Considerations for Adopting Local Reduction Targets

In states with officially adopted GHG emissions reduction targets, cities should consider adopting consistent targets or targets directed by any other guidance. For example, the State of California is recommending that local jurisdictions adopt “targets of no more than six metric tons CO_2e per capita by 2030 and no more than two metric tons CO_2e per capita by 2050.”20 As of 2018, no state had mandated local targets, but some states have policies and programs that may make consistency beneficial by providing access to grants or by easing other regulatory requirements.

Most communities, recognizing the urgency of the climate crisis and the 1.5°–2°C target established in the Paris Agreement, are choosing to set 2050 goals of reducing GHG emissions by 80%–100%. Interim goals—which also should be established—are then determined based on the local feasibility of bending the emissions curve down toward 2050. For example, Cincinnati, Ohio, has targets of 8% below 2006 levels by 2012 (which they achieved), 40% below 2006 levels by 2028, and 84% below 2006 levels by 2050.

The issue of whether to adopt a percentage reduction of total emissions or a per-capita target is not critical and should be a local preference. Communities should be at least tracking both. For communities that are growing fast, though, per-capita targets may make the most sense. At least over the short- and midterm, reduction of total emissions in a fast-growing community could be daunting and not realistic to the community. Fast-growing communities will likely increase their emissions simply because they are adding people versus slow-growth communities that will see little increase over baseline even if they do nothing.

This does raise the question of whether 80%–100% by 2050 is fast enough (100% essentially being carbon-neutral or zero-carbon). Currently, 2050 is the most common target year for becoming low- or zero-carbon, but a number of cities are pursuing much more aggressive goals. The City of Copenhagen, Denmark, has a goal of carbon neutrality by 2025, and the City of San Luis Obispo, California, has adopted a goal to be carbon-neutral by 2035. Are these realistic? Both cities assert these are achievable goals and are pursuing aggressive action to get there. It is almost certain that waiting until 2050 is waiting too long. The 2018 special report Global Warming of 1.5°C from the Intergovernmental Panel on Climate Change (IPCC) suggests significant global action is needed before 2030:

Estimates of the global emissions outcome of current nationally stated mitigation ambitions as submitted under the Paris Agreement would lead to global greenhouse gas emissions in 2030 of 52–58 GtCO_2eq yr−1 (medium confidence). Pathways reflecting these ambitions would not limit global warming to 1.5°C, even if supplemented by very challenging increases in the scale and ambition of emissions reductions after 2030 (high confidence). Avoiding overshoot and reliance on future large-scale deployment of carbon dioxide removal (CDR) can only be achieved if global CO₂ emissions start to decline well before 2030 (high confidence).21

The following summarize our recommendations:

1. 1. If your state has a reduction target, consider adopting that target, especially if there are benefits to consistency (such as access to grants or protection from state regulatory action).
2. 2. Consider being consistent with the Paris Agreement and adopting an 80%–100% GHG emissions reduction by 2050 or sooner, with appropriate interim goals.
3. 3. Consider adopting the Under2 Coalition per-capita target of 2 metric tons CO_2e per person, especially if in a fast-growing community.
4. 4. Given the urgency of the climate crisis, all communities should aspire to be highly ambitious and consider becoming carbon neutral by 2035 as a goal.

Quantifying Greenhouse Gas Emissions Reductions

Determining the anticipated GHG reductions from each policy or strategy, a process called “quantification,” makes it easier to assess whether climate action strategies will achieve the identified reduction targets (see box 4.4). Quantification is therefore one of the most important components of climate action planning and is regarded as the key criterion for evaluating reduction strategies. Unfortunately, there are no standardized GHG emissions reduction estimates that can be assigned to reduction strategies. GHG reductions are estimated based on a variety of measures and assumptions that differ by community or region. For example, electricity in the Midwest is largely produced from coal, whereas in the West it is from natural gas and hydropower, resulting in very different GHG emissions reductions for the same energy efficiency strategies, just as these distinctions result in very different GHG emissions in the inventory.

Box 4.4

Examples of Greenhouse Gas Emissions Reduction Estimation

The City of Cincinnati, Ohio, adopted the following policy: “Continue to support Red Bike (bike share) as an equitable mobility solution.” The following description from their 2018 Green Cincinnati Plan explains the data and assumptions necessary to calculate the annual emissions reductions that would result from implementation of the strategy: “If Red Bike grows by 20,000 rides per year and the average ride is 1.5 miles, and cars emit 4.2 tons of CO₂ per 10,000 miles traveled, this recommendation will avoid 12.6 tons in year 1, and an additional 12.6 tons per year for each subsequent expansion.”

The description shows that the source metric is based on assumptions about ridership growth and average ride length. There is also an assumption that these trips will replace car trips. The emissions factor for these displaced car trips is a readily available estimate of CO₂ emissions per mile. From this, the City estimated a 2023 reduction potential of 63 mtCO_2e.1

Contra Costa County, California, adopted the following policy: “Promote installation of alternative energy facilities on homes and businesses.” The policy includes numerous specific actions:

1. 1. Amend the County Zoning Code to designate areas and development standards that are appropriate for and supportive of small- and medium-sized alternative energy and energy storage installations not covered by AB 2188
2. 2. Train planning staff to provide guidance and information on the streamlined process and available incentives
3. 3. Create development standards allowing for the ministerial approval of rooftop energy systems on commercial buildings, with a focus on warehouses and other structures with large surface area roofs
4. 4. Encourage participation in PG&E’s [utility company] green tariff program

In calculating the annual emissions reduction that would result from implementation, the County made assumptions about the specific number of new and existing home and businesses that would be influenced by the various programs and add solar arrays by 2020 and 2035.

They then explained their method:

Forecasted residential and nonresidential solar installations as a result of the California Solar Initiative and BayREN programs were used to identify solar installations in 2020 and 2035. The county identified a target increase from that number and reductions were estimated based on average kW by installation type. Green tariff reductions are based on expected increases in renewable energy as a result of residential and nonresidential participation in educational and incentive programs. Reductions were applied to forecasted energy usage. These reductions were applied to participating households and businesses, which were identified by applying target participation rates to relevant building types. The sum of these reductions was then converted to MTCO_2e.

From this, the county estimated that the strategy would reduce 14,840 MT CO_2e per year by 2035.2

1. City of Cincinnati, Green Cincinnati Plan (2018), https://www.cincinnati-oh.gov/oes/citywide-efforts/climate-protection-green-cincinnati-plan/.

2. Contra Costa County, Climate Action Plan (2015), http://www.co.contra-costa.ca.us/4554/Climate-Action-Plan.

Successful and useful quantification will clearly show the level of participation needed to achieve the intended reduction. For example, if a strategy to conduct home energy efficiency retrofits is quantified as reducing GHG emissions by 5,000 metric tons of CO_2e by 2030, the quantification should clearly say how many houses need to undergo retrofits to reduce emissions by this amount. This level of participation is also called a performance indicator. The quantification should also clearly identify the methods and any assumptions used in determining the GHG reductions. This allows a community to monitor whether it is implementing a strategy at the necessary level to achieve the desired reductions and to make changes to the policy if circumstances change.

Emissions reduction calculations can be detailed quantifications or rough estimates. Most efforts will likely include both depending on the measure type, level of importance, and certainty with which assumptions can be made. In some cases, there will be high levels of uncertainty in estimating strategy effectiveness. This is particularly true for strategies that rely on voluntary community action. Due to high levels of uncertainty, conservative estimates or an estimate range may be enough. Also, strategies that comprise a very small portion of total GHG emissions reduction may not require precise estimates of GHG reductions. For example, an incentive program encouraging drought-tolerant landscaping will reduce GHG emissions associated with the treatment and delivery of water. However, water often represents a very small portion of community emissions, and it is difficult to estimate the level of community participation in this program and the amount of water that will be saved. In this case, a simple set of assumptions that are locally appropriate, such as the percentage of participation and the percentage of water use reduction per participating household, is likely to be enough. If this strategy was a major portion of overall GHG reductions, it may be appropriate for factors such as evapotranspiration rates, wind, and average yard size to be considered in the reduction estimate.

An increasingly popular tool for quantifying the emissions reduction potential of climate action strategies is the World Bank’s CURB tool: “CURB is an interactive tool that is designed specifically to help cities take action on climate by allowing them to map out different action plans and evaluate their cost, feasibility, and impact.”22 It can be tailored using city-specific data, and it is an Excel-based tool, free, and endorsed by the C40 Cities Climate Leadership Group and the Global Covenant of Mayors. Training and technical support are available. In addition to CURB, the ICLEI ClearPath tool includes modules for GHG emissions reduction quantification and can be useful to communities that conduct their inventories through ClearPath. A challenge with these types of tools is that the default assumptions and parameters may not be representative of any specific community. In addition, software tools inevitably have a level of opaqueness that may make complete understanding, documentation, and additional application more challenging.

Some communities choose to conduct their own GHG emissions reduction calculations. One of the most complete references for quantifying reduction strategies is the August 2010 California Air Pollution Control Officers Association (CAPCOA) guide for local governments, Quantifying Greenhouse Gas Emissions Measures, though it is increasingly out of date. The goal of the report is “to provide accurate and reliable quantification methods that can be used throughout California and adapted for use outside of the state as well.”23 The report contains a series of fact sheets on particular types of reduction strategies and accompanying guides on how to use the fact sheets. The quantification methods are based on using readily available data gathered by the planning team. The CAPCOA report describes the basic logic of emissions quantification.24 It does not include all potential reduction strategies, and some of the methods it includes may not be appropriate for all communities. If a community cannot use the CAPCOA guide or another resource to quantify GHG reductions, planners may create their own method or modify an existing one. These custom methods should be defensible, and as with all quantification, all methods and assumptions should be well documented.

The general equation for emissions quantification is shown here for each GHG:

GHG emissions = [source metric] × [emissions factor] × [GWP],

where source metric and emissions factor are defined as follows:

• • Source metric: The “source metric” is the unit of measure of the source of the emissions. For example, for transportation sources, the metric is vehicle miles traveled; for building energy use, it is “energy intensity,” that is, the energy demand per home or per square foot of building space. Mitigation measures [reduction strategies] that involve source reduction are measures that reduce the source metric. For example, if a source metric is the number of vehicle miles driven, a reduction in miles will generally lead to a reduction in emissions. Similarly, a reduction in home electricity use by installing energy efficient appliances and lighting will typically reduce the emissions associated with total electricity assigned to dwelling units.
• • Emission factor: The “emission factor” is the rate at which emissions are generated per unit of source metric (see above). Reductions in the emission factor happen when fewer emissions are generated per unit of source metric—for example, a decrease in the amount of emissions that are released per kilowatt-hour of electricity used or per ton of waste thrown away. Such a decrease may apply if a carbon-neutral electricity source (e.g., from photovoltaics) is used in place of grid electricity, which has higher associated emissions, or if electricity is used instead of combustion fuel, such as with electric cars. Reductions can also occur if a fuel with lower GHG emissions is used in the place of one with higher GHG emissions. From a quantification standpoint, for this type of measure, it is the “emission factor” in the equation that changes.25

Including Science in a GHG Emissions Accounting Inventory or Report

The scientific and technical issues in doing GHG accounting raise the issue of whether and how to address the basic science of climate change when documenting or reporting the results. For example, should a community-wide GHG inventory or climate action plan include a section that explains the basics of climate change and GHG emissions? Although this is not necessary, especially given that numerous references on the topic are available, it is common practice to include this information. The Chicago Climate Action Plan has a graphically interesting two-page spread that provides a very brief primer on climate change, and the San Francisco climate action plan has 20 pages of climate change science, though mostly on the effects of climate change on the city. Other communities that may not have climate action plans may include webpages on the topic or staff reports or other public documents.

A primer on the science of climate change, if developed, should answer the following questions for the reader:

1. 1. How do we know the planet is warming?
2. 2. What causes global warming?
3. 3. What are the consequences of global warming?
4. 4. What are the primary sources of anthropogenic greenhouse gases?

The answers to the last two questions should specifically address the local community to the degree possible. For example, it is not expected that global warming will affect all places equally on the globe with respect to heat waves, drought, rainfall, and the like. Nor do all communities produce the same amounts or types of GHGs.

The third question, on the consequences of warming, is difficult to answer for any specific locality given that the science to predict regional changes with confidence is only now emerging. A very useful starting point for understanding the potential local impacts of global warming is the 2017–2018 Fourth National Climate Assessment produced by the U.S. Global Change Research Program. Volume 1 reviews the science of climate change in the United States, while volume 2 focuses on identifying the impacts and risks of these changes.26 In addition to this report, many states have also prepared reports on the anticipated impacts of climate change. For example, the State of California produces a biennial climate change assessment report that identifies the impact of climate change on key sectors based on a variety of climate change scenarios.27 The fourth question, on the source of GHG emissions, can be answered locally through the preparation of a local GHG emissions inventory.

The purpose of explaining the science will vary by community. In some communities, the science simply serves to define the issue. In other communities, the science may be needed to inform a skeptical public of the need for climate action or to explain why the jurisdiction has been motivated to act. Whatever the case, the primer and associated education and outreach should explain to the community the purpose of knowing the science. Thinking this through will help planners focus on what content and what level of detail are actually needed.

Next Steps

Best practice standards for GHG emissions accounting are changing and improving regularly. The choices and assumptions made in GHG emissions inventories, forecasts, and reduction targets influence selection and implementation of climate strategies. Following the process outlined in this chapter is recommended to ensure the effectiveness of the next steps in the climate action planning process.