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State and Local Climate and Energy Program

Developing a Greenhouse Gas Inventory

What is a Greenhouse Gas Inventory?

A greenhouse gas inventory is an accounting of greenhouse gases (GHGs) emitted to or removed from the atmosphere over a period of time. Policy makers use inventories to establish a baseline for tracking emission trends, developing mitigation strategies and policies, and assessing progress. An inventory is usually the first step taken by entities that want to reduce their GHG emissions. An inventory can help local governments:

  • Identify the sectors, sources, and activities within their jurisdiction that are responsible for greenhouse gas emissions
  • Understand emission trends
  • Quantify the benefits of activities that reduce emissions
  • Establish a basis for developing a local action plan
  • Track progress in reducing emissions
  • Set goals and targets for future reductions

Why Complete a GHG Inventory?

Estimating GHG emissions enables local governments to create an emissions baseline, monitor progress,assess the relative contributions of emission sources, communicate with stakeholders, and create an informed mitigation strategy based on this information. Understanding the scope of GHG emissions can help inform the development of a climate action plan or the implementation of climate policies.

For this reason, local governments often complete a GHG inventory before implementing a comprehensive climate action plan. However, there are many reasons to begin reducing GHG emissions before or during the completion of a formal inventory:

  • Measures with no implementation costs or short pay-back periods, such as simple behavioral changes and some energy efficiency technologies, should be implemented right away to begin accruing economic benefits and achieving GHG reductions.
  • Integrating GHG reduction measures into already planned infrastructure or policy development can save time and money and reduce waste.
  • Local governments may want to take advantage of short-term funding opportunities to implement mitigation actions before performing a GHG inventory.
  • Future state and federal legislation may require that local governments take certain mitigation actions, such as Renewable Portfolio Standards, cap and trade programs, and mandatory reporting laws.
  • Information on local emissions may already be available from an existing state or regional GHG inventory.

Local governments can choose to estimate emissions from government operations only, estimate emissions community-wide, or join with other municipalities to create a regional inventory.

  • Government operations inventories include emissions from all of the operations that a local government owns or controls. Common sectors in a government operations inventory include local government buildings and other facilities, streetlights and traffic signals, waste, and water delivery facilities. After completing a government operations inventory, the local government can lead by example by pursuing mitigation efforts that illustrate the possibilities of mitigation actions to the community.
  • Community-level inventories include emissions from community activities within the local government’s jurisdiction, including emissions from sources and/or activities in that community, such as energy, transportation, agricultural, industrial, and waste. A community-wide inventory is a useful planning tool in developing mitigation actions for the entire community.
  • Regional inventories include emissions from multiple communities. Local governments may join with other communities in the area to create a regional inventory. This option can be valuable for small communities that may not have the capacity or resources to conduct inventories individually.

Examples of GHG inventories completed by local governments are available on the local examples page.

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Data Needed to Complete a GHG Inventory

For community inventories, energy use in the residential and commercial sectors and transportation are likely to be among the biggest contributors to emissions.

The primary type of data needed to quantify GHG emissions within each sector is a time series of basic activity data and emission factors for each sector. For example, emissions from vehicles could be estimated by multiplying gallons of motor gasoline consumed per year by an emissions factor for pounds of CO2 per gallon of gasoline. Since emission factors are difficult to calculate and also likely to be the same across similar regions, a number of protocols and guidance documents are available to provide default values.

There are two approaches for collecting activity data: "top down" and "bottom up."

  • Top-down inventories rely on data collected and aggregated by state, national, and international agencies.
  • Inventories that use a bottom-up approach generally collect and aggregate data from local end users, such as utilities. Since local government inventories have a smaller geographic and operational scope than other types of inventories, they often take a bottom-up approach.

In contrast to corporate, national, or international inventories that are compiled annually, local inventories may be completed just once or every few years. It is therefore important that local inventories establish a clear emissions baseline that can be used monitor future progress.

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Steps to Conducting a GHG Inventory

The steps below apply to regional, community-wide, and local government operation inventories.
Set boundaries Define an inventory's physical, organizational, and operational boundaries.
Define scope Decide which emissions source and/or activity categories and subcategories should be included in the inventory as well as which specific GHGs.
Choose quantification approach Depending on the data available and the purposes of the inventory, choose to take a top–down, bottom–up, or hybrid approach to data collection.
Set a baseline When choosing a baseline year to provide a benchmark to compare progress going forward, consider whether (1) data for that year are available, (2) the chosen year is representative, and (3) the baseline is coordinated to the extent possible with baseline years used in other inventories.
Engage stakeholders Bring stakeholders into the inventory development process early on to provide valuable input on establishing a baseline; help build public acceptance of policies to address climate change; and provide data, information on data resources, and personnel resources or outreach assistance.
Procure certification Consider a third-party review and certification of the methods and underlying data in an inventory to assure that the inventory is high quality and that it is complete, consistent, and transparent. Certification may be required for participation in some greenhouse gas registries.

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Training

EPA's Webcast Training Series: Greenhouse Gas Inventory 101 for Local, Regional, and State Governments recordings and transcripts can be downloaded below.

Creating an Inventory
Topics include understanding the purpose and scope of a GHG inventory, inventories vs. registries, setting a boundary, setting a baseline, quantification approaches, certification and reporting protocols, comparability, and level of effort.

Translating Inventory Results into Action
Topics include describing the various uses of GHG inventories, including benchmarking, tracking emissions and progress over time, setting emission reduction goals, policy options for meeting goals, evaluating policy options, and processes for setting goals and policies.

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Tools

Inventory Tools | Calculators | Energy Tools | Waste Management Tools

Inventory Tools

EPA's Greenhouse Gas Reporting Program

Through EPA's Greenhouse Gas Reporting Program facilities that emit 25,000 metric tons or more per year of GHGs are required to annually report their GHG emissions to EPA. Well over half of total U.S. greenhouse gas emissions are accounted for in this facility level data set, including nearly complete coverage of major emitting sectors such as power plants and refineries. This "bottom up" data can be used to supplement or complement a top-down inventory developed using the State Inventory and Projection Tool. For more information about accessing the data and how it may be used in state inventories, please see the materials from our March 2012 webcast.

Clean Air and Climate Protection Software

Local governments can use the Clean Air and Climate Protection Software (CACPS) Exit EPA disclaimer to develop greenhouse gas and criteria air pollutant inventories for government operations, or to create a community-wide emissions estimate. CACPS also allows users to forecast emissions and create an emissions reduction plan. Members of the National Association of Clean Air Agencies (NACAA) or ICLEI - Local Governments for Sustainability should contact ICLEI directly to receive the tool and access to training. Local governments that are not members of either organization may contact Denise Mulholland (mulholland.denise@epa.gov) to receive a copy of the software.

Climate CHECK

EPA's Climate CHange Emission Calculator Kit (Climate CHECK) estimates a school's greenhouse gas emissions and conceptualizes ways to mitigate the school's climate impact.

ENERGY STAR Portfolio Manager

Portfolio Manager is an interactive energy management tool that allows users to track and assess energy and water consumption across their entire portfolio of buildings in a secure online environment. Local governments can use the tool to create an inventory of greenhouse gas emissions from government buildings, set efficiency investment priorities, identify under-performing buildings, verify efficiency improvements, and receive EPA recognition for superior energy performance. Online trainings are available.

Local Government Greenhouse Gas Protocol

ICLEI - Local Governments for Sustainability Exit EPA disclaimer, in collaboration with the California Air Resources Board, The California Climate Action Registry, and The Climate Registry, has developed a community greenhouse gas protocol Exit EPA disclaimer for local government operations in the United States. The protocol is a guidance document that provides a framework for consistent quantification and categorization of greenhouse gas emissions at a local government level. A community-wide protocol is in development.

Office Carbon Footprint Tool

The Office Carbon Footprint Tool can assist offices in making decisions to reduce GHG emissions associated with their activities. This tool will allow the user to estimate GHG emissions from a variety of sources, including company-owned vehicle transportation; purchased electricity; waste disposal; and leased assets, franchises, and outsourced activities.

Regional Greenhouse Gas Protocol

EPA is in the process of developing a Regional Greenhouse Gas Inventory Guidance document to address regional inventory needs as multi-county regions and Metropolitan Planning Organizations (MPOs) are becoming increasingly interested in climate change and more regional groups are attempting to inventory their GHG emissions. The methods contained in the guidance document were developed in part by working with inventories created by two regional governments, the Delaware Valley Regional Planning Commission and the Washington Council of Governments. These inventories served as pilot studies, providing methods and indicators that were evaluated for their potential use in other regional settings. Contact Andrea Denny (denny.andrea@epa.gov) for more information.

Calculators

GHG Equivalency Calculator

The GHG Equivalency Calculator translates emissions amounts into terms that are more easily understandable. For example, the calculator translates emissions in metric tons of carbon dioxide equivalent (CO2e) into "emissions of X number of cars annually" and other metrics.

Personal Emissions Calculator

The Personal Emissions Calculator calculates a rough estimate of an individual or family's greenhouse gas emissions and explores the impact of taking various actions to reduce those emissions.

Energy Tools

Emissions & Generation Resource Integrated Database (eGRID)

eGRID contains a comprehensive inventory of environmental attributes of electric power systems including air emissions data for nitrogen oxides, sulfur dioxide, carbon dioxide, and mercury. The data are organized in a series of Microsoft Excel files that local governments can use to find data on emissions from electricity use and/or generation within their area.

Green Power Equivalency Calculator

The Green Power Partnership's Green Power Equivalency Calculator can help a local government better communicate a green power purchase to interested stakeholders by translating it from kilowatt-hours purchased into more understandable terms, such as an equivalent number of passenger vehicles, homes, or coal plants.

Power Profiler

Local governments can use this tool to evaluate the environmental benefits of choosing cleaner sources of energy. The Power Profiler is a Web-based tool that allows users to evaluate the air pollution and greenhouse gas impact of their electricity choices. Using only a ZIP code, the tool generates a report describing the characteristics of one's electricity use.

Waste Management Tools

Durable Goods Calculator

The Durable Goods Calculator calculates the GHG and energy benefits of increasing the recycling rates of goods that are disposed.

Landfill Gas Energy Benefits Calculator

The Landfill Methane Outreach Program's Landfill Gas Energy Benefits Calculator estimates direct, avoided, and total greenhouse gas reductions—as well as environmental and energy benefits—for the current year of a landfill gas energy project. For both electricity generation and direct-use projects, reductions of greenhouse gas emissions are derived from capturing and destroying landfill methane.

Recycled Content (ReCon) Tool

ReCon helps companies and individuals estimate life-cycle GHG emissions and energy impacts from purchasing and/or manufacturing materials with varying degrees of post-consumer recycled content.

WAste Reduction Model (WARM)

EPA created the WAste Reduction Model (WARM) to help solid waste planners and organizations track and voluntarily report greenhouse gas emissions reductions from several different waste management practices. WARM calculates and totals GHG emissions of baseline and alternative waste management practices—source reduction, recycling, combustion, composting, and landfilling.

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