User's Guide for WARM
Calculating Greenhouse Gas Emissions with the Waste Reduction Model
What is the Waste Reduction Model?
The Waste Reduction Model (WARM) was created by the U.S. Environmental Protection Agency (EPA) to help solid waste planners and organizations estimate greenhouse gas (GHG) emission reductions from several different waste management practices. WARM is available in a Web-based calculator format and as a Microsoft Excel© spreadsheet. Both versions of WARM are available on EPA's Web site.
WARM calculates GHG emissions for baseline and alternative waste management practices, including source reduction, recycling, combustion, composting, and landfilling. The model calculates emissions in metric tons of carbon dioxide equivalent (MTCO2E) and metric tons of carbon equivalent (MTCE) across a wide range of material types commonly found in municipal solid waste (MSW).1
The user can construct various scenarios by simply entering data on the amount of waste handled by material type and by management practice. WARM then automatically applies material-specific emission factors for each management practice to calculate the GHG emissions and energy use of each scenario. Several key inputs, such as landfill gas recovery practices and transportation distances to MSW facilities, can be modified by the user.
ReCon and WARM were developed for purchasers and waste managers, respectively. ReCon calculates the benefits of alternative recycled content purchasing decisions. WARM, on the other hand, calculates the benefits of alternative end-of-life waste management decisions. Both tools calculate the benefits of an alternative scenario versus a business-as-usual scenario.
The WARM and ReCon tools are based on a life-cycle approach, which reflects emissions and avoided emissions upstream and downstream from the point of use. As such, the emission factors provided in these tools provide an account of the net benefit of these actions to the environment. This life-cycle approach is not appropriate for use in inventories because of the diffuse nature of the emissions and emission reductions contained in a single emission factor.
The GHG emission factors were developed following a life-cycle assessment methodology using estimation techniques developed for national inventories of GHG emissions. The model documentation describes this methodology in detail.
For some material types, WARM indicates that recycling reduces more GHG emissions than does source reduction. This is because recycling is assumed to displace 100 percent virgin inputs, whereas source reduction is assumed to displace some recycled and some virgin inputs. For more information, please see "Why Recycling Some Materials Reduces GHG Emissions More than Source Reduction."
Who Should Use WARM?
WARM was developed for solid waste managers (from state and local governments and other organizations) who want to calculate the GHG emissions associated with different waste management options. Emissions estimates provided by WARM are intended to support voluntary GHG measurement and reporting initiatives, such as waste management components of state and local climate change action plans, and other waste management projects for which an understanding of GHG emissions is desired. WARM is not a GHG inventory tool.
Before using WARM, you first need to gather data on your baseline waste management practices and an alternative scenario. In order to effectively use the tool, users should know how many tons of waste was managed (or will be managed) for a given time period by material type and by waste management practice. The "mixed" material types are defined in the documentation.
Both models allow you to customize your results based on project-specific landfill gas recovery practices and transportation distances. Note that you may use default values if you are unsure of landfill gas recovery practices and/or transportation distances.
- To use the web-based version of WARM, you will need Firefox (version 3 or higher), Chrome, Safari, or Internet Explorer (version 6 or higher).
- For the web-based WARM model to be able to calculate your GHG emissions you must enter the tons of each material type managed into the baseline and alternative management tables. The boxes in the baseline and alternative tables correspond to specific material types and management practices. Be sure to enter your data in the correct boxes.
- Answer the questions pertaining to landfill gas recovery and transportation distance by selecting the appropriate toggle buttons. If the requested data are not available, WARM will use the national average defaults.
- Select a format to display your results by selecting the corresponding toggle button for MTCO2E, MTCE, or energy units (million BTU).
- To customize your report, enter your name, organization, and reporting period in the input cells.
- Once you have completed the tables and answered all of the questions on the inputs page, WARM will calculate the GHG emissions associated with the baseline and alternative waste management scenarios you specified. Click "Create Summary" to see your results.
- The summary sheet provides a concise report of GHG emissions from the baseline and alternative waste management scenarios, as well as an estimate of the net change in emissions.
- Once you have seen your results, you can return to the inputs page to run additional scenarios by selecting the button labeled "Exit Summary."
- Alternatively, you can view the emission factors used to estimate emissions for various materials and management practices; note that these emission factors will reflect national average default values for landfill gas recovery and transportation distances in the units you select. To access these emission factors, click the link labeled "View Emission/Energy Factors" from either the inputs page or the summary page.
- Please note that third-party web-browser tool-bars (such as GoogleTM) may attempt to “autofill” input cells, resulting in a yellow highlight. To prevent this, please disable the autofill function of any third-party tool bars.
Microsoft Excel ® Version:
- To use the Microsoft Excel© version of WARM, follow the directions on the Web site for downloading and installing Microsoft Excel© WARM. After successfully downloading the file, open the spreadsheet.
- Now, click on the "Analysis Inputs" tab at the bottom center of the screen to open the input sheet. Follow the instructions for Steps 1 and 2. This involves filling in the tables describing your baseline and proposed alternative waste management scenarios.
- Fill in the data requested in Steps 3-7. WARM will use the answers to these questions to customize its GHG estimates to reflect your waste management situation. If the requested data are not available, WARM will use the national average defaults.
- Step 8 allows you to customize your report, with your name, organization, and project period.
- Once you have completed Steps 1-8 on the "Analysis Inputs" sheet, WARM will calculate the GHG emissions attributable to the baseline and alternative waste management scenarios you have specified. Emissions and energy calculations are presented on separate output sheets, as described below. From the "Analysis Inputs" sheet, click on a tab at the bottom of the screen for the results sheet you want to view first.
- The "Summary Report (MTCO2E)", “Summary Report (MTCE)”, and “Summary Report (energy)” sheets provides a concise report of GHG emissions or energy from the baseline and alternative waste management scenarios, as well as an estimate of net emissions or energy in each of the three units provided in WARM.
- The "Analysis Results (MTCO2E)", “Analysis Results (MTCE)”, and “Analysis Results (energy)” sheets show GHG emissions or energy for each scenario each of the three units provided in WARM. You can compare the total impact of the baseline and alternative scenarios, or, if you want more detail, you can scroll down to view GHG emissions or energy results by material type and management practice.
If you need additional assistance with using WARM, please email orcrWARMquestions@epa.gov.
1 MTCE and MTCO2E are units of measurement that express the heat-trapping effects of various greenhouse gas emissions in carbon and carbon dioxide equivalent, respectively. An international protocol has established carbon dioxide (CO2) as the reference gas.