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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.

Using WARM

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.

Web-based version:
Microsoft Excel ® Version:

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.

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