The US EPA maintains a number of greenhouse gas (GHG) emission factor sets. One specialized set of conversion factors is the Waste Reduction Model (WARM). WARM is a tool that the EPA offers to solid waste planners and organizations [who] track and voluntarily report greenhouse gas emissions reductions and energy savings[1].
The factors published in this library are not suitable for formal GHG emissions inventories as they are calculated from a complete life-cycle perspective. Instead, the factors should be viewed as tools in evaluating the emissions costs and benefits from treating a particular waste type through a particular waste stream.
The WARM tool is used to calculate GHG emissions (and energy) resulting from applying different waste management practices to different waste material types.
The waste management practices considered include source reduction, recycling, combustion, composting, and landfilling. The Scope 5 implementation of the WARM resource library quantifies GHG emissions for these waste management practices for each of the waste material types identified in the WARM tool.
What’s Included
The resources in the current Scope 5 WARM Resource Library include GHG conversion factors for each of the managed waste streams identified by EPA in the WARM tool. Resources are identified as either “absolute” or “relative”. Resources identified as “absolute” quantify the GHG emissions resulting from a specific waste management practice applied to a specific type of waste material across its life cycle, such as the combustion of newspaper. Resources identified as “relative” quantify the difference in GHG emissions between one specific waste management practice and the alternative emissions that would result from disposing the same type of waste material in a landfill. (For the Landfill waste management practice, there is only an absolute option as a relative option would be meaningless). See the following example.
Many offices use lots of paper, sometimes thousands of pounds per year. Our example has an office staff consciously working on reducing paper use over time. Tracking this paper use source reduction, the Scope 5 user has chosen to use the WARM resource, "Mixed Paper (primarily from offices) Source Reduction (absolute)". The associated tracker requires the activity input be the amount of reduced paper use, or the difference between baseline paper use, as compared to the current paper consumption amount. The resulting information in Scope 5 shows the amount of GHGs avoided through waste reduction.
Example Using a Relative WARM Resource
Our sample office has decided to recycle paper rather than dispose of it along with general land-filled waste. The company collecting the waste paper for recycling provides a monthly report of the amount of paper collected (diverted from landfill) and recycled. The Scope 5 administrator in this case uses the "Mixed Paper (primarily from offices) Recycling (relative)" Scope 5 WARM resource. The tracker connected to this resource will capture the amount of paper recycled. The resulting information in Scope 5 quantifies the amount of GHGs avoided by recycling as compared to landfilling.
Waste Management Practices
Six waste management practices are included in the WARM library. They are briefly defined below. For more details on each waste stream, please refer to the Documentation for Greenhouse Gas Emission and Energy Factors Used in the Waste Reduction Model (WARM) from the EPA.
- Anaerobic Digestion refers to decomposing degradable materials “in a reactor in the absence of oxygen to produce biogas that is between 50-70 percent methane (CH4). This biogas is then typically burned on-site for electricity generation.”
- Combustion refers to burning municipal solid waste in a waste-to-energy (WTE) facility.
- Compost refers to large scale, centralized decomposition of organic materials in open-air windrow piles.
- Landfill refers to waste that is buried and covered, creating an anaerobic environment
- Recycling refers to “the separation and collection of wastes, their subsequent transformation or remanufacture into usable or marketable products or materials, and the purchase of products made from recyclable materials” (EPA, 2012).
- Source Reduction refers to “waste prevention”, including reducing upstream inputs and emissions, or avoiding sending materials to waste streams.
Where the Numbers Come From
All factors in Scope 5’s WARM library are sourced from the EPA’s Versions of the Waste Reduction Model (WARM) page. To identify the source of a specific set of emissions factors in Scope 5, please refer to the Source for the specific conversion factor set, as illustrated in the following example:
Assumptions
For each waste category, WARM publishes multiple variations on each emissions factor to account for changes in specific variables that contribute to that waste type and stream’s emissions factor. All factors in the Scope 5 library are based on the "default options in WARM (i.e., typical landfill gas collection practices, average landfill moisture conditions, and U.S.-average non-baseload electricity grid mix)". If a variation on any of these factors would be useful to you, please contact us at support@scope5.com.
Global Warming Potentials (GWPs)
All emissions factors in the WARM library are expressed in units of CO2e; as such GWPs are not explicitly defined.
Updates
The resources contained in the Scope 5 WARM Resource Library are current through WARM Version 15 (September 2022).
Disclaimer
Scope 5 cannot guarantee that by using the Scope 5 WARM Resource Library users will produce a report that is fully compatible with the EPA WARM tool. We recommend working with a sustainability consultant well versed in waste management, lifecycle analysis and GHG emissions reporting to be sure that your report will be fully compliant with the intended use. Please review the EPA Waste Reduction Model (WARM) to learn more about the intended use of the WARM tool.
Scope 5 can provide other customized resource libraries on a case-by-case basis.
[1] https://www.epa.gov/warm/versions-waste-reduction-model-warm#15
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