This chapter describes the development of material‐specific emission factors for source
reduction in EPA’s Waste Reduction Model (WARM). Source reduction, or waste prevention, refers to
practices that reduce the amount of materials entering the waste stream, including changes in the
design, manufacture, purchase or use of materials. This document provides examples of source
reduction and a summary of how EPA estimates the GHG benefits from source reduction of materials.
1 TYPES OF SOURCE REDUCTION
Source reduction can result from any activity that reduces the amount of a material needed and
therefore used to make products. Some specific examples of source reduction practices are:
• Redesigning products to use fewer materials (e.g., lightweighting, material substitution).
• Reusing products and materials (e.g., a refillable water bottle).
• Extending the useful lifespan of products.
• Avoiding using materials in the first place (e.g., reducing junk mail).
In addition to the activities above, there are limited circumstances where the emission factors
can be used to estimate GHG benefits of substituting one material or product for another material or
product. Section 3.2 presents considerations for estimating the GHG effects of material substitution.
2 A SUMMARY OF THE GHG IMPLICATIONS OF SOURCE REDUCTION
When a material is source reduced, GHG emissions associated with producing the material
and/or manufacturing the product and managing the post‐consumer waste are avoided. Consequently,
source reduction provides GHG emission benefits by: (1) avoiding the “upstream” GHGs emitted in the
raw material acquisition, manufacture and transport of the source‐reduced material; (2) increasing the
amount of carbon stored in forests (when wood and paper products are source reduced); and (3)
avoiding the downstream GHG emissions from waste management.
Because many materials are manufactured from a mix of virgin and recycled inputs, the quantity
of virgin material production that is avoided is not always equal to the quantity of material source
reduced. Therefore, to estimate GHG emissions associated with source reduction, WARM uses a mix of
virgin and recycled inputs, based on the national average for each material. However, WARM also
allows users to evaluate the benefits of source reducing materials manufactured from 100‐percent
virgin inputs, instead of a mix of virgin and recycled inputs.
WARM assumes that source reduction of paper and wood products increases the amount of
carbon stored in forests by reducing the amount of wood harvested. For more information on the
calculations that went into creating the forest carbon storage offset, see the Forest Carbon Storage
chapter.
In order to measure the full GHG impact of source reduction, the user must compare the GHG
emissions from source reduction to the GHG emissions of another materials management option. For
example, a user could compare the benefits from source reducing one short ton of office paper instead
of sending the paper to the landfill. This approach enables policy‐makers to evaluate, on a per‐ton basis,
the overall difference in GHG emissions between (1) source reducing one short ton of material, and (2)