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Basic Information about the Waste Reduction Model (WARM)

EPA created the Waste Reduction Model (WARM) to help solid waste planners and organizations track and voluntarily report greenhouse gas (GHG) emissions reductions from several different waste management practices.

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What is WARM?

WARM is a tool that calculates and totals GHG emissions of baseline and alternative waste management practices—source reduction, recycling, combustion, composting, anaerobic digestion and landfilling. The model calculates emissions across a wide range of material types commonly found in municipal solid waste in the following:

  • metric tons of carbon dioxide equivalent (MTCO2E),
  • metric tons of carbon equivalent (MTCE), and
  • energy units (million British Thermal Unit - BTU). 

WARM is currently available as a tool based on a database developed in open life cycle assessment (openLCA) software, with versions available for both Windows and Macintosh users. WARM is also available as a downloadable Microsoft Excel spreadsheet.

GHG savings are calculated by comparing the emissions associated with managing materials under an alternative scenario with the emissions associated with the user’s baseline scenario (i.e., current practices), as opposed to simply multiplying the quantity of materials managed by an emission factor. For example, the GHG savings of recycling one (1) short ton (standard U.S. ton) of aluminum cans instead of landfilling them would be calculated as follows:

(1 short ton × -9.11 MTCO2E/short ton) - (1 short ton × 0.02 MTCO2E/short ton) = -9.13 MTCO2E

WARM is periodically updated as new information becomes available and new material types are added. Users may refer to the model history to better understand the differences among various versions of WARM. WARM was last updated in March 2016.

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Who Should Use WARM?

WARM helps solid waste planners and organizations track and voluntarily report greenhouse gas (GHG) emissions reductions from six different waste management practices – source reduction, recycling, composting, anaerobic digestion, combustion and landfilling. WARM can be used by individuals and organizations ranging from state and local governments, solid waste planners, students, small businesses, and other organizations interested in the energy and GHG impacts form materials management decisions.

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What Materials Are in WARM?

WARM now recognizes 54 material types, which are presented in the table below. Their emission factors are available for viewing in units of metric tons of carbon dioxide equivalent (MTCO2E) or metric tons of carbon equivalent (MTCE). 

Material Types Recognized by WARM
Aluminum Cans Food Waste (non-meat) Mixed Recyclables
Aluminum Ingot Food Waste (meat only) Newspaper
Asphalt Concrete Fruits and Vegetables Office Paper
Asphalt Shingles Glass Personal Computers
Beef Grains Mixed Plastics
Branches Grass PET (polyethylene terephthalate)
Bread HDPE (high-density polyethylene) Phonebooks
Carpet LDPE (low-density polyethylene) PLA (polylactic acid)
Clay Bricks Leaves Poultry
Concrete LLDPE (linear low-density polyethylene) PP (polypropylene)
Copper Wire Magazines/Third-Class Mail PS (polystyrene)
Corrugated Cardboard Medium Density Fiberboard PVC (polyvinyl chloride)
Dairy Products Mixed Metals Steel Cans
Dimensional Lumber Mixed MSW (municipal solid waste) Textbooks
Drywall Mixed Organics Tires
Fiberglass Insulation Mixed Paper (general) Vinyl Flooring
Fly Ash Mixed Paper (primarily from offices) Wood Flooring
Food Waste Mixed Paper (primarily residential) Yard Trimmings

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