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The availability of updated information has necessitated updates to the emission factors used in WARM and the ReCon tool. Since some companies and waste managers have used older versions of the tool, the purpose of this page is to explain the changes incorporated with each version.

Below is a brief chronology of changes made to WARM and the ReCon tool. Starting with the most recent edition, brief summaries of changes and updates since the previous version are provided below. The objective is to provide users with a transparent picture of the evolution of the tools and to provide context for comparisons of results obtained from different versions of ReCon. Users can browse the supporting documentation for these changes in the Background Documents for Solid Waste Management and GHG Report.

WARM

Waste Reduction Model (WARM) Version 13
This version of WARM, released in June 2014, contains a variety of new material categories and revisions to existing numbers and methodology. The majority of the updates in WARM version 13 concern the modelís handling of organics, including new source reduction emission factors for food waste, an updated methodology for estimating landfill gas emissions, the inclusion of fugitive gas emissions from composting, and updates to the global warming potential (GWP) values in the model.

The new emission factors contained in this version of WARM cover non-meat sources of food waste, including grains, bread, dairy products, and fruits and vegetables. These emission factors include the energy and emissions associated with the upstream production of food products from farm to retail. The revisions to the landfilling waste management pathway, prepared using a landfill gas Monte Carlo analysis model developed by James Levis and Morton Barlaz, more accurately estimate the fraction of total produced landfill gas that is used beneficially, flared, and vented to the atmosphere at landfills that manage landfill gas. This analysis improves upon the landfill gas collection efficiency modeling in WARM and updates the methane oxidation rates. In addition, the Excel version of WARM now allows users the option of selecting and reviewing results based on California regulatory gas collection scenario as one of four landfill gas collection scenarios. For information on the major changes to the landfill emissions methodology for WARM version 13, please see the Landfilling Chapter and the Landfill Gas Monte Carlo Model Documentation and Results. The composting pathway has been updated to include emissions of CH4 and N2O occurring during the composting process based on recent literature estimates.

GWP values in WARM have been updated to include those from the Intergovernmental Panel for Climate Change (IPCC) Fourth Assessment Report. In addition, EPA made its regular updates to various factors in the model using current data sources. The latest 2012 statistics on the carbon content of fuels, landfill methane generation distribution (by type of landfill), and landfill gas recovery and flaring rates have been incorporated from EPA's Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2012. Retail transport emissions for various materials were updated based on the Bureau of Transportation Statistics (BTS) 2012 Commodity Flow Survey. The non-biogenic carbon content of mixed MSW was updated using annual waste disposal data from EPA's Municipal Solid Waste in the United States, Facts and Figures. Various aspects of the U.S. average electricity mix were updated based on EIA's 2014 Monthly Energy Review while state electricity grid emission factors were updated based on the 2014 update to the eGRID database. These updates resulted in changes to the majority of emission factors in WARM.

Other EPA tools that rely on emission factors from WARM such as ReCon and iWARM have not been updated. Therefore, there may be inconsistencies between the estimates provided by the tools.

The documentation files for the model are in the process of being updated to describe the development of the emission factors for the new materials, to discuss any revisions to previously-included materials, and to incorporate the new energy and emissions data calculated by EPA.

Waste Reduction Model (WARM) Version 12
This version of WARM, released in February 2012, contains several updates and improvements from the previous WARM Version 11. In this latest version of WARM, the interface displays results in metric tons of carbon dioxide equivalent (MTCO2E) as the default unit for GHG emissions, but results are still available in units of metric tons of carbon equivalent (MTCE). Additionally, this version of WARM no longer maintains macros. The removal of macros does not affect the results or functionality of the tool. All of the energy and emissions (both MTCO2E and MTCE) results are displayed automatically. New emission factors were added for four plastics, linear low-density polyethylene (LLDPE), polypropylene (PP), polystyrene (PS) and polyvinyl Chloride (PVC). Additionally, new emission factors were developed for polylactide (PLA) and aluminum ingot. Several other emission factors were revised: the emission factor for aluminum cans has been updated to include additional can manufacturing steps in the updated life cycle data as well as factor in industry-specific electricity grid mix assumptions, the combustion and open-loop recycling pathways for residential broadloom carpeting now incorporate new data from Dr. Matthew Realff and the emission factors for three plastics, high-density polyethylene (HDPE), low-density polyethylene and polyethylene terephthalate (PET) were updated using new life-cycle data. The mixed recycling and mixed plastics recycling factors have both changed due to 1) revisions to the underlying numbers in the virgin and recycled HDPE and PET emission factors, 2) the removal of the LDPE recycling pathway, and 3) updates to the waste generation and recovery numbers based on EPA's "Municipal Solid Waste (MSW) in the United States: Facts and Figures" report. The documentation files for the model have also been updated to describe the development of the emission factors for the new materials, any revisions to previously-included materials and have incorporated the new energy and emissions data calculated by EPA. For information on the major changes to the updated Aluminum Cans and new Aluminum Ingot material GHG emission and energy Factors for WARM version 12, please see the Aluminum FAQ document.

In addition, EPA made its annual updates to various factors in the model using current data sources. The latest 2010 statistics on the carbon content of fuels, landfill methane generation distribution (by type of landfill), and landfill gas recovery and flaring rates have been incorporated from EPA's Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009. The non-biogenic carbon content of mixed MSW was updated using annual waste disposal data from EPA's Municipal Solid Waste in the United States, Facts and Figures and BioCycle's State of Garbage in America report. Various aspects of the U.S. average electricity mix were updated based on EIA's 2010 Annual Energy Review while state electricity grid emission factors are updated based on the eGRID database. These updates resulted in changes to the majority of emission factors utilized in WARM; due to these and other past changes, the emission factors differ from those in EPA's 2006 report Solid Waste Management and Greenhouse Gases: A Life-Cycle Assessment of Emissions and Sinks (3rd Edition). Other EPA tools which rely on emission factors from WARM such as ReCon and iWARM have not been updated. Therefore, there may be inconsistencies between the estimates provided by the tools.

Waste Reduction Model (WARM) Version 11
This version of WARM, released in August 2010, contains several updates and improvements from the previous WARM Version 10. In this latest version of WARM, EPA modified the interface to display results in metric tons of carbon dioxide equivalent (MTCO2E) as the default unit for GHG emissions, but results are still available in units of metric tons of carbon equivalent (MTCE). New emission factors were added for six construction and demolition (C&D) materials: asphalt concrete, asphalt shingles, drywall, fiberglass insulation, vinyl flooring, and wood flooring. Emission factors for tires were also updated: the tire recycling pathway now encompasses ground and shredded rubber applications and no longer includes retreading as a recycling application. Additionally, the Excel version of WARM now incorporates region-specific electricity grid factors to more accurately model emissions associated with avoided generation of electricity due to landfill gas recovery in the landfilling pathway and waste-to-energy in the combustion pathway. The Excel version of WARM also includes an updated method for estimating the landfill gas collection efficiency, allowing the user to select between three landfill gas collection efficiency scenarios based on specific landfill recovery characteristics: typical operation, worst-case collection, and aggressive gas collection. Component-specific decay rates were added for all organic materials to more accurately model the rate at which each material decays within a landfill under given landfill moisture conditions. The component-specific decay rates modeled in WARM are also available as a user-defined input in the Excel version of WARM and are based on selecting one of four landfill climate/moisture characteristics: dry, average, wet, or bioreactor. The updated research from Dr. Morton Barlaz on component-specific decay rates and landfill gas collection efficiency, upon which these new factors are based, is described further in the memo to EPA (PDF, 16 pp., 192 KB, About PDF) entitled “WARM component-specific decay rate methods,” available among the WARM background documents.

In addition, EPA made its annual updates to various factors in the model using current data sources. Statistics on the carbon content of fuels, landfill methane generation distribution (by type of landfill), and landfill gas recovery and flaring rates have been incorporated from EPA’s Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008. The non-biogenic carbon content of mixed MSW was updated using annual waste disposal data from EPA’s “Municipal Solid Waste in the United States, 2008 Facts and Figures” and BioCycle’s “State of Garbage in America” 2008 report. These updates resulted in changes to the majority of emission factors utilized in WARM.

Waste Reduction Model (WARM) Version 10 (356 kb WinZip archive)
This version was released in November 2009 and contains updates and improvements from the previous version 9. Both the web-based and Excel versions of WARM were updated to a new “side-by-side” interface to facilitate user input entry. The latest statistics from 2008 on national average electricity generation fuel mix, transmission and distribution losses, coal weighting for electricity generation, and generation per fuel type were added. Also added were updates on the carbon content of fuels, landfill methane generation distribution (by type of landfill), landfill gas recovery and flaring rates, and waste generation and recovery rates. The non-biogenic carbon content of mixed MSW was updated using annual waste disposal data. The landfill carbon storage factors for mixed MSW were revised to reflect new data from Dr. Morton Barlaz and the GHG equivalencies were updated to match EPA's GHG Equivalency Calculator. New GHG equivalencies were added to show the change in emissions calculated by the user in terms of gallons of gasoline, cylinders of propane, railway cars of coal, as a percentage of the annual CO2 emissions from the U.S. transportation sector, and as a percentage of the annual CO2 emissions from the U.S. electricity sector.  The recycling emission factors for the mixed paper material types were modified to include updated recycled boxboard data. These updates resulted in changes to the majority of emission factors utilized in WARM.

Waste Reduction Model (WARM) Version 9 (310 kb WinZip archive)
This version was released in August 2008 and contains updates and improvements from the previous version 8. The latest statistics from 2007 on national average electricity generation fuel mix were added along with updates on the carbon content of fuels, landfill methane generation distribution (by type of landfill), and waste generation and recovery rates. The landfill carbon storage factors were revised to reflect new data from Dr. Mort Barlaz and the GHG equivalencies were updated to match EPA's GHG Equivalency Calculator. Also, the 1605(b) functionality in the Excel version of WARM was removed since 1605(b) no longer supports reporting of savings from waste reduction. Finally, the waste-to-energy combustion pathway energy values (MMBTU) incorporates a revised methodology that considers the ratio of mass burn combustion facilities (17.8%) and the national average electric utility electricity combustion efficiency (32%). These updates resulted in changes to the majority of emission factors utilized in WARM.

Waste Reduction Model (WARM) Version 8 (494 kb WinZip archive)
This version was released in August 2006 and contains several updates and improvements from the previous version. The latest statistics from 2006 on national average electricity generation fuel mix were added along with research on landfill methane generation and forest carbon sequestration, and tires were added as a new material type. These updates resulted in relatively minor changes to the majority of emission factors utilized in WARM.

Waste Reduction Model (WARM) Version 7 (486 kb WinZip archive)
This version was released in August 2005 and contains several updates and improvements. Copper wire was added as a new material type providing additional resolution to the metals category. The latest statistics on national average electricity generation fuel consumption were added along with recent research on landfill methane generation and carbon sequestration associated with organic matter; the retail transportation component of the life-cycle was also added to the methodology. The computational methodology for landfill carbon storage and methane generation was adjusted slightly to reflect the carbon content of methane. Generation and recovery percentages were also updated based on the MSW in the United States: 2003 Facts and Figures report. These updates resulted in relatively minor changes to the majority of emission factors utilized in WARM.

Waste Reduction Model (WARM) Version 6.1 (480 kb WinZip archive)
This version was released in December 2004 and included a couple of minor revisions to the prior WARM version 6. The emission factor for transportation of waste to landfill by combination truck was revised. In addition, revisions were made to the landfill-gas-to-energy offsets for users interested in reporting to the U.S. Department of Energy’s 1605(b) program. The landfill-gas-to-energy offsets for 1605(b) users were revised to be phased in over 30 years, rather than the total offset being applied in year one.

Waste Reduction Model (WARM) Version 6 (463 kb WinZip archive)
This version was released in March 2004 and incorporated several updates/improvements. Five new material types were added: personal computers, carpet, clay bricks, aggregate, and fly ash. Emission factors for all other materials were updated based on new information related to the current mix of recycled and virgin inputs; new data on municipal solid waste generation and recovery from the 2001 Facts and Figures; and the energy and greenhouse gas equivalencies were updated based on more recent statistics from the U.S. Department of Energy (DOE) Energy Information Administration (EIA). These equivalencies are intended to put results in units that may be more “tangible” than British thermal units or metric tons of carbon (e.g., number of barrels of oil, number of households’ annual energy consumption, and number of gallons of gasoline).

Waste Reduction Model (WARM) Version 5 (395 kb WinZip archive)
This version was released in December 2003 and included revised estimates for PFC emissions and carbon anode carbon dioxide emissions associated with aluminum production based on data reported in the Inventory of U.S. Greenhouse Gases and Sinks: 1990-2000.

Waste Reduction Model (WARM) Version 4 (422 kb WinZip archive)
This version was released in May 2002 and included the latest data on municipal solid waste characterization based on the 2000 Facts and Figures Report, and electricity generation data for the year 2000 from the DOE’s EIA. Additionally, this version uses life-cycle energy data sources from ORD (RTI), rather than OSW (Franklin) as used in previous versions. In general, ORD's data set of energy, fuel mix, and loss rates is likely to be more up-to-date than some of the information from OSW. The ORD data was used for those materials with a complete set of ORD energy intensity and fuel mix data. This information was not available for wood products or steel because ORD did not develop emission factors for wood products and the ORD steel data was not sufficiently disaggregated to replace the existing OSW data.

Waste Reduction Model (WARM) Version 3 (1,986 kb WinZip archive)
This version was released in November 2001 and reflected several improvements made to the previous version of WARM (version 2). For participants in the U.S. Department of Energy’s 1605(b) program, results and summaries could now be viewed by gas, phased over time, and phased over time by gas. The ability to view results by gas shows emissions for carbon dioxide, methane, nitrous oxide, tetrafluoromethane, hexafluoroethane specifically, rather than only total emission reductions in terms of metric tons of carbon or carbon dioxide equivalent. The phased results and summaries show the emissions of the waste management practices for year one, for years 2-15, for years 16-30, and for all years. Results and summaries phased by gas shows results for the five gases for year one, years 2-15, years 16-30, and for all years. New materials were also added to this version and the transportation to landfill calculations were updated using data on carbon dioxide emissions per mile of freight transport.

WARM Version 1 & Version 2 (690 kb WinZip archive)
The first version of WARM was released in 1998, followed by the release of version 2 in December of 1999. At this stage, WARM was undergoing rapid change and growth in terms of its capabilities. These first versions included 17 material types (metals, plastics, organics, and mixed paper and recyclables) as well as the basic options still available in WARM such as the ability to specify current mix or virgin materials, the type of landfill gas control system, and the transportation distance to the waste management options.

ReCon

ReCon Version 5
This is the latest edition of the tool available to the public. Released in October 2010, Version 5 contains updates to the underlying GHG emission factors that match the latest version of WARM (Version 11). Additionally, EPA modified the interface to display results in metric tons of carbon dioxide equivalent (MTCO2E) as the default unit for GHG emissions, but results are still available in units of metric tons of carbon equivalent (MTCE).

ReCon Version 4
This version was released in April 2010 and contains updates to the underlying emission factors that match WARM Version 10. Additionally, assumptions about the percent of materials being landfilled versus combusted at the end of life were updated.

ReCon Version 3
This version was released in August 2006 and contains several updates and improvements. The latest statistics on national average electricity generation fuel mix were added along with recent research on landfill methane generation and forest carbon sequestration.

ReCon version 2
This version was released in July 2005 and contains several updates and improvements. Copper wire was added as a new material type providing additional resolution to the metals category. The latest statistics on national average electricity generation fuel consumption were added along with recent research on landfill methane generation and carbon sequestration associated with organic matter; the retail transportation component of the life-cycle was added to the methodology. Disposal percentages were also updated based on the MSW in the United States: 2003 Facts and Figures report. These updates resulted in relatively minor changes to the majority of emission factors utilized in ReCon.

ReCon version 1
The first version of ReCon was released in March 2004. This first version included 16 material types (metals, glass, plastics, paper types, and wood) as well as the ability to specify the percent of recycled content in the alternative and baseline scenarios or use default recycled content values. As part of the avoided disposal calculation the national average disposal rates for combustion and landfilling were based on the MSW in the United States: 2000 Facts and Figures report.


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