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LCI Methodology and Data Sources

We provide here a description and outline of the methodology and key data sources used to compile our life cycle inventory (LCI) database of greenhouse gas emissions (embodied carbon), primary energy use (embodied energy) and water use (embodied/virtual water). The methodology used to build the database is consistent with international standards (the ISO 14040, PAS 2050, GHG Protocol).

Methodology

Data obtained from external data sources include both activity data and emission factors. Activity data characterize the life cycle of a product/process by accounting for all material and energy inputs consumed, material and energy outputs generated, transport, storage, and waste outputs generated throughout the life cycle. The system boundary for the process modeling is "cradle to factory gate", "cradle to farm gate", "well to wheel", or "cradle to grid" as appropriate. Emission factors are then used to translate this process activity data into GHG emissions, covering both energy-related and non-energy-related GHG emissions (CO2, as well as other significant non-CO2 greenhouse gas emissions). Variations due to different production methods and geographical regions are preserved as much as possible in the database.

Modeling Carbon Storage: Carbon storage in products/processes lasting more than a year -- including a variety of wood-based manufactured products, textiles incorporating natural fibers, concrete structures, planted trees, etc. -- are modeled based on methodologies and parameters adapted from IPCC tier 1/2 and the Danish Technological Institute.

Modeling Waste Processing: Both solid waste and waste water streams are modeled in detail based on methodologies and parameters adapted from IPCC tier 1/2 for a broad range of industries. Solid waste modeling includes aerobic/anaerobic landfilling, incineration, composting, and recycling/reuse. Waste water modeling includes aerobic and anaerobic treatments. Methane and energy recovery options are included with waste processing steps. Recycling is modeled using the "recycled content" method which allocates the costs and benefits of recycling to the input side of product systems; the system boundaries are drawn such that the system that produces the recyclable waste is responsible up to the point of delivering the waste to a recycling facility, and then any subsequent transport, processing and use of that material is included within other systems that use the material in some form. Other types of waste material that may be useful elsewhere, such as manure from animal systems, are handled in a similar manner: The product systems that use the material, such as organic crop systems that use manure as a substitute for fertilizers, get credit for avoiding the resource use and emissions associated with fertilizer manufacture; and these systems also bear the burden of actually applying the manure and the subsequent nitrous oxide emissions from the soil.

Modeling Land Use: Land use modeling is based on methodologies and parameters adapted from IPCC tier 1/2, and includes two specific scenarios: unchanged land use and changes in land use. All common land use categories are included. Factors considered include changes in above-ground and below-ground biomass and changes in soil carbon -- during land use change as well as over time.

Modeling Dynamic Emissions/Sequestration: Dynamic, or time-dependent, GHG emissions and carbon sequestration are modeled by explicitly considering the time dimension over a specific assessment period (such as the standard 100 years). Emission and sequestration events are weighted according to the timing of the events within the assessment period, as part of our Deep Carbon Footprintingmethodology.

Allocation Methods: Allocation of resource use and emissions between co-products is performed by dividing a process into distinct sub-processes, or by using mass-weighted economic value or a biophysical measure (such as mass, energy or nutrition content) as appropriate. We have generally avoided system expansion because of the inherent difficulties and uncertainties involved in identifying and characterizing appropriate marginal product systems. Mass-weighted economic value has proven to be the most reliable method of allocation in many real-world scenarios, particularly for product systems that produce highly dissimilar co-products. Low-value (and often high-volume) waste outputs that may be useful elsewhere, such as recyclable material waste or manure from animal systems, are handled as part of the waste processing algorithm described above.

Modeling Agricultural Processes: Agricultural processes such as the production of food commodities are modeled uniformly based on a detailed inventory of inputs and outputs as indicated below.

  • Fertilizer application (both synthetic and organic)
  • Pesticide application
  • Other inputs such as lime, gypsum, sulfur, etc.
  • Irrigation -- including district-supplied water, ground water (pumped), and  surface water from natural sources such as rivers
  • Electricity and fuel use
  • Feeds for animals
  • Transport of material inputs to farm
  • Any processing of raw products
  • Non-energy GHG emissions and sequestration at the farm level:
    • CO2 from lime and urea application
    • Direct/indirect N2O emissions from soils and water due to nitrogen fertilizer application (both synthetic and organic)
    • Direct/indirect N2O emissions from soils due to crop residues and biological nitrogen fixation
    • CH4 from flooded rice fields
    • CH4 from enteric fermentation in ruminant animals
    • CH4 and N2O emissions from manure management
    • Carbon storage in the biomass of perennial species such as fruit trees during growth and at maturity
    • Changes in the carbon content of soils (emissions/sequestration) due to land management methods -- for general scenarios such as changing from conventional to organic crop production, or for specific changes related to tillage, application of organic amendments, etc.
  • All inputs, outputs and emissions occurring during the establishment years for perennial species such as fruit trees
  • All inputs and emissions related to the planting and maintenance of cover crops
  • Other factors:
    • Direct land use is generally assumed to have been unchanged since 1990 for most agricultural production systems and thus GHG emissions/sequestration from land use change are excluded, except where we have specific information to the contrary. This is handled on a case-by-case basis.
    • Energy use and emissions related to the production of capital goods and infrastructure are currently excluded.

Data Sources

Emission Factors: Emission factors for extraction and combustion of primary fuels -- as well as non-energy-related emission factors for GHG emissions inherent in industrial, agricultural, transport, and other processes -- are consistently derived and calculated using the following two sources:

Electricity: Primary energy use and GHG emissions per unit of electricity supplied through the grid are calculated using activity data -- consisting of fuel and power plant mixes for various grid regions (both US and international), as well as transmission losses and other details -- from these sources:

Transport: Primary energy use and GHG emissions per tonne-km of freight transport for all transport modes (road, rail, ocean, and air) are calculated using activity data from these sources:

Refrigeration: Primary energy use and GHG emissions for refrigerated storage in warehouses and transportation are calculated using activity data from EPA Energy Star.

Materials: GHG emissions, primary energy use, and water use for many basic manufacturing processes and materials (including metals, plastics, cement, timber, fibers, fabrics, etc.) used in construction, manufacturing and packaging are calculated through an analysis of the US Life-Cycle Inventory Database. Additional data sources for materials include the Inventory of Carbon and Energy, Eco-Profiles of the European Plastics Industry, Copper Development Association LCA, NIST's Building and Fire Research Laboratory, peer-reviewed research publications, LCA/LCI studies available in the public domain, and industry sources. Data for fertilizer production are based on IFA publications, pesticide data are derived from the Encyclopedia of Pest Management, and water/wastewater treatment data are from ACEEE and IPCC.

Food and Agriculture: GHG emissions, primary energy use, and water use for food and agricultural products and processes are calculated using activity and other data from numerous credible sources, including university agricultural extensions, agro-economics departments, government agencies and peer-reviewed research publications. Representative data sources include:


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