Carbon Footprints

A carbon footprint is the total greenhouse gas emissions for a given person, place, event or product.

Carbon footprints are created using a process called life cycle assessment. Life cycle assessment or LCA is a method of resource accounting where quantitative measures of inputs, outputs and impacts of a product are determined.

Life cycle assessment is commonly used to:

  • find process or production improvements
  • compare different systems or products
  • find the ‘hot spots’ in a product’s life cycle where the most environmental impacts are made
  • help businesses or consumers make informed sourcing decisions

LCA Methods

There are several standard approaches for developing a life cycle assessment including the International Dairy Federation, the U.S. EPA, and two European standards: ISO 14040, and PSA 2050.  While this can be completed with a simple spreadsheet, there are several software packages available to help complete the LCA

Steps to a Life Cycle Analysis:

  1. Define the goal & scope of the LCA. This includes determining the purpose for the analysis.
  2. Set the boundaries of the system: each higher tier provides a more complete picture of the product’s impacts, however requires more time and resources to complete.
    1. Gate to Gate (LCA Tier I) – inventories the direct emissions for a single product of process
    2. Cradle to Gate (Tier II) – inputs are taken back to the initial extraction as natural resources up to a certain point in the product’s life such as its sale from the farm, i.e. farm gate.  This will include both direct  and indirect emissions from the product.
    3. Cradle To Grave (Tier III) – the product is followed through the consumer to its eventual recycling or disposal.
  3. Determine how the impacts will be measured, also known as the functional unit. This can be expressed as the net sum of all impacts per unit of product, or the opposite: for a given amount of product, the amount of impact e.g. pounds of greenhouse gas emissions produced per pound of energy corrected milk.
    • Example impacts: greenhouse gas emissions, water use, land use, health impact
    • Example livestock products: Pound of meat, dozen eggs, energy corrected milk production, nutritional content.
  4. Inventory the needed data. Information is gathered to identify and quantify energy, water and materials usage and the environmental releases associated with each step of the process. These data are collected through research and modeling for many different inputs, from coal mining to equipment manufacturing, and are available through worldwide databases. However, some of the needed data may not yet be available so research articles, models and assumptions must be used to fill in the final informaion.
  5. Allocate resources and impacts to co-products. For example in dairy production, feeder cattle for meat production are also grown. The impacts of dairy feeder production can be included in the milk LCA, because calves are necessary for milk production, or a portion of the impacts can be allocated to beef production. This allocation can be made several ways, with the most common being economic, i.e. the calves are 10% of the value of dairy enterprise, or mass, i.e. the calves are 1% of the mass leaving the farm.
  6. Impact assessment. This is where all the impacts are totaled and summarized. If the purpose of the LCA was to produce a carbon footprint, then only greenhouse gas impacts need totaled. However, multiple impacts can be compared and given different weighting if an overall score for a product is part of the purpose for the LCA.

Sources of variation

Different researchers may get different results when performing a LCA on the same product. This can happen for many reasons:

  • System boundary definition
  • Inclusion/exclusion of secondary/ indirect sources
  • Inclusion/exclusion of biogenic carbon (stored in organisims)
  • Inclusion/exclusion of carbon dioxide from fuel combustion
  • Functional relationships used
  • Global warming potential indexes
  • Inclusion/exclusion of carbon sequestration

Additional Resources

Additional Animal Agriculture and Climate Change Resources

Climate Science Resources

Basic Climate Science (Texas A&M AgriLife Extension, 2012)

2007 IPCC Fourth Assessment Report (AR4) on Climate Change

Global Climate Change Impacts in the United States (Karl, T. et al., 2009)

Carbon, Climate Change and Controversy (Shepherd, J. M., 2011)

Global Climate Change Causes – web site (NASA, 2012)

Center for Climate and Energy Solutions

The Modern Temperature Record (American Institute of Physics)

Author: Crystal A. Powers – UNL
Reviewers: J. Harrison – WSU, J. Heemstra – UNL, S Mukhtar – TAMU, D. Smith – TAMU