Q7: Embodied Energy vs. Embodied Carbon

What’s the difference between embodied energy and embodied carbon?  Can I just scale embodied carbon results to embodied energy?

Author: Kathrina Simonen, Dirk Kestner; Contributors: Frances Yang, Kelly Roberts, Lionel Lemay

Embodied energy and embodied carbon are similar yet distinct metrics to evaluate the environmental impact of a material, product or building.  Table 7.1 summarizes the key differences between operational and embodied impacts as well as energy and carbon.

Table 7.1: Summary differences between embodied and operational energy and carbon

Embodied Energy

Embodied energy reports the total energy (kilojoules) used to produce a building, building product or material.  Total energy use is different and is a typical output of a comprehensive LCA. Total energy use should reflect all life cycle phases including use and disposal, but embodied energy does not include use and may or may not include installation, maintenance and disposal.  Although products with higher embodied energy often have higher embodied carbon, the two are not always proportional as carbon emissions depend upon the energy source.   For example, an energy-intensive production process that used mostly renewable or low carbon fuel sources could have a very small embodied carbon footprint, yet a high embodied energy.    Energy use is a direct measure of manufacturing energy needs combined with energy efficiency.  A carbon footprint, on the other hand, measures a combination of energy use efficiency and fuel source emissions.  

Embodied Carbon

While many are familiar with the terms “carbon footprint” or “embodied carbon”, use of the term carbon has been used loosely in many circles.  In some cases “carbon” may mean CO2e, or the total equivalent Global Warming Potential.  However, there are other cases, such as some of the more accessible structural material databases, where embodied carbon means only the CO2 emissions associated with a quantity of material.  For this reason it is best to speak of embodied CO2e, or “'climate change impact in CO2e”.

Embodied CO2e is an estimate of the contribution to climate change made by the production (rather than use or disposal) of a product. Thus, it represents a portion of an LCA that estimates only the contribution to climate change and only through certain initial phases of its life.  The Global Warming Potential (GWP) is a widely recognized environmental impact metric reporting the greenhouse gas (GHG) emissions that have been identified to impact climate change.  It is measured in units of kilograms of carbon dioxide equivalents and includes contributions from multiple greenhouse gasses (GHG) such as carbon dioxide, methane, nitrous oxide and others.  The mass of each of these GHGs is converted to represent the equivalent impact of a kilogram of carbon dioxide and thus summed to an equivalent mass of carbon dioxide or CO₂e.  The Kyoto protocol tracks six primary greenhouse gasses (UNFCCC, while the EPA’s TRACI model (EPA 2011) and CML’s Characterization Factor Database (CML-IA 2010) track over 90. 

 

Reporting Standards

Standards for tracking and reporting the carbon footprint of companies, organizations and products have been/are being developed.  The Greenhouse Gas Protocol (GHG Protocol) is a widely used greenhouse gas emission accounting standard that has been developed in cooperation between the World Resource Institute and the World Business Council for Sustainable Development (WRI/WBCSD 2011).  The GHG Protocol divides GHG emissions into categories referred to as scopes (See Figure 7.1).

Figure 7.1.  Defining GHG emissions by source type (scope), (WRI/WBCSD, 2011)

 

Scope 1 defines the emissions directly under the control of the company that are related to the generation of energy used to power facilities and vehicles.   These are categorized as direct emissions because the company reporting the emissions directly controls them.  Scope 2 defines those emissions related to the generation of energy purchased by a company.   These are categorized as indirect as the company only has indirect control over the process.  Scope 3 defines the emissions related to other indirect emissions, such as the extraction and production of purchased materials and fuels, transport-related activities in vehicles not owned or controlled by the reporting entity, outsourced activities, waste disposal, etc. Upstream activities of Scope 3 are those that are purchased by a company and used in the primary activities of the company (or production of a product). Downstream activities of Scope 3 occur after the product leaves the company ‘gate’ and include use and disposal impacts.

While initial standards focused on reporting corporate carbon footprints, in October of 2011, the WRI/WBSCD released a Product Standard (WRI/WBCSD 2011).  This standard, which is based on LCA methodology, articulates methods appropriate for evaluating and tracking the carbon footprint of a material or product. Efforts to harmonize these standards with ISO are underway.

Summary

So what does this mean to a practicing structural engineer?  Both embodied carbon and embodied energy are valuable metrics. If you are concerned about climate change impacts, you should focus on understanding and reducing GHG emissions or the embodied ‘carbon footprint’.   If you are concerned about fossil fuel depletion and energy independence, you should focus on understanding and reducing total energy consumption. For some, one issue may be more important than another, for others, both will be equally important.

References

This post was adapted from the University of Washington report on LCA for the Washington State Senate, (Simonen and Haselbach 2012) by permission of the co-authors, one of who is on the SEI Sustainability Committee.

CML-IA (2010). CML-IA Characterization Factor Database. Published by the Institute of Environmental Sciences (CML) at the Universiteit Leiden.  Accessed April 8, 2013 from http://cml.leiden.edu/software/data-cmlia.html.

EPA (2011).  Tool for the Reduction and Assessment of Chemcial and Other Environmental Impacts (TRACI) TRACI_2_1.xlsx.  Database published by the U.S. Environmental Protection Agency. Details accessed April 8, 2013 from http://www.epa.gov/nrmrl/std/traci/traci.html.

Simonen, K. and Haselbach, L. (2012). LCA for WA: Life Cycle Assessment and Buildings Research for Washington State. Final report submitted to Washington State Legislature, Olympia, WA.   Accessed April 8, 2013 from http://courses.washington.edu/lcaforwa/wordpress/?page_id=213.

UNFCC (2012). United Nations Framework Convention on Climate Change.  Accessed April 8, 2013 from http://unfccc.int/resource/docs/publications/08_unfccc_kp_ref_manual.pdf.

WRI/WBCSD (2011).  Product Life Cycle Accounting and Reporting Standard.  Report of the World Resources Institute and World Business Council for Sustainable Development.  Accessed April 8, 2013 from http://www.ghgprotocol.org/files/ghgp/Product%20Life%20Cycle%20Accounting%20and%20Reporting%20Standard.pdf.

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