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Learn about SM Single Score results

How SM Single Scores are calculated

Introduction to the impact factor creation process

The SM Impact Assessment Methodology is a single figure life cycle assessment (LCA) that combines the inventory calculation and the proceeding assessment calculations in one multiplication factor, leading to the impact factor. Figure 1 shows the LCA data progression that is embedded behind each impact factor.

1 System bill of materials Materials, processes, energy used, transport, end-of-life Length of list depends on the product
2 Inventory Emissions, resource depletion and land-use Can be hundreds of chemicals per material
3 Characterization Environmental impacts: global warming, carcinogens, etc. Typically 8–12 categories, via scientific, peer reviewed formulae
4 Normalization Scales impact according to average impacts of a person in a contintental area North American or European normalization available
5 Weighting Scales impact according to signifigance of impacts

Figure 1 – Steps in LCA data progression

1. System bill of materials (SBOM)

The SBOM includes materials and inputs to the whole product system. SM quantifies the materials of the product itself and the packaging, major material processing steps in manufacturing, energy, fuel and extra materials used during the use, end of life and transportation stages. The user conducting an SM LCA for a product system builds the SBOM. A simple SBOM could be blow molding of a plastic container that is delivered to the user. Table 1 shows what the SBOM could look like.

System bill of materials for blow molding of a plastic container that is delivered to the user

  • 1.2 pounds of plastic granulate [purchased]
  • 1.2 pounds of plastic blow molding
  • 1.2 pounds of product delivered by truck over 250 miles
  • Landfilling all of the part at end of life

Table 1 – System bill of materials for blow molding of a plastic container delivered to the user

2. Process inventory data collection

Inputs in the SBOM are multiplied by the specific chemical emissions (to air, water or soil), land-use factors and resource depletion values that have been collected for each type of material or process. In simple terms this can be considered as pollution. This creates a list of up to 3000 types of chemical emissions and resource attributes for each material or process in a product. Table 2 shows part of the process inventory data, strictly edited for this discussion, for a process that we are all familiar with: filling up a car with gas and driving with it.

Process inventory data for the production and combustion of ten gallons of unleaded gasoline

Carbon dioxide [to air] 109 kg
Zinc [to soil] 0.00109 kg
657 others

Table 2 – Process inventory data for the production and combustion of ten gallons of gasoline

The production and combustion of the unleaded gasoline emits considerable carbon dioxide (CO2) to air, less aluminum to water and even less lead to water. There are also 656 additional data points for other emissions, land use effects and resource depletion effects

3. Impact characterization

Characterization converts the inventory emissions into environmental impacts via scientific formulae. Methods to estimate environmental impacts have been developed over many decades by scientists in their respective fields. They will continue to evolve both in the accuracy of the base information about a particular material or process, and the scientific understanding of how to accurately model and compare environmental impacts.

The SM methodology uses a life cycle impact assessment method called TRACI (Tool for Reduction and Assessment of Chemical and other Environmental Impacts). Teams of environmental scientists at the US EPA developed TRACI using North American environmental data. Characterization of each impact type uses a different equivalency unit. Carbon dioxide is the equivalency unit for global warming impacts, so these values remain unchanged. Ecotoxicity is measured in Comparative Toxic for ecosystems based on the USEtox™ methodology. These quantities of impacts may be easier than the raw process inventory data to understand, most people have difficulty in determining the relative significance of each impact.

4. Normalization

Normalization is a step that divides the impact in each category by the estimated impacts from a reference system. It relates the magnitude of the impact category indicator results in relation to the society’s entire annual production / consumption activities.

In the SM methodology, the normalization uses the total environmental impact in the United States (in 2008) as the reference system and expresses the environmental impact of your product system as a fraction of it (i.e. as a fraction of the total annual environmental impacts in the United States). SM normalization also includes an expression of each US citizen in its results. Therefore, normalization is not only done by utilizing the entire environmental impacts of the United States, but by also assigning the individual share of those impacts to each US citizen1.

The SM impact factors represent the estimated impacts in each impact category to be produced by the average person in the United States in one year. This somewhat abstract denominator creates normalized impact results that have the same units. In SM these are defined as a point (Pt). If the result for a product reads one point, it represents the total environmental impact of the share of one person for one year of the total United States economy. This formula is repeated for all the ten environmental impact categories of TRACI. The result is a fraction.

5. Weighting

Weighting is the last step that multiplies each normalized impact by a percentage point to adjust the relative significance of each impact category and then aggregates the impacts. Weighting is socially defined and is based on the importance that society attaches to the different environmental impact categories. Different individuals, organizations and societies may have different preferences. The U.S. National Institute of Standards and Technology (NIST) defined the units used in SM impact factors. The weighting factors reflect the relative importance that NIST assigns to the different impact categories. This is always subjective. The NIST factors are the most respected weighting factors that are available in North America (Table 6).

Weighting is allowed by ISO 14044 as part of the interpretation because it facilitates the reflection on the comprehensive set of environmental issues related to the product being studied. However, assessment results to be used in public claims should always be presented with the disaggregated (non-normalized and weighted) data. That is why both are reported. All methods and calculations used by Sustainable Minds are documented pursuant to ISO standards.

SM impact factors are provided in millipoints (mPt) and CO2 equivalents (kg):

IMPACT CATEGORY 2 Normalization Factor 3 Unit Weighting Factor4
Ecological damage
Acidification 90.9 kg SO2eq (sulphur dioxide) /year /capita 0.036
Ecotoxicity 11000 CTUe /year /capita 0.084
Eutrophication 21.6 kg Neq (nitrogen) /year /capita 0.072
Global warming 24200 kg CO2eq (carbon dioxide) /year /capita 0.349
Ozone depletion 0.161 kg CFC-11eq /year /capita 0.024
Human health damage
Carcinogenics 5.07E-05 CTUh /year /capita 0.096
Non-carcinogenics 1.05E-03 CTUh /year /capita 0.060
Respiratory effects 24.3 kg PM2.5eq (fine particulates) /year /capita 0.108
Smog 1390 kg O3eq (ozone) /year /capita 0.048
Resource depletion
Fossil fuel depletion 17300 MJ surplus /year /capita 0.121

Table 3 – TRACI impact categories, normalization and weighting factors used to create the SM impact factors.

1 A. Lautier, et al. (2010). Development of normalization factors for Canada and the United States and comparison with European factors. Science of the Total Environment. 409: 33-42.

2 J. Bare (2014). Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI) TRACI version 2.1 User’s Guide. US EPA Office of Research and Development, Washington, DC, EPA/600/R-12/554.

3 Ryberg, Morten, et al. "Updated US and Canadian normalization factors for TRACI 2.1." Clean Technologies and Environmental Policy (2013): 1-11.

4Gloria, T. P., B. C. Lippiatt & J. Cooper (2007). ‘Life cycle impact assessment weights to support environmentally preferable purchasing in the United States.’ Environmental Science & Technology, 41(21), 7551-7557.

What do the SM Single Scores mean

What do points (Pt) and millipoints (mPt) represent?

In the SM Impact Assessment Methodology, a point (Pt) represents the annual environmental load (i.e. entire production/consumption activities in the economy) in the US divided up into the share of one American (for explanation, see the Normalization and Weighting sections at left). It is important to understand that one point is not an individual’s very own environmental impact. It represents the individual’s annual share regardless of whether that individual participated in the economy’s environmental impacts directly or indirectly.

In the SM methodology, the single score indicator, the impact factor, is expressed in millipoints (mPts). One millipoint is 1/1000th of a point. It enables the measurement of smaller systems since most products have a lower impact than one point. If we used points for most products, the results would be in small numbers with many zeros after the decimal point. Millipoint results are more practical for most expressing the environmental impacts of most products.

In the design process, when estimating, evaluating and comparing using Sustainable Minds Eco-concept & LCA software, the results of each product concept represent the contribution to one person's share of the environmental impacts of the entire United States in one year. As a summary of the set of the 10 TRACI environmental impact categories, millipoints represent a total impact score in one number.

What does a single score mean to you and me?

The single score serves as an easy starting point to get to know the product under consideration based on the environmental impact it creates. It relates the product’s environmental impact to the overall environmental impacts in the US. Simply put, a higher score correlates to contributing more.

If SM single scores were used to evaluate the environmental performance of your personal life, you would add the millipoint results of every consumption, activity and purchase you make. At the end of one year, the total sum of millipoints will show whether you consumed more or less than a 1000 millipoints (1 Pt), the average person’s annual share of the environmental impacts of the entire United States.

You could also identify which purchases you made during that year that made the highest contribution to the environmental performance of your personal life. For example, buying a car will consume a significant portion of your annual share/budget, buying a cup of coffee is far less. In short, the single score makes it easy to understand the relative impact of the products you are evaluating. This will become easier and more meaningful over time as you evaluate more products and their environmental performance results.

Why SM uses a single score indicator in its software and Transparency Reports

Sustainable Minds is dedicated to operationalizing environmental performance in mainstream product development and manufacturing in an understandable, empowering and credible way. Sustainable Minds’ easy-to-use, standardized solutions make it possible for manufacturers – large and small – to dynamically evaluate, compare and improve their products' environmental performance by integrating life cycle thinking and LCA into their product design and marketing processes.

Single figure scores makes it easier for non-LCA experts to understand the meaning of LCA results. While having indicator results stated by individual impact categories enables LCA experts to make impact comparisons between products on a granular level, single figure scores assist the non-LCA expert to understand the relative environmental performance either when evaluating products in a purchasing process or developing product concepts in the design process.

In both SM Eco-concept & LCA software and SM Transparency Reports, the total impacts of each concept and product are represented by a single score. That score is also broken down by life cycle stage to highlight where in the life cycle the greatest impacts are occurring.

Such insightful information allows manufacturers to focus their efforts on improving the product’s environmental performance by taking effective steps where and when it matters the most. It also enables purchasers to understand whether the manufacturer’s efforts to improve that performance is meaningful.

Sustainable Minds complies with ISO14044 and makes data and indicator results (or normalized indicator results) available together with the weighted results. This ensures that 1) trade-offs and other information remain available to decision-makers and 2) users can appreciate the full extent and implications of the results.


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