# Methodology

## How do you calculate a carbon footprint?

The carbon footprints you’ll see on Carbonfact’s product pages are calculated using a life cycle analysis (LCA).

Let’s take an example. Suppose we want to calculate the carbon footprint of a 100g bath duck made out of 50% polyester and 50% synthetic rubber, manufactured in China and delivered right to your door in San Francisco, California. Here is how you would decompose its carbon footprint:

• 50 g of polyester (0.05 kg * 29 kgCO2eq /kg)

1.5 kgCO2eq

• 50 g of synthetic rubber (0.05 kg * 6 kgCO2eq /kg)

0.3 kgCO2eq

• 6 kWh of electricity in China (6 kWh * 0.6 kgCO2eq /kWh)

3.6 kgCO2eq

• Transport China > U.S. (100 g * 10^-6 * 0.6 kgCO2eq/t.km * 10 000 km)

0.6 kgCO2eq

• Truck delivery (1gCO2eq)

~0 kgCO2eq

• Total

6.0 kgCO2eq

Sources

## Are there different ways to calculate a carbon footprint?

Indeed. Taking our bath duck example, one could argue that the shop is responsible for the delivery options. One could also argue that the customer is responsible since he is choosing one option.

At Carbonfact, we use one method per category in order to compare multiple products. Our methods are open source, meaning that any member of our community can help us improve or refine. See below an example of the sneaker category methodoloy.

## How do you go about choosing one method?

We have the following principles in mind when designing a method:
• Based on science. We review the scientific literature for the concerned product category.
• Rocks, pebbles and sand. We focus on collecting the main information first and then refine.
• Comparison over perfection. We want a good enough model to start comparing.
• Always be improving. We welcome constructive feedback and build with our community.

## What is the method currently used for the Sneaker category?

Our Sneaker category method is inspired by the work conducted by ADEME(1) and MIT(2). The following steps are identified and our current method focuses on (A) Materials, (B) Assembling, (D) Distribution and (F) End of life (which covers 98 % of the average carbon footprint).

(A) Materials
Accounts for:
• Production of raw materials (e.g. extraction for synthetic ones, growing vegetal or animal for natural ones)
• Pre-assembling of materials (e.g. extruding or molding plastics, weaving fabrics, tanning leather)
NB: the assembly of the materials into the final product is step (C).
On average, 54 % of the total emissions -> included in our model
Emissions of materials are estimated using the weight of the pair of shoes and the proportion of the 2 main components: the upper and the outsole.
We use 0.7 kg as the default weight value. This is a bit higher than the value from ADEME's BaseImpact model for fabric shoes (0.6 kg) but better matches the first other values we could find (by our own measures or from LCA results shared by Caval', one of our first partner brands (average weight is 0.68 kg).
NB: we still need to define a reference for weight measurements (e.g. "Size 39 (FR) Women").
The LCA results of Caval, one of our first partner brands, measured that the upper represents on average 30 % of the weight of their shoes, and the outsole 55 %.
Though it may not be representative of all sneakers and brands, it is for now the most accurate data we found. We use this as default values when the exact weight of each component cannot be found.
The remaining unidentified materials are applied an average emission factor for shoe materials we calculated from ADEME BaseImpact LCA models.
(B) Assembling
Assembling the different materials and pre-assembled components of the product together into the final product.
On average, accounts for 29 % of the total emissions -> included in our model.
The average assembling process consumes 6 kWh. Multiplying it by the carbon intensity of the manufacturing country’s electricity gives us the carbon emissions of the assembling.
(C) Upstream transport
Accounts for:
• Transport of materials from the extraction or production site to the pre-assembling factory.
• Transport of the pre-assembled materials to the assembling factory.
On average, accounts for 2 % of the total emissions -> not included in our model.
(D) Distribution
Packaging and transporting the final product to the consumers.
On average, accounts for 11 % of the total emissions -> included in our model.
For now, we consider products manufactured in Asia make a long distribution trip, partly boat (87%, 18 000 km), partly airplane (13%, 12 000 km), since we assume our current audience reside mostly in Europe or USA. (NB: the distribution is based on ADEME BaseImpact shoe LCA model.)
• Boat: 18 000 km * ((0.7+0.2) / 1 000) t * 0.015 kgCO2eq/t.km = 0.243 kgCO2eq
• Airplane: 12 000 km * ((0.7+0.2) / 1 000) t * 0.60 kgCO2eq/t.km = 6.48 kgCO2eq
• Result: 13 % * 6.48 kgCO2eq + 87 % * 0.243 kgCO2eq = 1.05381 kgCO2eq
For products manufactured out of Asia, we consider they are produced closer to the consumer's market. We consider a 2 500 km truck trip on average. Using the same source for emission factors, the value we apply is:
2 500 km * ((0.7+0.2 kg) / 1 000 kg/t) * 0.06 kgCO2eq/t.km = 0.135 kgCO2eq
NB: the transported package weight is 0.7 + 0.2 kg, considering our average weight of 0.7 kg and a packaging weight of 0.2 kg.
(E) Use
On average, accounts for 0 % of the total emissions -> not included in our model.
(F) End of life
Accounts for collecting, sorting, recycling or other ways of disposal (e.g. incinerating).
On average, accounts for 4 % of the total emissions -> included in our model.
ADEME’s data regarding end of life solely applies to plastic. Since we target to evaluate a large array of materials and that each material has supposedly an end of life process, we chose to apply 1.4 kgCO2eq if the brand doesn't enforce any recycling practice and to apply 0.7 kgCO2eq when it does.

Sources

• ADEME. J.Lhotellier, E.Less, E.Bossanne, S.Pesnel. March 2018. LCA Modeling and Evaluation of Consumer Products and Goods (link)
• Lynette Cheah, Natalia Duque Ciceri, Elsa Olivetti, Seiko Matsumura, Dai Forterre, Richard Roth, Randolph Kirchain, Manufacturing-focused emissions reductions in footwear production, Journal of Cleaner Production, Volume 44, 2013 (link)

Known limitations

• Shoes contain more than 2 materials
• The energy consumed by the assembling process probably depends on the sophistication of the shoes.
• Embodied emissions from packaging are not taken into account.

Auditing the calculations

The source code used to compute product footprints is public and available as open-source: kansoapp/carbonfact-models.