- 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)
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)
50 g of synthetic rubber (0.05 kg * 6 kgCO2eq /kg)
6 kWh of electricity in China (6 kWh * 0.6 kgCO2eq /kWh)
Transport China > U.S. (100 g * 10^-6 * 0.6 kgCO2eq/t.km * 10 000 km)
Truck delivery (1gCO2eq)
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?
- 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).
- Transport of materials from the extraction or production site to the pre-assembling factory.
- Transport of the pre-assembled materials to the assembling factory.
- 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
- 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)
- 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.