How are CO2 savings calculated?
When you buy a second-hand (donated) item from a charity shop the till calculates the carbon dioxide emissions savings that were made by not buying an equivalent new item.
Three figures are used to calculate the saving - average weight, conversion factor and substitution percentage. Here are some example figures; each charity can control the exact numbers used in this calculation:
Ladies Tops average weight = 0.3kg
Conversion Factor = 11.2kg of CO2 generated in the manufacture of 1kg of textiles
Substitution Percentage = 91% - the degree to which this second-hand purchase stopped the purchase of an equivalent new Item (the displacement factor)
CO2 saved buying second-hand:
0.3 x 11.2 x 0.91 = 3.1kg
Average Weight
All donated Items have a shop department, for example Ladies Tops, Bric-a-Brac, or Jewellery. The till knows the average weight for an item in that department and uses this as an estimate for the weight of your purchase, for example the average weight of a ladies top is around 0.35 kilograms, but each charity decides on their own estimates.
CO2 Conversion Factor
For every 1kg of the purchased item a conversion factor is applied multiplying the weight by the amount of CO2 generated per kilogram of newly manufactured item.
Studies, such as Green Story’s Comparative Lifecycle Assessment of second hand vs. new clothing, and the Furniture Industry Research Association’s business emissions study, provide the CO2 conversion factors for each shop department.
Substitution Percentage
This is a displacement factor representing the degree to which a second hand purchase stops the purchase of an equivalent new item.
Studies such as The power of secondhand: how resale slows consumption commissioned by Depop provide the substitution percentages for each shop department.