Measuring product carbon footprint

Examining key considerations that can lead to a reduction in your footwear’s environmental impact.

by Nicola Pichel-Juan

The term ‘carbon footprint’ is frequently used in relation to the environmental impact of a particular product, process, or even organisation. This article will focus on what a product carbon footprint is, provide context to the values generated, and discuss the data that is required in order to create a carbon footprint for footwear, as well as some of the challenges that are likely to be encountered in the sector.

What is a product carbon footprint, and why is it important to measure this? A product carbon footprint is a calculation of the estimated total sum of greenhouse gas (GHGs) emissions – ‘CO₂e’ (the ‘e’ stands for ‘equivalent’) – produced during a product’s lifecycle. This makes for a complex calculation so, for the sake of simplicity, emissions for all GHGs are converted to a CO₂e value. If considering how much damage each gas will cause over a 100-year period, methane will do most of its damage in the first ten years, whereas carbon will only have done one tenth of its damage during that time. The CO₂ equivalent value is a very convenient way of harmonising these chemical differences, and therefore CO₂e expresses the amount of carbon dioxide that would have the same impact over a 100-year period.

An increase in the amount of greenhouse gases in the atmosphere as the result of the burning of fossil fuels is causing climate change, the impacts of which are being felt worldwide – with humanity facing such increasing challenges as extreme weather conditions, rising sea levels and melting polar ice. Many countries and organisations have committed to achieving net zero emissions targets by 2050, in line with the Paris Agreement which was adopted in 2015. An important part of achieving that goal is to understand exactly where emissions are being generated and at what levels, so that they can be reduced or eliminated. This is why calculating product and organisational carbon footprints is becoming increasingly important.

Global warming potential comparison of greenhouse gases
Greenhouse gas	Warming potential in CO2e
Carbon dioxide	1
Methane	25
Nitrous oxide	298
Hydrofluorocarbons	124 to 14,800
Perfluorocarbons	7,390 to 12,200
Sulphur hexafluoride	22,800
Nitrogen trifluoride	17,200
1 kg of methane causes 25 times more warming over a 100-year period than 1 kg of carbon dioxide does. The high short-term global warming potential of methane is being tackled by the ‘Global Methane Pledge’ signed at the COP26 summit. This is looking to reduce global methane emissions by 30 per cent by 2030 from 2020 levels which, it is believed, could eliminate 0.2°C of warming by 2050. It is worth noting, however, that globally 11 to 12 per cent of methane is estimated to come from landfill sites, so this problem will be a hard one to fix.

The boundaries of a carbon footprint are usually defined as ‘cradle to gate’ or ‘cradle to grave’. A cradle to gate footprint would consider the emissions that are incurred when extracting and producing raw materials, transporting them to the finished goods manufacturing plant, and the subsequent manufacture of the finished item. A cradle to grave approach would also consider the shipping and distribution of the item to the final consumer, but also include its use as well as the impacts of what is likely to happen to that product at the end of its life – for example, being sent to landfill or for incineration. As organisations increasingly aim to transition to a circular economy approach, another analysis – ‘cradle to cradle’ – will become more prevalent, considering how a product or its constituent parts can be kept in use for as long as possible or be reused or reprocessed into new items.

It is important when reporting any carbon footprint information that the scope used is also clearly communicated. Studies have found that most of the carbon footprint for footwear comes from materials and manufacturing, which would be captured in the cradle to gate model. However, there can still be considerable impacts after that point, such as if air freight is used to get the goods to their final destination. In addition, the challenge of what happens to the footwear at the end of its life should be risk assessed rather than this issue being ignored.

Footwear carbon footprint in context

Published data suggests that the carbon footprint of a ‘typical’ pair of adult’s synthetic running shoes would be in the region of 12 to 15 kg CO₂e per pair. Leather upper footwear would generally be higher, whereas simple moulded sandals could be as low as a few kilos per pair. This compares with a pair of men’s jeans at around 19 kg and a return economy flight from London to Hong Kong, which would be well in excess of 1 tonne. These are indicative carbon footprints from particular data sets or studies and, of course, within each particular product type there will be huge variations in the carbon footprints, depending on some of the factors discussed in more detail below.

Key considerations

Some of the main areas that will impact on the carbon footprint of footwear include the type and quantity of materials used, how those materials are made, where they are made, how far each item needs to be transported and the mode of transport used. For instance, if an identical process is carried out in one country where the vast majority of energy is generated from coal-fired power stations and in a second country where there is a mix of energy sources including nuclear and renewable, the process that is being carried out in the second country will be reported as producing a lower carbon footprint.

The data captured can be adjusted accordingly if the exact source of energy for a particular process is known – such as if a company is purchasing or generating all the energy required for its factory through renewable sources. The heavier an item is, the more likely it is to have a higher footprint, as the emissions associated with each material or component are based on weight. It would therefore be expected that industrial footwear incorporating steel toe caps will probably have a greater footprint than other types of footwear. Another obvious example would be the use of air freight versus sea freight, with one study calculating that shipping by air generates 47 times more greenhouse gas emissions than sea freight does per tonne-mile.

Correct use of data

The data used to calculate a product carbon footprint will be a combination of primary and secondary data. Primary data will generally need to be provided by the organisations involved in the development and production of the footwear and could include the following:

• sufficient information to accurately identify each material or component – for instance, if the lining is a mono-material or a blend and, if it is the latter, from which materials it has been made and in what proportion
• the weights of each material or component being used
• details of where each material or component is produced, how far it must be transported to the footwear production site and how it was moved
• information on the distinct production processes which are being carried out at the production site, including cutting, stitching, assembly or injection moulding
• waste/scrap percentages created during production
• energy consumption and energy sources utilised
• the origin and destination ports for shipping finished goods
• finished goods warehouse locations
• the mode of transport used to ship finished goods
• the likely end-of-life scenario.

Most companies will not have records of energy and material flows, which is where secondary data is also required to evaluate the emissions for a particular item or process. Commonly-used sources of secondary data would be: i) lifecycle inventory databases, ii) industry bodies, iii) government publications, iv) regional and national statistics, v) environmental product declarations, and vi) verified carbon footprints.

These sources can be used to determine the carbon footprint of producing a specific item in a particular country or region (taking into account how energy is usually generated in that region), plus the emissions associated with moving it the relevant number of miles to the next downstream production site via the mode of transport used.

Although considerable data is available – either free of charge or through subscription – there are a number of challenges associated with ensuring that this information is reliable and accurate.

Firstly, the data can be very inconsistent. When checking the carbon footprint value for a return flight from London to Hong Kong across a number of different sources, the results varied from 0.7 tonnes all the way up to 4 tonnes, with most being in the region of 1 to 1.5 tonnes (depending on the age and efficiency of the aircraft fleet). Secondly, the data is not necessarily representative, or could be out of date. A good example of this would be concerns raised by the leather industry in 2020 about the emissions impacts assigned to leather in some of the most commonly-used databases, as these only included data for herds farmed in Brazil and the US, with no differentiation made for the type of leather produced. For any activity undertaken to calculate a product carbon footprint, it is important to understand exactly from where each piece of data originates and to be aware that some data may be useful as an indicator of a particular impact, but will not necessarily be exactly representative of the exact location or process being assessed.

While there are clearly challenges in gathering all of the required data to complete a product carbon footprint, it is still an excellent process to support organisations to understand ‘hot spots’ that can be targeted for emissions reductions, with a reduction in emissions being the ultimate goal of the carbon footprint process.

Longevity

Although many carbon footprints will take into account expected end-of-life impacts incurred in the disposal of a product, they generally do not consider the anticipated life and durability of a product. In SATRA’s view, a product with a slightly higher footprint that is able to last a lot longer than an alternative item could actually be a more sustainable solution. We would always recommend that products are designed to be as durable (and therefore long-lasting) as possible, and we can advise our members on how this can be achieved.

In conclusion

As a final question, it may be asked if it is possible to produce a carbon-neutral or carbon-negative shoe. A number of different sports footwear manufacturers have recently published details of projects initiated with the specific aim of making carbon-neutral products. The results have been impressive, with carbon footprints calculated at 2.9 to 3.7 kg CO₂e per pair having been achieved by using innovative materials and production techniques, compared with a traditional 12 to 15 kg CO₂e per pair for a typical sports shoe. As innovative new materials and production processes are introduced, it surely will not be too long until the arrival of the first carbon-neutral shoe is announced to the world.

Publishing Data

This article was originally published on page 10 of the February 2022 issue of SATRA Bulletin.

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