Humans Leave Significant Carbon Footprint With Running Shoes
May 22, 2013

Humans Leave Significant Carbon Footprint With Running Shoes

Peter Suciu for — Your Universe Online

While it is nearly impossible for a running shoe not to leave a footprint, new research suggests that a typical pair of running shoes could leave behind a significant carbon footprint as well. A new study from MIT found that the running shoes generate 30 pounds of carbon dioxide emissions, which is equivalent to keeping a 100-watt incandescent light bulb on for one week.

A team of researchers led by Randolph Kirchain, principal research scientist in MIT´s Materials Systems Laboratory (MSL), and research scientist Elsa Olivetti, investigated the various steps that are involved in both the materials extraction and manufacturing process of a pair of running shoes.

The team published their paper, titled “An industry of that scale and geographic footprint has come under great pressure regarding its social and environmental impact,” in the Journal of Cleaner Production.

From this the researchers looked to identify hotspots of greenhouse gas emissions. The team discovered that much of the carbon impact came from powering manufacturing plants. At present time a significant portion of the world´s shoe manufacturers are located in China where coal is the dominant source of electricity, as it is also typically used to generate steam or run other processes in the plant.

Thus it wasn´t the size of the shoe´s carbon footprint that was surprising but rather that the majority of the emissions — more than two-thirds of it — that come from the actual manufacturing process. Only a smaller percentage actually arises from the acquisition or extraction of raw materials.

While this breakdown between extraction and manufacturing is expected in the production of more complex products including consumer electronics, where the energy that goes into manufacturing fine, integrated circuits can outweigh the energy expended in processing raw materials, it was not expected in these so-called “less-advanced” products.

In the case of running shoes, which can comprise of up to 65 discrete parts, more than 360 processing steps are included in the assembly process. This can range from sewing and cutting to injection molding, foaming and heating. The MIT team found that for these small, lightweight components the processes can be quite energy-intensive and therefore carbon-intensive.

This can be even more energy-intensive compared to the energy that goes into producing materials such as polyester and polyurethane.

This research could help shoe designers identify ways to improve designs and even reduce the carbon footprint. It may also offer insight to other industries by assessing the carbon impact of similar consumer products more efficiently.

“Understanding environmental footprint is resource intensive. The key is, you need to put your analytical effort into the areas that matter,” Kirchain told MIT News. “In general, we found that if you have a product that has a relatively high number of parts and process steps, and that is relatively light [weight], then you want to make sure you don´t overlook manufacturing.”

Of the 25 billion shoes that have been purchased around the world as of 2010, the majority were produced in China and other developing nations.

Already Kirchain and his team could be making a difference. As a response to their research, some companies have started to take account of their products´ greenhouse gas contributions, in part by measuring the amount of carbon dioxide associated with every process throughout a product´s life cycle.

Athletic equipment company ASICS, which is based in Japan, has approached Kirchain to perform a life-cycle assessment for running shoe manufacturing in China. In this case the team took a so-called “cradle-to-grave” approach, which involved breaking down every possible greenhouse gas-emitting step. This went from the point at which the shoes´ raw materials are extracted and produced to the shoes´ eventual demise, whether it was eventually burned, placed in a landfill or even recycled.

In this study, the team was able to divide the life cycle of the running shoes into five major stages. These included materials, manufacturing, usage, transportation and end-of-life. The team found the last three stages actually contributed very little to the product´s carbon footprint.

Running shoes, unlike electronics or other eWaste, utilize little energy other than what is needed to wash the shoes. However, the bulk of the emissions were found to come from the manufacturing process.

Part of this process is attributable to a facility´s energy source, while other emissions came from processes in the production, which included foaming and injection molding of the shoe´s soles. These expended a large amount of energy, even for small, lightweight parts.

“What stood out was this manufacturing burden being on par with materials, which we hadn´t seen in similar products,” Olivetti noted. “Part of that is because it´s a synthetic product. If we were looking at a leather shoe, it would be much more materials-driven because of the carbon intensity of leather production.”

The researchers were able to determine where reductions could be made, and these included the fact that manufacturing facilities tended to throw out unused material. Instead, the research team offered the suggestion that by recycling these scraps, along with combining certain parts of the shoe to eliminate cutting and welding steps, manufacturers could streamline the assembly process.

“When people are trying for streamlined approaches to [lifecycle assessments], often they put emphasis on the materials impact, which makes a lot of sense,” Olivetti added. “But we tried to identify a set of characteristics that would point you to making sure you were also looking at the manufacturing side – when it matters.”