More than two-thirds of a running shoe’s carbon footprint can come from manufacturing processes, with a smaller percentage arising from acquiring or extracting raw materials, according to Massachusetts Institute of Technology researchers. The MIT team says a typical pair of running shoes generates 30 pounds of carbon dioxide emissions.
The fact that sneakers emit so much more CO2 in the manufacturing phase surprised researchers, who published their paper in the Journal of Cleaner Production.
This breakdown is expected for more complex products such as electronics, where the energy that goes into manufacturing fine, integrated circuits can outweigh the energy expended in processing raw materials. But for less-advanced products — that don’t require electronic components — the opposite is often the case.
The study’s results will help shoe designers identify ways to improve designs and reduce shoes’ carbon footprint, researchers say. The findings may also help industries assess the carbon impact of similar consumer products more efficiently.
In the MIT-led lifecycle assessment, researchers broke down the various steps involved in both materials extraction and manufacturing of one pair of running shoes to identify hotspots of greenhouse gas emissions. The group found that much of the carbon impact came from powering manufacturing plants: A significant portion of the world’s shoe manufacturers are located in China, where coal is the dominant source of electricity. Coal is also typically used to generate steam or run other processes in the plant itself.
A typical pair of running shoes comprises 65 discrete parts requiring more than 360 processing steps to assemble, from sewing and cutting to injection molding, foaming and heating. The researchers found that for these small, light components such processes are energy-intensive — and therefore, carbon-intensive — compared with the energy that goes into making shoe materials, such as polyester and polyurethane.
In contrast to the MIT study, Nike says materials make up about 60 percent of the environmental footprint of a pair of its shoes. In an effort to shrink its footprint — and that of the more than 400 billion square meters of fabric the global apparel industry is expected to produce every year by 2015 — Nike, along with partners NASA, the US Agency for International Development and the US Department of State, have challenged materials manufacturers and others to create new, sustainable materials.