A typical pair of running shoes generates 30
pounds of carbon dioxide emissions, equivalent to keeping a 100-watt
light bulb on for one week, according to a new MIT-led lifecycle

But whats surprising to researchers isnt the size
of a shoes carbon footprint, but where the majority of that footprint
comes from.

The researchers found that more than two-thirds of a
running shoes carbon impact can come from manufacturing processes,
with a smaller percentage arising from acquiring or extracting raw
materials. 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 – particularly those that
dont require electronic components – the opposite is often the case.

why does a pair of sneakers, which may seem like a relatively simple
product, emit so much more carbon dioxide in its manufacturing phase?

team led by Randolph Kirchain, principal research scientist in MITs
Materials Systems Laboratory, and research scientist Elsa Olivetti 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
worlds 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. Olivetti, Kirchain and their colleagues
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

The groups results, Kirchain says, will help shoe
designers identify ways to improve designs and reduce shoes carbon
footprint. He adds that the findings may also help industries assess the
carbon impact of similar consumer products more efficiently.

environmental footprint is resource intensive. The key is, you need to
put your analytical effort into the areas that matter, Kirchain says.
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 dont overlook manufacturing.

Kirchain and his colleagues have published their results in the Journal of Cleaner Production.

The sum of a shoes parts

2010, nearly 25 billion shoes were purchased around the world, the
majority of them manufactured in China and other developing countries.
As Kirchain and his co-authors write in their paper, An industry of
that scale and geographic footprint has come under great pressure
regarding its social and environmental impact.

In response,
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 products lifecycle. One such
company, ASICS, an athletic equipment company based in Japan,
approached Kirchain to perform a lifecycle assessment for a running shoe
manufactured in China.

The team took a cradle-to-grave
approach, breaking down every possible greenhouse gas-emitting step:
from the point at which the shoes raw materials are extracted to the
shoes demise, whether burned, landfilled or recycled.

researchers divided the shoes lifecycle into five major stages:
materials, manufacturing, usage, transportation and end-of-life. These
last three stages, they found, contributed very little to the products
carbon footprint. For example, running shoes, unlike electronics,
require very little energy to use, aside from the energy needed to
infrequently wash the shoes.

The bulk of emissions, they found,
came from manufacturing. While part of the manufacturing footprint is
attributable to a facilitys energy source, other emissions came from
processes such as foaming and injection molding of parts of a sneakers
sole, which expend large amounts of energy in the manufacture of small,
lightweight parts. As Kirchain explains it, You have a lot of effort
going into the molding of the material, but youre only getting a very
small part out of that process.

What stood out was this
manufacturing burden being on par with materials, which we hadnt seen
in similar products, Olivetti adds. Part of that is because its 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

An improved design

tallying the carbon emissions from every part of a running shoes
lifecycle, the researchers were also able to spot places where
reductions might be made. For example, they observed that manufacturing
facilities tend to throw out unused material. Instead, Kirchain and his
colleagues suggest recycling these scraps, as well as combining certain
parts of the shoe to eliminate cutting and welding steps. Printing
certain features onto a shoe, instead of affixing them as separate
fabrics, would also streamline the assembly process.

Kirchain and Olivetti view their results as a guide for companies looking to evaluate the impact of similar products.

people are trying for streamlined approaches to [lifecycle
assessments], often they put emphasis on the materials impact, which
makes a lot of sense, Olivetti says. 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.