carbon footprints…

2 06 2009

Please be aware that our suggestions are just starting points for you to consider when looking at a fabric, because actually calculating a carbon footprint is very complex and time consuming.  Peter Tydemers, who is an ecological economist at Dalhousie University in Nova Scotia, has warned that many of the energy calculators we see should be taken with a pinch of salt – because every detail of where and how something is produced can change and therefore affect the outcome. For example, simply changing an animals feed can have an influence on its CO2 footprint. “It’s all very fluid”, he says, “There’s a tremendous hunger for these sorts of numbers and this has created the assumption that any existing figures are robust. They’re not.” We suggest that you examine carefully any studies to see the variables and the assumptions  made.  Something else to determine is who funded the study!  I was really perplexed to see a web site which had “data” on the energy used to create various fibers; the conclusions being drawn were just a bit outside the limits of any studies I had seen earlier.  But when I saw the industry group that funded the study it all became clear.

That being said, to begin to evaluate the carbon footprint of any fabric the first thing you have to do is  figure out what the fabric is made of  – the fiber.    The fiber tells you a lot about the energy needed to make the yarns, and then the fabric.  The energy needed to produce different fibers varies a lot.

To make it easy to compare the fibers, I”ll divide them into two types: “natural” (from plants, animals and – less commonly – minerals), and “synthetic” (man made)

For synthetics, it’s important to remember that most synthetic fibers  started as fossil fuel, an inherently non renewable resource.  Very high amounts of energy are needed to both extract the oil from the ground as well as to produce the polymers (as it is done under high temperatures).

For natural fibers you must look at field preparation, planting and field operations (mechanized irrigation, weed control, pest control and fertilizers (manure vs. synthetic chemicals)), harvesting and yields.  Synthetic fertilizer use is a major component of the high cost of conventional agriculture:  making just one ton of nitrogen fertilizer emits nearly 7 tons of CO2 equivalent greenhouse gases.

A study done by the Stockholm Environment Institute on behalf of the BioRegional Development Group  concludes that the energy used (and therefore the CO2 emitted) to create 1 ton of spun fiber is much higher for synthetics than for hemp or cotton:

KG of CO2 emissions per ton of spun fiber:

crop cultivation

fiber production

TOTAL

polyester USA

0.00

9.52

9.52

cotton, conventional, USA

4.20

1.70

5.89

hemp, conventional

1.90

2.15

4.10

cotton, organic, India

2.00

1.80

3.75

cotton, organic, USA

0.90

1.45

2.35

The table above only gives results for polyester; other synthetics have more of an impact:  acrylic is 30% more energy intensive in its production than polyester and nylon is even higher than that.

Not only is the quantity of GHG emissions of concern regarding synthetics, so too are the kinds of gasses produced during production of synthetic fibers.  Nylon, for example, creates emissions of Nitrous Oxide,  N2O, which is 300 times more damaging than CO2.[1] In fact, during the 1990s, N2O emissions from a single nylon plant in the UK were thought to have a global warming impact equivalent to more than 3% of the UK’s entire CO2 emissions.[2] A study done for the New Zealand Merino Wool Association shows how much more total energy is required for the production of  synthetics than any natural fibers:

Energy used in production of various fibers:

energy use in MJ perKG of fiber:
flax fibre (MAT)

10

cotton

55

wool

63

Viscose

100

Polypropylene

115

Polyester

125

acrylic

175

Nylon

250

SOURCE:  “LCA: New Zealand Merino Wool Total Energy Use”, Barber and Pellow,      http://www.tech.plym.ac.uk/sme/mats324/mats324A9%20NFETE.htm

Natural fibers, in addition to having a smaller carbon footprint in the production of the spun fiber, have the benefit of

  1. being able to be degraded by micro-organisms and composted; in this way the fixed CO2 in the fiber will be released and the cycle closed.  Synthetics do not decompose.
  2. sequestering carbon.  Sequestering carbon is the process through which CO2 from the atmosphere is absorbed by plants through photosynthesis and stored as carbon in biomass (leaves, stems, branches, roots, etc.) and soils.

As I said, looking at the production of the fiber is just the first part of the equation.  It is clear that, in terms of energy use and CO2 emissions, synthetics are  significantly higher in both cases than any natural fiber.  How the fibers are grown or managed also makes a huge contribution to energy use, and as you might have suspected, organic methods improve these results even more and widen the gap between synthetic and natural fibers.  That’s next week’s topic.


[1] “Tesco carbon footprint study confirms organic farming is energy efficient, but excludes key climate benefit of organic farming, soil carbon”, Prism Webcast News, April 30, 2008, http://prismwebcastnews.com/2008/04/30/tesco-carbon-footprint-study-confirms-organic-farming%E2%80%99s-energy-efficiency-but-excludes-key-climate-benefit-of-organic-farming-%E2%80%93-soil-carbon/

(2) Fletcher, Kate, Sustainable Fashion and Textiles,  Earthscan, 2008,  Page 13

Advertisements