Monday, 25 June 2018

Savings Claims for Recycled Clothing

A friend of mine reposted a thread from 1 Million Women, stating that "If one million women bought their next item of clothing second-hand instead of new, we would save 6 million kg of carbon pollution from entering the atmosphere".  While this was a great thing to pick up on - yes, we buy far too many clothes, and forget what an impact we are making on global resources while we are doing it - the first thing I thought it that the saving would rather depend on how heavy each item was.

So I went briefly looking. There were so many items to choose from, depending on seasonality, country of origin and fabric used in manufacture. I wanted to see if there was a quick way to check the poster's claims.

The first thing I found is that the factorisation for cotton is 54kg of greenhouse gases per kilo (kg). So if everyone got a recycled long cotton shirt with a net weight of 220 grams, it would be 220,000kgs of shirt x 10.75kg CO2 and other greenhouse gases (GHG), which is 2,365,000kgs of GHG consumption in manufacture (Systain, 2009). That's a under half of the 6 million kg savings the poster promises.

Hmm... well, some items are a lot heavier - a pair of trousers might be nearly a kg. Hmm. But I didn't factor in the numbers for wool... or polar fleece.

OK, so moving to wool. That would be lower than cotton, as, while it is a natural fibre, it is grown outside with few herbicides, pesticides or fertiliser (here in New Zealand farmers mostly lime their paddocks, and not much else, to minimise costs). I found a study by Barber and Pellow (2006) detailing that the energy consumed for a merino top to land in China from NZ is 63MJ/kg whereas polyester is 125MJ/kg (download here). Right. So I still needed to know the carbon footprint of polar fleece/polyester in order to create a bit of a comparison.

Polar fleece works out as having the following relationship with carbon: 1kg polar fleece x 5.55kg carbon footprint (Wikipedia, n.d.). So half that of cotton ...which amazed me (despite this having been calculated by Tom Berners-Lee for Wikipedia, I'm unsure about this. So if anyone has better info, please comment. Oecotextiles - 2011 - seems to think that polyesters are a lot more GHG intensive than this). A polar fleece jumper weighs about twice that of a cotton shirt, so would work out at about the same value. Interesting.

Now I appreciate that this is guestimation as the measures aren't necessarily similar - it is not even estimation - but this gives us wool at 1/2 the GHG cost of polar fleece, which is again about a half of cotton. Some clothes are much heavier than a long shirt: jeans are about a kg, coats might even be two kgs. However, we wear many more tops, pieces of underwear, scarves, socks and tights than we do trousers. A summer dress is likely to be roughly the same weight as a long shirt. 

Seeing as humans wear a lot of polar fleece, wool and light fabrics, the original post numbers above are possibly... probably inaccurate. I suspect a more accurate figure lies between my original fast and dirty calculation of the cotton shirts and the poster, especially when we factor in men's clothing.

However, the 1 Million Women message is STILL a great one, even if their maths are off. Not buying is still one of the easiest things we can do to cut consumption - regardless if we are women or men :-D. 

The 7 Rs (read more here) start with "Refuse" to buy, and limiting purchasing is an inaction we can all take...


Sam

 
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