How your score is calculated:
Your score reflects the average amount of GHG emissions produced in the entire life cycle of the bag you chose, from production, distribution, manufacturing and disposal (or recycling). Each type of bag ‘s score reflects their typical use over a 52 week period (plastics and paper disposables are estimated at 520 bags per year, while reusables range from 4-9 bags per year).
Plastic/Paper: It takes 4 times as much energy to produce paper bags than plastic, and it takes 9 times as much energy to recycle paper rather than plastic. Paper’s production also uses twenty times as much fresh water vs plastic bags. Paper also consumes trees, which means less CO2 can be recovered from the atmosphere. Plastic is not biodegradable (but most paper bags are not recycled anyway), and paper takes up more space by volume and weight in landfills than plastic.
Reusable bags: come in many forms, the most common of which are manufactured out of woven cotton materials or durable plastic materials. While there is a high initial energy cost per bag in their production and distribution (as compared to paper or plastic disposables), overall the environmental impact during the life cycle of a reusable bag is minimal compared to disposable plastic or paper options, because fewer bags are used, reducing overall emissions and waste over time.
Sources:
http://www.washingtonpost.com/wp-dyn/content/graphic/2007/10/03/GR2007100301385.html
http://www.reuseit.com/learn-more/myth-busting/why-paper-is-no-better-than-plastic
http://www.enviroliteracy.org/article.php/1268.php
Muthu, S.S., Li, Y., Hu, J., Mok, P. & Liao, X. (2010) An Exploratory Comparative Life Cycle Assessment Study of Grocery Bags – Plastic, Paper, Non-woven and Woven Shopping bags. Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Kowloon, Hong Kong, China. [ http://static.reuseit.com/PDFs/life_cycle_2010.pdf ]
Nolan ITU, Centre for Design [RMIT], and Eunomia Research and Consulting Ltd (2002) Plastic Shopping Bags – Analysis of Levies and Environmental Impacts, Environmental Australia, Department of the Environment and Heritage, Commonwealth Government: Canberra.
