In February the United Kingdom Environment Agency published a report entitled Life Cycle Assessment of Supermarket Carrier Bags. The report concluded that single-use carrier bags have the lowest carbon footprint per bag when the use part of the life cycle is not taken into account – in other words when you consider only the resources used to make the bag and not how many times it can be used and hence the total amount of shopping it will carry. Not surprisingly, paper, heavy plastic and cotton bags all use more resources and energy for their production. However, all of these last more round trips than the single use bag and when the multiple uses are taken into account the stronger bags win in terms of carbon footprint per use.
Key finding: whatever type of bag you use, the key is to reuse it as many times as possible to achieve the lowest possible carbon footprint.
The report is available at http://www.environment-agency.gov.uk/news/127553.aspx?page=3&month=2&year=2011