Why you need to use your 'environmentally friendly' cotton carrier bag 131 times to be green

Cotton bags offered by many supermarkets may be less 'green' than plastic carriers - and may cause more global warming, according to scientists.

As a greater amount of energy goes into making a cloth carrier than a polythene one, a cotton bag has to be used 131 times before it has the same environmental impact than its plastic counterpart

And if a plastic bag is re-used as a bin liner, a cotton bag has to be used 173 times - nearly every day of the year - before its ecological impact is as low as a plastic bag on a host of factors including greenhouse gas emissions over its lifetime.

But most of us only use the bags around 51 times before they are thrown away, researchers found.

Paper bags - used by some clothes chains such as Primark - need to be used three times to fall below the environmental impact of the thin plastic carrier, while bags for life - made of stronger plastic - have to be used four times to start having less ecological impact.

The government sponsored research, 'Life Cycle Assessment of Supermarket Carrier Bags' by Dr Chris Edwards and Jonna Meyhoff Fry looked at the environmental impact of six different types of bags.

Although completed in 2008, it has not yet been published, with plastic bag makers claiming the findings have been suppressed - although the Environment Agency said it is awaiting 'peer review' - checks by other scientists.
Using a thin plastic bag equates to generating 1.57kg of carbon dioxide. A cotton bag would have to be re-used 171 times to emit the same level of CO2

Using a thin plastic bag equates to generating 1.57kg of carbon dioxide. A cotton bag would have to be re-used 171 times to emit the same level of CO2

Using a thin plastic bag - made from a plastic called high-density polyethylene (HDPE) - equates to generating 1.57kg of carbon dioxide, the greenhouse gas that scientist believe leads to global warming according to the report. A cotton bag would have to be re-used 171 times to emit the same level of CO2.

Cotton bags typically made in China have a greater environmental impact because of the water and fertiliser required in their production, as well as their transportation and greater weight.

The researchers concluded: 'The HDPE bag had the lowest environmental impacts of the single use options in nine of the 10 impact categories. The bag performed well because it was the lightest single use bag considered.'

Plastic bags have also come under fire for using up oil and for littering the countryside and fouling the marine environment for wildlife.
A study into the impact of different bags was finished in 2008 but has not yet been published

A study into the impact of different bags was finished in 2008 but has not yet been published

However, the research found that biodegradable bags made of starch were not a greener option than HDPE bags as they are less environmentally friendly to make and heavier.

The authors write: 'In practical terms of global warming potential, eutrophication [a form of river pollution] ozone layer depletion, toxicity and ecotoxicity the current starch polyester blend bag is significantly worse than conventional single-use options due to the high impact of raw material production on those categories.'

The Daily Mail, through its 'Banish the Bags' campaign has spearheaded efforts to avoid using plastic bags wherever possible to save the environment and the public are reducing their use of plastic bags.

Figures from WRAP, the government's Waste and Resources Action Program, show a total decline in all types of carrier bags issued to 4.5 billion (41%) over the years 2006-2010 – effectively saving 39,700 tonnes of material from entering the waste stream

Peter Woodall, speaking on behalf of the Packaging and Films Association, which represents plastic bag makers, said: 'This analysis shows what we have been saying for years. Plastic bags are a more environmentally friendly option than cotton bags.

'It comes down to reducing, reusing and recycling.' He also cited Canadian research that cotton bags can harbour can harbour germs and mould which can be harmful to health - unless they are washed.

An Environment Agency spokesperson said: 'The report focuses on the greenhouse gas emissions of manufacturing different types of carrier bags.

'Much of the environmental impact of these bags is associated with the primary resource use and production.

'The final report due to be published in the next two weeks, will show that all multi-use bags - plastic, cotton or paper - need to be reused on multiple occasions to justify the additional carbon footprint of their production.