The Finnish Environment Institute and the Lappeenranta University of Technology have carried out a comparative life cycle analysis of the greenhouse gas emissions related to shopping bags made of different materials. The starting point of the study was the consumer's need to choose a bag at the cash desk. The common plastic bags were compared with paper bags, cotton bags, plastic bags made of recycled material, and biodegradable plastic bags. It was found that the greenhouse gas emissions from production, use and waste treatment of shopping bags make only a minor contribution to the total emissions from consumption. A surprise was that the plastic bag made of recycled material is more environment-friendly than the cotton bag.

According to the results of the project, the plastic bag made of recycled material seems to be the best alternative in the present situation. It is not easy to tell whether a paper bag is better than a common plastic bag. The result of the comparison depends mostly on the weight of the waste bags, the recycling percentage of paper and the decomposition degree of paper at landfills. If most paper bags are recycled, the paper bag is probably more environment-friendly than the plastic bag. This is true of white paper bags. The brown bags cannot be recycled through the waste paper collection system.

Cotton bags have been regarded as environment-friendly, but the results show that they are not the best alternative. This is because large amounts of energy and irrigation water used in cotton production. The greenhouse gas emissions in the production phase are high. Moreover, if cotton bags or other fabric bags are used, some other bags must be used as waste bags. The essential question is the weight of the waste bags used instead of the plastic shopping bags. If the cotton bag is used sufficiently many times and if the mass of the waste bags is small enough, the combination may be better than the plastic bag - but it does not beat the paper bag or the plastic bag of recycled material. If permanent shopping bags are used, they should be made of other fibres than cotton.

It turned out that the biodegradable shopping bag was the worst alternative. The present biodegradable bags contain substances that increase their durability, but those substances are of fossil origin. The decomposition of such bags will thus contribute to the climate change if the bags end up in a compost or in a landfill. The biodegradable bag is an acceptable alternative only if it is burned for replacing fossil energy sources or if it is used in biogas production.

The shopping bag is just one aspect of the consumption process. Consumers should consider how to change their shopping habits and waste management practises into a more climate-friendly direction, and one of the things to be considered is the use of shopping bags. The most efficient means to cut down the climate impact of shopping is to go shopping less often and to fill the bags efficiently.